***** Myocardial Infarction – (AP 16, API 17, TSI 19, TS 22, AP 24) a. Risk Factors & Etiopathogenesis b. Classification of Infarcts c. Morphology (Gross & Microscopy) d. Clinical Features & Complications e. Diagnosis of MI CASE – Dyspnoea & Chest Pain, Excessive Sweating, Pain radiating to Left Shoulder, Diabetic, Hypertensive, Troponins + in Blood Essay for 10 marks in pathology

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Myocardial Infarction - Complete 10-Mark Essay (Pathology)

Case Analysis

The patient presents with dyspnoea, chest pain, diaphoresis (excessive sweating), pain radiating to the left shoulder, with background history of diabetes mellitus and hypertension, and positive serum troponins - this is a classic presentation of Acute Myocardial Infarction (AMI).

Definition

Myocardial infarction (MI), commonly called a "heart attack," is necrosis of cardiac muscle resulting from prolonged ischemia. The 2018 joint task force defines it as "acute myocardial injury detected by abnormal cardiac biomarkers in the setting of evidence of acute myocardial ischemia."

Robbins & Kumar Basic Pathology, p. 334
Robbins Cotran Kumar Pathologic Basis of Disease, p. 511

A. Risk Factors & Etiopathogenesis

Risk Factors

Modifiable	Non-Modifiable
Hypertension	Age (risk rises progressively)
Diabetes mellitus	Male sex (females protected premenopausally)
Dyslipidemia (high LDL, low HDL)	Family history
Smoking / tobacco use	Genetic predisposition
Obesity
Sedentary lifestyle
Stress

In the given case: The patient has diabetes + hypertension - both are established independent risk factors for atherosclerosis and MI. Studies show 90% of MI patients have at least one established risk factor prior to their first event.

Etiopathogenesis

The vast majority of MIs result from acute thrombosis within coronary arteries following disruption of an atherosclerotic plaque. The sequence is:

Plaque disruption - An atheromatous plaque is eroded or suddenly disrupted by endothelial injury, intraplaque hemorrhage, or mechanical forces, exposing subendothelial collagen and necrotic plaque contents to blood.
Platelet activation - Platelets adhere, aggregate, and are activated, releasing thromboxane A2, ADP, and serotonin, causing further platelet aggregation and vasospasm.
Coagulation activation - Tissue factor exposure activates the coagulation cascade, adding to the growing thrombus.
Occlusion - Within minutes, the enlarging thrombus may completely occlude the coronary artery lumen.

Angiography within 4 hours of MI onset demonstrates coronary thrombosis in almost 90% of cases.

Important: The culprit plaque often has less than 70% stenosis pre-event - it is vulnerable plaque with a large lipid core and thin fibrous cap that ruptures unpredictably.

In ~10% of cases, MI occurs without typical atherothrombosis - causes include:

Coronary vasospasm (with or without atherosclerosis)
Emboli from mural thrombi (e.g., atrial fibrillation) or valve vegetations
Vasculitis, amyloid deposition, sickle cell disease
Cocaine-induced vasospasm

B. Classification of Infarcts

1. By Depth (Extent)

Type	Description	Cause
Transmural (Full-thickness)	Entire wall thickness involved; involves epicardium, myocardium, endocardium	Complete occlusion of a major coronary artery; associated with STEMI on ECG
Subendocardial (Non-transmural)	Limited to inner 1/3 to 1/2 of wall; inner myocardium is most vulnerable (furthest from epicardial supply)	Partial or transient occlusion; diffuse hypoperfusion; associated with NSTEMI

2. By ECG Pattern (Clinically Used Classification)

Type	ECG	Troponin	Description
STEMI (ST-Elevation MI)	ST elevation → Q waves	Positive	Transmural; complete occlusion
NSTEMI (Non-ST-Elevation MI)	ST depression / T-wave changes / normal	Positive	Subendocardial; incomplete occlusion
UA (Unstable Angina)	ST/T changes	Negative	No necrosis

3. By Anatomical Location

Coronary Artery	Territory Infarcted
Left Anterior Descending (LAD) - most common (~40-50%)	Anterior wall, anterior septum, apex
Right Coronary Artery (RCA)	Posterior/inferior wall, posterior septum, RV
Left Circumflex (LCX)	Lateral wall

