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Systemic Pathology - Guyton and Hall Notes

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PART I: CARDIOVASCULAR SYSTEM PATHOLOGY

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1. Heart Failure

1.1 Circulatory Dynamics in Heart Failure

1. Reduced cardiac output
2. Damming of blood in the veins - causing elevated venous pressure

1.2 Acute Effects of Heart Failure

• Cardiac output drops from the normal 5 L/min to ~2 L/min (about two-fifths of normal)
• Right atrial pressure rises to +4 mm Hg (blood dams up)
• Symptoms: dizziness/fainting, fatigue, shortness of breath on exertion

• Baroreceptor reflex activates; chemoreceptor and CNS ischemic responses also contribute
• Parasympathetic signals to the heart are simultaneously inhibited
• Effects:
  • Strengthens damaged ventricular musculature
  • Increases heart rate
  • Increases venous tone, raising mean systemic filling pressure from ~7 mm Hg to 12-14 mm Hg (nearly 100% above normal)
  • Increases venous return

1.3 Compensated vs. Decompensated Heart Failure

• Increased venous pressure
• Edema
• Reduced exercise tolerance

• Progressive fluid retention further dilates and weakens the heart
• A "vicious cycle" ensues: more fluid retention → more cardiac distension → weaker pumping → more fluid retention
• Ultimately leads to pulmonary edema and death if untreated

• Excessive cardiac dilation stretches sarcomeres beyond optimal length, reducing force of contraction
• Edema of the heart muscle reduces efficiency
• Fibrosis replaces functional myocardium

1.4 Unilateral Left Heart Failure

• Left atrial pressure rises markedly
• Pulmonary capillary pressure rises, often causing pulmonary edema
• Right side continues to pump blood into the lungs
• Result: fluid accumulates in the pulmonary interstitium and alveoli
• This is the pathological basis of cardiac asthma (paroxysmal nocturnal dyspnea)

1.5 Low-Output Cardiac Failure

• Myocardial infarction
• Cardiomyopathy
• Severe valvular disease

1.6 High-Output Heart Failure

• Causes: severe anemia, thyrotoxicosis, beriberi (thiamine deficiency), arteriovenous fistulas
• The heart works harder than normal but still cannot maintain adequate tissue oxygen delivery relative to demand

1.7 Heart Failure with Preserved Ejection Fraction (HFpEF)

• EF is normal (≥50%) but the heart is stiff and cannot fill properly (diastolic dysfunction)
• The ventricle fills at abnormally high pressures
• Results in elevated left atrial and pulmonary venous pressures → pulmonary congestion
• Common in hypertension, diabetes, obesity, and the elderly
• Pathology: myocardial fibrosis, impaired calcium re-uptake in cardiomyocytes, decreased compliance of the LV

1.8 Cardiogenic Shock

• Survival rate is often less than 30% even with appropriate medical care
• The vicious cycle: low BP → reduced coronary perfusion → further myocardial damage → even lower BP
• In healthy hearts, this cycle begins at BP <45 mm Hg
• In hearts with already-blocked coronary vessels, the cycle starts at BP 80-90 mm Hg - hence even mild hypotension is dangerous in MI patients

• Positive inotropes (increase contractile strength)
• Vasopressors (raise arterial pressure)
• Mechanical circulatory support:
  • Intra-aortic balloon pump (IABP) - inflates in diastole (increases coronary flow), deflates in systole (reduces afterload)
  • Ventricular assist devices (VADs) - left ventricle pumps blood through a cannula into the aorta
• Revascularization:
  • Coronary angioplasty (PTCA) to restore coronary flow
  • Thrombolytic therapy to dissolve clots

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2. Hypertension

2.1 Renal Artery Stenosis and Two-Kidney Hypertension

• The ischemic kidney secretes excess renin → angiotensin II → aldosterone
• The contralateral (normal) kidney is exposed to high arterial pressure from angiotensin II
• It responds by pressure natriuresis, attempting to normalize BP
• A state of elevated renin-dependent hypertension results
• Known as renovascular hypertension or Goldblatt hypertension

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PART II: RESPIRATORY SYSTEM PATHOLOGY

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3. Respiratory Insufficiency - Principles of Diagnosis

1. Inadequate ventilation
2. Abnormalities of diffusion across the pulmonary membrane
3. Abnormal blood transport of gases

• Blood gas analysis (PO2, PCO2, pH)
  • Blood pH measured by glass electrode (Henderson-Hasselbalch principle)
  • Blood CO2 measured via bicarbonate equilibrium: pH = 6.1 + log (HCO3⁻/CO2)
  • Blood PO2 measured by polarography (platinum electrode, current proportional to O2 concentration)
• Pulmonary function tests: vital capacity, tidal volume, FRC, dead space, physiological shunt

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4. Chronic Pulmonary Emphysema

1. Chronic infection - irritants in smoke cause:
   • Partial paralysis, then destruction of respiratory cilia
   • Excess mucus secretion
   • Inhibition of alveolar macrophages → reduced infection defense
2. Infection + mucus + inflammatory edema → chronic obstruction of small airways
3. Obstruction causes air trapping (especially on expiration) → alveolar overdistension → destruction of up to 50-80% of alveolar walls

1. Increased airway resistance → greatly increased work of breathing; expiration especially difficult (bronchioles collapse during expiratory effort)
2. Loss of alveolar walls → reduced diffusing capacity → impaired O2 uptake and CO2 removal
3. Ventilation-perfusion (V/Q) mismatch:
   • Low V/Q zones → physiological shunt → poor blood oxygenation
   • High V/Q zones → physiological dead space → wasted ventilation
4. Loss of alveolar walls = loss of pulmonary capillaries → pulmonary hypertension → right heart overload → cor pulmonale (right heart failure)

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5. Bronchial Asthma

• Contractile hypersensitivity of bronchioles to foreign substances
• ~70% of patients under 30: allergic (extrinsic) asthma - sensitivity to pollens, dust mites
• Older patients: hypersensitivity to non-allergenic irritants in smog (intrinsic/non-allergic asthma)

1. Person forms excess IgE antibodies against specific allergens
2. IgE attaches to mast cells in lung interstitium near bronchioles and small bronchi
3. On allergen exposure, antigen-IgE reaction triggers mast cell degranulation, releasing:
   • Histamine
   • Slow-reacting substance of anaphylaxis (SRSA) - mixture of leukotrienes (LTC4, LTD4, LTE4)
   • Eosinophilic chemotactic factor
   • Bradykinin
4. Combined effects → (a) localized edema in bronchiolar walls + thick mucus secretion; (b) bronchial smooth muscle spasm

• Greatly increased airway resistance
• Expiration more affected than inspiration (external pressure collapses already-narrowed bronchioles)
• Markedly reduced maximum expiratory flow rate and reduced timed expiratory volume (FEV1)
• Dyspnea (air hunger)
• Increased FRC and residual volume (air trapping)
• Chronic: permanent "barrel chest" with chronically elevated FRC and residual volume

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6. Tuberculosis

1. Tissue invasion by macrophages
2. Granuloma formation (tubercle) - fibrous tissue walls off the lesion, limiting spread

1. Extensive fibrosis → increased work of breathing, reduced vital capacity and breathing capacity
2. Reduced total respiratory membrane surface area → impaired gas diffusion
3. V/Q mismatch from irregular fibrosis
4. If severe: hypoxemia, pulmonary hypertension, right heart failure

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7. Pulmonary Edema

• Pulmonary capillary hydrostatic pressure exceeds plasma oncotic pressure (normal capillary pressure ~7 mm Hg)
• In left heart failure: pulmonary capillary pressure may rise to 30-40 mm Hg
• Once capillary pressure exceeds ~28-30 mm Hg, rapid flooding of alveoli occurs

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PART III: RENAL AND URINARY SYSTEM PATHOLOGY

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8. Overview of Kidney Diseases

1. Acute Kidney Injury (AKI) - abrupt loss of function within days
2. Chronic Kidney Disease (CKD) - progressive loss of nephron function

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9. Acute Kidney Injury (AKI)

9.1 Classification

9.2 Prerenal AKI

• Kidneys normally receive 1100 mL/min (~20-25% of cardiac output)
• Reduced blood flow → reduced GFR → oliguria (urine output below fluid intake)
• Complete cessation of urine = anuria
• As long as renal blood flow does not fall below ~20-25% of normal, AKI can be reversed if cause is corrected before cell damage occurs
• Key protective mechanism: as GFR falls, less sodium chloride is filtered → less needs to be reabsorbed → less O2 consumed by tubules
• If blood flow falls below the basal metabolic requirement of tubular cells (usually <20-25% of normal), tubular cells become hypoxic and may die
• Prolonged ischemia → transition to intrarenal AKI (tubular necrosis)

9.3 Intrarenal AKI

1. Conditions damaging glomerular capillaries/small vessels
2. Conditions damaging renal tubular epithelium (acute tubular necrosis - ATN)
3. Conditions damaging renal interstitium

9.4 AKI Caused by Acute Glomerulonephritis

• Most common type of intrarenal AKI caused by immune injury to glomeruli
• In ~95% of cases: immune-mediated damage occurs 1-3 weeks after infection elsewhere in the body (commonly streptococcal throat infection - "post-streptococcal GN")
• Mechanism: Antigen-antibody complexes deposit in glomerular membrane → activate complement → inflammatory cell infiltration → membrane thickening and damage
• Results in: protein in urine (proteinuria), red cells in urine (hematuria), reduced GFR, fluid retention, hypertension

• Most patients recover (especially children)
• ~1% progress to rapidly progressive (crescentic) GN → chronic renal failure

9.5 Chronic Kidney Disease (CKD)

• Progressive nephron loss, with remaining nephrons hypertrophying to compensate
• CKD is classified in stages by GFR (Stage 1-5, where Stage 5 = GFR <15 mL/min = kidney failure requiring dialysis or transplant)

• Uremia (accumulation of urea, creatinine, other nitrogenous wastes)
• Fluid and electrolyte imbalances (hyperkalemia, metabolic acidosis, fluid overload)
• Renal anemia (reduced erythropoietin production)
• Renal osteodystrophy (impaired vitamin D activation → hypocalcemia → secondary hyperparathyroidism → bone disease)
• Hypertension (RAAS activation, fluid retention)
• Cardiovascular disease (accelerated atherosclerosis)

9.6 Glomerular Injury as a Cause of Chronic Renal Disease

• Repeated episodes of glomerular injury or progressive glomerulosclerosis → irreversible reduction in GFR
• The podocyte (visceral epithelial cell of the glomerular capillary) is key - podocyte loss = permanent glomerular scarring
• Even after the initial insult resolves, secondary hyperfiltration in remaining nephrons accelerates further damage

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PART IV: GASTROINTESTINAL AND LIVER PATHOLOGY

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10. Peptic Ulcer Disease

• Within a few centimeters of the pylorus (most common)
• Lesser curvature of the antral stomach
• Lower esophagus (acid reflux zone)
• Marginal ulcers after gastrojejunostomy

1. Mucous barrier - mucus from gastric glands, mucous neck cells, pyloric glands, Brunner glands of duodenum
2. Alkaline duodenal secretions:
   • Pancreatic sodium bicarbonate neutralizes HCl and inactivates pepsin
   • Bile and Brunner gland secretions
3. Feedback control:
   • Acid in duodenum inhibits gastric secretion and peristalsis (neural + hormonal)
   • Acid releases secretin → pancreatic bicarbonate secretion (additional neutralization)

• Acid/pepsin secretion (aggressive factors), AND
• Mucosal protective mechanisms (defensive factors)

• Gram-negative bacterium colonizes the mucous layer of gastric mucosa
• Produces urease → splits urea into NH3 + CO2 → locally destroys the mucous barrier
• Also produces cytotoxins directly damaging mucosal cells
• H. pylori infection is found in ~70-85% of gastric ulcer patients and ~95% of duodenal ulcer patients
• Eradication with antibiotics heals ulcers and dramatically reduces recurrence

