Anti-Tubercular Drugs (KDT Style - Detailed)

Overview

Classification

First-Line (Preferred) Drugs

Second-Line Drugs

Standard Treatment Regimen

FIRST-LINE DRUGS (Detailed)

1. ISONIAZID (INH)

• INH is a prodrug activated by the mycobacterial catalase-peroxidase enzyme KatG
• The activated form covalently binds to acyl carrier protein reductase (InhA) and β-ketoacyl-ACP synthase (KasA)
• This inhibits mycolic acid synthesis, destroying the integrity of the mycobacterial cell wall
• Active against both intracellular (inside macrophages) and extracellular organisms
• MIC: inhibits most M. tuberculosis at ≤0.2 mcg/mL

• Well absorbed orally; peak plasma level 3-5 mcg/mL at 1-2 hours; absorption reduced by 50% with fatty meals
• Penetrates all body fluids including CSF (CSF level = 20-100% of serum level), caseous material, and macrophages
• Metabolized by N-acetyltransferase (NAT2) in the liver - genetically polymorphic
  • Fast acetylators: half-life <1 hour (common in East Asians, Eskimos)
  • Slow acetylators: half-life ~3 hours (common in Egyptians, Scandinavians)
• Slow acetylators accumulate more drug and parent compound but generally similar efficacy with daily dosing; risk of toxicity is higher
• Inhibits CYP450 enzymes - raises levels of phenytoin, carbamazepine, benzodiazepines

• Mutation/deletion of KatG gene → inability to activate prodrug (high-level resistance)
• Overexpression of inhA → low-level resistance (also cross-resistance with ethionamide)
• Mutations in KasA or ahpC

• Peripheral neuropathy (most common): due to pyridoxine (B6) deficiency caused by INH competing with pyridoxal phosphate. Prevented by co-administering pyridoxine 10-25 mg/day. Seen more in slow acetylators, malnourished, diabetics, alcoholics, pregnant women
• Hepatotoxicity: elevated transaminases in 10-20% of patients; clinical hepatitis in 1%; more common in >35 years and with alcohol use. Fatal hepatitis rare
• CNS effects: memory impairment, psychosis, seizures (especially in overdose)
• Lupus-like syndrome (antinuclear antibodies)
• Drug interactions: inhibits metabolism of phenytoin (toxicity), carbamazepine, warfarin

2. RIFAMPICIN (Rifampin)

• Binds to the beta subunit of DNA-dependent RNA polymerase (rpoB gene product)
• Blocks RNA transcription → inhibits mRNA synthesis
• Bactericidal; active against M. tuberculosis, MAC, M. leprae, as well as many gram-positive and gram-negative bacteria
• Active against both intracellular and extracellular organisms, including dormant/persister bacilli

• Good oral absorption; taken on an empty stomach (food reduces absorption)
• Widely distributed; penetrates CSF, cells, and caseous material
• Half-life 1.5-5 hours; undergoes enterohepatic recirculation
• Metabolized to desacetylrifampin (still active); excreted primarily in bile/feces
• Colours body secretions red-orange (urine, tears, saliva, sweat, sputum) - warn patients; can stain soft contact lenses

• Mutations in rpoB gene (beta subunit of RNA polymerase) - >96% of resistant strains
• Resistance develops rapidly with monotherapy (never give alone for active TB)
• Cross-resistance between rifampicin and rifabutin is virtually complete

• Hepatotoxicity: liver enzyme elevation; dose-related
• GI upset: nausea, vomiting, abdominal pain
• "Flu-like" syndrome: fever, chills, myalgias - especially with intermittent therapy (hypersensitivity)
• Thrombocytopenia, hemolytic anemia (rare)
• Drug interactions (most important): Rifampicin is a potent inducer of CYP3A4 and other CYP enzymes and P-glycoprotein. It reduces levels of: oral contraceptives (use alternative contraception!), warfarin, antiretrovirals (PIs, NNRTIs), methadone, corticosteroids, azole antifungals, digoxin, phenytoin, sulfonylureas

3. PYRAZINAMIDE (PZA)

• Pyrazinamide is a prodrug hydrolyzed by pyrazinamidase (encoded by pncA gene) to the active form pyrazinoic acid
• Exact mechanism not fully established; likely acidifies intracellular environment of mycobacteria
• Only active in acidic pH (inside macrophage phagolysosomes and necrotic/caseous lesions - pH 5-5.5)
• Active against intracellular organisms and slowly metabolizing "persister" bacilli
• Bactericidal at acidic pH; bacteriostatic at neutral pH
• This unique activity in acidic environments allows the treatment duration to be shortened from 9 months to 6 months

• Good oral absorption; widely distributed; penetrates CSF
• Metabolized by liver; excreted by kidneys
• Half-life ~9 hours

• Loss of pyrazinamidase activity (mutations in pncA)
• Resistance is NOT cross-resistant with other first-line drugs (important advantage)

• Hyperuricemia (most common): inhibits renal tubular secretion of uric acid; asymptomatic in most; rarely precipitates gout
• Hepatotoxicity: most significant toxicity; dose-related elevation of liver enzymes; serious hepatitis possible
• Arthralgia/joint pains (common, related to hyperuricemia)
• Nausea, rash
• Used only for the first 2 months in the standard 6-month regimen (most benefit early in treatment)

4. ETHAMBUTOL (EMB)

• Inhibits arabinosyl transferase (encoded by embCAB operon)
• Arabinosyl transferase is essential for synthesis of arabinogalactan, a major component of the mycobacterial cell wall
• Bacteriostatic (not bactericidal); specific for mycobacteria
• Prevents incorporation of arabinose into the cell wall

• Good oral absorption; penetrates most tissues well
• CNS penetration is variable (adequate in meningeal inflammation, questionably adequate in tuberculous meningitis)
• Excreted mainly in urine (parent drug + metabolites); dose reduction needed in renal failure

• Mutations in embB gene (arabinosyl transferase)

• Optic neuritis (most important and distinctive toxicity): dose-dependent
  • Reduced visual acuity, loss of red-green color discrimination, central scotoma
  • More common at higher doses (25 mg/kg) and in renal impairment
  • Baseline visual acuity and color vision testing is mandatory; repeat monthly
  • Usually reversible if drug stopped early
• Hyperuricemia (decreased uric acid excretion)
• Peripheral neuropathy (rare)

5. STREPTOMYCIN

• Aminoglycoside that binds to 30S ribosomal subunit → inhibits protein synthesis
• Bactericidal; active against extracellular organisms
• Poor intracellular penetration (inactive against intracellular bacilli)

• Given intramuscularly (IM) or IV; not absorbed orally
• Does NOT penetrate CSF (poor in normal meningitis; better in inflamed meninges)
• Excreted unchanged by kidneys; accumulates in renal failure

• Mutations in 16S rRNA (rrs gene) or ribosomal protein S12 (rpsL)

• Ototoxicity: both vestibular (balance disturbance, nystagmus, vertigo) and auditory (irreversible hearing loss)
• Nephrotoxicity: dose-dependent; monitor renal function
• Neuromuscular blockade

SECOND-LINE DRUGS

Bedaquiline

• First novel anti-TB drug approved in 40 years (FDA 2012) - a diarylquinoline
• Mechanism: inhibits mycobacterial ATP synthase (novel target) → depletes energy
• Active against both replicating and non-replicating bacilli
• Used in MDR-TB and XDR-TB regimens; part of the BPaL regimen (Bedaquiline + Pretomanid + Linezolid)
• Adverse effects: QT prolongation (serious - ECG monitoring required), hepatotoxicity, nausea
• Dose: 400 mg/day for 2 weeks, then 200 mg 3x/week for 22 weeks

Fluoroquinolones (Levofloxacin, Moxifloxacin)

• Inhibit DNA gyrase (topoisomerase II) and topoisomerase IV
• Used in MDR-TB regimens
• Moxifloxacin is part of the newer 4-month regimen (RPMZ = Rifapentine + Moxifloxacin + Pyrazinamide + INH)
• Adverse effects: QT prolongation (moxifloxacin), tendinopathy, GI upset

Cycloserine

• Structural analogue of D-alanine
• Inhibits D-alanine racemase and D-Ala-D-Ala ligase → blocks cell wall peptidoglycan synthesis
• Used in MDR-TB
• Adverse effects: CNS toxicity (seizures, depression, psychosis) - pyridoxine supplementation required
• Dose: 500-1000 mg/day in divided doses

Ethionamide

• Prodrug structurally similar to INH; also inhibits InhA (mycolic acid synthesis)
• Cross-resistance with INH (inhA mutations)
• Used in MDR-TB
• Adverse effects: GI intolerance (major problem), hepatotoxicity, hypothyroidism (with prolonged use), teratogenic

Para-Aminosalicylic Acid (PAS)

• Inhibits folate synthesis in mycobacteria (similar to sulfonamides)
• Also interferes with iron metabolism and mycobactin synthesis
• Second-line; used in MDR-TB
• Adverse effects: severe GI intolerance, hepatotoxicity, hypothyroidism

Rifabutin

• Rifamycin derivative; similar mechanism to rifampicin (rpoB inhibition)
• Cross-resistance with rifampicin nearly complete
• Preferred over rifampicin in HIV patients on antiretroviral therapy (less potent CYP inducer)
• Adverse effects: hepatotoxicity, leukopenia, thrombocytopenia, optic neuritis; uveitis (dose-related)

Linezolid

• Oxazolidinone; inhibits 50S ribosomal subunit (23S rRNA binding site)
• Active against MDR-TB and XDR-TB; part of BPaL regimen
• Adverse effects: bone marrow suppression (anemia, thrombocytopenia), peripheral neuropathy, optic neuropathy (with prolonged use), serotonin syndrome (with serotonergic agents)
• Pyridoxine supplementation recommended

Capreomycin / Amikacin

• Capreomycin: cyclic polypeptide antibiotic; inhibits protein synthesis (30S ribosome)
• Amikacin: aminoglycoside; inhibits 30S ribosome
• Both given parenterally (IM/IV)
• Adverse effects: ototoxicity, nephrotoxicity

Pretomanid

• Nitroimidazole prodrug; activated in anaerobic conditions
• Inhibits cell wall synthesis and generates cytotoxic nitric oxide
• Used in combination (BPaL regimen) for MDR/XDR-TB
• FDA approved 2019

MDR-TB and XDR-TB Treatment

Adverse Effects - High-Yield Summary

Key Pharmacological Facts (KDT High-Yield Points)

1. INH is the most active drug for drug-susceptible TB; the only one with confirmed bactericidal activity across all mycobacterial populations
2. Rifampicin is the most important "sterilizing" drug - eradicates persister bacilli
3. Pyrazinamide - allows shortening from 9 to 6 months due to activity in acidic environments
4. Ethambutol - primarily bacteriostatic; used to protect against undetected resistance
5. Fast vs. slow acetylators of INH: peripheral neuropathy more in slow acetylators; hepatotoxicity more in fast acetylators
6. INH + rifampicin + B6 is the regime for latent TB infection (LTBI) prophylaxis (preventive therapy)
7. Directly Observed Therapy (DOT) is the standard strategy to improve adherence
8. Rifampicin increases metabolism of oral contraceptive pills - use alternative contraception
9. All first-line drugs are active orally except streptomycin (parenteral only)
10. Bedaquiline has the novel mechanism of ATP synthase inhibition - first new TB drug in 40 years

Antifungal Drugs (KDT Style - Detailed)

Why Fungal Infections Are Difficult to Treat

Classification of Antifungal Drugs

By Site of Action:

Sites of action diagram:

GROUP 1: POLYENE MACROLIDES

AMPHOTERICIN B

• Binds specifically to ergosterol in the fungal cell membrane
• Forms transmembrane pores (ion channels) in the membrane
• Pores cause leakage of K⁺, Mg²⁺, and other intracellular contents
• Results in depolarization and osmotic lysis → fungicidal
• Human cell membranes contain cholesterol (not ergosterol), so there is selective toxicity - but amphotericin B still has some affinity for cholesterol, explaining its toxicity

• Candida spp., Cryptococcus neoformans, Aspergillus spp.
• Endemic fungi: Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis
• Mucor spp. (Mucormycosis)
• Resistance is rare

• Nearly insoluble in water; formulated as colloidal suspension with sodium deoxycholate for IV use
• NOT absorbed orally (used only topically/orally for GI candidiasis)
• Widely distributed; penetrates most tissues including pleural, peritoneal, synovial fluids
• Poor CSF penetration with IV administration → requires intrathecal injection for fungal meningitis
• Half-life biphasic: initial ~24 hours, terminal ~15 days
• Excreted very slowly; detected in urine for up to 7 weeks after stopping

• Fever, chills, rigors, muscle spasms, vomiting, headache, hypotension - nearly universal
• Management: Slow infusion rate; premedicate with antipyretics, antihistamines, meperidine (for rigors), or corticosteroids
• Give a 1 mg test dose IV first to gauge severity

• Nephrotoxicity (most serious and clinically significant): occurs in almost all patients
  • Azotemia (BUN/creatinine rise) - partly reversible (vasoconstriction/prerenal) and partly irreversible (tubular injury)
  • Renal tubular acidosis - K⁺ and Mg²⁺ wasting (hypokalemia, hypomagnesemia)
  • Risk reduced by sodium loading (normal saline infusion before each dose)
  • Irreversible damage usually with >4 g cumulative dose
• Normocytic normochromic anemia: reduced erythropoietin production from damaged renal tubular cells
• Liver function abnormalities (occasional)
• Intrathecal administration: seizures, chemical arachnoiditis, serious neurological sequelae

• Drug of choice for severe, life-threatening systemic fungal infections
• Cryptococcal meningitis (with flucytosine)
• Invasive aspergillosis (now often superseded by voriconazole)
• Invasive candidiasis
• Mucormycosis (only effective option)
• Empirical therapy in febrile neutropenic patients