C. Morphology (Gross & Microscopy)

Gross Morphology - Time-Based Changes

Time	Gross Appearance
0 - 12 hours	No gross change visible; detected by TTC stain (pale unstained zone = infarct; brick-red = normal)
12 - 24 hours	Reddish-blue discoloration from congestion and extravasated blood (dark mottling)
1 - 3 days	Mottling with yellow-tan infarct center
3 - 7 days	Hyperemic border; central yellow-tan softening; most vulnerable to rupture
7 - 10 days	Maximally yellow-tan and soft; depressed red-tan margins
10 - 14 days	Red-gray depressed infarct borders
2 - 8 weeks	Gray-white scar, progressing from border toward core
> 2 months	Dense fibrous scar (complete)

Triphenyl tetrazolium chloride (TTC) stain: Intact myocardium turns brick-red (preserved lactate dehydrogenase); infarcted tissue remains pale because dehydrogenases have leaked out through damaged membranes.

Microscopic Morphology - Time-Based Changes

Time	Light Microscopy	Electron Microscopy
0 - 0.5 hr	None	Myofibril relaxation; glycogen loss; mitochondrial swelling
0.5 - 4 hrs	Usually none; wavy fibers at border (non-contractile dead fibers stretched by adjacent viable contracting myocardium)	Sarcolemmal disruption; mitochondrial amorphous densities
4 - 12 hrs	Onset of coagulative necrosis; edema; hemorrhage; nuclear pyknosis	-
12 - 24 hrs	Ongoing coagulative necrosis; pyknosis; hypereosinophilic myocytes; marginal contraction band necrosis; early neutrophilic infiltrate	-
1 - 3 days	Coagulative necrosis with loss of nuclei and striations; brisk neutrophilic infiltrate	-
3 - 7 days	Disintegration of dead myofibers; dying neutrophils; early macrophage phagocytosis at border; early granulation tissue	-
7 - 10 days	Well-developed phagocytosis; granulation tissue (most prominent) at margins	-
10 - 14 days	Well-established granulation tissue with new blood vessels; collagen deposition begins	-
2 - 8 weeks	Increased collagen deposition, decreased cellularity	-
> 2 months	Dense collagenous scar (complete)	-

Key histological markers:

Wavy fibers - earliest microscopic sign (0.5-4 hrs)
Coagulative necrosis - hallmark (4-12 hrs)
Contraction band necrosis - especially in reperfused infarcts (intense eosinophilic bands of hypercontracted sarcomeres due to calcium influx)
Neutrophils - peak 1-3 days
Macrophages - peak 5-10 days
Granulation tissue - 7-14 days
Dense scar - >2 months

Robbins Cotran Kumar, p. 513 (Table 12.5)

D. Clinical Features & Complications

Clinical Features

Symptoms:

Chest pain - severe, crushing, pressure-like, substernal (most common); lasts >20-30 minutes (unlike angina)
Radiation - to left arm/shoulder, jaw, neck, back, epigastrium (as in the case above)
Diaphoresis (excessive sweating) - due to sympathetic activation
Dyspnoea - due to LV dysfunction / pulmonary edema
Nausea, vomiting - common
Sense of impending doom

Silent MI: Up to 10-15% of MIs are clinically silent, especially in diabetics (impaired pain perception due to neuropathy) and elderly patients - relevant here as the patient has diabetes.

Signs:

Tachycardia, may have bradycardia in inferior MI (vagal effect)
S3 or S4 gallop
Hypotension (cardiogenic shock in severe cases)
Friction rub (pericarditis - 2-3 days after)

Complications (in order of timing)

Complication	Timing	Details
Arrhythmias	Immediate (first hours/days)	Most common complication; leading cause of death pre-hospital; ventricular fibrillation, heart block, PVCs
Left ventricular failure / Pulmonary edema	Early	Due to loss of contractile myocardium
Cardiogenic shock	Early	Occurs when >40% LV mass is infarcted; high mortality
Myocardial rupture	3-7 days (peak softening)	Three types: (1) Free wall rupture → hemopericardium → cardiac tamponade; (2) Interventricular septum rupture → acute VSD; (3) Papillary muscle rupture → acute MR
Pericarditis (Fibrinous)	2-3 days (early)	Overlying epicarditis; friction rub; Dressler syndrome (autoimmune) at 2-10 weeks
Mural thrombus	Days-weeks	On akinetic wall → risk of systemic embolism (stroke)
Ventricular aneurysm	Weeks-months	Paradoxical bulge on systole; risk of mural thrombus, arrhythmias, heart failure
Progressive CHF / Ischemic cardiomyopathy	Long-term	Due to scar remodeling and progressive myocyte loss