• Zollinger-Ellison syndrome: gastrin-secreting tumors (gastrinomas) in pancreas or duodenum → massively elevated acid secretion → multiple, refractory peptic ulcers

• NSAIDs inhibit cyclooxygenase (COX-1) → reduced prostaglandin synthesis
• Prostaglandins normally maintain mucosal blood flow, stimulate mucus and bicarbonate secretion, and inhibit acid secretion
• Their reduction impairs mucosal defenses

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11. Gastrointestinal Obstruction

• Obstruction of the pylorus or small intestine leads to projectile vomiting and progressive distension
• Intestinal obstruction → bacterial overgrowth → translocation of bacteria → sepsis
• Proximal dilation + increased intraluminal pressure → ischemia → necrosis → perforation

• Pyloric obstruction: metabolic alkalosis (loss of HCl in vomitus), hypokalemia
• Small intestinal obstruction: mixed metabolic disturbances, severe fluid and electrolyte loss

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12. Malabsorption Syndromes

12.1 Celiac Disease (Non-Tropical Sprue)

• Autoimmune-mediated enteropathy triggered by gluten (protein in wheat, rye, barley)
• More common in women
• Mechanism: gluten elicits autoimmune reaction → inflammation → destruction of intestinal enterocytes
• Mild form: only microvilli destroyed → 2-fold reduction in absorptive surface area
• Severe form: villi completely blunted or absent → severe malabsorption

1. Steatorrhea (fat malabsorption - fat appears in stools as fatty acid salts)
2. Protein-energy malnutrition with severe bodily wasting
3. Osteomalacia - bone demineralization (calcium malabsorption)
4. Impaired coagulation (vitamin K malabsorption)
5. Macrocytic anemia - pernicious type (B12 and folic acid malabsorption)

12.2 Tropical Sprue

• Occurs in tropical regions
• Believed to be caused by intestinal bacterial infections causing mucosal inflammation
• Treated with antibacterial agents

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13. Large Intestine Disorders

13.1 Constipation

• Slow movement of feces through the large intestine
• Causes: excessive fluid absorption from feces, insufficient fluid intake, obstruction (tumors, adhesions, ulcers), voluntary suppression of defecation reflexes
• Chronic inhibition of defecation reflexes eventually leads to loss of reflex sensitivity

13.2 Diarrhea

• Rapid movement of feces
• Causes: intestinal infection, inflammation, osmotic agents, increased motility
• Risks: dehydration, electrolyte loss (hypokalemia, metabolic acidosis)

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SUMMARY TABLE - Key Pathological Mechanisms

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• Cardiovascular: Heart failure (acute, compensated, decompensated, HFpEF, high-output), cardiogenic shock with treatment, renovascular hypertension
• Respiratory: Emphysema pathogenesis and physiology, asthma (IgE/mast cell mechanism), tuberculosis, pulmonary edema
• Renal: AKI classification (pre/intra/post-renal), glomerulonephritis mechanism, CKD consequences
• GI: Peptic ulcer (H. pylori, NSAIDs, Zollinger-Ellison), celiac disease, GI obstruction, diarrhea/constipation

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SYSTEMIC PATHOLOGY - ROBBINS & KUMAR

(Pathologic Basis of Disease, Latest Edition)

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PART I: CARDIOVASCULAR PATHOLOGY

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1. ISCHEMIC HEART DISEASE (IHD)

• 90% due to obstructive atherosclerotic lesions in epicardial coronary arteries (CAD)

• Other causes: coronary emboli, vasculitis, vascular spasm, severe demand states (hypertrophy, tachycardia, shock)
• Note: Tachycardia is doubly harmful - increases O2 demand AND reduces coronary perfusion time (diastole shortened)

1. Myocardial infarction (MI) - ischemic necrosis
2. Angina pectoris - ischemia without infarction
3. Chronic IHD with heart failure
4. Sudden cardiac death (SCD)

1A. Myocardial Infarction (MI)

• STEMI (transmural) - complete occlusion, usually plaque rupture + thrombosis
• NSTEMI/UA (subendocardial) - incomplete occlusion, or demand > supply

1. Chronic atherosclerotic plaque builds up over decades
2. Plaque disruption (rupture or erosion) exposes subintimal collagen/lipid core
3. Platelet aggregation + thrombus formation → acute occlusion
4. Ischemia → necrosis within 20-40 minutes if flow not restored

• Triphenyltetrazolium chloride (TTC) - infarcted tissue fails to take up stain (remains pale/white), viable tissue stains brick-red
• Nitroblue tetrazolium (NBT) - similar principle; dead tissue pale

1. Arrhythmias (most common cause of death in first 24 hrs)
2. Cardiogenic shock
3. Cardiac rupture - free wall (days 3-7; hemopericardium, tamponade), interventricular septum (VSD), papillary muscle (mitral regurgitation)
4. Ventricular aneurysm (late complication)
5. Fibrinous pericarditis (Dressler syndrome - weeks later, immune mediated)
6. Mural thrombus → systemic embolism
7. Heart failure

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2. VALVULAR HEART DISEASE

• Stenosis - failure to open completely; virtually always chronic (fibrosis/calcification)
• Insufficiency (regurgitation) - failure to close; can be acute or chronic

• Stenosis → pressure overload → concentric hypertrophy
• Insufficiency → volume overload → eccentric hypertrophy → both eventually → heart failure

2A. Calcific Aortic Stenosis

• Heaped-up calcified masses on outflow surface of aortic cusps
• Cusps remain mobile but calcification protrudes into sinuses, preventing opening
• Stain: Von Kossa stain (calcium deposits appear black), H&E (calcification appears as dark blue/basophilic)

2B. Rheumatic Heart Disease (Mitral Stenosis)

• Aschoff bodies - pathognomonic; foci of fibrinoid necrosis with lymphocytes, plasma cells, and Aschoff cells (plump macrophages with "owl-eye" nuclei and "caterpillar" chromatin)
• Anitschkow cells (caterpillar cells) - activated macrophages, pathognomonic for rheumatic carditis
• Pancarditis: pericarditis, myocarditis, endocarditis
• McCallum plaques on posterior left atrial wall
• Fibrinous pericarditis ("bread-and-butter" pericarditis)
• Vegetations: small, warty vegetations along line of valve closure
• Stain: H&E shows Aschoff bodies well

• Leaflet thickening and retraction
• Commissural fusion (classic "fish-mouth" or "buttonhole" orifice of mitral valve)
• Chordal thickening and fusion
• Stain: H&E shows dense fibrosis and calcification

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3. CARDIOMYOPATHY

3A. Dilated Cardiomyopathy (DCM) - 90% of cardiomyopathies

• Pathophysiology: Systolic (contractile) dysfunction
• Causes:
  • Up to 50%: autosomal dominant loss-of-function mutations in cytoskeletal/sarcolemmal/nuclear envelope genes; titin (TTN) truncations account for ~20%
  • Myocarditis (viral - especially coxsackievirus B)
  • Toxic (alcohol, doxorubicin/anthracyclines, cocaine)
  • Peripartum cardiomyopathy
  • Hemochromatosis, thiamine deficiency
• Morphology:
  • Massive 4-chamber dilation; weight >900 g (normal ~300 g)
  • Thin ventricular walls
  • Mural thrombi common (especially in LV apex)
  • Histology: myocyte hypertrophy, increased interstitial fibrosis, only scattered myocyte necrosis
  • Stains: H&E (myocyte changes), Masson Trichrome (fibrosis = blue)

3B. Hypertrophic Cardiomyopathy (HCM)

• Pathophysiology: Diastolic (relaxation) dysfunction
• Genetics: Autosomal dominant gain-of-function mutations in sarcomeric proteins; most common: beta-myosin heavy chain and myosin-binding protein C
• Morphology:
  • Massive cardiac hypertrophy (often asymmetric - especially septum: ASH - asymmetric septal hypertrophy)
  • Banana-shaped LV cavity
  • Histology - PATHOGNOMONIC: myocyte hypertrophy + myofiber disarray (chaotic, haphazard arrangement of myocytes and myofibrils within cells) + interstitial fibrosis
  • Stain: H&E shows myofiber disarray; Masson Trichrome shows fibrosis

3C. Restrictive Cardiomyopathy

• Pathophysiology: Stiff, noncompliant myocardium; diastolic dysfunction
• Causes:
  • Amyloid deposition - most common
  • Radiation-induced fibrosis
  • Endomyocardial fibrosis (tropical; eosinophilia)
  • Sarcoidosis
  • Hemochromatosis
• Amyloid (Cardiac):
  • Stain: Congo Red - salmon-pink on H&E, apple-green birefringence under polarized light (pathognomonic)
  • Grossly: stiff, rubbery myocardium; "waxy" appearance

3D. Myocarditis

• Causes: Viral (coxsackievirus B, HIV, parvovirus B19), bacterial, parasitic (T. cruzi - Chagas), autoimmune
• Morphology:
  • Active myocarditis (Dallas criteria): interstitial lymphocytic inflammatory infiltrate + adjacent myocyte necrosis/damage
  • Giant cell myocarditis: multinucleated giant cells with lymphocytes, eosinophils - poor prognosis
  • Stain: H&E is key; immunohistochemistry for T-cell markers

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4. PERICARDIAL DISEASE

• Pericardial Effusion: Normal <50 mL; >200-300 mL rapid accumulation → cardiac tamponade
• Hemopericardium: Blood in pericardium; causes: MI wall rupture, aortic dissection
• Fibrinous Pericarditis:
  • Causes: uremia, MI (Dressler syndrome), rheumatic fever
  • Gross: "bread-and-butter" pericarditis (shaggy fibrinous exudate)
  • Stain: H&E shows fibrin; PTAH (phosphotungstic acid-hematoxylin) stains fibrin blue
• Constrictive Pericarditis: Fibrous obliteration of pericardial sac → cardiac compression; causes: TB, pyogenic

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PART II: RESPIRATORY PATHOLOGY

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5. EMPHYSEMA

1. Smoking/irritants → chronic inflammation → neutrophils/macrophages release elastase, metalloproteinases
2. Normally countered by alpha-1 antitrypsin (AAT) and other antiproteases
3. Protease-antiprotease imbalance → elastin breakdown in alveolar walls → destruction
4. In AAT deficiency: genetic; severe, early-onset panacinar emphysema; AAT gene = SERPINA1 (chromosome 14)
5. Smoking also causes oxidative stress directly damaging antiproteases

• Gross: Voluminous, pale lungs; do not collapse; bullae (large air spaces) especially in paraseptal type; barrel chest on CXR
• Microscopy:
  • Enlarged airspaces with thin, delicate walls
  • Loss of alveolar septa
  • Reduced capillary bed
  • No significant fibrosis (distinguishes from fibrosis)
• Stains: H&E (loss of septa seen); Elastic-van Gieson (EVG) - highlights elastin loss in alveolar walls (elastin = black/dark purple); Verhoeff-van Gieson (VVG)

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6. CHRONIC BRONCHITIS

• Gross: Hyperemia, edema, mucosal secretions; thickened bronchial wall
• Microscopy:
  • Hypertrophy and hyperplasia of mucous glands (submucosal) in trachea/bronchi
  • Goblet cell metaplasia in small airways (normally no goblet cells there)
  • Reid index = (mucous gland thickness)/(total bronchial wall thickness) - normally <0.4; in chronic bronchitis >0.5
  • Inflammatory infiltrate (lymphocytes, macrophages); neutrophils in acute exacerbations
  • Squamous metaplasia of bronchial epithelium
• Stains: H&E for Reid index measurement; Alcian blue/PAS for mucus

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7. BRONCHIAL ASTHMA

1. Atopic (extrinsic/allergic) asthma - most common; IgE-mediated; type I hypersensitivity; begins in childhood
2. Non-atopic (intrinsic) asthma - non-immune; triggered by respiratory infections, irritants, cold, exercise
3. Drug-induced asthma - especially aspirin (aspirin-sensitive asthma); blocks COX → leukotrienes > prostaglandins; no IgE involvement
4. Occupational asthma - fumes, organic/chemical dusts