NYSTATIN

• Polyene macrolide, same mechanism as amphotericin B (binds ergosterol, forms pores)
• TOO TOXIC for parenteral use - used only topically
• Not absorbed from skin, mucous membranes, or GI tract → minimal systemic toxicity
• Available as creams, ointments, lozenges, vaginal suppositories
• Uses: Oropharyngeal candidiasis (thrush), vaginal candidiasis, intertriginous candidal infections, oral GI candidiasis (swish-and-swallow)
• Adverse effects: Unpleasant bitter taste (oral preparations)

GROUP 2: AZOLES

• Inhibit fungal cytochrome P450 enzyme CYP51 (also called lanosterol 14-α-demethylase)
• This enzyme is essential for converting lanosterol → ergosterol in the ergosterol biosynthesis pathway
• Result: depletion of ergosterol + accumulation of toxic methylated sterols → impaired cell membrane function → fungistatic (mostly)
• Triazoles have greater selectivity for fungal CYP than imidazoles → less human toxicity and fewer drug interactions

• Overexpression of efflux pumps (MDR1, CDR1/CDR2)
• Mutations in ERG11 gene (CYP51) reducing azole binding affinity
• Upregulation of ERG11

Pharmacokinetic Comparison Table

IMIDAZOLES

Ketoconazole

• First systemic azole; now largely replaced by triazoles
• Limited spectrum; poor CNS penetration; significant drug interactions and toxicity
• Adverse effects:
  • Inhibits adrenal and gonadal steroid synthesis (CYP11A1, CYP17A1): gynecomastia, menstrual irregularities, impotence, adrenal insufficiency - unique among azoles
  • Hepatotoxicity (most significant)
  • GI intolerance
• Still used topically: seborrheic dermatitis, pityriasis versicolor (shampoo, cream)

Clotrimazole, Miconazole

• Used topically only - too toxic for systemic use
• Available OTC; used for vulvovaginal candidiasis, tinea infections, oral thrush (clotrimazole loches)
• Negligible systemic absorption; adverse effects rare

TRIAZOLES (The "Big Four")

1. Fluconazole

• Most widely used antifungal; excellent oral bioavailability and safety
• Unique features:
  • Water-soluble → excellent distribution including CSF (CSF:serum >0.7 - best of all azoles)
  • Renally excreted (only azole primarily excreted by kidneys); dose adjustment in renal failure required
  • Available both oral and IV (same bioavailability - oral preferred when possible)
• Spectrum: Candida (most species), Cryptococcus neoformans
  • Resistance: C. krusei (inherently resistant), C. glabrata (often resistant/dose-dependent)
  • NOT active against Aspergillus
• Clinical Uses:
  • Drug of choice for oropharyngeal and esophageal candidiasis
  • Cryptococcal meningitis (maintenance/consolidation after AmB induction)
  • Vaginal candidiasis (single 150 mg oral dose)
  • Prophylaxis in immunocompromised patients (neutropenia, HIV)
  • Coccidioidomycosis
• Adverse effects: generally well tolerated; GI upset, headache; hepatotoxicity (rare but reported); teratogenic (avoid in pregnancy)
• Drug interactions: CYP2C9 and CYP3A4 inhibitor → raises levels of warfarin, phenytoin, sulfonylureas, cyclosporine

2. Itraconazole

• Broadest spectrum among older azoles - covers Aspergillus (unlike fluconazole)
• Spectrum: Candida, Aspergillus, Cryptococcus, endemic mycoses (Histoplasma, Blastomyces, Sporothrix, Coccidioides)
• Pharmacokinetics: poor/variable absorption (requires acidic pH; absorption reduced by antacids, PPIs); highly lipophilic; poor CSF penetration
  • Take capsules with food; oral solution (cyclodextrin vehicle) taken fasting - better absorbed
• Clinical Uses: Histoplasmosis, blastomycosis, aspergillosis (mild), dermatophytosis, onychomycosis, sporotrichosis
• Adverse effects: GI upset, hepatotoxicity; negative inotropic effect - contraindicated in heart failure; peripheral edema
• Drug interactions: CYP3A4 inhibitor; raises levels of digoxin, cyclosporine, warfarin, statins

3. Voriconazole

• Drug of choice for invasive aspergillosis (superior to amphotericin B in clinical trials)
• Extended spectrum: all Candida including fluconazole-resistant strains, Aspergillus, Fusarium, Scedosporium
• Good oral bioavailability; good CNS penetration; available oral and IV
• Adverse effects (unique):
  • Hepatotoxicity (common, dose-related)
  • Reversible visual disturbances: photopsia (flashes, color changes, blurred vision) - occurs in ~30% of patients, especially within first week; generally transient
  • Photosensitivity (long-term): increases risk of skin cancers
  • Peripheral neuropathy (with long-term use)
  • Hallucinations and encephalopathy (rare)
• Drug interactions: potent inhibitor of CYP2C19, CYP2C9, CYP3A4; complex interactions; rifampicin markedly reduces voriconazole levels (contraindicated together)

4. Posaconazole

• Broadest spectrum triazole - includes Mucor (mucormycosis) and Rhizopus
• Used for prophylaxis of invasive fungal infections in high-risk patients (AML, HSCT)
• Treatment of refractory aspergillosis and mucormycosis
• Oral (tablet or suspension) and IV
• Adverse effects: QT prolongation, hepatotoxicity, GI intolerance

5. Isavuconazole

• Similar spectrum to posaconazole; licensed for invasive aspergillosis and mucormycosis
• Half-life ~130 hours (very long; less frequent dosing)
• Generally better tolerated than voriconazole (less photosensitivity, fewer visual disturbances)
• Causes QT shortening (unique - other azoles cause QT prolongation)

GROUP 3: ALLYLAMINES

TERBINAFINE

• Inhibits squalene epoxidase (an enzyme in the ergosterol biosynthesis pathway, upstream of azoles)
• Blocks conversion of squalene → squalene epoxide
• Results in: (1) depletion of ergosterol + (2) accumulation of squalene (which is toxic to fungi)
• Fungicidal (unlike azoles, which are mostly fungistatic)

• Well absorbed orally; 250 mg/day
• Highly keratophilic and lipophilic - concentrates in skin, nails, and hair follicles
• Long half-life allows drug to persist in nails for months after stopping

• Onychomycosis (nail fungal infection) - drug of choice; 250 mg/day for 6 weeks (fingernails) or 12 weeks (toenails); cure rate up to 90%
• More effective than griseofulvin or itraconazole for onychomycosis
• Tinea pedis, tinea cruris, tinea corporis (oral and topical)

GROUP 4: ECHINOCANDINS

Caspofungin, Micafungin, Anidulafungin

• Inhibit β-1,3-D-glucan synthase - the enzyme that synthesizes β-1,3-glucan, a key structural polysaccharide in the fungal cell wall
• Depletion of glucan compromises cell wall integrity → osmotic instability → fungicidal against Candida, fungistatic against Aspergillus
• Highly selective: β-1,3-glucan is absent from human cells → minimal human toxicity
• No action against Cryptococcus neoformans, zygomycetes (Mucor), or dermatophytes (they lack the target or have different cell wall composition)

• Available IV only (large cyclic peptides; not orally absorbed)
• Widely distributed; poor CNS penetration
• Metabolized in liver; excreted in urine and feces
• Caspofungin: 70 mg loading dose, then 50 mg/day
• Micafungin: 100-150 mg/day
• Anidulafungin: 200 mg loading dose, then 100 mg/day

• Invasive candidiasis (first-line, including candidemia)
• Esophageal candidiasis
• Invasive aspergillosis (alternative to voriconazole)
• Empirical antifungal therapy in febrile neutropenia (caspofungin)
• Treatment of candidiasis in ICU patients

• Caspofungin: infusion-related reactions (histamine-mediated flushing, rash), hepatotoxicity (mild elevation of LFTs)
• Micafungin: hepatotoxicity (increased risk in patients with hepatic impairment)
• Anidulafungin: diarrhea, hypokalemia; rare infusion reactions
• Echinocandins are safe in pregnancy compared to azoles

GROUP 5: PYRIMIDINE ANALOG

FLUCYTOSINE (5-Fluorocytosine, 5-FC)

• Prodrug; taken up by fungi via cytosine permease
• Converted intracellularly: flucytosine → 5-fluorouracil (5-FU) by cytosine deaminase
• 5-FU is incorporated into fungal RNA → disrupts RNA function → interferes with protein synthesis
• Also phosphorylated to 5-fluorodeoxyuridine monophosphate → inhibits thymidylate synthase → blocks DNA synthesis
• Selective: human cells lack cytosine deaminase → minimal conversion of 5-FC to 5-FU in human cells

• Well absorbed orally (>90%); peak levels 1-2 hours
• Excellent CSF penetration (CSF = 70-80% of serum)
• Excreted unchanged by kidneys (GFR); dose adjustment required in renal failure
• Half-life 3-4 hours (normal renal function)
• Removed by hemodialysis

• Combined with amphotericin B for cryptococcal meningitis (synergistic combination; standard of care)
• Never used as monotherapy (resistance develops rapidly)

• Bone marrow suppression: leukopenia, thrombocytopenia, anemia (due to conversion to 5-FU)
• Hepatotoxicity: elevated liver enzymes
• GI: nausea, vomiting, diarrhea
• Monitor serum levels: therapeutic range 25-100 mcg/mL; toxic at >100 mcg/mL

GROUP 6: GRISEOFULVIN

• Fungistatic against dermatophytes only (Trichophyton, Microsporum, Epidermophyton)
• Mechanism: binds to microtubules (tubulin polymerization) → disrupts mitotic spindle → arrests fungal cell division at metaphase
• Also: deposited in newly forming keratin of skin, hair, and nails → binds keratin → protects new keratin from fungal infection

• Orally administered (microcrystalline form, 1 g/day); absorption improved with fatty meals
• Concentrated in keratin-containing structures (skin, hair, nails)
• Metabolized by liver; induces CYP enzymes

• Drug only prevents infection of new keratin - old infected keratin must be shed
• Skin and hair: 2-6 weeks
• Nails: months (often 6-12 months for toenails); high relapse rate

• Allergic reactions: serum-sickness-like syndrome, urticaria
• Serious skin reactions (rarely)
• Lupus-like syndrome
• Hepatotoxicity
• Drug interactions: CYP inducer → reduces warfarin levels (anticoagulant effect decreases), reduces OCP efficacy; antagonized by phenobarbital

High-Yield Comparison Summary Table

Key High-Yield Points (KDT Exam Facts)

1. Ergosterol is the main target of antifungal drugs (polyenes and azoles both target it at different steps)
2. Amphotericin B - broadest spectrum, drug of choice for life-threatening fungal infections; the "gold standard" but major nephrotoxicity
3. Fluconazole - best CSF penetration among azoles; renally excreted; drug of choice for Candida and Cryptococcus
4. Voriconazole - drug of choice for invasive aspergillosis; causes visual disturbances (unique)
5. Terbinafine - inhibits squalene epoxidase (not CYP51); fungicidal; drug of choice for onychomycosis
6. Echinocandins - target fungal cell wall (not membrane); IV only; best tolerated; drug of choice for invasive candidiasis especially in ICU
7. Flucytosine - NEVER used alone (rapid resistance); always combined with amphotericin B for cryptococcal meningitis
8. Griseofulvin - only for dermatophytes (not yeasts); binds keratin; arrests mitosis; largely replaced now
9. Nystatin - too toxic for systemic use; topical only
10. Ketoconazole - only azole that inhibits steroid synthesis (used to treat Cushing's syndrome off-label); causes gynecomastia, adrenal suppression
11. Amphotericin B + flucytosine = synergistic for cryptococcal meningitis
12. Posaconazole is the only azole with reliable activity against Mucor (mucormycosis)
13. Echinocandins have no activity against Cryptococcus (lacks β-1,3-glucan synthase target)
14. All azoles are inhibitors of CYP enzymes → multiple drug interactions (ketoconazole > itraconazole > fluconazole)
15. Rifampicin is a CYP inducer - contraindicated with voriconazole (dramatically reduces voriconazole levels)

Gastrointestinal Tract Pathology

(Robbins & Cotran Pathologic Basis of Disease - Chapter 17)

PART I: ESOPHAGUS

Normal Anatomy

1. ESOPHAGEAL OBSTRUCTION & DYSMOTILITY

Functional Obstruction (Dysmotility)

• Nutcracker esophagus: High-amplitude, uncoordinated contractions of inner circular + outer longitudinal smooth muscle. Diagnosed by manometry.
• Diffuse esophageal spasm (corkscrew esophagus): Repetitive, simultaneous contractions of normal amplitude in the distal esophagus. Barium swallow shows corkscrew appearance.
• Lower esophageal sphincter (LES) dysfunction: High resting pressure or incomplete relaxation; may occur alone or with the above patterns.