Robbins Cotran Kumar, p. 519

E. Diagnosis of MI

1. Cardiac Biomarkers (Most Important - as in the Case)

Marker	Onset	Peak	Normalizes	Notes
Troponin I / Troponin T	3-6 hrs	24-48 hrs	7-10 days (cTnI); 10-14 days (cTnT)	Gold standard - most sensitive and specific; present in the case
CK-MB (Creatine kinase-MB)	3-6 hrs	24 hrs	48-72 hrs	Useful for reinfarction (re-elevation)
Myoglobin	1-2 hrs	4-8 hrs	24 hrs	First to rise; non-specific
LDH (LDH1 > LDH2)	24-48 hrs	3-5 days	7-14 days	"Flipped pattern"
SGOT (AST)	6-12 hrs	24-48 hrs	3-5 days	Rarely used now

In this case: Positive troponins confirm irreversible myocardial necrosis - diagnostic of MI.

2. ECG Changes

Phase	Changes
Hyperacute (minutes-hours)	Tall, peaked T waves (first change)
Acute (hours)	ST-segment elevation (STEMI) or depression (NSTEMI); T-wave inversion
Evolving (days)	Q waves develop (pathological Q = >0.04 sec wide, >1/3 R height)
Old/Healed (weeks-months)	Persistent Q waves; T-wave normalization

3. Imaging

Echocardiography - Regional wall motion abnormalities; ejection fraction assessment
Coronary angiography (Gold standard for anatomy) - identifies site of occlusion
Cardiac MRI - late gadolinium enhancement shows scarring
Radionuclide imaging (Thallium-201, Tc-99m sestamibi) - perfusion defects

4. Other Lab Findings

Leukocytosis (neutrophilia) - reflects inflammatory response to necrosis
Elevated ESR, CRP (acute phase response)
Hyperglycemia (even in non-diabetics, due to stress response)

Case Summary (Applying Pathology to the Case)

Feature	Pathological Basis
Chest pain radiating to left shoulder	Ischemic pain referred via T1-T4 dermatomes
Diaphoresis	Sympathetic nervous system activation
Dyspnoea	LV dysfunction → elevated LVEDP → pulmonary congestion
Diabetes	Accelerates atherosclerosis + increases risk of silent MI
Hypertension	Promotes atherosclerosis; increases cardiac afterload
Troponin positive	Sarcolemmal disruption → troponin release from necrotic myocytes

Quick Summary Table for Exam

Aspect	Key Point
Most common cause	Atherosclerotic plaque rupture + thrombosis
Most common vessel	LAD (anterior MI)
First gross change	Detectable by TTC stain at 2-3 hrs
Earliest microscopic sign	Wavy fibers (0.5-4 hrs)
Most vulnerable to rupture	3-7 days (maximal softening)
Best diagnostic marker	Troponin I/T (gold standard)
Most common complication	Arrhythmias (leading cause of early death)
Most dangerous complication	Free wall rupture → cardiac tamponade (3-7 days)
Long-term complication	LV aneurysm, ischemic cardiomyopathy

Sources: Robbins & Kumar Basic Pathology (p. 334-340) | Robbins, Cotran & Kumar Pathologic Basis of Disease (pp. 511-519)

Glioblastoma for 5 Mark

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Glioblastoma - 5-Mark Essay (Pathology)

Definition & Introduction

Glioblastoma (GBM), IDH-wildtype, WHO Grade 4 is the most common and most malignant primary brain tumor in adults, arising from astrocytes. It accounts for approximately 50% of all primary malignant brain tumors (and >50% of all CNS malignancies). It is always considered a Grade 4 lesion with no lower-grade precursors, and carries a very poor prognosis.