1. Prior sensitization → production of IgE antibodies against allergen
2. IgE binds to mast cells in bronchial submucosa
3. Re-exposure: allergen cross-links IgE → mast cell degranulation
4. Early phase (minutes): histamine, prostaglandins, leukotrienes (LTC4, LTD4, LTE4) → bronchoconstriction, mucus secretion, vasodilation
5. Late phase (4-8 hrs): eosinophil/neutrophil recruitment → eosinophilic inflammation → epithelial damage; major basic protein (MBP) from eosinophils → further injury

• Gross: Lungs overinflated; airways plugged with thick, viscid mucus
• Microscopy:
  • Curschmann spirals - mucous plugs with epithelial cells (shed in sputum)
  • Charcot-Leyden crystals - eosinophil membrane protein (elongated, double-pointed) in sputum
  • Subepithelial fibrosis (airway remodeling)
  • Basement membrane thickening ("subepithelial collagen deposition")
  • Goblet cell hyperplasia
  • Smooth muscle hypertrophy/hyperplasia
  • Eosinophilic infiltrate (hallmark)
  • Mucous gland hyperplasia
  • Edema and vascular congestion
• Stains: H&E (eosinophils - bright pink granules; mast cells); Congo Red or Luna stain for eosinophils; PAS for mucus; Alcian blue for acidic mucins

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8. PNEUMONIA

8A. Acute (Bacterial) Lobar Pneumonia

1. Congestion (1-2 days): congested, heavy lung; serous exudate; numerous bacteria; few neutrophils - Stain: H&E shows vascular congestion
2. Red hepatization (2-4 days): lung red, firm, airless (like liver); alveoli filled with neutrophils, red cells, fibrin - Stain: H&E (pink fibrinous exudate with neutrophils)
3. Gray hepatization (4-8 days): gray-brown color; RBCs lysed; fibrinopurulent exudate persists; macrophages appear - Stain: H&E
4. Resolution (8+ days): exudate enzymatically digested; macrophages clear debris; normal architecture restored

8B. Bronchopneumonia (Lobular Pneumonia)

• Patchy consolidation of multiple lobules
• Associated with H. influenzae, S. aureus, K. pneumoniae, P. aeruginosa
• Histology: neutrophilic infiltration centered on bronchioles/bronchi, spreading to alveoli

• Bacterial pneumonia: intraalveolar neutrophilic inflammation
• Viral pneumonia: interstitial lymphocytic inflammation

8C. Atypical (Interstitial) Pneumonia

• "Walking pneumonia" - mild symptoms despite radiographic infiltrates
• Causes: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella, viruses (influenza, COVID-19)
• Histology: interstitial inflammation (lymphocytes, macrophages); alveolar walls thickened; no intraalveolar exudate
• Legionella: silver stain (Warthin-Starry or Dieterle stain) to visualize organisms

8D. Aspiration Pneumonia

• Debilitated patients; gastric content aspiration
• Chemical + bacterial (mixed aerobic/anaerobic oral flora)
• Necrotizing pneumonia → lung abscess
• Microaspiration: non-necrotizing granulomas with multinucleated foreign body giant cells

8E. Lung Abscess

• Local suppurative necrosis of lung tissue
• Most common cause: aspiration (~60% are anaerobic organisms - Bacteroides, Fusobacterium, Peptococcus)
• Morphology: cavity filled with pus, fibrous wall
• Stains: H&E (necrosis + neutrophils); culture of organism required

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9. INTERSTITIAL LUNG DISEASES

9A. Pulmonary Fibrosis (UIP/IPF)

• Usual Interstitial Pneumonia (UIP) is the histologic pattern of Idiopathic Pulmonary Fibrosis (IPF)
• Morphology:
  • Temporal heterogeneity (old and new fibrosis coexist) - pathognomonic
  • Dense subpleural fibrosis
  • Honeycombing (cystic spaces lined by bronchiolar epithelium)
  • Fibroblastic foci (active fibrosis - key diagnostic feature)
  • Relatively mild inflammation
• Stains: H&E; Masson Trichrome (fibrosis = blue/green); EVG for elastic fibers

9B. Sarcoidosis

• Non-caseating granulomas involving lungs (and other organs)
• Morphology:
  • Non-caseating granulomas: epithelioid macrophages + Langhans giant cells + lymphocytes; NO necrosis
  • Schaumann bodies - laminated concentric calcified inclusions inside giant cells
  • Asteroid bodies - stellate inclusions inside giant cells
• Stains: H&E (granulomas); ZN (Ziehl-Neelsen) or Fite used to exclude TB (negative in sarcoidosis); PAS or Grocott to exclude fungi

9C. Malignant Mesothelioma

• Aggressive tumor of pleural mesothelium; linked to asbestos exposure (latency 25-45 years)
• Morphology:
  • Grows as sheets/nodules encasing lung; tumor "rind" on pleura
  • Three histologic subtypes: epithelioid (most common; best prognosis), sarcomatoid, biphasic
  • Epithelioid: tubular/papillary structures resembling adenocarcinoma
• Key stains to distinguish from adenocarcinoma:
  • Positive in mesothelioma: calretinin (nuclear + cytoplasmic), WT-1, CK5/6, D2-40 (podoplanin), mesothelin
  • Negative in mesothelioma (positive in adenocarcinoma): CEA, TTF-1, CD15, MOC-31, BerEP4
  • PASD (PAS with diastase) - neutral mucin positive in adenocarcinoma; negative in mesothelioma

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PART III: RENAL / URINARY PATHOLOGY

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10. GLOMERULAR DISEASES

• Glomerular filtration barrier: fenestrated endothelium + GBM (collagen IV, laminin, heparan sulfate) + podocyte foot processes
• Charge barrier (anionic heparan sulfate in GBM) prevents albumin passage
• Mesangial cells: phagocytic, structural, contractile

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10A. Acute Proliferative (Post-Streptococcal) Glomerulonephritis

• Light microscopy: Enlarged, hypercellular glomeruli (diffuse proliferative); hypercellularity due to: (1) infiltrating leukocytes (neutrophils + monocytes); (2) proliferation of endothelial and mesangial cells; (3) in severe cases, crescents
• Immunofluorescence (IF): Granular ("lumpy-bumpy") deposits of IgG and C3 along GBM and mesangium - "starry sky" pattern
• Electron microscopy (EM): Subepithelial electron-dense "humps" (immune complex deposits)

• Children: hematuria ("smoky/cola urine"), periorbital edema, hypertension, oliguria; 1-2 weeks post-sore throat
• Labs: elevated ASO titer, low C3, RBC casts in urine

• 95% children recover; adults have worse prognosis

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10B. Rapidly Progressive (Crescentic) Glomerulonephritis (RPGN)

• Crescents = proliferating parietal epithelial cells + infiltrating monocytes/macrophages filling Bowman space
• Fibrin deposition within crescents
• Stain: H&E (crescents); PAS (Bowman capsule highlighted); Fibrin stain (PTAH or MSB) shows fibrin in crescents

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10C. Nephrotic Syndrome - Major Causes

• Deranged glomerular permeability → protein leakage
• Massive proteinuria (>3.5 g/day) → hypoalbuminemia → decreased oncotic pressure → edema + sodium retention
• Compensatory hepatic lipoprotein synthesis → hyperlipidemia → lipiduria
• Loss of immunoglobulins → susceptibility to infections (especially pneumococcus, staphylococcus)
• Loss of antithrombin III + protein C/S → hypercoagulability → renal vein thrombosis, DVT, PE

• Oval fat bodies (lipoproteins reabsorbed by tubular cells) - Maltese cross pattern under polarized light
• Fatty casts
• Stain: Oil Red O or Sudan IV for fat in urine/tissue

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10D. Minimal Change Disease (MCD) / Lipoid Nephrosis

• Dysfunction of T-cells → circulating "permeability factor" → podocyte injury
• Loss of slit diaphragm proteins (nephrin, podocin)
• Selective proteinuria (mainly albumin loss)
• Associated with atopy, Hodgkin lymphoma (paraneoplastic)

• Light microscopy: NORMAL glomeruli (hence "minimal change")
• IF: NEGATIVE (no immune deposits)
• EM: DIFFUSE EFFACEMENT (fusion) of podocyte foot processes - pathognomonic
• Stains: H&E (normal LM); EM is essential for diagnosis
• Excellent response to corticosteroids

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10E. Focal Segmental Glomerulosclerosis (FSGS)

• Primary (idiopathic) - podocyte injury
• Secondary: HIV (HIVAN), heroin, sickle cell, obesity, congenital nephron loss

• Light microscopy: Focal (some glomeruli) and segmental (part of each glomerulus) sclerosis - collapse of capillary loops with increased matrix; hyalinosis; foam cells
• Perihilar variant (most common), tip variant (best prognosis), collapsing variant (worst prognosis; HIVAN)
• IF: Nonspecific IgM and C3 in sclerotic segments
• EM: Diffuse foot process effacement (like MCD) + focal basement membrane thickening
• Stains: PAS (sclerosis highlighted by PAS-positive matrix increase); JMS/PASM (Jones methenamine silver) (silver stains GBM black; sclerotic areas show collapse)

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10F. Membranous Nephropathy

• Most cases (~70-80%): anti-phospholipase A2 receptor (PLA2R) antibodies → subepithelial immune complex deposits
• Secondary: SLE, hepatitis B, drugs (penicillamine, gold), malignancy

• LM: Diffuse thickening of GBM; "spikes" projecting from GBM around subepithelial deposits
• IF: Granular IgG (and C3) along GBM in a subepithelial pattern (characteristic)
• EM: Subepithelial electron-dense deposits; GBM spikes between deposits
• Stain: JMS (Jones Silver) - GBM black; deposits appear as "spikes" and "holes" (holes = where deposits were, spikes = new GBM around deposits); PAS highlights thickened GBM

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10G. Membranoproliferative GN (MPGN)

• Type I: Immune complex mediated (subendothelial deposits; Hep B, Hep C, cryoglobulinemia)
• Type II (Dense Deposit Disease - DDD): Complement dysregulation; C3 nephritic factor

• LM: Mesangial cell proliferation + GBM thickening; "lobular" appearance; "tram-track" or "double-contour" GBM (pathognomonic) - due to mesangial interposition between endothelium and GBM
• IF: Granular C3 ± IgG (Type I); C3 alone (Type II/DDD)
• EM: Type I - subendothelial deposits; Type II - dense deposits within GBM (ribbon-like)
• Stain: PAS and JMS - tram-tracking of GBM highlighted; Masson Trichrome - deposits appear fuchsinophilic

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10H. IgA Nephropathy (Berger Disease)

• Aberrant glycosylation of IgA1 (deficient O-linked galactosylation in hinge region)
• Aberrantly glycosylated IgA is deposited in mesangium
• Alternative complement pathway activation (C3 present; C1q and C4 absent)
• Associated with celiac disease, liver disease, HSP (systemic form)

• LM: Mesangial proliferation and increased matrix; mesangioproliferative pattern
• IF: IgA (dominant), often with IgG, IgM, C3 in mesangium - pathognomonic
• EM: Electron-dense mesangial deposits
• Stains: H&E (mesangial expansion); PAS (matrix increase); IF is diagnostic

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10I. Lupus Nephritis

• Class III (focal proliferative) and Class IV (diffuse proliferative) - most severe
• Class V (membranous) - nephrotic syndrome

• Diffuse endocapillary and mesangial proliferation
• "Wire-loop" lesions: subendothelial deposits create thickened GBM
• IF: "Full house" pattern - IgG, IgA, IgM, C3, C1q all positive (characteristic of lupus)
• EM: Subendothelial deposits (wire loops), mesangial deposits, "fingerprint" deposits (tubuloreticular inclusions) in endothelial cells (due to IFN-alpha)
• Stains: H&E, PAS, JMS, Trichrome - all used; IF critical

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11. TUBULAR AND INTERSTITIAL DISEASES

11A. Acute Tubular Injury (ATI) / Acute Tubular Necrosis (ATN)