Zenker (Pharyngoesophageal) Diverticulum

• Caused by impaired relaxation and spasm of the cricopharyngeus muscle
• Located immediately above the upper esophageal sphincter
• Develops after age 50; may reach several cm
• Accumulates food → regurgitation, halitosis, neck mass

Achalasia

• Failure of LES to relax during swallowing + absence of peristalsis in the esophageal body
• Progressive dysphagia, regurgitation, weight loss
• Caused by loss of inhibitory (nitrergic/VIP) neurons in the myenteric plexus
• Marked dilation of the esophagus above the LES ("bird beak" appearance on barium swallow)

Benign Strictures

• Fibrous thickening of submucosa; caused by chronic GERD, irradiation, or caustic injury
• Progressive dysphagia for solids; weight maintained

Esophageal Webs and Rings

• Webs: Semi-circumferential mucosal protrusions, usually upper esophagus; associated with GERD, graft-versus-host disease
• Plummer-Vinson syndrome: Webs + iron deficiency anemia + glossitis + cheilosis in females
• Rings (Schatzki rings): Circumferential lesions; more common than webs; related to GERD

2. ESOPHAGITIS AND RELATED DISORDERS

Lacerations (Mallory-Weiss Tear)

• Longitudinal mucosal tears at the gastroesophageal junction
• Due to severe retching/vomiting (classic after alcohol binge)
• Presents with hematemesis
• Usually heals spontaneously; rarely requires surgery

Chemical and Infectious Esophagitis

• Caustic injury: alkalis are more damaging than acids (penetrate deeper)
• Infectious: most common in immunocompromised patients
  • Candida esophagitis: white pseudomembranes; dysphagia/odynophagia
  • Herpes simplex: punched-out ulcers; intranuclear inclusions (Cowdry A bodies)
  • CMV esophagitis: linear ulcers; intranuclear AND intracytoplasmic inclusions

Reflux Esophagitis (GERD)

• Decreased LES tone (alcohol, smoking, obesity, hiatal hernia)
• Increased abdominal pressure (pregnancy, obesity)
• Delayed gastric emptying

• Basal zone hyperplasia (>20% of epithelial thickness)
• Elongation of vascular papillae (>two-thirds of epithelial thickness)
• Intraepithelial eosinophils and neutrophils
• Erosions and ulceration in severe disease

Eosinophilic Esophagitis

• Allergic/immune-mediated; increasing incidence
• Dense eosinophil infiltration (>15 eos/HPF) in mid or proximal esophagus (vs. distal eosinophils in GERD)
• Endoscopy: rings, furrows, plaques, strictures ("ringed esophagus")
• Presents with dysphagia, food impaction, chest pain

Esophageal Varices

• Portal hypertension (most commonly cirrhosis) → increased pressure in portal system → collateral channels form including submucosal veins of the esophagus
• Varices can rupture → massive upper GI hemorrhage (life-threatening)

3. BARRETT ESOPHAGUS

• Salmon-colored (pink-red) mucosa replacing the pearly-white squamous lining proximally from GEJ
• Histology: Goblet cells (hallmark) - identify intestinal metaplasia
• Risk of dysplasia → adenocarcinoma: Barrett esophagus increases risk ~40-fold

4. ESOPHAGEAL TUMORS

Adenocarcinoma

• Arising in Barrett esophagus → sequence: metaplasia → dysplasia → adenocarcinoma
• Location: Distal esophagus/GEJ (nearly always)
• Epidemiology: Most common esophageal cancer in the United States and Western Europe; increasing incidence; more common in white males
• Risk factors: GERD, obesity, Barrett esophagus, smoking
• Molecular: ERBB2 amplification, TP53 mutations, chromosomal instability
• Morphology: Flat/raised patches → nodular mass → ulcerated/exophytic tumor (Fig 17.11A). Gland-forming adenocarcinoma with irregular lumens (Fig 17.12A).
• Clinical: Progressive dysphagia, weight loss; late presentation → poor prognosis

Squamous Cell Carcinoma (SCC)

• Location: Middle third of esophagus most frequently; also upper third
• Epidemiology: More common in developing countries (Iran, China, East Africa); in USA it is more common in urban areas and in Americans of African descent (8× more frequent than Northern Europeans)
• Risk factors: Alcohol + tobacco (synergistic), caustic injury, achalasia, Plummer-Vinson syndrome, tylosis (autosomal dominant palmoplantar hyperkeratosis), dietary nitrosamines, very hot beverages, nutritional deficiencies, HPV (in high-risk regions)
• Molecular: Three subtypes - Nrf2 pathway mutations (subtype 1); immune infiltration + caspase-7 cleavage (subtype 2); SMARCA4 + PIK3CA/PTEN mutations (subtype 3)
• Morphology: Stricture with ulcerated mass; nests of malignant squamous cells with keratin pearls (Fig 17.12B)
• Clinical: Dysphagia (progressive), weight loss, pain; invades mediastinum, trachea, aorta

PART II: STOMACH

Normal Anatomy

• Cardia/Antrum: mucin-secreting foveolar cells; antrum also contains G cells (secrete gastrin)
• Fundus/Body: Parietal cells (secrete H⁺ and intrinsic factor) + Chief cells (secrete pepsinogen/digestive enzymes)

5. GASTROPATHY AND ACUTE GASTRITIS

• Gastritis = mucosal inflammation with neutrophils present
• Gastropathy = mucosal injury with no or rare inflammatory cells

• Mucus + phospholipid layer (prevents direct epithelial contact)
• Bicarbonate secretion (creates neutral pH "unstirred layer")
• Physical barrier of surface epithelial cells
• Rapid epithelial turnover (every 3-7 days)
• Rich mucosal vasculature

• NSAIDs: Inhibit COX-1/2 → reduce prostaglandin E2 and I2 → impair mucus, bicarbonate, phospholipid secretion + vasoconstriction → ischemia
• Alcohol: Direct mucosal toxicity
• H. pylori: Bacterial virulence factors, urease-mediated ammonia production, inflammatory mediators
• Bile reflux: From duodenum into stomach (after surgery or pyloric dysfunction)
• Stress: Reduced mucosal blood flow → ischemia

• Mucosal edema, congestion, neutrophil infiltration
• Erosions: defects in mucosa without penetrating through muscularis mucosae
• Ulcers: deeper defects extending into or beyond muscularis mucosae

6. STRESS-RELATED MUCOSAL DISEASE (Stress Ulcers)

• Reduced mucosal blood flow → ischemia → breakdown of mucosal defenses
• Curling ulcers: Associated with burn injuries (duodenal/gastric)
• Cushing ulcers: Associated with raised intracranial pressure (gastric, duodenal, esophageal); very deep, risk of perforation; caused by vagal stimulation → excess acid secretion

7. CHRONIC GASTRITIS

A. Helicobacter pylori Gastritis

• H. pylori is a gram-negative, spiral-shaped, flagellated bacterium that colonizes the mucus overlying antral epithelium
• Urease produces ammonia → neutralizes local pH → allows bacterial survival
• CagA (cytotoxin-associated gene A): virulence factor; strains carrying CagA have higher risk of peptic ulcer and cancer
• VacA (vacuolating cytotoxin A): forms channels in epithelial membranes
• Inflammation: IL-8 production → neutrophil recruitment; chronic infiltrate with lymphocytes, plasma cells
• Host genetic factors (e.g., IL-10 polymorphisms) determine whether infection remains antral or progresses to pangastritis with atrophy and intestinal metaplasia → gastric cancer

• Organisms visible in superficial mucus on H&E; best seen with Warthin-Starry silver stain or immunostain
• Antrum preferred biopsy site
• Lamina propria: sheets of plasma cells + lymphocytes + macrophages + neutrophils
• Pit abscesses: Neutrophils accumulated in gland lumens
• Lymphoid aggregates with germinal centers = induced MALT (→ risk of MALToma/lymphoma)
• Thickened rugal folds in intense infection (can mimic carcinoma)

B. Autoimmune Atrophic Gastritis (Type A Gastritis)

• Autoimmune attack on parietal cells (fundus/body)
• Antibodies to parietal cells (anti-H⁺/K⁺ ATPase)
• Antibodies to intrinsic factor (blocks B12 binding or receptor binding)
• Loss of parietal cells → achlorhydria (no acid) → antral G-cell hyperplasia (tries to stimulate acid)
• Loss of intrinsic factor → failure to absorb vitamin B12 → pernicious anemia

• Spares the antrum (contrast with H. pylori which affects antrum predominantly)
• Fundus/body: atrophy of oxyntic glands, intestinal metaplasia
• Enterochromaffin-like (ECL) cell hyperplasia: Due to hypergastrinemia (G-cell hyperplasia → gastrin excess → stimulates ECL cells)

8. PEPTIC ULCER DISEASE

• ~95% are associated with H. pylori or NSAID use
• H. pylori → antral gastritis → increased gastrin → increased acid → duodenal/gastric ulcer
• Location: Duodenum > Stomach (4:1 ratio)
  • Duodenal ulcers: usually first part of duodenum (D1), associated with H. pylori + hyperacidity
  • Gastric ulcers: lesser curvature; associated with H. pylori + impaired mucosal defense

• Gross: Round/oval ulcer with sharply punched-out edges; base is clean (vs. ragged, heaped-up edges of malignant ulcers)
• Histology (4 zones from surface to base):
  1. Surface: fibrin and necrotic debris
  2. Second: Acute inflammatory cells (neutrophils)
  3. Third: Granulation tissue
  4. Deepest: Fibrous scar tissue (fibrosis)
• Surrounding mucosa shows evidence of chronic gastritis

• Hemorrhage (most common): erosion of gastroduodenal artery
• Obstruction: pyloric stenosis from scarring
• Perforation: acute peritonitis
• Sinister transformation: gastric ulcers rarely → carcinoma (duodenal ulcers do NOT)

9. HYPERTROPHIC GASTROPATHIES

Ménétrier Disease

• Rare; caused by excessive TGF-α secretion → foveolar cell hyperplasia (mucus-secreting cells)
• Massive hypertrophy of rugal folds (cerebroid appearance) in fundus/body; spares antrum
• Loss of parietal cells → achlorhydria
• Protein loss from hypertrophied mucosa → protein-losing enteropathy → hypoalbuminemia, edema
• Risk of gastric adenocarcinoma

Zollinger-Ellison Syndrome

• Caused by gastrin-secreting tumor (gastrinoma) - most often in pancreas or duodenum
• Excess gastrin → parietal cell hyperplasia → massive acid hypersecretion
• 60-90% of gastrinomas are malignant
• Results in: multiple peptic ulcers (often in unusual locations - second/third part of duodenum, jejunum), refractory to treatment
• Associated with MEN1 (Multiple Endocrine Neoplasia type 1)

10. GASTRIC TUMORS

Gastric Polyps

• Inflammatory/hyperplastic polyps (75% of all gastric polyps): associated with H. pylori gastritis; dysplasia risk 1-20% in large polyps
• Fundic gland polyps: Associated with PPI use and FAP (familial adenomatous polyposis)
• Gastric adenomas: True neoplastic polyps; risk factors = intestinal metaplasia, chronic gastritis

Gastric Adenocarcinoma

• Most common malignant gastric tumor
• Major cause of cancer death worldwide (especially East Asia)

• Sequence for intestinal type: normal mucosa → H. pylori gastritis → multifocal atrophic gastritis → intestinal metaplasia → dysplasia → carcinoma (Correa cascade)
• Molecular: Chromosomal instability (CIN), microsatellite instability (MSI), EBV-associated, and genomically stable subtypes
• Risk factors: H. pylori (most important), diet (smoked/pickled foods, nitrites), blood group A, Lynch syndrome, familial diffuse gastric cancer (CDH1/E-cadherin mutations)

• Intestinal type: Bulky, exophytic/ulcerating tumor; gland-forming; associated with intestinal metaplasia background
• Diffuse type: Poorly cohesive tumor cells; signet ring cells (mucin-filled cells that push the nucleus to periphery); infiltrates entire gastric wall → linitis plastica ("leather bottle stomach") - stomach loses distensibility

Gastric Lymphoma (MALT Lymphoma)

• B-cell lymphoma arising from MALT induced by H. pylori
• Eradication of H. pylori can induce regression of early-stage MALTomas
• Advanced disease: Chromosomal translocation t(11;18) → independent of H. pylori → requires chemotherapy/radiation

Gastrointestinal Stromal Tumor (GIST)

• Most common mesenchymal tumor of the GI tract
• Originates from interstitial cells of Cajal (pacemaker cells of the gut)
• KIT (CD117) mutation in ~75-80% → constitutive activation of receptor tyrosine kinase
• PDGFRA mutation in ~10%
• Treated with imatinib (Gleevec) - KIT inhibitor; revolutionized treatment
• Morphology: Spindle cells or epithelioid cells; immunohistochemistry shows CD117, CD34, DOG1 positivity

Gastric Neuroendocrine Tumors (Carcinoid)

• Arise from ECL cells; well-differentiated
• Types 1 and 2: associated with hypergastrinemia (autoimmune gastritis or ZES); usually benign
• Type 3: sporadic; NO hypergastrinemia; highest malignant potential

PART III: SMALL INTESTINE AND COLON

11. INTESTINAL OBSTRUCTION

1. Hernias (most common worldwide): Weakness in abdominal wall → external herniation of bowel (inguinal > femoral > umbilical) → incarceration → strangulation → infarction
2. Adhesions: Post-surgical/inflammatory fibrous bridges → internal herniation; leading cause of obstruction in USA
3. Volvulus: Twisting of bowel loop about its mesenteric attachment → both luminal and vascular obstruction; most common in sigmoid colon and cecum
4. Intussusception: Telescoping of proximal bowel into adjacent distal segment; in children often triggered by Peyer's patch hypertrophy (viral illness); in adults suggests neoplasm as a lead point

12. ISCHEMIC BOWEL DISEASE

• Arterial thrombosis/embolism (SMA occlusion)
• Venous thrombosis
• Non-occlusive: low-flow states (heart failure, septic shock)
• Watershed areas most vulnerable: splenic flexure (junction of SMA/IMA territories) and rectosigmoid

• Mucosal infarction: Superficial; limited to mucosa; may recover
• Mural infarction: Mucosa + submucosa; hemorrhagic necrosis
• Transmural infarction: Full-thickness necrosis → perforation, peritonitis
• "Thumbprinting" on imaging = submucosal hemorrhage/edema

13. MALABSORPTION AND DIARRHEA

1. Intraluminal digestion (luminal phase): pancreatic enzymes, bile acids
2. Mucosal absorption (mucosal phase): epithelial transport
3. Lymphatic transport (transport phase): chylomicrons
4. Endocrine/neuroendocrine regulation

Celiac Disease (Celiac Sprue / Gluten-Sensitive Enteropathy)

• Immune-mediated enteropathy triggered by gluten (wheat, rye, barley)
• Genetic predisposition: HLA-DQ2 (up to 90% of cases) or HLA-DQ8
• Gluten → intestinal deamidation by tissue transglutaminase 2 (TG2) → negatively charged peptides → bind DQ2/DQ8 on APCs → activate CD4+ T cells (IFNγ, IL-21, IL-2) → villous atrophy
• CD4+ T cells + IL-15 → expand intraepithelial CD8+ T cells → destroy enterocytes
• Anti-TG2 IgA and anti-gliadin antibodies: diagnostically useful