Robbins & Kumar Basic Pathology, p. 802
Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 1194

Epidemiology & Site

Predominantly affects older adults in their 6th to 8th decades of life
Location: Cerebral hemispheres - temporal, parietal, and frontal lobes; basal ganglia and thalamus
De novo (primary) GBM is most common - arises without a preceding low-grade precursor
Secondary GBM is rare - may arise from progression of lower-grade IDH-mutant astrocytoma

Pathogenesis & Molecular Genetics

GBM is defined by IDH-wildtype status (no IDH1/IDH2 mutation). It harbors multiple key genetic alterations:

Genetic Alteration	Consequence
TERT promoter mutation	Telomerase activation → evasion of senescence
EGFR gene amplification	Activation of growth factor signaling
Combined +7 / -10 (gain chr.7, loss chr.10)	Most characteristic chromosomal change
Homozygous CDKN2A deletion	Loss of p16 → escape from growth controls
TP53 mutation	Resistance to apoptosis
MGMT promoter methylation	Silences DNA repair enzyme (predicts better response to chemotherapy with temozolomide)
PDGFR amplification	Additional growth factor pathway activation
VEGF overproduction	Drives microvascular proliferation (response to hypoxia)

Even an adult diffuse astrocytoma without high-grade histology is still classified as GBM if it is IDH-wildtype and has TERT mutation, EGFR amplification, or +7/-10 copy number changes.

Morphology

Gross Appearance

Glioblastoma - Gross and microscopic appearance showing necrotic hemorrhagic mass and palisading necrosis with microvascular proliferation

Fig. 21.31 - Glioblastoma. (A) Cross-section of brain showing necrotic, hemorrhagic, infiltrating mass. (B) Serpiginous palisading necrosis with microvascular proliferation (inset). - Robbins & Kumar

The gross appearance varies characteristically from region to region:

Firm, white areas - solid tumor
Soft, yellow areas - tissue necrosis
Red/dark areas - hemorrhage
Cystic areas - cystic degeneration
Overall: necrotic, hemorrhagic, infiltrating mass

Butterfly glioma: Rapid infiltration through the corpus callosum leads to bilateral, symmetrical involvement of both hemispheres - a pathognomonic pattern.

Microscopic Appearance

The key diagnostic histological features are:

High cellularity - densely packed, pleomorphic tumor cells
Nuclear atypia - bizarre, pleomorphic nuclei
Brisk mitotic activity - numerous mitoses
Palisading (Pseudopalisading) necrosis - serpiginous/serpentine zones of necrosis surrounded by rows of tumor cells aligned perpendicular to the necrotic edge ("tumor nuclei palisade around necrotic zones") - pathognomonic
Microvascular (endothelial) proliferation - tufts of multilayered cells bulging into vessel lumens ("glomeruloid bodies"), driven by VEGF released by hypoxic tumor cells - pathognomonic
GFAP positive (glial fibrillary acidic protein) on immunohistochemistry

The two hallmark features that distinguish GBM from lower-grade gliomas are: Palisading necrosis + Microvascular proliferation.

Clinical Features

Seizures - common presenting symptom
Headache - severe, pulsating (raised ICP)
Focal neurological deficits - depending on location (motor weakness, aphasia, visual field defects)
Neurocognitive impairment - memory, personality changes
Nausea, vomiting - raised ICP
Rapid progression - symptoms develop over weeks

Imaging (MRI): Ring-enhancing lesion with central necrosis and surrounding edema (contrast enhancement due to leaky, abnormal blood-brain barrier). The ring-enhancing pattern on MRI is characteristic.

Diagnosis

MRI with contrast - ring-enhancing lesion (imaging of choice)
Biopsy + histopathology - gold standard for diagnosis
Molecular profiling - IDH status (wildtype), TERT, EGFR, +7/-10, MGMT methylation
GFAP immunostaining - confirms glial origin

Treatment & Prognosis

Standard treatment (Stupp Protocol): Surgical resection + Radiotherapy + Temozolomide (alkylating agent)
MGMT promoter methylation: Predicts better response to temozolomide chemotherapy
Prognosis: Extremely poor - median survival is only 15-18 months even with aggressive treatment