• Ischemic ATN: prolonged hypoperfusion (shock, sepsis, severe hemorrhage)
• Nephrotoxic ATN: aminoglycosides, contrast agents, cisplatin, heavy metals, myoglobin (rhabdomyolysis), hemoglobin

• Ischemic ATN: focal tubular necrosis with skip lesions; most severe at corticomedullary junction (where straight proximal tubule and thick ascending limb are hypoxia-sensitive); tubular rupture (tubulorrhexis); casts in distal tubules; vascular congestion
• Nephrotoxic ATN: uniform proximal tubular damage; intact tubular basement membrane (no tubulorrhexis)
• Stains: H&E (tubular cell loss, nuclear necrosis); PAS (loss of brush border in proximal tubules)

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PART IV: GASTROINTESTINAL PATHOLOGY

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12. ESOPHAGUS

12A. Barrett Esophagus

• Gross: Red, velvety "tongues" extending upward from GEJ; alternates with pale squamous mucosa
• Microscopy:
  • Intestinal-type metaplasia: goblet cells with mucus vacuoles that stain pale blue (conspicuous among gastric-type foveolar cells)
  • Goblet cells are diagnostic - classic wine-goblet shape with pale cytoplasm
  • Low-grade vs. high-grade dysplasia: nuclear hyperchromasia, increased N:C ratio, failure of maturation
  • High-grade dysplasia: atypical mitoses, gland budding/irregularity, cellular crowding
• Stains: H&E (goblet cells identified by their pale blue mucin); Alcian blue (pH 2.5) - goblet cell mucin = bright blue (intestinal-type mucin); PAS - foveolar cell mucin = magenta

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13. STOMACH

13A. Gastritis

• NSAIDs: inhibit COX-1 → ↓ prostaglandins (PGE2, PGI2) → ↓ mucus, bicarbonate, mucosal blood flow → mucosal erosion
• Alcohol, bile, stress: disrupt tight junctions + increase acid back-diffusion
• Morphology (H&E): erosion (loss of surface epithelium), neutrophils in lamina propria, vascular congestion

• H&E: Dense lymphoplasmacytic infiltrate in lamina propria + neutrophils in epithelium and gland lumina ("active" chronic gastritis); lymphoid follicle formation
• Warthin-Starry stain or Giemsa stain - demonstrates H. pylori organisms (curved gram-negative rods) in mucous layer
• Modified Giemsa stain - most commonly used in clinical practice for H. pylori
• Urease test (CLO test): rapid bedside test (H. pylori produces urease → converts urea to ammonia → pH rise → color change)

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14. SMALL INTESTINE AND COLON

14A. Inflammatory Bowel Disease (IBD)

• Transmural inflammation with all wall layers involved
• Non-caseating granulomas (50%; even in normal-looking areas outside bowel)
• Linear, deep "knife-like" ulcers
• Cobblestone mucosa (islands of intact mucosa surrounded by ulcers)
• Fissures and fistulae
• Fat wrapping (creeping fat over serosal surface)
• Stains: H&E (granulomas - epithelioid macrophages + Langhans giant cells); ZN stain to exclude TB (negative in CD)

• Mucosal and submucosal inflammation only
• Crypt abscesses (neutrophils filling crypts) - hallmark
• Cryptitis (neutrophils invading crypt epithelium)
• Goblet cell depletion (mucus depletion)
• Pseudopolyps (islands of regenerating mucosa)
• No granulomas
• Paneth cell metaplasia in left colon
• Stains: H&E (crypt abscesses + goblet cell depletion); PAS/Alcian blue for mucus depletion; Movat pentachrome for wall layers

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15. LIVER

15A. Cirrhosis

1. Chronic viral hepatitis (B and C) - worldwide leading cause
2. Alcohol-associated liver disease
3. Metabolic dysfunction-associated steatotic liver disease (MASLD/MAFLD - formerly NASH)
4. Autoimmune hepatitis
5. Primary biliary cholangitis (PBC)
6. Primary sclerosing cholangitis (PSC)
7. Metabolic (hemochromatosis, Wilson disease, AAT deficiency)

• Gross: Bumpy, nodular liver surface; nodules separated by fibrous bands; late stage: shrunken liver
• Microscopy:
  • Parenchymal nodules (regenerative; lack central veins) surrounded by dense fibrous bands
  • Two types: micronodular (<3 mm - alcohol-related) and macronodular (>3 mm - viral hepatitis)
  • Mixed pattern in advanced disease
• Stains:
  • H&E - baseline; shows hepatocyte changes
  • Masson Trichrome - fibrosis/collagen = blue (key stain for staging fibrosis)
  • Sirius Red - fibrosis red (quantitative; used in research)
  • Reticulin (Gordon-Sweet silver) - normal lobular architecture highlighted; loss of reticulin in nodules shows regeneration
  • PAS with diastase (PASD) - Mallory-Denk bodies in alcohol-related cirrhosis; PAS-positive diastase-resistant granules in AAT deficiency (stored AAT globules in hepatocytes)
  • Prussian Blue (Perls stain) - iron = blue (hemochromatosis)
  • Rhodanine or Rubeanic acid stain - copper = orange-red (Wilson disease)
  • Orcein or Victoria Blue stain - HBsAg-containing hepatocytes; AAT globules

1. Portal hypertension → esophageal varices, splenomegaly, caput medusae, ascites
2. Hepatic failure → coagulopathy, jaundice, encephalopathy, hypoalbuminemia
3. Hepatorenal syndrome
4. Increased risk of hepatocellular carcinoma (HCC) - especially Hep B + C

15B. Viral Hepatitis

• Hepatocyte ballooning degeneration
• Acidophil (Councilman/Mallory) bodies - pyknotic shrunken hepatocytes
• Lobular disarray with necrosis
• Kupffer cell hyperplasia
• Portal and lobular inflammation (lymphocytes)
• Stains: H&E (ballooning, necrosis, inflammation); Immunohistochemistry (IHC) for HBsAg, HBcAg (chronic HBV)

• Portal and periportal inflammation (lymphocytes, plasma cells)
• Interface hepatitis (piecemeal necrosis of hepatocytes at portal-parenchymal interface) - marker of activity
• Bridging necrosis (portal to portal or portal to central necrosis) - severe disease
• Stains: H&E; Masson Trichrome for fibrosis staging; Orcein/Victoria Blue for ground-glass hepatocytes (HBsAg)

15C. Alcoholic Liver Disease

1. Hepatic steatosis (fatty liver) - reversible; >5% hepatocytes contain fat
2. Alcoholic hepatitis - acute; can be fatal
3. Alcoholic cirrhosis - irreversible end-stage

• Macrovesicular steatosis (large fat vacuoles displacing nucleus to periphery)
• Mallory-Denk bodies (Mallory hyaline) - tangled intermediate filaments (cytokeratin 8/18) in hepatocyte cytoplasm; eosinophilic, irregular, rope-like inclusions - key finding
• Neutrophilic (not lymphocytic) lobular inflammation
• Hepatocyte ballooning degeneration
• Pericellular/perisinusoidal fibrosis ("chicken wire" fibrosis)
• Stains: H&E (Mallory-Denk bodies = eosinophilic); Masson Trichrome (pericellular fibrosis = blue); Ubiquitin immunostain (Mallory-Denk bodies = positive)

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PART V: SPECIAL STAINS MASTER TABLE

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• Every major disease and its pathogenesis
• Gross and microscopic morphology for each condition
• Every special stain with colors and diagnostic context
• Clinical features and syndrome correlations
• Immunofluorescence patterns for all major glomerular diseases
• Detailed cardiomyopathy genetics and histology
• Complete GI spectrum from Barrett esophagus to IBD to cirrhosis

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ROBBINS & KUMAR - PATHOLOGIC BASIS OF DISEASE

Chapters 8, 14–22 | Systemic Pathology with Stains & Microscopy Images

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CHAPTER 8 - NEOPLASIA

Key Concepts: Benign vs. Malignant Tumors

Epidemiology of Cancer (2023 US Data)

• Estimated cancer deaths worldwide (2020): 9.9 million (~1 in 6 deaths)
• Projected to reach 13.2 million by 2030
• Males: prostate, lung, colon/rectum
• Females: breast, lung, colon/rectum
• These four cancers = >50% of US diagnoses and deaths

Molecular Basis of Cancer

1. Proto-oncogene mutations → gain-of-function (RAS, MYC, HER2)
2. Tumor suppressor gene loss → loss-of-function (TP53, RB1, APC, BRCA1/2)
3. DNA repair gene mutations → microsatellite instability (MLH1, MSH2 - Lynch syndrome)
4. Telomerase activation → immortality
5. Epigenetic alterations → methylation silencing of tumor suppressors

• Self-sufficiency in growth signals
• Insensitivity to growth inhibitors
• Evasion of apoptosis
• Limitless replicative potential
• Sustained angiogenesis
• Tissue invasion and metastasis
• Reprogramming of energy metabolism
• Evading immune destruction

Grading and Staging

• Grade: Degree of differentiation (I - well differentiated to IV - anaplastic)
• Stage: Extent of spread (TNM: Tumor size, Node status, Metastasis)
• Staging is more clinically important for prognosis

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CHAPTER 14 - BLOOD VESSELS

Atherosclerosis

1. Endothelial injury/dysfunction (from hyperlipidemia, HTN, smoking, toxins)
2. Endothelial dysfunction → increased permeability + VCAM-1/ICAM-1 expression → monocyte recruitment
3. Monocytes enter intima → become macrophages → ingest oxidized LDL → foam cells
4. Smooth muscle cells (SMCs) migrate from media to intima, proliferate, produce ECM → fibrous cap
5. Lipid core accumulates with foam cell death, cholesterol crystals, calcification
6. Plaque grows → luminal stenosis OR plaque rupture → thrombosis

• Stable plaque: dense fibrous cap, minimal lipid, little inflammation - produces chronic ischemia
• Vulnerable/unstable plaque: thin cap, large lipid core, dense macrophage infiltrate - prone to rupture → acute MI/stroke

• Gross: fatty streaks (earliest lesion, reversible) → raised yellow-white plaques → ulcerated/calcified plaques
• LM: intimal thickening, foam cells (lipid-laden macrophages), fibrous cap (collagen, SMCs), necrotic core
• Stains: H&E (foam cells); Masson Trichrome (fibrous cap = blue collagen); Oil Red O/Sudan on frozen sections (lipid = red); Von Kossa (calcification = black); EVG (elastic lamina disruption)

Aneurysms

• True aneurysm: involves all layers of intact (but thinned) wall (atherosclerotic, congenital, post-MI ventricular)
• False aneurysm (pseudoaneurysm): wall defect → extravascular hematoma communicating with lumen (post-MI rupture contained by pericardium; graft anastomosis leak)
• Dissection: blood enters a wall defect and tunnels through medial planes; can occur without aneurysm

• Most >55 years; M>F; strongly linked to smoking and atherosclerosis

• 90% below renal arteries

• Risk of rupture increases with size (>5.5 cm = surgical repair threshold)
• Morphology: atherosclerosis with thinned, focally destroyed media; aneurysm lined by mural thrombus
• Stain: EVG - elastic fiber fragmentation in media

• Causes: hypertension, Marfan syndrome (fibrillin-1 mutation), Ehlers-Danlos, bicuspid aortic valve
• Cystic medial degeneration - loss of elastic tissue and SMCs in aortic media (medial degeneration)
• Stain: EVG or Movat pentachrome - elastic fiber fragmentation + mucoid/cystic spaces in media

Vasculitis

• Giant cell (temporal) arteritis:
  • Chronic granulomatous inflammation of large-to-medium arteries
  • Affects temporal, ophthalmic, vertebral arteries; almost always in >50 yr
  • Granulomas with Langhans giant cells; involvement of internal elastic lamina
  • Risk: blindness from ophthalmic artery involvement
  • Stain: H&E (granulomas + giant cells); EVG (fragmented internal elastic lamina)
• Takayasu arteritis:
  • Granulomatous vasculitis affecting aorta and its main branches
  • Young Asian women (<40); "pulseless disease"
  • Irregular thickening of aortic wall with intimal hyperplasia; narrowing of branch ostia
  • Stain: H&E (granulomas, giant cells); EVG (elastic fiber disruption)