• Villous atrophy (blunting/effacement of villi)
• Crypt hyperplasia (compensatory)
• Intraepithelial lymphocytosis (CD8+ T cells in surface epithelium - hallmark)
• Increased plasma cells, mast cells, eosinophils in lamina propria

• Complications: Refractory celiac disease, enteropathy-associated T-cell lymphoma (EATL), small intestinal adenocarcinoma
• Treatment: Strict gluten-free diet → histological recovery

14. INFECTIOUS ENTEROCOLITIS

Typhoid Fever - Morphology

• Peyer's patches swell → "button ulcers" along long axis of ileum
• Macrophage predominance (not neutrophils)
• Ulcers can perforate → peritonitis (complication)
• "Typhoid nodules" in spleen/liver
• Rose spots on skin (transient)

Pseudomembranous Colitis (C. difficile)

• Following antibiotic therapy → loss of normal flora → C. difficile overgrowth
• Toxin A + Toxin B → enterocyte injury
• Morphology: Yellow-green pseudomembranes (fibrin, mucus, neutrophils, necrotic cells) attached to damaged mucosa; "volcano" lesions
• Clinical: Profuse watery diarrhea, cramping, fever; can progress to toxic megacolon

15. INFLAMMATORY BOWEL DISEASE (IBD)

• Dysregulated immune response to intestinal microbiota in genetically susceptible individuals
• Key genetic loci: NOD2 (first gene identified for CD; involved in bacterial sensing in macrophages), IL-23R, ATG16L1 (autophagy)
• Proposed mechanism: Loss of immune tolerance to normal gut flora → mucosal immune activation → tissue damage

Comparison Table: Crohn Disease vs Ulcerative Colitis

Crohn Disease - Morphology

• Skip lesions; terminal ileum most commonly affected
• Aphthous ulcers → elongated serpentine ulcers along bowel axis → cobblestone mucosa
• Fissures → perianal abscesses, fistulae (entero-enteric, enterovesical, enterovaginal, perianal)
• Creeping fat (mesenteric fat extends over serosal surface)
• Transmural inflammation; non-caseating granulomas (35%)
• Crypt abscesses, crypt distortion, pyloric metaplasia (in ileum)

Ulcerative Colitis - Morphology

• Always involves rectum; extends proximally in continuous fashion; may involve entire colon (pancolitis)
• Backwash ileitis: Superficial ileal inflammation in pancolitis
• Pseudopolyps (inflammatory polyps): Regenerating mucosa islands surrounded by deep ulcers - looks like polyps but they are not neoplastic
• Mucosa is hyperemic, granular; broad-based, superficial ulcers
• Inflammation limited to mucosa/submucosa; no transmural involvement, no granulomas
• Crypt abscesses and crypt distortion

Extraintestinal Manifestations (Both IBD)

• Joints: Peripheral arthritis, ankylosing spondylitis (HLA-B27 associated)
• Skin: Erythema nodosum, pyoderma gangrenosum
• Eyes: Uveitis, episcleritis
• Liver: Primary Sclerosing Cholangitis (PSC) - strongly associated with UC
• Blood: Anemia (blood loss, B12/folate deficiency)

Colitis-Associated Neoplasia

• IBD patients (especially UC) have increased risk of colorectal adenocarcinoma
• Sequence: Dysplasia-associated lesion or mass (DALM) → adenocarcinoma
• Surveillance colonoscopy with biopsies recommended after 8-10 years of pancolitis

16. DIVERTICULAR DISEASE

• Pseudodiverticula: Herniation of mucosa and submucosa through defects in muscularis propria (not true diverticula as they lack all wall layers)
• Most common in sigmoid colon; related to low-fiber diet (increased intraluminal pressure)
• Asymptomatic in most; Diverticulitis: infection/perforation of a diverticulum → left lower quadrant pain, fever, "left-sided appendicitis"
• Complications: abscess, perforation, fistula, obstruction

17. INTESTINAL POLYPS AND COLORECTAL NEOPLASIA

Polyp Types

Adenomas

• Epithelial neoplasms; present in ~30% of Western adults by age 60
• Hallmarks of epithelial dysplasia: nuclear hyperchromasia, elongation, stratification, prominent nucleoli
• Risk of malignant transformation correlates with: size >1 cm, villous architecture, and high-grade dysplasia

Familial Adenomatous Polyposis (FAP)

• Autosomal dominant mutation in APC (adenomatous polyposis coli) gene on chromosome 5q21
• 100s to 1000s of polyps throughout colon; virtually 100% risk of colon cancer by age 40 if untreated
• APC is a tumor suppressor that regulates WNT/β-catenin signaling; loss → excess β-catenin → nuclear transcription → cell proliferation
• Gardner syndrome: FAP + desmoid tumors + osteomas + epidermoid cysts
• Turcot syndrome: FAP + medulloblastoma (or HNPCC + glioblastoma)
• Treatment: prophylactic colectomy

Hereditary Non-Polyposis Colorectal Cancer (HNPCC / Lynch Syndrome)

• Autosomal dominant mutations in DNA mismatch repair (MMR) genes: MSH2, MLH1 (most common), MSH6, PMS2
• Leads to microsatellite instability (MSI) → accumulation of mutations
• Cancer risk: colorectal (right-sided, multiple primaries), endometrial (most common extracolonic), ovarian, gastric, urinary tract
• Fewer polyps than FAP but markedly increased cancer risk
• Testing: Immunohistochemistry for MMR proteins on tumor; genetic testing for germline mutations

18. COLORECTAL ADENOCARCINOMA

• Most common malignancy of the GI tract; 2nd leading cause of cancer death in the USA (after lung)
• Incidence peaks at 60-70 years; <20% occur before age 50 (but increasing in young adults)
• High risk: North America, Australia, Europe, Japan; Low risk: India, Africa, South America

1. APC/β-catenin (WNT) pathway - Chromosomal Instability (CIN) - "Classic" pathway
   • Normal mucosa → APC mutation → adenoma → KRAS mutation → DCC loss → TP53 mutation → carcinoma
   • APC loss → excess β-catenin → proliferation
   • Most sporadic colon cancers (85%)
   • Associated with FAP
2. Mismatch Repair Deficiency - Microsatellite Instability (MSI) pathway
   • MMR gene mutation/silencing (MLH1 hypermethylation in sporadic; germline mutation in HNPCC)
   • Rapid accumulation of mutations in microsatellite regions → MSI
   • Associated with HNPCC; better prognosis; responds to immune checkpoint inhibitors (PD-L1 high)

• Right colon (cecum, ascending): Polypoid/exophytic fungating mass; rarely obstructs (wide lumen); presents with occult blood loss → anemia
• Left colon (descending, sigmoid): Annular, napkin-ring lesion → constricts lumen → obstruction, change in bowel habits
• Histology: Gland-forming adenocarcinoma; variable mucin production; necrotic centers; desmoplastic stroma

• Direct: penetrates bowel wall into adjacent structures
• Lymphatic: mesenteric lymph nodes
• Hematogenous: Liver (most common distant metastasis), then lungs
• Transcoelomic: peritoneal seeding

• Right colon: Fatigue, weakness (from anemia), occult blood, palpable mass
• Left colon: Change in bowel habits, blood in stool, crampy pain, obstruction
• Both: Weight loss, anorexia
• CEA (carcinoembryonic antigen): Used for monitoring recurrence after surgery (not a screening test)

Key Concepts Summary (Exam High-Yield Points)

Hepatobiliary System Pathology

(Robbins & Cotran Pathologic Basis of Disease - Chapter 18)

PART I: THE LIVER

Normal Anatomy & Physiology (Key Points)

1. LIVER FAILURE

• A: Acetaminophen overdose, Hepatitis A, Autoimmune hepatitis
• B: Hepatitis B
• C: Hepatitis C, Cryptogenic
• D: Drugs/toxins, Hepatitis D
• E: Hepatitis E; Esoteric causes (Wilson disease, Budd-Chiari syndrome, lymphoma)
• F: Fatty change (microvesicular) - fatty liver of pregnancy, valproate, tetracycline, Reye syndrome

• Coagulopathy: Reduced synthesis of coagulation factors (I, II, V, VII, IX, X) → bleeding tendency; PT/INR elevated
• Hepatic encephalopathy: Accumulation of nitrogenous wastes (ammonia) + false neurotransmitters → asterixis, confusion, coma
• Portal hypertension: Cirrhosis → increased resistance in portal venous system → esophageal varices, ascites, splenomegaly, hemorrhoids (caput medusae)
• Hepatorenal syndrome: Renal failure (reversible with liver transplant) in severe liver disease; decreased renal perfusion from renin/angiotensin activation in portal hypertension
• Portopulmonary hypertension: Increased pulmonary arterial pressure
• Jaundice: Inability to conjugate/excrete bilirubin

2. CIRRHOSIS

1. Chronic hepatitis B
2. Chronic hepatitis C
3. Metabolic dysfunction-associated steatotic liver disease (MASLD)
4. Alcohol-associated liver disease

• Gross: Smooth liver capsule → bumpy surface with depressed scar areas + bulging regenerative nodules
• Micro: Parenchymal nodules surrounded by dense fibrous bands (highlighted with Masson's trichrome stain for collagen)
• Micronodular cirrhosis (nodules <3 mm): Typically seen in alcoholic liver disease and hemochromatosis
• Macronodular cirrhosis (nodules >3 mm): Typically seen in viral hepatitis
• Thin incomplete scars with ductular reaction = morphologic regression of cirrhosis (can occur with treatment)

• Portal hypertension → esophageal varices (rupture = massive haematemesis), ascites, splenomegaly
• Hepatocellular failure → coagulopathy, encephalopathy, jaundice, hypoalbuminemia
• Hepatocellular carcinoma (increased risk in all forms of cirrhosis)

3. VIRAL HEPATITIS

Hepatitis Virus Comparison Table

Hepatitis A (HAV)

• Self-limited; no chronicity, no carrier state
• Most common cause of symptomatic acute hepatitis worldwide
• Shed in stool 2-3 weeks before AND 1 week after onset of jaundice (peak infectivity)
• Complications: Acute liver failure (~0.5%); cholestatic hepatitis (prolonged cholestasis)
• Prevention: HAV vaccine (excellent efficacy); passive immunization with Ig

Hepatitis B (HBV)

• Serology interpretation:
  • HBsAg: Current infection (acute or chronic); first marker to appear (4-8 weeks post-exposure)
  • Anti-HBs: Recovery/immunity (protective); appears after HBsAg disappears
  • Anti-HBc IgM: Acute HBV infection (the "window period" marker when HBsAg has cleared but anti-HBs not yet appeared)
  • Anti-HBc IgG: Past infection or ongoing; persists for life
  • HBeAg: Active viral replication; high infectivity
  • Anti-HBe: Declining replication; lower infectivity
  • HBV DNA: Most sensitive marker of active infection/replication (PCR)
• "Window period": HBsAg has cleared but anti-HBs not yet detectable; only anti-HBc IgM is positive - do not miss this!
• Course: 90-95% of immunocompetent adults recover fully; 5-10% develop chronic infection; neonates infected perinatally have 90% risk of chronicity
• Complications of chronic HBV: Cirrhosis → HCC (HBV integrates into host genome; HCC can occur even without cirrhosis)
• Morphology (acute): Ground-glass hepatocytes (HBsAg accumulation in ER); acidophil bodies (apoptotic hepatocytes = Councilman/Mallory bodies); lobular disarray; inflammation; ballooning degeneration

Hepatitis C (HCV)

• Most common cause of chronic liver disease in the USA (before MASLD surpassed it)
• High propensity for chronicity (>80%) due to rapid viral mutation (quasispecies) → evades immune clearance
• Mechanism of liver injury: Immune-mediated (CD8+ T cells attack infected hepatocytes) rather than direct viral cytotoxicity
• Morphology: Lymphoid follicles in portal tracts (characteristic); bile duct damage; steatosis; lobular inflammation
• Natural history: Chronic hepatitis → cirrhosis (20% over 20 years) → HCC
• Treatment: Direct-acting antivirals (DAAs) achieve >95% sustained virologic response (cure); e.g., sofosbuvir + ledipasvir

Hepatitis D (HDV)

• Defective virus - requires HBsAg envelope from HBV for its own packaging and transmission
• Co-infection (HBV + HDV simultaneously): Generally self-limited; better prognosis; <5% chronicity
• Superinfection (HDV in chronic HBV carrier): 90-100% chronicity; severe disease; rapidly progresses to cirrhosis

Hepatitis E (HEV)

• Fecal-oral transmission; large epidemics in South Asia, Africa, Mexico (contaminated water)
• Usually self-limited in healthy individuals (similar to HAV)
• Exception: Very high mortality in pregnant women (20-25% in third trimester) → acute liver failure
• Chronic HEV seen in immunocompromised patients (transplant recipients)

Clinicopathologic Syndromes of Viral Hepatitis

• Hepatocyte injury: ballooning degeneration, acidophil/Councilman bodies (apoptotic hepatocytes with pyknotic nuclei)
• Lobular disarray; Kupffer cell hyperplasia
• Portal tract inflammation: lymphocytes, plasma cells, macrophages
• Cholestasis: bile plugs in canaliculi

1. Asymptomatic with recovery (most common)
2. Acute symptomatic hepatitis with recovery: 4 phases - incubation → preicteric (nausea, fever, malaise) → icteric (jaundice, dark urine, pale stools) → convalescence
3. Acute liver failure (~1% of symptomatic acute hepatitis)
4. Chronic hepatitis (only with HBV, HCV, HDV)
5. Carrier state (HBV, HCV)