• Polyarteritis nodosa (PAN):
  • Necrotizing vasculitis of medium-sized muscular arteries; spares pulmonary vasculature
  • Associated with Hep B in ~30%
  • Nodular thickening at branch points; aneurysmal dilation; NOT associated with ANCA
  • Stain: H&E (fibrinoid necrosis of vessel wall, acute and chronic inflammation); Elastic stain (disruption of elastica)

• Granulomatosis with Polyangiitis (GPA, formerly Wegener):
  • Triad: upper respiratory necrotizing granulomas + lower respiratory granulomatous vasculitis + glomerulonephritis
  • c-ANCA (PR3-ANCA) positive ~90%
  • Saddle-nose deformity (cartilage destruction)
• Microscopic Polyangiitis (MPA):
  • Necrotizing vasculitis without granulomas; p-ANCA (MPO-ANCA) positive
  • Pulmonary-renal syndrome (like GPA but no granulomas)
• Eosinophilic Granulomatosis with Polyangiitis (EGPA/Churg-Strauss):
  • Asthma + eosinophilia + granulomatous vasculitis
  • p-ANCA positive in ~40%

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CHAPTER 15 - THE HEART (see previous detailed notes from Chapter 12)

Additional: Congenital Heart Disease

• Initially acyanotic; over time: pulmonary hypertension → reversal → Eisenmenger syndrome (right-to-left shunt → cyanosis)

• Tetralogy of Fallot (most common cyanotic CHD): VSD + overriding aorta + pulmonary stenosis + RVH
• Transposition of great arteries

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CHAPTER 16 - RED CELLS, BLEEDING DISORDERS, LYMPHOID & MYELOID NEOPLASMS

Lymphoid Neoplasms

1. Precursor B-cell neoplasms (immature B cells)
2. Peripheral B-cell neoplasms (mature B cells)
3. Precursor T-cell neoplasms
4. Peripheral T-cell/NK-cell neoplasms
5. Hodgkin lymphoma

• Leukemias: widespread bone marrow + peripheral blood involvement
• Lymphomas: discrete tissue masses (usually lymph nodes)
• These are a continuum - many "lymphomas" can evolve to "leukemic" presentation

Key Lymphoid Neoplasms:

• Pathognomonic cell: Reed-Sternberg (RS) cell - large, bilobed or multinucleated, "owl-eye" nucleoli; derived from germinal center B cells
• Stain: H&E (RS cells); CD30+ and CD15+ (immunohistochemistry); PAX5+ (weak B-cell marker)
• Four subtypes: nodular sclerosis (most common, young women, mediastinum) > mixed cellularity > lymphocyte-rich > lymphocyte-depleted

• Most common adult NHL (~30%)
• Large lymphoid cells with vesicular nuclei, multiple nucleoli
• CD20+, CD79a+; Germinal center B-cell type (GCB) vs. activated B-cell type (ABC)
• Stain: H&E (diffuse large cells); IHC panel: CD20, BCL-6, MUM-1, Ki-67

• Indolent; t(14;18)(q32;q21) - BCL-2/IgH translocation → BCL-2 overexpression → apoptosis block
• Morphology: follicular (nodular) pattern throughout lymph node; cells in follicles are centrocytes (small, cleaved) + centroblasts (large)
• Stain: H&E (follicular pattern); IHC: CD10+, BCL-6+, BCL-2+, CD20+

• Highly aggressive; associated with EBV and HIV
• "Starry sky" pattern (macrophages ingesting apoptotic cells among sea of lymphoma cells)
• t(8;14) MYC/IgH translocation → MYC overexpression
• Stain: H&E (starry sky); IHC: CD20+, CD10+, BCL-6+, BCL-2-, Ki-67 ~100%

• Plasma cell neoplasm; monoclonal Ig production (M spike on SPEP)
• "Fried-egg" or "clock-face" chromatin in malignant plasma cells
• Lytic bone lesions, hypercalcemia, renal failure (light chain cast nephropathy), anemia, infections
• Stain: H&E (plasma cells); IHC: CD138+, MUM-1+, CD38+; kappa or lambda light chain restriction by IHC or ISH

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CHAPTER 17 - GASTROINTESTINAL TRACT

Esophagus

Stomach

• NSAIDs → inhibit COX-1 → ↓ PGE2, PGI2 → ↓ mucus, bicarbonate, mucosal blood flow → erosion
• Alcohol, bile, stress: disrupt tight junctions
• Morphology (H&E): erosion, mucosal congestion, neutrophilic infiltrate

• Curved gram-negative rods in mucous layer
• Dense lymphoplasmacytic lamina propria infiltrate + neutrophils in glands (active gastritis)
• Lymphoid follicle formation
• Stains: Modified Giemsa (organisms = blue, curved rods); Warthin-Starry (organisms = black); H&E (active chronic gastritis); CLO test (urease-based rapid test)

• Disrupted mucosal barrier → acid injury → ulcer
• Gross: sharply punched-out, smooth edges (benign), ~95% in duodenal bulb or gastric antrum
• Compare malignant ulcer: irregular heaped-up edges
• Histology (H&E): fibrinopurulent exudate → granulation tissue → fibrosis

• Two types:
  1. Intestinal type (Lauren): gland-forming, arises in intestinal metaplasia (H. pylori → chronic gastritis → metaplasia → dysplasia → carcinoma); hematogenous spread; better prognosis
  2. Diffuse type (Lauren): no gland formation; signet-ring cells (mucin pushes nucleus to periphery); linitis plastica (leather-bottle stomach); peritoneal dissemination; worse prognosis
• Stains: H&E (both types); PAS/Alcian blue (mucin in signet-ring cells); IHC: CK7, CK20, CDX2 (intestinal type)

Small Intestine and Colon

• Hernia - inguinal/femoral/umbilical (3% most common cause worldwide)
• Adhesions - post-surgical/inflammatory fibrous bridges
• Volvulus - loop twists on mesenteric axis; sigmoid or cecum most common
• Intussusception - telescoping; ileum into cecum most common; in children = lead point is Meckel's; adults = neoplasm

• Most common GI malignancy in Western nations
• Two pathways:
  1. APC/beta-catenin pathway (80%): APC tumor suppressor loss → Wnt pathway activation → polyp → carcinoma (adenoma-carcinoma sequence, FAP)
  2. Microsatellite instability (MSI) pathway (15-20%): MLH1/MSH2 loss → Lynch syndrome or sporadic (MLH1 methylation)
• Gross: polypoid (right colon) vs. annular "napkin ring" constricting (left colon)
• Stains: H&E (gland-forming adenocarcinoma with necrotic luminal debris); IHC: CK20+, CDX2+, CK7- (colorectal pattern); MMR protein IHC (MLH1, MSH2, MSH6, PMS2 - loss of nuclear staining indicates MSI)

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CHAPTER 18 - LIVER, GALLBLADDER, AND BILIARY TRACT

Cirrhosis

• 40% asymptomatic until advanced disease
• Cause of death: hepatic encephalopathy, variceal bleeding, infections, HCC
• Hyperestrogenemia → spider angiomas, palmar erythema, gynecomastia (males)
• Hypoalbuminemia → ascites, edema
• Pruritus from bile salt deposition

Alcoholic Liver Disease

1. Hepatic steatosis: >5% hepatocytes with fat; macrovesicular (large fat vacuole displacing nucleus); Oil Red O (fat = red); reversible
2. Alcoholic hepatitis: macrovesicular steatosis + Mallory-Denk bodies + neutrophilic lobular inflammation + ballooning degeneration + satellite necrosis + pericellular "chicken wire" fibrosis
3. Alcoholic cirrhosis: irreversible; micronodular initially; Masson Trichrome for fibrosis

• Tangled cytokeratin 8/18 intermediate filaments
• H&E: eosinophilic, rope-like cytoplasmic inclusions in balloned hepatocytes
• Ubiquitin IHC - positive (Mallory-Denk bodies are ubiquitinated)
• p62 IHC - also positive

Viral Hepatitis

• Cytoplasm packed with smooth ER containing HBsAg
• H&E: finely granular, pale, ground-glass cytoplasm
• Orcein stain / Victoria Blue: HBsAg = brown
• IHC: HBsAg (cytoplasmic); HBcAg (nuclear or cytoplasmic in high replication)

• Periportal hepatocytes destroyed at interface with portal tract
• Indicates active disease and progressive fibrosis

Hepatocellular Carcinoma (HCC)

• Most common primary liver malignancy worldwide
• Strongly linked to: chronic HBV, chronic HCV, alcoholic cirrhosis, hemochromatosis, MASLD/NASH
• AFP (alpha-fetoprotein) elevated in ~75%
• Gross: single or multinodular; hemorrhagic/necrotic; portal vein invasion
• Morphology:
  • Trabecular pattern most common (hepatocytes in cords separated by sinusoids)
  • Pseudoglandular (acinar) pattern
  • Scirrhous (fibrous stroma) pattern
  • Well-differentiated HCC: polygonal cells with prominent nucleoli; retain hepatocytic features
• Stains: H&E (trabecular pattern); Reticulin (thickened trabeculae; normal liver = 1-2 cells thick, HCC = 3+ cells thick); IHC: HepPar-1, Arginase-1, GPC3 (glypican-3 - strong positive in HCC); CK7-, CK20-; AFP+

Primary Biliary Cholangitis (PBC)

• Autoimmune destruction of small intrahepatic bile ducts
• Middle-aged women; anti-mitochondrial antibodies (AMA) >95% sensitive/specific
• Morphology: florid duct lesion - lymphocytic infiltrate destroying bile duct epithelium; non-caseating granulomas around bile ducts
• Progression: chronic cholestasis → ductopenia → cirrhosis
• Stains: H&E (duct destruction); CK7 or CK19 IHC (highlights bile ducts)

Primary Sclerosing Cholangitis (PSC)

• Fibro-obliterative inflammation of intra- and extrahepatic bile ducts
• Strongly associated with ulcerative colitis (70-80%)
• p-ANCA positive
• "Onion-skin" periductal fibrosis - pathognomonic - concentric rings of fibrosis around bile ducts
• Stains: H&E + Masson Trichrome (periductal fibrosis = blue)
• High risk of cholangiocarcinoma

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CHAPTER 19 - PANCREAS

Pancreatitis

• Gallstones (most common, ~40%)
• Ethanol/alcohol (second most common, ~35%)
• Trauma
• Steroids
• Mumps (and other viruses)
• Autoimmune (IgG4-related)
• Scorpion venom
• Hyperlipidemia / Hypercalcemia
• ERCP (iatrogenic)
• Drugs (azathioprine, statins, GLP-1 agonists)

• PRSS1 gain-of-function (cationic trypsinogen) - prevents trypsin self-inactivation → hereditary pancreatitis
• SPINK1 loss-of-function - trypsin inhibitor gone
• CFTR loss-of-function - inspissated secretions, duct obstruction
• CASR mutations - calcium dysregulation

• Interstitial (edematous) pancreatitis: edema, slight parenchymal inflammation, no necrosis; mild, self-limited
• Necrotizing pancreatitis (severe):
  • Fat necrosis: chalky-white areas of saponification (calcium soaps from lipase digestion of mesenteric/peripancreatic fat)
  • Hemorrhage: red-black hemorrhagic areas
  • Microvascular injury → parenchymal necrosis
  • Inflammatory infiltrate (initially neutrophilic)
• Stains: H&E (fat necrosis - ghost outlines of adipocytes, basophilic calcium deposits); Von Kossa (calcium = black in fat necrosis areas)
• Pseudocyst formation (late): cyst lined by fibrous wall, no epithelial lining

• Recurrent or continuous inflammation → progressive fibrosis + destruction of acinar cells → exocrine insufficiency
• Causes: alcohol (most common in adults), hereditary, autoimmune, idiopathic
• Morphology: irregular fibrosis, acinar atrophy, ductal dilation and plugging with protein-rich secretions (calcifications in duct), relative preservation of islets
• Stains: H&E (fibrosis, acinar loss, preserved islets); Masson Trichrome (fibrosis = blue)
• Clinical: steatorrhea, malabsorption, diabetes (late - islet loss)

Pancreatic Carcinoma

• 4th leading cause of cancer death in US; 5-year survival <10%

• 90% = ductal adenocarcinoma

• Location: head of pancreas (60%) > body (15%) > tail (5%); 20% diffuse
• Precursor lesions: PanIN (Pancreatic Intraepithelial Neoplasia) 1→2→3 = carcinoma in situ; also IPMN, MCN

1. KRAS mutation (>90%; earliest and most common; codon 12)
2. p16/CDKN2A loss (>90%; telomere shortening, cell cycle dysregulation)
3. SMAD4 (DPC4) loss (~55%; TGF-beta pathway; loss = poor prognosis marker)
4. TP53 loss (~75%; late event)

• Gross: hard, gray-white scirrhous mass; head lesions obstruct CBD → obstructive jaundice (Courvoisier sign)
• LM: moderately differentiated gland-forming adenocarcinoma in dense desmoplastic stroma; perineural invasion (characteristic)
• Stains: H&E (glands in desmoplastic stroma); IHC: CK7+, CK20-, CA19-9+, CEA+; SMAD4 loss by IHC (absent nuclear staining)

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CHAPTER 20 - KIDNEY AND URINARY TRACT

Emphysema - Microscopy Images from Robbins:

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Post-Streptococcal GN - Microscopy Image from Robbins:

Glomerular Diseases (Chapter 20 - extended)

• Ascending route (most common): E. coli → colonizes urethra → bladder → kidney
• Predisposing: vesicoureteral reflux, obstruction, catheterization, female sex (short urethra)
• Hematogenous route: less common; septicemia, endocarditis; staphylococci, fungi

• Patchy suppurative inflammation; PMNs within tubular lumens and interstitium
• White cell casts (tubular leukocyte casts) - pathognomonic of pyelonephritis
• Abscesses in cortex and medulla
• Stain: H&E (suppurative inflammation, WBC casts); PAS (disrupted tubular BM)

• Coarse, irregular cortical scarring with underlying blunted, deformed calyx
• Microscopy: tubular atrophy, interstitial fibrosis; "thyroid-like" tubules (dilated tubules filled with eosinophilic casts resembling thyroid follicles) = characteristic
• Stain: H&E; Masson Trichrome for interstitial fibrosis

• Key stain: PAS - loss of brush border (proximal tubule)
• Ischemic ATN: tubular rupture (tubulorrhexis); skip lesions; worst at corticomedullary junction
• Nephrotoxic ATN: uniform proximal tubule involvement; intact BM

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CHAPTER 21 - GENITAL TRACT (Male and Female)

Male Genital Tract

• Germ cell tumors (95%): Seminoma vs. Non-seminoma (NSGCT)

• Seminoma stain: H&E (lymphocytic fibrous stroma, sheets of large clear cells); IHC: PLAP+, OCT3/4+, D2-40+, CD117+, AFP-, hCG-
• Yolk sac tumor (endodermal sinus tumor): Schiller-Duval bodies (glomeruloid structures); IHC AFP+
• Choriocarcinoma: syncytiotrophoblasts (multinucleated) + cytotrophoblasts; hCG+; most aggressive (hematogenous spread)

• Most common cancer in American males
• Peripheral zone (posterior lobe) - 70%; transition zone (anterior) - 20%
• Gleason grading (1-5 for predominant + secondary pattern = total score/Grade Group)
• Morphology: small, closely packed glands with prominent nucleoli; lacks basal cell layer; perineural invasion characteristic
• Stains: H&E (small glands, nucleoli); IHC: PSA+ (staining), p63-/HMWCK- (absent basal cells), AMACR (racemase, P504S) - positive in cancer, negative in benign; PIN4 cocktail (p63 + HMWCK + AMACR)

Female Genital Tract

• Most linked to HPV 16 and 18 (squamous carcinoma and adenocarcinoma)
• Progression: normal → HPV infection → LSIL (CIN1) → HSIL (CIN2/3) → invasive carcinoma
• Koilocytes (HPV cytopathic effect): squamous cells with perinuclear halo + wrinkled nucleus
• Stain: Pap smear (koilocytes, dysplastic cells); H&E (CIN grading, invasive carcinoma); p16 IHC (strong block positivity in HSIL/carcinoma - surrogate for high-risk HPV); Ki-67 (increased proliferation)

• Stain: H&E (glandular proliferation, back-to-back glands, endometrioid carcinoma); IHC: ER+, PR+ (type I); TP53 mutant-type staining (type II); MMR proteins for Lynch screening

• Surface epithelial tumors (70%): serous (most common), mucinous, endometrioid, clear cell
• Serous cystadenocarcinoma: Papillary architecture; psammoma bodies (concentric laminated calcifications) characteristic
• Stain: H&E (papillary serous with psammoma bodies); IHC: PAX8+, WT-1+, CK7+, CA-125+; p53 aberrant staining (high-grade)
• Germ cell tumors: Dermoid cyst (mature cystic teratoma) most common benign ovarian tumor; Dysgerminoma = malignant equivalent of seminoma
• Sex cord-stromal tumors: Granulosa cell tumor (Call-Exner bodies = small follicle-like spaces with eosinophilic secretion in H&E; produces estrogen → precocious puberty or postmenopausal bleeding); Inhibin+ IHC

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CHAPTER 22 - BREAST

Fibrocystic Changes

• Most common breast lesion in women 25-50 yr
• Non-proliferative: cysts, fibrosis, apocrine metaplasia - no increased cancer risk
• Proliferative without atypia: mild epithelial hyperplasia - slightly increased risk
• Atypical hyperplasia (ADH/ALH) - 4-5x increased cancer risk

Breast Carcinoma

1. In situ carcinomas: DCIS (ductal), LCIS (lobular) - no invasion
2. Invasive carcinomas: Invasive ductal NOS (most common), Invasive lobular, Medullary, Mucinous, Tubular

• Most common (75%); hard, gritty texture (desmoplastic stroma)
• Morphology: irregular nests/cords/glands; nuclear pleomorphism; mitotic figures
• Stain: H&E (infiltrative glands in desmoplastic stroma); IHC panels:
  • ER/PR status (estrogen/progesterone receptors) - 70-80% positive
  • HER2 (ERBB2) - amplified/overexpressed in 20%
  • Ki-67 (proliferation index)
  • Triple-negative (ER-/PR-/HER2-) - most aggressive; BRCA1 linked

• E-cadherin loss (CDH1 mutation) → cells don't form glands; grow as "single file/Indian file" pattern
• Dyscohesive cells in linear cords through stroma
• Stain: H&E (single file pattern); IHC: E-cadherin negative (diagnostic)

• Malignant cells confined to ductal system, no basement membrane breach
• Comedo type: central necrosis; calcifications ("malignant-type calcifications" on mammography)
• Stain: H&E (cells filling ducts, central necrosis + calcification); IHC: p63/HMWCK (absent myoepithelial layer distinguishes from benign lesions)

• Signet-ring cell morphology; dyscohesive; fills and distends acini
• IHC: E-cadherin negative

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MASTER IMAGE GALLERY - KEY Robbins Pathology Microscopy

1. Emphysema - Types Diagram (Robbins Fig. 15.6)

• (A) Normal acinus: respiratory bronchiole + alveolar duct + alveoli all clearly defined
• (B) Centriacinar: respiratory bronchioles (pink/dilated) destroyed proximally; distal alveoli (blue) spared
• (C) Panacinar: entire unit uniformly enlarged from bronchiole to alveolus

2. Emphysema - CXR and Gross Pathology (Robbins Fig. 15.7)

• (A) CXR: flattened diaphragm (arrow) - classic sign of hyperinflation
• (B) Centriacinar (centrilobular): central emphysematous spaces (E = holes) surrounded by preserved alveolar parenchyma
• (C) Panacinar: uniformly enlarged, thin-walled airspaces throughout; no preserved islands of parenchyma

3. IgA Nephropathy - H&E and Immunofluorescence (Robbins Fig. 20.18)

• (A) H&E: mesangial cell proliferation + increased mesangial matrix; capillary lumens narrowed
• (B) Immunofluorescence (FITC-labeled anti-IgA): bright green granular deposits exclusively in mesangium - diagnostic of IgA nephropathy (Berger disease)

4. Cirrhosis - Masson Trichrome (Robbins Fig. 18.7)

• (A) Active cirrhosis: thick blue collagen bands (Masson Trichrome) surround and isolate rounded red hepatocyte regenerative nodules; complete fibrous septa; portal-to-central bridging
• (B) After 1 year abstinence: dramatic regression - only thin, incomplete blue fibers remain; nodular architecture partially restored; near-normal hepatic parenchyma visible

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COMPREHENSIVE STAIN REFERENCE TABLE (Robbins Chapters 8-22)

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ROBBINS - SUPPLEMENTARY & MISSED DETAILS

Complete Gap-Fill Across Chapters 8, 14–22

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CHAPTER 8 - NEOPLASIA (Missed Details)

Tumor Immune Evasion Mechanisms (from text)

• Tumors downregulate MHC class I → avoid CD8+ T-cell recognition
• Expression of PD-L1 (CD274) → inhibits T-cell activation via PD-1 on T cells (basis of anti-PD-1/PD-L1 immunotherapy)
• Secretion of TGF-β and IL-10 → suppress immune effectors
• FOXP3+ regulatory T cells (Tregs) infiltrate tumor microenvironment → suppress anti-tumor immunity

Tumor Antigens (missed)

• Tumor-specific antigens (neoantigens): products of mutated genes unique to cancer cells → key targets for immune checkpoint therapy
• Tumor-associated antigens: shared between cancer and normal tissues (AFP in HCC, PSA in prostate, CEA in colorectal - all used as tumor markers)

Paraneoplastic Syndromes (missed completely)

Grading vs. Staging (missed nuance)

• Grade = histologic degree of differentiation (WHO Grades 1-4 for most tumors; Gleason score for prostate)
• Stage = anatomic extent of spread; TNM system is universal; stage is the single most important prognostic determinant

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CHAPTER 14 - BLOOD VESSELS (Missed Details)

Hypertension - Pathogenesis Expanded

1. Primary (essential) hypertension (~95%): polygenic; increased renin-angiotensin activity, sodium retention, adrenergic drive, endothelial dysfunction; associated with obesity, insulin resistance, family history
2. Secondary hypertension (~5%): identifiable cause:
   • Renovascular (renal artery stenosis) - most common secondary cause
   • Renal parenchymal disease (CKD)
   • Primary hyperaldosteronism (Conn syndrome) - hypokalemia + HTN
   • Pheochromocytoma (catecholamines)
   • Coarctation of aorta
   • Hypothyroidism/hyperthyroidism

• Hyaline arteriolosclerosis - plasma protein insudation into arteriolar walls; PAS-positive homogeneous pink hyaline thickening of arteriolar walls; common in benign hypertension and diabetes
• Hyperplastic arteriolosclerosis - "onion-skin" concentric thickening of arteriolar walls; smooth muscle cell lamination; seen in malignant hypertension (diastolic BP >120 mm Hg)
• Fibrinoid necrosis - acute arteriolar damage in malignant hypertension
• Stains: H&E (hyaline pink); PAS (hyaline = magenta); Masson Trichrome (fibrinoid necrosis = red/fuchsinophilic)

Vascular Tumors (missed entirely)