4. AUTOIMMUNE HEPATITIS

• Typically young to middle-aged women
• Positive ANA (antinuclear antibody), anti-smooth muscle antibody (anti-SMA), anti-LKM1 (liver-kidney microsomal antibody), elevated IgG
• Type 1 (most common): ANA + anti-SMA positive; better prognosis
• Type 2: Anti-LKM1 positive; younger patients; more severe
• Morphology: Interface hepatitis (lymphoplasmacytic infiltrate at the portal-lobular interface), emperipolesis (lymphocytes within hepatocytes), rosette formation
• Treatment: Corticosteroids ± azathioprine → excellent response in most

5. DRUG- AND TOXIN-INDUCED LIVER INJURY (DILI)

• Intrinsic (predictable, dose-dependent): e.g., Acetaminophen - toxic metabolite NAPQI → zone 3 (centrilobular) necrosis; antidote is N-acetylcysteine (NAC)
• Idiosyncratic (unpredictable, not dose-dependent): Hypersensitivity reaction; majority of DILI; e.g., isoniazid, halothane, diclofenac
• Drugs can mimic any pattern of liver injury - must always be considered in differential diagnosis
• Temporal correlation between drug initiation and liver disease onset is required for diagnosis

6. STEATOTIC LIVER DISEASE

A. Alcohol-Associated Liver Disease (ALD)

• Spectrum of disease: Steatosis → Alcoholic Hepatitis → Fibrosis/Cirrhosis
• Risk: >80 g/day for males; females more susceptible at lower doses
• Only 10-15% of heavy drinkers develop cirrhosis (other factors: sex, genetics, comorbidities)

• Alcohol → acetaldehyde (toxic) + excess NADH → impaired fatty acid oxidation → steatosis
• Acetaldehyde → adducts with proteins → Mallory-Denk bodies
• Oxidative stress + mitochondrial dysfunction + cytokine release (TNF-α via TLR4/Kupffer cells)
• Intestinal permeability increases (especially with estrogen) → LPS enters portal blood → Kupffer cell activation

1. Hepatic steatosis (fatty liver): Earliest change; macrovesicular fat accumulation (lipid droplets displace nucleus to periphery); reversible with abstinence
2. Alcoholic hepatitis (steatohepatitis):
   • Hepatocyte ballooning + necrosis
   • Mallory-Denk bodies (dense eosinophilic intracytoplasmic inclusions of aggregated cytokeratin intermediate filaments)
   • Neutrophil infiltration (lobular)
   • Pericellular fibrosis ("chicken wire" fibrosis) around hepatocytes
   • Megamitochondria (large eosinophilic inclusions)
3. Cirrhosis: Micronodular → macronodular; end-stage

B. Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) [formerly NAFLD/NASH]

• Most common liver disease worldwide; closely linked to metabolic syndrome (obesity, T2DM, hypertension, dyslipidemia)
• Spectrum: Steatosis (MASLD) → Steatohepatitis (MASH) → Fibrosis → Cirrhosis → HCC

• Insulin resistance → increased free fatty acid delivery to liver → hepatic steatosis
• "Multiple hits": oxidative stress + mitochondrial dysfunction + gut-derived endotoxins + adipokine imbalance → hepatocyte injury → inflammation → fibrosis

• Similar to ALD: macrovesicular steatosis, ballooned hepatocytes, Mallory-Denk bodies, lobular inflammation with neutrophils
• Key difference: MASLD/MASH predominantly affects zone 3 (centrilobular); ALD is similar
• Progressive fibrosis: pericellular ("chicken wire") → bridging → cirrhosis

7. INHERITED LIVER DISEASES

A. Hereditary Hemochromatosis

• Autosomal recessive mutation in HFE gene (chromosome 6p; C282Y most common mutation) → abnormal HFE protein → failure to reduce intestinal iron absorption → iron overload
• HFE normally interacts with transferrin receptor to sense body iron stores; mutant HFE fails to upregulate hepcidin (the iron-regulatory hormone) → excessive iron absorption continues unchecked
• Iron deposits primarily in: liver, pancreas, heart, joints, skin, pituitary/gonads
• Iron causes injury through: oxidative stress (Fenton reaction → free radical generation), direct organelle damage

1. Micronodular cirrhosis (100%)
2. Diabetes mellitus ("bronze diabetes") (75-80%)
3. Abnormal skin pigmentation - bronze-gray skin (75-80%)

• Golden-brown hemosiderin granules in hepatocytes, Kupffer cells, bile duct cells
• Perls' Prussian blue stain confirms iron deposits
• Micronodular cirrhosis; iron also in pancreatic acinar cells, cardiac myocytes, adrenal cells

B. Wilson Disease

• Autosomal recessive mutation in ATP7B gene (chromosome 13q14) encoding a copper-transporting ATPase expressed in hepatocytes
• Defective copper transport → failure to incorporate copper into ceruloplasmin + failure to excrete copper in bile → copper accumulates in liver first, then brain, eyes, kidneys

• Liver: chronic hepatitis → cirrhosis; may present as acute liver failure
• Brain: Lenticular degeneration (basal ganglia) → tremors, rigidity, psychiatric disturbances, dysarthria, dysphagia
• Eyes: Kayser-Fleischer rings - golden-brown rings at periphery of cornea (Descemet membrane); seen on slit-lamp examination; virtually pathognomonic
• Kidneys: Fanconi syndrome (proximal tubular dysfunction → aminoaciduria, phosphaturia)
• Hemolytic anemia (copper released into blood from damaged hepatocytes)

• Liver: steatosis → hepatocyte necrosis → portal inflammation → cirrhosis
• Rhodanine stain (red-orange) or orcein stain: highlights copper deposits
• Electron microscopy: mitochondrial changes (distinctive early finding)

C. α1-Antitrypsin (A1AT) Deficiency

• Autosomal recessive mutation in SERPINA1 gene (chromosome 14q32)
• PiZZ genotype (most severe): Mutant Z protein misfolds and accumulates as aggregates in hepatocyte ER (instead of being secreted) → ER stress + apoptosis → liver disease
• Absent serum A1AT → uninhibited elastase activity in lungs → panacinar emphysema (lower lobes)

• PAS-positive, diastase-resistant intracytoplasmic globules in hepatocytes (periportal) - hallmark
• Ranges from neonatal hepatitis to cirrhosis in adults

8. CHOLESTATIC DISEASES

Bilirubin Metabolism & Jaundice

1. Senescent RBCs degraded by macrophages (spleen/liver/bone marrow) → Heme → Biliverdin → Bilirubin (unconjugated, insoluble, albumin-bound)
2. Hepatocyte uptake → conjugation with glucuronic acid (UGT1A1 enzyme) → bilirubin glucuronides (water-soluble, non-toxic)
3. Excretion into bile → intestine → bacterial deconjugation → urobilinogen (colorless) → stercobilin (brown feces color)
4. Enterohepatic circulation: ~20% urobilinogen reabsorbed → liver → re-excreted in bile; small amount in urine

• Gilbert syndrome: Mild UGT1A1 promoter mutation → reduced conjugation; benign; elevated unconjugated bilirubin especially with fasting/stress; no treatment needed
• Crigler-Najjar syndrome Type I: Complete absence of UGT1A1 → severe unconjugated hyperbilirubinemia → kernicterus → fatal unless treated (liver transplant)
• Crigler-Najjar Type II: Partial deficiency; responds to phenobarbital (induces residual UGT1A1)

• Dubin-Johnson syndrome: Defect in MRP2 (canalicular transport protein for conjugated bilirubin) → conjugated bilirubin regurgitated into blood; black-pigmented liver (lipofuscin-like pigment); benign
• Rotor syndrome: Similar to Dubin-Johnson but no liver pigmentation; benign

Primary Biliary Cholangitis (PBC)

• T-cell-mediated attack on bile duct epithelium
• Hallmark: Antimitochondrial antibody (AMA) directed against PDC-E2 (E2 component of pyruvate dehydrogenase complex) - present in 95% of cases
• Retention of bile salts → secondary hepatocellular injury → cirrhosis

• "Florid duct lesion": Dense lymphocytic + granulomatous infiltrate destroying small bile ducts
• Poorly formed granulomas in portal tracts centered on bile ducts
• Portal lymphoplasmacytic inflammation with ductular reaction
• Progressive: bile duct loss → ductopenia → biliary-type cirrhosis

Primary Sclerosing Cholangitis (PSC)

• Inflammatory bowel disease (70%) - especially ulcerative colitis (IBD precedes PSC in most cases)
• 65% ANCA-positive; AMA typically negative

• Concentric periductal fibrosis ("onion-skin" fibrosis) obliterating medium-sized ducts
• Alternating strictures and dilations of bile ducts → "beads on a string" pattern on MRCP/cholangiography
• Progressive bile duct loss → biliary cirrhosis

9. HEPATIC VASCULAR DISORDERS

Budd-Chiari Syndrome (Hepatic Vein Thrombosis)

• Thrombosis of 2 or 3 hepatic veins → impaired hepatic venous outflow → congestion + necrosis
• Causes: Polycythemia vera (most common), myeloproliferative disorders, hypercoagulable states (factor V Leiden, antiphospholipid syndrome, paroxysmal nocturnal hemoglobinuria, oral contraceptive use), pregnancy, HCC invasion
• Morphology: Severe centrilobular congestion and necrosis; marked hepatomegaly; ascites; "nutmeg liver" (mottled appearance)
• Clinical: Abdominal pain, hepatomegaly, ascites; Doppler US shows absent hepatic vein flow; chronic cases → cirrhosis

Passive Congestion (Right Heart Failure / Cardiac Cirrhosis)

• Chronic right-sided heart failure → elevated central venous pressure → hepatic venous congestion
• "Nutmeg liver": Alternating areas of red congestion (centrilobular) and yellow fat (periportal)
• Morphology: Centrilobular (zone 3) sinusoidal dilation and congestion; with severe/prolonged cases → centrilobular necrosis → fibrosis → cardiac cirrhosis

Portal Vein Obstruction and Thrombosis

• Non-cirrhotic portal hypertension; causes: neonatal omphalitis/umbilical vein infection, intraabdominal sepsis, pancreatitis, hypercoagulable states, HCC invasion
• Clinical: portal hypertension, varices, splenomegaly WITHOUT significant liver dysfunction (liver parenchyma is intact)

Sinusoidal Obstruction Syndrome (SOS, formerly Veno-Occlusive Disease)

• Obstruction of hepatic sinusoids and terminal hepatic venules (not large veins)
• Causes: Bone marrow transplant conditioning regimens (cyclophosphamide + whole body radiation), pyrrolizidine alkaloids (herbal teas)
• Morphology: Sinusoidal fibrin deposition → fibrosis of terminal hepatic venules
• Clinical: Jaundice, hepatomegaly, weight gain, ascites within weeks of BMT

10. LIVER TUMORS

Benign Liver Tumors

• Most common benign liver tumor; incidental finding; no malignant potential
• Blood-filled vascular spaces lined by endothelium; "light-up" on contrast MRI

• Benign hepatocyte tumor; strongly associated with oral contraceptive use in young women; also anabolic steroids
• Molecular subtypes: HNF1A-mutated (steatotic), β-catenin-activated (risk of HCC), inflammatory
• Risk of rupture and hemorrhage (especially during pregnancy)
• May undergo malignant transformation (β-catenin-activated subtype)
• Morphology: Well-demarcated, pale yellow-tan mass; no bile ducts, no portal tracts; hepatocytes in sheets and cords

• Non-neoplastic hyperplastic response to a pre-existing vascular anomaly; not a true neoplasm
• Central stellate scar with thick-walled blood vessels (pathognomonic on imaging)
• No malignant potential; not hormone-dependent; no risk of rupture

Hepatocellular Carcinoma (HCC)

• 5th most common cancer globally; 3rd most common cause of cancer death

• 85% occur in Asia and sub-Saharan Africa (HBV endemic areas)

• Pronounced male predominance (up to 8:1 in high-incidence areas)
• In Asia: peak 20-40 years (perinatal HBV); In West: older adults (cirrhosis from HCV/MASLD)

• Chronic HBV (most important globally; HCC can occur without cirrhosis via HBV DNA integration)
• Chronic HCV (virtually only in cirrhotic livers)
• Aflatoxin B1 (Aspergillus-contaminated crops; synergizes with HBV; causes TP53 R249S mutation)
• Alcohol-associated cirrhosis
• MASLD/MASH (even without cirrhosis)
• Hemochromatosis, Wilson disease, α1-AT deficiency (increased risk)

• Most HCC arise in cirrhotic livers (but 15-20% in non-cirrhotic liver)
• Driver mutations: β-catenin activating mutations (40%), TERT promoter mutations (50-60%), TP53 inactivating mutations (up to 60%), HBx protein disrupts tumor suppression
• Precursor lesions: Large cell change, small cell change, dysplastic nodules (low grade → high grade → early HCC)
• Special subtype: Fibrolamellar HCC - adolescents/young adults; no underlying cirrhosis; DNAJB1::PRKACA fusion gene; fibrous bands between tumor cells; better prognosis

• Gross: Single large mass, multifocal nodules, or diffusely infiltrating
• Cut surface: green (bile-secreting), yellow-white (fatty), hemorrhagic
• Micro: Hepatocytes in trabecular/acinar pattern; bile production (pathognomonic); vascular invasion is common (portal vein)
• CD10, Hep Par-1, Glypican-3 (GPC3), AFP immunostaining useful for diagnosis

• Often asymptomatic until advanced stage (right upper quadrant pain, weight loss, hepatomegaly, ascites)
• Alpha-fetoprotein (AFP): Tumor marker - elevated in 50-70% of HCC; >400 ng/mL strongly suggests HCC
• Surveillance: Ultrasound ± AFP every 6 months in cirrhotic patients
• Spread: intrahepatic (via portal vein), lung, regional lymph nodes, adrenals
• Poor prognosis if not detected early; treatment: resection, ablation, sorafenib, immunotherapy, liver transplant (Milan criteria)

Cholangiocarcinoma (Malignant Biliary Tumors)