• Hemangioma: Most common vascular tumor; two types:
  • Capillary hemangioma - lobular clusters of capillary-sized vessels lined by plump endothelium; in skin/subcutaneous tissue
  • Cavernous hemangioma - large dilated thin-walled vascular channels (also most common benign liver tumor); can bleed; H&E: dilated channels with RBCs
• Pyogenic granuloma (lobular capillary hemangioma) - polypoid; skin/mucous membranes; associated with pregnancy; histology: lobular proliferation of capillaries in edematous stroma; H&E
• Lymphangioma - dilated lymphatic channels lined by endothelium; no RBCs in lumen; H&E + D2-40 IHC (marks lymphatic endothelium)

• Angiosarcoma: Highly malignant tumor of endothelial cells
  • Associated with: liver (vinyl chloride, arsenic, Thorotrast exposure), breast (post-radiation), lymphedema (Stewart-Treves syndrome)
  • Morphology: irregular vascular channels lined by atypical pleomorphic endothelial cells; poorly differentiated areas appear as solid sheets
  • Stains: H&E (vascular channels with malignant cells); IHC: CD31+ (most sensitive), CD34+, ERG+ (nuclear), FLI-1+ (nuclear); Factor VIII-related antigen
• Kaposi Sarcoma (KS):
  • Four clinical forms: classic (Mediterranean elderly men), African endemic, AIDS-related (most common), iatrogenic (immunosuppressed)
  • All associated with HHV-8 (Kaposi sarcoma herpesvirus)
  • Morphology: spindle-shaped cells forming vascular slits with RBC extravasation; hemosiderin deposition; "promontory sign" (vascular channels projecting into dilated spaces)
  • Stains: H&E; IHC: HHV-8 latent nuclear antigen (LANA-1) - pathognomonic positive; CD31+, CD34+

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CHAPTER 15 - HEART (Missed Details)

Infective Endocarditis (IE) - Detailed

• Large, irregular, destructive masses on valve cusps (can extend onto chordae)
• Composed of: thrombotic debris + organisms + fibrin
• Can cause: valve destruction/perforation, ring abscess, septic emboli
• Compare: Rheumatic = small warty; NBTE = small bland; Libman-Sacks = both sides of valve

• Acute IE: Bulky, destructive vegetations; underlying valve necrosis/perforation
• Subacute IE: Less destructive; may have healed areas
• Stain: H&E (fibrinous vegetation, organisms); Gram stain (bacteria); PAS (fungi); Warthin-Starry (some bacteria); Culture is essential

• Regurgitation → acute heart failure
• Perforation of valves
• Septic emboli → brain, kidney, spleen infarcts
• Mycotic aneurysms (infected emboli weaken vessel walls)
• Glomerulonephritis (immune complex deposition from chronic bacteremia)

Non-Bacterial Thrombotic Endocarditis (NBTE) / Marantic Endocarditis

• Small (1-5 mm) sterile, bland thrombi on line of valve closure
• No inflammation, no valve destruction
• Seen in: cancer (especially mucinous adenocarcinoma, Trousseau), DIC, hyperestrogenic states, debilitated/cachectic patients
• Complication: systemic emboli to brain/kidney (despite being sterile)

Libman-Sacks Endocarditis (SLE)

• Small-to-medium sterile vegetations on both surfaces of leaflets (unlike other endocarditides)
• Due to immune complex deposition + fibrinoid necrosis
• Can cause valvular scarring similar to RHD (late)
• Associated with antiphospholipid antibody syndrome too

Carcinoid Heart Disease (missed in previous notes)

• Occurs in ~50% of patients with carcinoid syndrome
• Requires liver metastases (liver normally degrades serotonin, bradykinin, etc.)
• Mediators: serotonin (5-HT), kallikrein, bradykinin, histamine, tachykinins; urinary 5-HIAA correlates with severity
• Right heart exclusively affected (pulmonary vasculature degrades mediators before reaching left heart; left heart involved if R-to-L shunt or primary pulmonary carcinoid)
• Morphology: fibrous intimal plaques (glistening white) on tricuspid and pulmonary valves/endocardium; valve leaflets become thick, stiff, resembling pearly plaques
• Tricuspid regurgitation and pulmonary stenosis are classic findings
• Stain: H&E (fibrosis of valve leaflets/endocardium); Masson Trichrome (fibrous plaques = blue)

Hypertensive Heart Disease (missed details)

• Left-sided HHD:
  • Diagnostic criteria: (1) LV hypertrophy (concentric, without other pathology) + (2) clinical/pathologic evidence of HTN elsewhere
  • Heart weight can exceed 500 g; LV wall thickness >2.0 cm
  • Microscopy: myocyte transverse diameter increase; perivascular + interstitial fibrosis
  • AHA threshold: >130/80 mmHg; European: >140/90 mmHg
  • Outcomes: (1) normal longevity, (2) IHD due to potentiated atherosclerosis + increased O2 demand, (3) renal/cerebrovascular damage, (4) CHF or SCD
• Right-sided HHD (Cor Pulmonale):
  • Isolated hypertrophy/dilation of RV due to pulmonary hypertension from primary lung disease
  • Causes: COPD, pulmonary fibrosis, recurrent pulmonary emboli, primary pulmonary hypertension
  • Acute cor pulmonale: rapid RV dilation (e.g., massive pulmonary embolism)
  • Chronic cor pulmonale: RV hypertrophy + dilation

Sudden Cardiac Death (SCD) - Expanded

• Defined as unexpected cardiac death within 1 hour of symptom onset (or within 24 hrs of last being well)
• 325,000 individuals/year in US; 4-5 million worldwide
• Mechanism: almost always lethal arrhythmia (ventricular fibrillation or asystole)
• #1 cause: CAD (usually chronic severe fixed stenoses; acute plaque rupture found in only 10-20%)
• 80-90% of successfully resuscitated patients have NO evidence of acute MI by enzymes or ECG
• In young patients: HCM, congenital coronary anomalies, myocarditis, channelopathies (LQTS, Brugada), mitral valve prolapse, pulmonary hypertension
• Treatment: ICD (implantable cardioverter-defibrillator)

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CHAPTER 16 - WHITE CELLS & LYMPHOID NEOPLASMS (Missed Details)

Immune Cell Antigen Reference Table (from Robbins Table 13.5)

ALL (Acute Lymphoblastic Leukemia/Lymphoma) - Expanded

• Most common cancer of children (peak age 3 years for B-ALL)
• 85% B-ALL; 15% T-ALL (adolescent males, presents as mediastinal/thymic mass)
• Key cytogenetics:
  • t(12;21) ETV6::RUNX1 - most common translocation in childhood B-ALL; favorable prognosis
  • t(9;22) BCR::ABL1 (Philadelphia chromosome) - in 25% of adult ALL; adverse prognosis; treated with TKIs (imatinib, dasatinib)
  • Hyperploidy (>50 chromosomes) - favorable prognosis in children
  • Hypoploidy - adverse prognosis
  • KMT2A (MLL) rearrangements - infant ALL; poor prognosis
• NOTCH1 mutations - most T-ALLs
• Morphology: lymphoblasts with scant cytoplasm, fine chromatin, inconspicuous nucleoli, numerous mitoses; TdT+ (terminal deoxynucleotidyl transferase) - pathognomonic nuclear marker of lymphoblasts
• Stains: H&E; PAS (lymphoblasts show block positivity in B-ALL); IHC: TdT+ (nuclear), CD10+, CD19+, PAX5+ (B-ALL); CD3+, TdT+ (T-ALL)

CLL/SLL (Chronic Lymphocytic Leukemia / Small Lymphocytic Lymphoma)

• Most common leukemia of adults (Western countries)
• Indolent tumor of mature B cells
• Morphology: monotonous small lymphocytes + "prolymphocytes" + "smudge cells" on peripheral blood smear (characteristic)
• Proliferation centers (pseudofollicles) in lymph nodes - pathognomonic
• IHC: CD5+, CD23+, CD20+ (weak), CD19+, BCL-2+; CD10-; cyclin D1- (negative distinguishes from Mantle cell)
• Complications: hypogammaglobulinemia → infections; autoimmune hemolytic anemia (warm AIHA); Richter transformation → DLBCL (very aggressive)

Mantle Cell Lymphoma (MCL) - Missed

• Moderately aggressive; t(11;14) cyclin D1/IgH → cyclin D1 overexpression
• Morphology: monotonous small-to-medium lymphocytes; mantle zone growth pattern; "blastoid" variant = more aggressive
• IHC: CD5+, CD19+, CD20+, CD23-, CD10-, cyclin D1+ (pathognomonic), SOX11+

Marginal Zone Lymphoma (MALT Lymphoma) - Missed

• Indolent; arises at chronic inflammatory sites
• Gastric MALT lymphoma: driven by H. pylori infection - eradication of H. pylori can cure early-stage disease
• Other sites: salivary gland (Sjögren), thyroid (Hashimoto), lung
• Morphology: lymphoepithelial lesions - neoplastic B cells infiltrating and destroying epithelial glands; monocytoid B cells; plasma cell differentiation
• IHC: CD20+, CD19+; CD5-, CD23-, CD10-, cyclin D1-
• Stain: H&E (lymphoepithelial lesions); Giemsa (H. pylori in associated gastritis)

Hairy Cell Leukemia - Missed

• Very indolent; involves spleen and bone marrow predominantly
• BRAF V600E mutation in virtually all cases (diagnostic and therapeutic target)
• Morphology: medium-sized lymphocytes with oval/folded nuclei and abundant pale cytoplasm with "hairy" cytoplasmic projections (best seen on peripheral blood smear by phase contrast)
• Spleen: characteristic red pulp infiltration (not white pulp) → massive splenomegaly
• Marrow: classic "fried egg" appearance with surrounding halos and reticulin fibrosis → "dry tap" on aspiration
• IHC: CD11c+, CD25+, CD103+, CD123+, TRAP (tartrate-resistant acid phosphatase)+, cyclin D1+ (weak); Annexin A1+ (highly specific)
• TRAP stain (enzyme cytochemistry): positive in hairy cells (not done routinely now; IHC preferred)

Hodgkin Lymphoma - Full Subtype Table (Robbins Table 13.8)

Multiple Myeloma - Expanded Morphology

• Bones: vertebrae, ribs, skull, pelvis, femur, clavicle, scapula (descending frequency)
• "Punched-out" lytic lesions on plain X-ray (1-4 cm); soft, gelatinous red tumor masses in bone
• Marrow: >30% plasma cells; eccentric nucleus, "clock-face" or "cartwheel" chromatin, perinuclear clearing (Golgi)
• Cytologic variants from abnormal Ig accumulation:
  • Flame cells - fiery red cytoplasm
  • Mott cells - multiple grapelike cytoplasmic droplets
  • Russell bodies - cytoplasmic globular Ig inclusions
  • Dutcher bodies - intranuclear Ig inclusions
• Amyloid (AL type) deposition in 10% → nephrotic syndrome, restrictive cardiomyopathy
• Stains: H&E (plasma cells); IHC: CD138+, CD38+, MUM-1+; kappa or lambda restriction (ISH or IHC); Congo Red if amyloid present
• CRAB criteria: Hypercalcemia, Renal failure, Anemia, Bone lesions

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CHAPTER 17 - GI TRACT (Missed Details)

GI Neuroendocrine Tumors (Carcinoid Tumors) - Full Detail

• Now termed: well-differentiated neuroendocrine tumors (WD-NETs); "carcinoid" still used colloquially
• Location: >40% small intestine; then tracheobronchial tree/lung; gastric NETs
• Gastric NETs associations: autoimmune atrophic gastritis, MEN1, Zollinger-Ellison syndrome; PPI therapy → ECL cell hyperplasia (minimal cancer risk)
• Morphology:
  • Yellow/tan, very firm (desmoplastic reaction); submucosal/intramural masses
  • Histology: islands, trabeculae, glands, sheets of uniform cells with scant pink granular cytoplasm and "salt and pepper" chromatin (dispersed nuclear chromatin)
  • Stains: H&E (uniform cells, salt-and-pepper nuclei); IHC: Synaptophysin+ and Chromogranin A+ (neuroendocrine markers); Ki-67 (grading: G1 <3%, G2 3-20%, G3 >20%)
  • Poorly differentiated NETs = neuroendocrine carcinoma (NEC): high Ki-67, TP53 and RB mutations; small cell or large cell type
• Carcinoid Syndrome (occurs <10% of patients):
  • Requires liver metastases (first-pass portal metabolism bypassed)
  • Symptoms: cutaneous flushing, sweating, bronchospasm, diarrhea, right-sided valvular fibrosis
  • Marker: urine 5-HIAA (5-hydroxyindoleacetic acid, serotonin metabolite)
  • Treatment: octreotide (somatostatin analogue)

Appendix (missed entirely)

• Acute Appendicitis:
  • Most common abdominal surgical emergency
  • Pathogenesis: obstruction of lumen (fecalith, hyperplastic lymphoid tissue, tumor) → increased intraluminal pressure → mucosal ischemia → bacterial invasion
  • Morphology: neutrophilic transmural inflammation; mucosal ulceration; periappendiceal fat inflammation (periappendicitis)
  • Complications: perforation → peritonitis, pelvic abscess, pylephlebitis
  • Stain: H&E (neutrophilic inflammation)
• Carcinoid (NET) of Appendix:
  • Most common appendiceal tumor; usually at the tip; <2 cm rarely metastasize
  • Typical "carcinoid" morphology
• Mucinous tumors of Appendix:
  • Spectrum: mucinous adenoma → low-grade appendiceal mucinous neoplasm (LAMN) → mucinous adenocarcinoma
  • Rupture of LAMN → pseudomyxoma peritonei (gelatinous mucinous ascites; "jelly belly")
  • Stain: H&E + PAS (mucin = magenta); IHC: CK20+, CDX2+, CEA+

Anal Canal (missed entirely)

• Squamous cell carcinoma of anus:
  • Associated with HPV 16, 18 (same as cervical carcinoma)
  • Risk factors: anal intercourse, HIV, immunosuppression
  • Preceded by anal intraepithelial neoplasia (AIN) - analogous to CIN
  • Stain: H&E; p16 IHC (positive - HPV surrogate)
  • Treatment: Nigro protocol (chemoradiation - cisplatin + 5-FU + radiation) avoids surgery
• Anorectal junction: transitional epithelium (cloacogenic); tumors here = basaloid/cloacogenic carcinoma (variant of squamous cell carcinoma)

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CHAPTER 18 - LIVER (Missed Details)

Hepatic Adenoma - Expanded Molecular Subtypes (missed)

1. HNF1A-inactivated (30-35%): Loss of HNF1A; female predominant; associated with MODY3; minimal HCC risk; steatosis prominent (Oil Red O positive)
2. Inflammatory (35-50%): Activating mutations in gp130 (IL-6 coreceptor) → JAK-STAT activation; obesity/metabolic syndrome; elevated CRP/serum amyloid A; 10% have beta-catenin mutations → higher HCC risk; IHC: SAA (serum amyloid A) and CRP positive
3. Beta-catenin-activated (15%): CTNNB1 (exon 3) mutations → nuclear beta-catenin; high HCC risk; males predominant; anabolic steroid use; IHC: nuclear beta-catenin positive, glutamine synthetase (GS) diffusely positive; exon 7/8 mutations = low activation = low HCC risk
4. Sonic hedgehog (SHH): GLI1 fusion genes; high propensity for hemorrhage; bleeding risk even when small

Cavernous Hemangioma of Liver

• Most common benign liver tumor
• <2 cm; subcapsular; incidental finding on imaging
• Morphology: dilated thin-walled vascular channels with RBCs; separated by fibrous stroma
• Stain: H&E (dilated channels lined by flat endothelial cells, no atypia); IHC: CD31+, CD34+ (endothelial)
• Never biopsied (risk of catastrophic hemorrhage)

Metabolic Liver Diseases (missed in previous session)

• Hereditary: HFE gene mutation (C282Y most common, especially in Northern Europeans) → excessive intestinal iron absorption
• Iron deposits in: liver (periportal hepatocytes first), pancreas (diabetes), heart (DCM), skin (bronze discoloration), joints, pituitary/gonads
• Stain: Prussian Blue (Perls) - iron = bright blue in hepatocytes; Grades 1-4 by zonal distribution
• Grading: Grade 1 (periportal only) → Grade 4 (all zones + fibrous septa + bile duct epithelium)

• Autosomal recessive; ATP7B gene mutation → defective biliary copper excretion → copper accumulates in liver, brain (basal ganglia), eyes (Kayser-Fleischer rings)
• Stain: Rhodanine or Rubeanic acid - copper = orange-red granules in hepatocytes
• Orcein stain - copper-binding protein positive
• Also: liver biopsy copper quantification (>250 mcg/g dry weight = diagnostic)
• Histology: steatosis + Mallory-Denk bodies + glycogenated nuclei (in early disease)

• Autosomal recessive; SERPINA1 gene; Pi*ZZ phenotype most common (PiMZ = carrier)
• AAT accumulates in hepatocytes as misfolded protein (cannot be secreted)
• Stain: PASD (PAS with diastase) - PAS-positive, diastase-resistant globules in periportal hepatocytes - pathognomonic
• Orcein also highlights AAT globules
• IHC: anti-AAT antibody - cytoplasmic globular positivity
• Leads to neonatal hepatitis, childhood cirrhosis, and adult HCC even without cirrhosis

• Spectrum: steatosis → steatohepatitis (MASH) → fibrosis → cirrhosis → HCC
• Morphology of MASH (H&E):
  • Macrovesicular steatosis (>5% hepatocytes)
  • Lobular inflammation (lymphocytes, neutrophils)
  • Hepatocyte ballooning degeneration (key feature)
  • Perisinusoidal/pericellular "chicken wire" fibrosis (zone 3; Masson Trichrome = blue)
  • Mallory-Denk bodies (less prominent than alcoholic)
• NAS (NAFLD Activity Score): steatosis + lobular inflammation + ballooning = scored 0-8; ≥5 = MASH
• SAF score (Steatosis, Activity, Fibrosis) - alternative
• Key stains: H&E (ballooning, steatosis, lobular inflammation); Masson Trichrome (pericellular zone 3 fibrosis); PASD, Prussian Blue to exclude other causes

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CHAPTER 19 - PANCREAS (Missed Details)

Pancreatic Cystic Neoplasms

• Arises from main pancreatic duct or its branches; produces copious mucin
• Main duct IPMN: higher malignant potential (~70% have high-grade dysplasia or invasive carcinoma)
• Branch duct IPMN: lower risk; often "wait and watch" if <3 cm without worrisome features
• Morphology: papillary projections lined by mucinous columnar epithelium; mucin fills and dilates the duct
• Associated genetic changes: KRAS mutations most common; GNAS mutations (activating, codon 201) - seen in ~50%; characteristic of IPMN (not seen in MCN)
• Stain: H&E + PAS (mucin); IHC: MUC2, MUC5AC (intestinal and gastric foveolar subtypes)

• Almost exclusively in women; body/tail of pancreas
• Pathognomonic: ovarian-type stroma beneath mucinous epithelium
• No communication with pancreatic ductal system (unlike IPMN)
• All MCNs should be resected due to malignant potential
• Stains: H&E (ovarian stroma + mucinous lining); IHC: ER+, PR+ in ovarian stroma (confirming diagnosis); MUC5AC+ in epithelium

• Almost always benign (serous cystadenocarcinoma extremely rare)
• Von Hippel-Lindau (VHL) gene mutations in sporadic cases; associated with VHL syndrome
• Morphology: innumerable small cysts lined by glycogen-rich cuboidal epithelium; central stellate scar with calcification; "honeycomb" appearance
• Stains: H&E (small cysts, cuboidal clear cells); PAS (glycogen-rich cells = magenta); IHC: MUC6+

Pancreatic Neuroendocrine Neoplasms (PanNENs) - Missed

• Insulinoma - most common functioning PanNET; beta cells; hypoglycemia; Whipple triad (hypoglycemia symptoms + low blood glucose + relief with glucose); H&E: uniform cells; IHC: insulin+; usually benign (>90%)
• Gastrinoma - G-cell; causes Zollinger-Ellison syndrome (multiple refractory peptic ulcers, diarrhea); 25% associated with MEN1 (along with parathyroid and pituitary tumors); often malignant; IHC: gastrin+
• Glucagonoma - alpha cells; necrolytic migratory erythema + diabetes; IHC: glucagon+
• VIPoma - massive watery diarrhea (WDHA / Verner-Morrison syndrome); IHC: VIP+
• Non-functioning PanNETs - most common; present with mass effect; often large at diagnosis

• Amyloid deposition in insulinomas (islet amyloid polypeptide = IAPP); Congo Red positive
• Stains: H&E (salt-and-pepper chromatin, trabeculae/nests); IHC: Synaptophysin+, Chromogranin A+; Ki-67 for grading

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CHAPTER 20 - KIDNEY (Missed Details)

Renal Cell Carcinoma (RCC) - Missed Entirely

• Mahogany brown tumor; central stellate scar
• Large cells with abundant eosinophilic granular cytoplasm (packed mitochondria)
• IHC: CD117+, CK7- (negative in nests); Hale's colloidal iron negative/limited
• EM: packed mitochondria (confirms diagnosis)

• Most common renal tumor of children (peak age 3-4 years)
• Associated with: WT1 gene deletion (chromosome 11p13) - also in WAGR syndrome (Wilms + Aniridia + GU malformations + mental Retardation); WT2 - Beckwith-Wiedemann syndrome
• Classic triphasic histology: blastema (small blue cells) + epithelium (primitive tubules/glomeruli) + stroma (fibroblasts/muscle)
• Stains: H&E (triphasic pattern); IHC: WT1+ (nuclear); Blastemal cells CD56+

Diabetic Nephropathy (mentioned only briefly in text)

• Leading cause of chronic kidney failure in the US (40% of type 1 and type 2 diabetics develop advanced nephropathy)
• Pathology described in Chapter 24 (endocrine)
• Key morphologic features:
  • Diffuse glomerulosclerosis - mesangial expansion + GBM thickening (most common)
  • Nodular glomerulosclerosis (Kimmelstiel-Wilson nodules) - pathognomonic; nodular PAS-positive deposits in mesangium; associated with microaneurysms; "ball-and-plug" appearance
  • "Capsular drop" lesion (homogeneous PAS-positive material between parietal epithelium and Bowman capsule)
  • "Fibrin cap" lesion (homogeneous eosinophilic cap over glomerular capillaries)
  • Arteriolar hyalinosis (both afferent AND efferent arterioles - efferent arteriolar hyalinosis = pathognomonic of diabetes)
• Stain: PAS (mesangial expansion, KW nodules = magenta); JMS (GBM thickening); H&E (all lesions)

Bladder Carcinoma (missed entirely)

• Urothelial (transitional cell) carcinoma (TCC) - ~90% of bladder tumors
• Risk factors: smoking (#1), aromatic amine exposure (aniline dyes), cyclophosphamide, Schistosoma haematobium (squamous cell type), chronic cystitis
• Two pathways:
  1. Low-grade papillary tumors: FGFR3 mutations → papillary low-grade, recurrent but rarely invasive
  2. High-grade/invasive carcinoma: TP53, RB mutations, CIS → flat high-grade → muscle-invasive
  • CIS (carcinoma in situ) = flat, high-grade; appears red velvety; poor prognosis marker despite being non-invasive
• Morphology:
  • Papillary: finger-like fronds with fibrovascular cores; lined by urothelium
  • Flat CIS: full-thickness nuclear atypia; no papillary architecture; cells are dyscohesive
  • Invasive: nests/cords/sheets infiltrating muscularis propria (detrusor muscle)
• Stains: H&E (grading, depth of invasion); IHC: CK7+, CK20+, GATA3+, p63+, uroplakin; p53 overexpression (high-grade); FISH for chromosome 3, 7, 9, 17 (UroVysion) - cytological detection in urine

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SUPPLEMENTARY STAIN ADDITIONS (Missed from Chapter Content)

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SUMMARY OF ALL MAJOR GAPS NOW FILLED