• Adenocarcinoma of biliary epithelium; intrahepatic or extrahepatic (Klatskin tumor at hilum)
• Risk factors: PSC (most important in West), liver flukes (Clonorchis sinensis, Opisthorchis viverrini - endemic in Southeast Asia), choledochal cysts, hepatolithiasis, chronic biliary inflammation
• Morphology: Dense desmoplastic stroma; CK7+ and CK19+ (biliary markers); often aggressive perineural invasion
• Clinical: Obstructive jaundice (Klatskin), elevated ALP/GGT; CA 19-9 tumor marker; very poor prognosis

Metastases to Liver

• Most common hepatic tumors overall (much more common than primary liver tumors in Western countries)
• Most frequent primaries: colon (via portal vein), stomach, pancreas, breast, lung
• Multiple nodules; "bull's-eye" appearance on imaging (central necrosis)

PART II: THE GALLBLADDER

11. CHOLELITHIASIS (GALLSTONES)

• Affect 10-20% of adults in Western countries; >95% of biliary tract disease is attributable to gallstones

• Pain (biliary colic): right upper quadrant colicky pain after fatty meals (cystic duct obstruction)
• Inflammation: Cholecystitis (acute or chronic)
• Pancreatitis: Stone impacted at ampulla of Vater → biliary pancreatitis
• Empyema, jaundice (common bile duct obstruction), gallbladder carcinoma (long-term), Mirizzi syndrome, gallstone ileus (rare)

12. CHOLECYSTITIS

Acute Cholecystitis

• Usually triggered by obstruction of the cystic duct by a stone → bile stasis → mucosal injury → secondary inflammation
• Chemical initially (prostaglandins, bile salts), bacterial superinfection later (E. coli, Klebsiella, anaerobes)
• Morphology: Enlarged, tense gallbladder; fibrinous exudate on serosa; turbid bile with fibrin and pus; stone in cystic duct/neck; wall edematous and hyperemic; neutrophil infiltrate
• Severe: Gangrenous cholecystitis (green-black necrosis + perforation); Empyema (pus-filled gallbladder); Emphysematous cholecystitis (gas-forming organisms - diabetics)

• In severely ill patients: major surgery, trauma, burns, sepsis, prolonged TPN
• Mechanism: gallbladder ischemia + bile stasis (no enteric stimulation → no CCK → no gallbladder contraction)
• More insidious; higher rate of gangrene and perforation (delayed diagnosis in critically ill); higher mortality

Chronic Cholecystitis

• Associated with gallstones in >90% of cases; may develop from repeated acute attacks or insidiously
• Rokitansky-Aschoff sinuses: Herniation of mucosa into the muscular layer (due to increased intraluminal pressure) - characteristic
• Morphology: Thickened fibrotic wall; variable lymphocytic infiltrate; mucosal atrophy
• Porcelain gallbladder: Extensive calcification of the gallbladder wall in chronic cholecystitis; historically associated with cancer risk (now debated)

13. GALLBLADDER CARCINOMA

• Most common malignancy of the extrahepatic biliary tract
• Gallstones present in 95% of cases - but only 1-2% of patients with stones develop cancer; common thread is chronic inflammation
• Risk factors: Female sex, gallstones, chronic biliary infection (Asia: liver flukes, bacteria), gallbladder adenoma, anomalous pancreatic ductal junction
• Molecular: EGFR/HER2 amplification, RAS mutation, TP53 mutation (up to 50%)

• Mainly adenocarcinoma (most common at the fundus)
• Firm, poorly circumscribed mass OR diffuse infiltration (mimics chronic cholecystitis)
• Precursor lesions: flat dysplastic lesions (biliary intraepithelial neoplasia), papillary-tubular neoplasm (intracholecystic)
• Desmoplastic stroma; perineural and vascular invasion; CK7/CK19+

14. BILIRUBIN METABOLISM DISORDERS (Key Syndromes)

High-Yield Key Concepts Summary

MUSEUM SPECIMEN GUIDE FOR PRACTICAL EXAMINATION

(Robbins & Cotran Pathologic Basis of Disease)

FEMALE REPRODUCTIVE SYSTEM

1. SEROUS CYSTADENOMA OF OVARY

• Unilocular or multilocular cyst - a single large cyst or several cysts divided by thin septa
• Wall: Thin, smooth, glistening inner surface
• Size: Can range from small (few cm) to very large (filling the abdomen)
• Contents: Watery, straw-colored (serous) fluid
• Surface: Smooth outer surface; may have small papillary projections on inner wall (if borderline, more papillary projections)
• Bilateral in ~15-20% of cases

• Cyst lined by a single layer of flattened to cuboidal epithelium resembling fallopian tube epithelium (ciliated cells)
• Psammoma bodies (laminated calcific concentric rings) - very characteristic, seen especially in borderline/malignant types

• Most common ovarian tumor - serous type
• 75% are benign or borderline; 25% malignant
• Benign: age 20-45; carcinoma: older age
• Risk factors for serous carcinoma: nulliparity, BRCA1/BRCA2 mutations
• BRCA1 increases ovarian cancer risk to 20-60% by age 70
• Psammoma bodies = calcified concentric rings - hallmark of papillary serous tumors
• Bilateral ovarian involvement suggests malignancy
• High-grade serous carcinoma: TP53 mutations; Low-grade: KRAS/BRAF mutations

2. DERMOID CYST (Mature Cystic Teratoma of Ovary)

• Unilocular cyst lined by skin-like gray-white wrinkled epidermis
• Contents: Hair (most striking feature), sebaceous/greasy material (yellow-white cheesy material)
• Protruding hair shafts visible from the cyst wall
• Tooth structures and areas of calcification commonly found in the wall
• Rokitansky's protuberance (dermoid plug): a solid nodule projecting into the cyst cavity - classic feature; teeth, bone, cartilage may be embedded here
• Size: Usually 5-15 cm
• Bilateral in 10-15% of cases
• One ovary usually affected

• Cyst wall: stratified squamous epithelium with sebaceous glands, hair follicles, sweat glands (skin adnexa)
• Other germ layers also present: cartilage, bone, thyroid tissue, neural tissue
• Goblet cells, bronchial epithelium may be seen

• Most common germ cell tumor of ovary - mature cystic teratoma
• Karyotype: 46,XX - arise from oocyte after 1st meiotic division
• Malignant transformation in 1% - most commonly to Squamous Cell Carcinoma
• Struma ovarii = teratoma where >50% thyroid tissue (can cause hyperthyroidism)
• Complications: torsion (most common), rupture (chemical peritonitis), malignant change
• Treatment: cystectomy (ovary-conserving)

3. DYSGERMINOMA

• Solid tumor - this is the key distinguishing feature from most other ovarian tumors
• Large, bulky mass - can fill the abdomen (range: barely visible to very large)
• Cut surface: Solid, yellow-white to gray-pink ("fish-flesh"), soft and fleshy in consistency
• Lobulated appearance - divided into lobules by fibrous septa
• 80-90% unilateral
• Smooth outer surface, may show areas of necrosis/hemorrhage in larger tumors

• Large vesicular cells (polyhedral) with clear cytoplasm, well-defined cell borders
• Large, centrally placed regular nuclei with prominent nucleoli
• Cells grow in sheets or cords separated by scant fibrous stroma
• Stroma infiltrated by lymphocytes (like seminoma)
• Non-caseating granulomas may be present
• IHC: KIT+, OCT3/4+, NANOG+ (stem cell markers); PLAP+

• 50% of all malignant germ cell tumors of ovary
• Age: 2nd and 3rd decade of life; 75% in teens/young adults
• Some arise in patients with gonadal dysgenesis/pseudohermaphroditism
• 15% have elevated hCG (if syncytiotrophoblasts present)
• Marker: Isochromosome 12p (i12p) - same as testicular seminoma
• KIT mutations in 30-50% - potential therapeutic target
• Highly radiosensitive and chemosensitive
• Unilateral, capsule-intact tumor: >90% 10-year survival after salpingo-oophorectomy
• Even with spread, often curable with chemotherapy

4. FIBROADENOMA (of Breast)

• Well-circumscribed, discrete, rubbery nodule - very clearly demarcated from surrounding breast tissue
• Gray-white in color
• Bulges above the cut surface (stands out clearly)
• Slit-like spaces (gland-like structures) visible on cut surface
• Size: Usually 1-3 cm; can be very large ("giant fibroadenoma")
• Capsule: Well-encapsulated
• Consistency: Rubbery/firm but not hard; mobile on palpation (clinically called "breast mouse")
• In older women: stroma becomes densely hyalinized, may show calcification

• Two patterns:
  • Pericanalicular: Stroma surrounds patent oval/rounded ducts
  • Intracanalicular: Stroma compresses and distorts ducts into curved/slit-like clefts
• Stroma: delicate, loose, often myxoid (resembles intralobular stroma)
• Epithelium: double-layered (inner epithelial + outer myoepithelial cells)
• Driver mutation: MED12 gene (also seen in uterine leiomyoma)

• Most common benign breast tumor in women under 35
• "Breast mouse" = clinically - mobile, non-tender, discrete lump
• Multiple and bilateral in young women
• Hormonally responsive: grows in pregnancy, regresses after menopause
• MED12 mutation in 2/3 of fibroadenomas
• NOT a premalignant lesion (no significant increase in breast cancer risk)
• Rarely undergoes infarction during pregnancy
• Giant fibroadenoma in adolescent = juvenile fibroadenoma

5. CARCINOMA OF BREAST (Invasive Breast Carcinoma)

• Irregular, stellate/star-shaped mass with poorly defined margins - classic "crab-claw" or spiculated appearance
• Rock-hard consistency (scirrhous/stony hard) - due to desmoplastic stroma
• Gray-white cut surface with yellow chalky streaks (necrotic areas or elastosis)
• Gritty sensation when cut with knife (calcium deposits)
• Skin changes if advanced: dimpling/peau d'orange (orange peel appearance), nipple retraction
• Size: Variable; screening detects small tumors <2 cm
• Fixity: Adherent to pectoralis fascia or skin in advanced disease

• Cords, nests, glands, or sheets of malignant epithelial cells
• Dense desmoplastic stroma surrounding tumor cells
• Pleomorphic nuclei, prominent nucleoli, mitotic figures
• Lymphovascular invasion may be seen

• Luminal A: ER+/PR+, HER2-, low grade - best prognosis
• Luminal B: ER+, HER2+ or high Ki-67
• HER2: HER2 overexpressed (gene amplified)
• Triple Negative (TNBC): ER-, PR-, HER2- - worst prognosis; associated with BRCA1 mutations

• Risk factors: female sex, age, early menarche/late menopause, nulliparity, exogenous estrogens, obesity, BRCA1/BRCA2/PALB2/TP53 mutations
• Familial breast cancer: 1/4 to 1/3 of all cases
• BRCA1: chromosome 17q21; BRCA2: chromosome 13q12
• Spread: axillary lymph nodes first (lateral and central tumors); internal mammary nodes (medial tumors)
• Peau d'orange: lymphatic obstruction causing skin edema
• Nipple retraction: Cooper's ligament involvement
• Paget's disease of nipple: large pale Paget cells in epidermis of nipple = underlying ductal carcinoma

6. RENAL CELL CARCINOMA (RCC)

• Location: Usually at one pole of the kidney (upper pole more common), within the renal cortex
• Spherical/ovoid mass - clearly demarcated, often with a pseudocapsule
• Cut surface: Bright yellow or orange-yellow color (due to lipid-laden clear cells) - most characteristic feature
• Variegated appearance: Yellow areas with foci of white (necrosis), red-brown (hemorrhage), gray (fibrosis), cystic areas
• Tumor thrombus in renal vein - classic and important finding; may extend into IVC and right atrium
• Size: Often large by the time of diagnosis (>10 cm) as it is silent
• Compressed adjacent renal parenchyma (pseudocapsule)

• Large cells with clear cytoplasm (glycogen and lipid washed out in processing)
• Cells arranged in nests/trabeculae surrounded by rich sinusoidal vasculature
• Nuclei: small to large with nucleoli
• Delicate fibrovascular stroma

• Classic triad: hematuria + loin pain + palpable flank mass (only 10% of cases)
• Most reliable sign: painless hematuria
• "Great mimic" in medicine - paraneoplastic syndromes: polycythemia (erythropoietin), hypercalcemia, hypertension, Cushing syndrome, feminization
• Metastases: lungs (>50%), bones (33%), lymph nodes, liver, brain
• In 15% of new patients, metastases already present at diagnosis
• Genetics: VHL gene mutation (chromosome 3p25) in clear cell RCC - leads to HIF-1 overactivation and angiogenesis (VEGF upregulation)
• VHL syndrome: bilateral, multiple clear cell RCCs
• Treatment: radical nephrectomy; VEGF inhibitors (sunitinib) + immune checkpoint inhibitors for metastatic disease
• 5-year survival: ~70% overall; ~100% without metastases

7. GRANULAR CONTRACTED KIDNEY (Nephrosclerosis / Hypertensive Kidney)

• Small, shrunken kidney - reduced in size bilaterally; weight 110-130 g (normal ~150 g)
• Cortical surface: Fine, even granularity - described as "grain leather" or "finely granular surface" - the hallmark feature
• Granules = small cortical scars (collapsed areas) alternating with tiny nodules (preserved parenchyma) = irregular bumpy surface but with FINE granules
• Color: Pale, gray-brown
• Cut surface: Thinned cortex
• Capsule: Adherent (cannot be stripped off easily)
• Bilateral involvement

Differentiate from large nodular kidneys of ARPKD or the coarse scarring of chronic pyelonephritis (irregular, asymmetric scarring with blunted calyces).

• Hyaline arteriolosclerosis - thickened arteriolar walls, hyaline pink deposits, narrowed lumens
• Fibroelastic hyperplasia of interlobular arteries
• Glomerulosclerosis - collapsed GBM, Bowman space collagen
• Tubular atrophy and interstitial fibrosis
• Alternating zones of atrophy with better-preserved parenchyma

• Cause: chronic hypertension (also aging, more common in Africans)
• Pathogenesis: HTN → arteriolar thickening → ischemia → glomerulosclerosis
• Fine granular surface = cortical scars + bulging preserved parenchyma
• Two processes: medial/intimal thickening + hyalinization of arterioles
• Rarely causes uremia unless malignant phase develops
• Malignant hypertension (5% of hypertensives): rapid rise in BP → flea-bitten kidney (petechial hemorrhages) on gross; onion-skin hyperplastic arteriolitis on microscopy

8. CARCINOMA OF URINARY BLADDER (Urothelial Carcinoma)

• Two main patterns:
  • Papillary (exophytic): Frond-like, cauliflower-like projections arising from mucosa - looks like a sea anemone or cauliflower floating into the lumen
  • Flat/Sessile (invasive): Solid, ulcerated, infiltrating mass with necrosis and hemorrhage
• Location: Most common at trigone (posterior wall, near ureteric orifices)
• Multifocal - multiple tumors often present (field effect/polyclonal origin)
• Hemorrhagic areas common
• In advanced cases: tumor may obstruct ureteric orifice → hydronephrosis

• Low-grade papillary: Papillary fronds lined by urothelium with mild-moderate atypia; cells maintain polarity
• High-grade papillary: Marked cytologic atypia, loss of polarity, frequent mitoses
• Invasive carcinoma: Nests/cords of malignant cells invading lamina propria and/or muscularis propria (detrusor muscle)
• CIS (carcinoma in situ): Flat lesion, cytologically malignant cells confined to urothelium without invasion

• Most common symptom: painless hematuria (intermittent)
• Frequency, urgency, dysuria may accompany
• Male:Female ratio = 3:1; age 50-80 years
• Risk factors: cigarette smoking #1 (3-7 fold increased risk; 50-80% of male bladder cancers), industrial exposure to aryl amines (2-naphthylamine), aniline dyes, Schistosoma haematobium (causes squamous cell carcinoma)
• Squamous cell carcinoma: associated with schistosomiasis/chronic infection
• Key prognostic factor: depth of invasion (T staging)
  • Non-muscle invasive = Ta/T1 (lamina propria): 98% 10-year survival; treat with TUR + BCG
  • Muscle-invasive (T2+): 30% 5-year mortality; requires radical cystectomy
• High recurrence rate (70%) for non-muscle-invasive tumors
• BCG (Bacillus Calmette-Guérin): intravesical immunotherapy for high-risk non-invasive tumors

MALE REPRODUCTIVE SYSTEM

9. SEMINOMA (of Testis)

• Testis enlarged but maintains its ovoid shape
• Well-circumscribed mass that may replace the entire testis
• Cut surface: Homogeneous, pale/cream-white to gray, lobulated appearance - described as "fish flesh"
• Soft, fleshy consistency
• NO hemorrhage or necrosis in pure seminoma (unlike embryonal carcinoma) - important distinguishing feature
• Fibrous septa may divide the tumor into lobules
• Tunica albuginea usually intact (not breached in early cases)

• Large polyhedral cells with clear cytoplasm (glycogen-rich)
• Well-defined cell borders
• Centrally placed nuclei with prominent nucleoli
• Cells arranged in sheets divided by fibrous septa
• Lymphocytic infiltrate in stroma (characteristic)
• Non-caseating granulomas may be present
• IHC: KIT+, OCT3/4+, NANOG+, PLAP+; Cytokeratin-

• Peak age: 30-40 years; most common testicular cancer
• Risk factors: cryptorchidism (#1), Klinefelter syndrome (for mediastinal GCTs), infertility, prior GCT in contralateral testis
• Germ cell neoplasia in situ (GCNIS) = precursor; 90% of invasive GCTs are preceded by GCNIS
• Marker: Isochromosome 12p (i12p) - found in virtually all GCTs
• Serum markers: AFP = NEGATIVE (AFP positive = non-seminomatous); hCG mildly elevated in 15% (if syncytiotrophoblasts); LDH may be elevated
• Spread: Para-aortic lymph nodes FIRST (not inguinal, because testes descend from retroperitoneum)
• Radiosensitive - treated with radiation to para-aortic nodes (Stage I/IIA)
• Excellent prognosis: Stage I - 99% cure rate
• Spermatocytic tumor: older men (>65 years), does NOT metastasize, not related to GCNIS

UTERUS

10. LEIOMYOMA (Fibroid) - Subserosal + Submucosal + Intramural

• Well-circumscribed, discrete, round/spherical nodules
• Firm, gray-white cut surface
• Whorled pattern on cut section - smooth muscle bundles arranged in interlacing whorls - MOST CHARACTERISTIC feature
• Multiple tumors usually (rarely single)
• Three locations (MUST know for exam):
  • Intramural: Within the myometrium - most common type; uterus uniformly enlarged
  • Submucosal: Just beneath endometrium; projects into uterine cavity; causes heavy menstrual bleeding; can become pedunculated and prolapse through cervix
  • Subserosal: Just beneath serosa; projects outward; can become pedunculated; may undergo torsion
• Size: Variable - mm to massive tumors filling pelvis
• Large tumors may show yellow-brown to red softening (degeneration)

• Fresh: pale gray-white
• Degenerated: yellow (hyaline), red (red degeneration in pregnancy), green/black (necrosis)

• Bundles of smooth muscle cells resembling normal myometrium
• Cells uniform in size, oval nuclei, long slender bipolar cytoplasmic processes (cigar-shaped nuclei)
• Scarce mitotic figures (KEY: <5 mitoses/10 HPF)
• No necrosis, no significant atypia
• Surrounded by compressed pseudocapsule

• Most common tumor in women (20-25% of women over 35)
• Mutation: MED12 gene (70% of cases); also chromosome 12q14 rearrangements
• Hormone-dependent: grows under estrogen stimulation; regresses post-menopause
• Symptoms: abnormal uterine bleeding (submucosal type), urinary frequency (compresses bladder), infertility, pressure symptoms
• Pregnancy complications: increased spontaneous abortion, malpresentation, postpartum hemorrhage; red degeneration = hemorrhagic infarction during pregnancy (acute pain)
• Malignant transformation to leiomyosarcoma: EXTREMELY RARE (<1 in 1000)
• Leiomyosarcoma: >10 mitoses/10 HPF + coagulative tumor cell necrosis + significant atypia

11. ENDOMETRIAL HYPERPLASIA

• Thickened, spongy endometrium - normally endometrium is 1-3 mm; in hyperplasia it may be 5-10+ mm
• Polypoid/velvety surface - irregular, sometimes polypoid projections
• Pale pink, soft, thick endometrial lining
• No specific unique gross features that distinguish it from carcinoma - requires biopsy/curettage for diagnosis

• Hyperplasia without atypia:
  • Increased gland-to-stroma ratio
  • Variable gland size and shape; may be dilated
  • Some intervening stroma preserved
  • Nuclei: round, uniform, basally oriented - NO atypia
  • Rarely progresses to carcinoma (1-3%)
• Atypical hyperplasia (Endometrioid Intraepithelial Neoplasia/EIN):
  • Back-to-back glands with minimal intervening stroma
  • Nuclear atypia: Enlarged, rounded, prominent nucleoli
  • Loss of polarity
  • ~30% progress to endometrial carcinoma
  • PTEN mutations in >20% of cases

• Obesity (peripheral conversion of androgens to estrogens in fat)
• Menopause
• Polycystic ovarian syndrome (PCOS)
• Functioning granulosa cell tumor of ovary
• Exogenous estrogen therapy (HRT without progesterone)

• Presentation: abnormal uterine bleeding (postmenopausal or irregular menstrual)
• PTEN tumor suppressor gene loss - most important molecular alteration (>20% hyperplasia, 30-80% endometrial carcinoma)
• Cowden syndrome (germline PTEN mutation): high incidence of endometrial carcinoma
• Without atypia: 1-3% progress to carcinoma
• With atypia (EIN): 30% progress to carcinoma; treat with hysterectomy
• Treatment: progesterone therapy (for hyperplasia without atypia); hysterectomy (for atypia)

12. CARCINOMA CERVIX

• Two main patterns:
  • Exophytic (fungating): Cauliflower-like mass projecting from the ectocervix - more visible on examination
  • Endophytic (infiltrative): Barrel-shaped cervix - tumor grows within cervical stroma, enlarging the cervix; less visible; worse prognosis
• Location: Most commonly at transformation zone (squamocolumnar junction)
• Ulceration with necrosis in advanced tumors
• Friable tissue that bleeds easily on touch
• In advanced disease: parametrial spread, bladder/rectal invasion, vesicovaginal fistula

• Squamous cell carcinoma: Nests and tongues of malignant squamous epithelium invading cervical stroma; may be keratinizing (keratin pearls) or non-keratinizing
• Adenocarcinoma: Malignant glandular epithelium with large hyperchromatic nuclei, mucin-depleted (dark) glands
• Koilocytic atypia in adjacent CIN: nuclear enlargement + perinuclear halo = HPV cytopathic effect

• LSIL (CIN1): Immature cells in lower 1/3 of epithelium; koilocytes present; usually regresses spontaneously
• HSIL (CIN2/3): Immature cells in upper 2/3 to full thickness; high risk of progression to invasive carcinoma

• HPV types: High-risk = 16, 18 (16 = squamous; 18 = adenocarcinoma)
• HPV encodes E6 (inactivates p53) and E7 (inactivates Rb) → cell cycle deregulation
• Peak age of invasive carcinoma: 45-50 years
• Screening: Pap smear (detects precursor lesions)
• Vaccine: HPV vaccine (quadrivalent: 6, 11, 16, 18) prevents infection
• Spread: direct extension to parametrium, rectum, bladder; lymphatics to pelvic nodes
• Staging is CLINICAL (FIGO staging)
• Koilocyte = diagnostic of HPV infection; nuclear enlargement + perinuclear halo
• p16 overexpression on IHC = surrogate marker for high-risk HPV integration

HEPATOBILIARY SYSTEM

13. CHRONIC CHOLECYSTITIS

• Gallstones present in the lumen (90%+ cases) - may be single large stone or multiple faceted stones; cholesterol stones (yellow) or pigment stones (dark brown/black)
• Thickened gallbladder wall - gray-white, fibrotic
• Bile: Green-yellow mucoid bile in lumen
• Serosa: Usually smooth and glistening; may be dull from fibrosis; dense adhesions may be present (sequelae of prior acute inflammation)
• Mucosa: Generally preserved; may appear flattened
• Wall: Variably thickened, opaque gray-white (fibrosis)
• Occasionally: Porcelain gallbladder = extensive dystrophic calcification of wall (associated with increased risk of gallbladder carcinoma)

• Chronic inflammatory infiltrate: Lymphocytes, plasma cells, macrophages in mucosa and subserosal fibrous tissue
• Subepithelial and subserosal fibrosis
• Rokitansky-Aschoff sinuses = outpouchings of mucosal epithelium through the gallbladder wall into the muscularis/serosa - pathognomonic of chronic cholecystitis
• Xanthogranulomatous cholecystitis: Foamy macrophages (xanthoma cells) in thickened wall (triggered by rupture of Rokitansky-Aschoff sinuses + biliary phospholipid accumulation)

• Rokitansky-Aschoff sinuses: diagnostic feature; sinus contains bile
• 90%+ cases have cholelithiasis; may occur without stones (acalculous)
• Porcelain gallbladder: calcification of wall; associated with carcinoma risk
• "5F" risk factors for gallstones: Female, Fat (obese), Forty, Fertile, Fair
• Cholesterol stones: radiolucent, yellow, smooth, often single; pure cholesterol
• Pigment stones: black = hemolytic anemia; brown = infection/bile stasis
• Complication: Mucocele (obstruction by stone + mucus accumulation), Empyema, perforation, carcinoma
• Mirizzi syndrome: stone in Hartmann's pouch compressing common bile duct

14. MICRONODULAR CIRRHOSIS

• Liver enlarged initially (fatty liver/hepatitis stage), later shrunken and firm in end-stage
• Capsular surface: Converted from smooth to uniformly bumpy with small nodules
• Nodule size: ALL nodules uniformly <3 mm (pinhead to millet-grain sized) - this is the KEY feature of micronodular cirrhosis
• Fibrous bands: Thin bands separating the nodules (not always clearly visible grossly)
• Color: Tan to yellow (fatty change) or brown-yellow
• Consistency: Firm, tough (due to fibrosis)
• Depressed areas = fibrous scars; elevated areas = regenerative nodules

Macronodular cirrhosis: Nodules >3 mm (up to several cm) - post-viral hepatitis (HBV/HCV). Mixed cirrhosis: both types.

• Parenchymal nodules surrounded by dense bands of fibrous tissue (collagen)
• Nodules contain hepatocytes (regenerative); loss of normal lobular architecture
• Vascular distortion - portal-to-portal and portal-to-central fibrous bridges
• Variable degrees of: fatty change, Mallory-Denk bodies (alcoholic), hepatocyte ballooning, inflammation

• Most common cause of micronodular cirrhosis: Alcoholic liver disease (also hemochromatosis, primary biliary cirrhosis early)
• Pathogenesis: chronic hepatocyte injury → stellate cell activation → collagen deposition → fibrosis → nodule formation
• Complications: portal hypertension → esophageal varices (hemorrhage), splenomegaly, ascites, caput medusae; hepatic encephalopathy (shunting); hepatorenal syndrome; hepatocellular carcinoma (HCC) risk
• Laboratory: elevated PT (synthetic failure), low albumin, raised bilirubin, raised AST/ALT
• Reversibility: thin incomplete scars may regress if cause removed (e.g., sobriety)
• Child-Pugh score: classifies severity; A=good, B=moderate, C=poor prognosis

GASTROINTESTINAL SYSTEM

15. CARCINOMA OF STOMACH

• Fungating/Polypoid mass projecting into lumen, OR
• Ulcerating mass with raised, irregular, everted (rolled-out) edges - most common for advanced carcinoma
• Borrmann classification:
  • Type I: Polypoid/fungating
  • Type II: Ulcerated with raised margins (most common)
  • Type III: Ulcerated with infiltrating margins
  • Type IV: Diffuse infiltrating (linitis plastica)
• Prepyloric location: Tumor at pyloric antrum/prepyloric region; causes gastric outlet obstruction
• Ulcer characteristics (malignant vs benign ulcer):
  • Malignant: Irregular edges, raised/heaped-up everted borders, nodular floor, necrotic base; folds DO NOT radiate to crater
  • Benign peptic ulcer: Regular round/oval, flat/punched-out edges, smooth floor; folds radiate to crater

• Diffuse infiltrating adenocarcinoma (signet ring cell type)
• Stomach wall is uniformly thickened and rigid
• Stomach cannot distend
• Cut section: thickened, rubbery gray-white wall
• Folds are absent or obliterated

• Intestinal type: Gland-forming adenocarcinoma; tumor cells form recognizable tubules/glands
• Diffuse type: Discohesive cells, often with signet ring cells (large mucin vacuole pushing nucleus to periphery); no gland formation; diffuse infiltration of wall

• H. pylori infection → chronic atrophic gastritis → intestinal metaplasia → dysplasia → carcinoma (Correa cascade)
• Risk factors: H. pylori, diet (smoked/salted foods, nitrites), atrophic gastritis, intestinal metaplasia, pernicious anemia, partial gastrectomy (remnant stomach)
• Most common site: Antrum and lesser curvature (intestinal type); Fundus/body (diffuse type)
• CDH1 mutation: familial diffuse gastric carcinoma (E-cadherin loss)
• Virchow's node: left supraclavicular node (Troisier's sign)
• Sister Mary Joseph nodule: periumbilical nodule (peritoneal spread)
• Krukenberg tumor: bilateral ovarian metastases (signet ring cells)
• Blumer's shelf: rectal/pelvic peritoneum deposit (felt on rectal exam)
• Irish node: left axillary node
• Staging by AJCC T-N-M system; surgical resection is mainstay

16. CARCINOMA OF SMALL INTESTINE

• Circumferential/annular "napkin ring" constriction - most classic presentation
• Or polypoid/fungating mass projecting into lumen
• Ulcerated surface with necrosis
• Causes intestinal obstruction due to annular constriction
• Adjacent bowel: dilated proximally (obstruction), collapsed distally

• Adenocarcinoma (most common in small intestine): Duodenum > jejunum > ileum
• Carcinoid tumor (neuroendocrine tumor): Most common in ileum; causes carcinoid syndrome when it metastasizes (flushing, diarrhea, bronchospasm, right heart valve disease)

• Most common small intestinal malignancy: adenocarcinoma (in duodenum/jejunum)
• Most common site for carcinoid tumor: ileum
• Risk factors for adenocarcinoma: Crohn's disease, FAP, celiac disease, Lynch syndrome
• Carcinoid syndrome: hepatic metastases → 5-HT (serotonin) reaches systemic circulation
• Carcinoid: argentaffinoma; Zollinger-Ellison syndrome (gastrinoma in duodenum)
• Presentation: obstruction, bleeding, perforation

17. CARCINOMA OF CAECUM (Right-Sided Colon Cancer)

• Large, polypoid/fungating mass projecting into the large lumen of the cecum
• Cauliflower-like growth pattern
• Ulcerated surface
• Does NOT cause obstruction early (cecal lumen is large and contents are liquid)
• Iron deficiency anemia is the usual presentation (occult bleeding from the polypoid mass)
• Less likely to be annular

• Right-sided colon cancers: polypoid/fungating, present with occult blood/anemia, larger tumors, better prognosis
• Left-sided colon cancers (sigmoid/rectum): annular/constricting "napkin ring," present with obstruction, change in bowel habits, fresh rectal bleeding
• Microsatellite instability (MSI-H): more common in right-sided/cecal cancers; Lynch syndrome
• KRAS mutation in ~40-50% of colorectal cancers
• Spread: direct → adjacent organs; lymphatic → regional nodes; hematogenous → liver first (via portal vein), then lungs
• CEA (carcinoembryonic antigen): tumor marker used for follow-up (not screening)
• FAP: APC mutation; >100 adenomatous polyps; 100% risk of carcinoma by age 40
• Lynch syndrome (HNPCC): mismatch repair gene mutation (MLH1, MSH2); right-sided predominance

18. CARCINOMA OF COLON (Left-Sided / Sigmoid)

• Annular/circumferential "napkin ring" or "apple core" constriction - the classic gross appearance
• Encircles the bowel wall circumferentially
• Causes obstruction: Luminal narrowing leads to change in bowel habits, obstipation, complete obstruction
• Ulcerated mucosa within the constriction
• Proximal bowel dilated (obstruction); distal bowel collapsed
• Wall: thickened, rigid, indurated
• Serosa: Puckered, retracted at the tumor site

• Dukes A = confined to mucosa/submucosa
• Dukes B = through muscularis (no nodes)
• Dukes C = lymph node metastases
• Dukes D = distant metastases

• Polyp-carcinoma sequence: Adenomatous polyp → dysplasia → carcinoma (APC → KRAS → TP53 cascade)
• Most colorectal cancers arise from adenomatous polyps
• Villous adenoma has highest malignant potential; tubular adenoma lowest
• Colonoscopy screening detects and removes polyps before malignant transformation
• Liver is the most common site of distant metastasis (portal venous drainage)
• Second most common cause of cancer death in Western world
• Synchronous tumors (multiple primary CRCs) possible; must examine entire colon

SOFT TISSUE / SYSTEMIC SPECIMENS

19. MILIARY TUBERCULOSIS

• Lung is studded with innumerable small white/gray nodules
• Nodules are uniformly sized (~1-2 mm), resembling millet seeds scattered throughout both lungs
• Nodules are discrete, firm, slightly raised
• Distribution: Random throughout all lobes and segments - no particular locus
• Color: Gray-white (pale, chalky) or yellow-white
• Total lung weight: Increased; lungs may feel heavier and firmer
• Cut surface: Same miliary nodules throughout the parenchyma
• Also seen in: liver (gray-white nodules on cut surface), spleen (grey-white spots on cut surface - "sago spleen"), meninges, kidneys, adrenals

• Epithelioid cell granulomas with central caseation necrosis
• Granuloma components: Langerhans giant cells (horseshoe-shaped nuclei), epithelioid macrophages, lymphocytic rim, central caseous necrosis
• Acid-fast bacilli (ZN stain): may be found in macrophages/necrotic center
• Granulomas are at the same stage of evolution (synchronous) as they all arrived via blood at the same time

• Cause: hematogenous spread of TB - can occur during primary progressive TB or reactivation
• Risk groups: immunocompromised (HIV, steroids, malnutrition, diabetes), infants/elderly
• Organs affected: lungs, liver, spleen, bone marrow, meninges, kidneys, adrenals
• "Simon's foci" - apical granulomas in lung from primary bacteremia (can reactivate)
• Mantoux test may be negative in miliary TB (anergy)
• Diagnosis: high-resolution CT chest (snowstorm pattern), bone marrow biopsy, fundoscopy (choroidal tubercles), liver biopsy; sputum AFB/culture
• Choroidal tubercles (eye) = pathognomonic of miliary TB
• Treatment: standard HRZE regimen; corticosteroids for TB meningitis

20. LIPOMA

• Soft, fluctuant, doughy/compressible mass - consistency of normal fat
• Well-encapsulated with a thin fibrous capsule
• Yellow color throughout - identical to normal fat
• Lobulated surface (fat lobules)
• Size: Usually 5-10 cm; can be larger
• Location: Subcutis of proximal extremities (thigh, shoulder, upper back) most common; also trunk
• Mobility: Freely mobile under skin
• Painless clinically

• Well-encapsulated mass of mature adipocytes - identical to normal fat
• Thin fibrous capsule
• Uniform cell size; peripheral nuclei; clear vacuolated cytoplasm (lipid)
• No atypia, no mitoses (if these are present → liposarcoma)
• Chromosomal rearrangements involving chromosome 12q (HMGA2 dysregulation)

• Most common benign soft tissue tumor in adults
• Multiple lipomas = lipomatosis (can involve a limb)
• Dercum's disease = painful multiple lipomas
• Madelung's disease = multiple symmetric lipomas of neck/shoulder
• Familial multiple lipomatosis = autosomal dominant
• Liposarcoma (malignant): most common sarcoma of adulthood; deep-seated; retroperitoneum or proximal extremity; MDM2 amplification in well-differentiated type; FUS::DDIT3 fusion in myxoid type
• Hibernoma: benign tumor of brown fat; brown-tan color; characteristic "mulberry cells"

CARDIOVASCULAR SYSTEM

21. ATHEROSCLEROSIS

• Intimal surface shows progressive changes:
  • Fatty streaks: Yellow, flat or slightly raised streaks on intima (earliest visible lesion; seen even in children); composed of lipid-laden macrophages (foam cells)
  • Fibrous plaques: Raised, white/pale yellow, firm plaques with well-defined borders; pearly white/glistening fibrous cap; MOST CHARACTERISTIC of established atherosclerosis
  • Complicated plaques:
    • Calcification: Hard, chalky deposits within plaque (gritty sensation)
    • Ulceration: Break in fibrous cap with eroded surface (thrombogenic)
    • Thrombosis: Overlying thrombus (red-brown/maroon) on an ulcerated plaque
    • Hemorrhage into plaque
    • Aneurysm formation (especially abdominal aorta)
• Distribution: Most severe at: abdominal aorta > coronary arteries > popliteal arteries > descending thoracic aorta > internal carotid arteries > Circle of Willis vessels
• Lower limbs: Atheromatous plaques cause pale/white patches on intima

• Fibrous cap: Dense fibrous tissue + smooth muscle cells + collagen
• Atheromatous core (necrotic lipid core): Foam cells, cholesterol crystals (cholesterol clefts), necrotic debris, calcification
• Shoulder region: Macrophages, T cells (most vulnerable to rupture)

• Intimal thickening
• Fibrous cap: smooth muscle cells, collagen, proteoglycans
• Core: cholesterol clefts (needle-shaped empty spaces), foam cells (lipid-laden macrophages), necrotic debris, calcification
• Inflammatory infiltrate: macrophages, T lymphocytes

• Response to injury hypothesis (Virchow/Ross): endothelial injury → lipoprotein accumulation → monocyte adhesion → foam cell formation → SMC migration and proliferation → fibrous cap
• Most important risk factors: hypercholesterolemia (LDL), smoking, hypertension, diabetes; plus genetics, male sex, age
• Stable plaque: thick fibrous cap, small lipid core, calcified
• Unstable/vulnerable plaque: thin fibrous cap, large lipid core, many inflammatory cells → rupture → acute coronary syndrome
• Plaque rupture → thrombus → MI/stroke/sudden death
• Abdominal aortic aneurysm: most common true aneurysm; atherosclerotic; below renal arteries; risk of rupture
• Monckeberg's medial calcification: calcification of tunica media of muscular arteries; does NOT cause luminal obstruction; incidental

22. LEFT VENTRICULAR HYPERTROPHY (LVH) / Hypertensive Heart Disease

• Heart is enlarged/heavy - normal adult heart ~300-350 g; in LVH may exceed 500 g (can weigh 600-800+ g)
• Left ventricular wall thickened - normally up to 1.2-1.5 cm; in LVH may exceed 2.0 cm
• Concentric hypertrophy: LV wall is thick, LV cavity is REDUCED/NORMAL in size (not dilated) - this is the initial stage
• Eccentric hypertrophy (late/dilated phase): LV cavity becomes dilated (heart failure stage)
• Papillary muscles: Prominent, bulging (also hypertrophied)
• Interventricular septum: Thickened
• Left atrium: Enlarged (due to impaired diastolic filling from stiff LV)
• The right heart is normal or minimally affected
• Ventricles on cut section: LV wall clearly thicker than RV; normal ratio LV:RV = 3:1; in LVH this increases

• Increase in transverse diameter of myocytes (myocyte hypertrophy - not hyperplasia, since cardiac cells are terminally differentiated)
• Nuclear enlargement - large, irregular, "box-car" nuclei (hallmark histologic feature)
• Variable perivascular and interstitial fibrosis
• No inflammatory infiltrate in pure hypertrophy

• Diagnostic criteria: LV hypertrophy (concentric) + clinical/pathologic evidence of hypertension in other organs (kidneys, blood vessels)
• Compensatory → maladaptive: initially useful, eventually leads to diastolic dysfunction, then systolic dysfunction → CHF
• LV wall >2 cm + heart weight >500 g = significant hypertrophy
• Concentric hypertrophy: wall thickens, cavity stays same/reduces - increased wall:radius ratio
• Eccentric hypertrophy: wall thickens + cavity dilates - seen in volume overload (aortic regurgitation, mitral regurgitation) or end-stage
• Complications: diastolic heart failure (stiff ventricle, impaired filling), atrial fibrillation (left atrial dilation), IHD risk, sudden cardiac death
• Can regress with effective antihypertensive treatment
• Echo: most sensitive diagnostic tool for LVH (increased LV mass index)

QUICK COMPARISON TABLE FOR VIVA

1. When you pick up a specimen, first identify: What organ? → Normal or abnormal? → What type of lesion?
2. Always note: size, color, consistency, surface, cut surface, any special features
3. For any cystic ovarian specimen: note whether it is unilocular/multilocular, wall thickness, contents, and any papillary projections
4. For GI specimens: always describe the mucosal pattern, any mass, and most importantly the shape of the mass (polypoid vs. annular)
5. For solid organ tumors: note the cut surface color (yellow = RCC; gray-white = most carcinomas; cream-white fleshy = seminoma)
6. Connect gross appearance to "what would the examiner ask" → pathogenesis, complications, markers, staging