Summary Table

Feature	Glioblastoma (IDH-Wildtype, WHO Grade 4)
Cell of origin	Astrocyte
WHO grade	4 (highest)
IDH status	Wildtype
Key molecular markers	TERT mut, EGFR amp, +7/-10, CDKN2A del
Age group	6th-8th decade
Site	Cerebral hemispheres
Gross	Necrotic, hemorrhagic, infiltrating
Hallmark microscopy	Palisading necrosis + Microvascular proliferation
Imaging	Ring-enhancing lesion (MRI)
IHC	GFAP positive
Prognosis	Median survival 15-18 months

Sources: Robbins & Kumar Basic Pathology (p. 802-803) | Robbins, Cotran & Kumar Pathologic Basis of Disease (pp. 1193-1196)

Pleomorphic adenoma

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Pleomorphic Adenoma (Mixed Tumor)

Definition

Pleomorphic adenoma (also called "mixed tumor") is the most common benign tumor of the salivary glands, characterized by a mixture of ductal (epithelial), myoepithelial, and mesenchymal (stromal) elements. The term "pleomorphic" refers to this morphological heterogeneity (diverse tissue types), not to nuclear pleomorphism.

Robbins & Kumar Basic Pathology, p. 543
Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 697

Incidence & Site

Feature	Detail
Most common salivary gland tumor	~60% of all parotid tumors
Most common gland affected	Parotid gland (superficial lobe) - 80%
Second most common site	Submandibular gland
Minor salivary gland site	Hard palate (most common intraoral site)
Age group	3rd-5th decade; any age
Sex	Slight female predominance

"Rule of 70" (exam-relevant): 70% of salivary gland tumors are in the parotid; 70% of parotid tumors are pleomorphic adenoma; 70% are benign.

Pathogenesis / Molecular Genetics

Cell of origin: All elements (epithelial, myoepithelial, mesenchymal-looking stroma) are believed to arise from myoepithelial or ductal reserve (stem) cells - hence the single-origin hypothesis despite the biphasic appearance.
Radiation exposure increases risk.
Key molecular alterations:
- PLAG1 gene overexpression (via chromosomal rearrangements, most commonly t(3;8)) - promotes growth factor receptor signaling
- HMGA2 gene mutation - in cases lacking PLAG1 overexpression

Morphology

Gross Appearance

Rounded, well-demarcated, encapsulated mass (rarely exceeds 6 cm)
Smooth surface (bosselated in some cases)
Cut surface: gray-white with areas of:
- Myxoid (mucoid) - translucent gray-blue zones
- Chondroid (cartilage-like) - blue translucent areas
- Rarely: cystic degeneration or foci of ossification
Capsule may be incomplete, especially on the palate, with tongue-like protrusions into surrounding tissue - important cause of recurrence after simple enucleation

Pleomorphic adenoma - Low-power histology showing well-demarcated encapsulated tumor with chondromyxoid stroma and adjacent normal salivary gland parenchyma

Fig. 16.20A - Low-power histologic view of pleomorphic adenoma: well-demarcated tumor (enclosed in capsule) with adjacent normal salivary gland parenchyma (right). Note the blue-purple chondromyxoid stroma within the tumor - Robbins Cotran Kumar

Microscopic Appearance

The hallmark is morphologic heterogeneity - a biphasic (dual-component) picture:

Component 1 - Epithelial/Myoepithelial elements:

Cells arranged as ducts, acini, irregular tubules, strands, or sheets
Ductal cells: cuboidal to columnar cells lining gland-like spaces
Myoepithelial cells: small, deeply chromatic, spindle-shaped cells underlying ducts
Islands of squamous epithelium may be present
No significant nuclear atypia, no dysplasia, minimal mitoses

Component 2 - Stromal/Mesenchymal elements:

Chondromyxoid matrix - loose myxoid tissue with islands of cartilage
Rarely: foci of bone (osseous metaplasia)
The stroma gives the "blue translucent" areas on gross

The ratio of epithelial to mesenchymal elements varies widely between tumors, but this does not affect prognosis.

Clinical Features

Slow-growing, painless, mobile, discrete mass in the parotid region (below and in front of the ear / angle of jaw)
Usually solitary; firm in consistency
No facial nerve involvement (distinguishes from malignant parotid tumors)
History of months to years of gradual enlargement
No skin fixation or lymphadenopathy (benign)

Complications

1. Recurrence

25% recurrence after simple enucleation (due to incomplete capsule and tumor protrusions into surrounding tissue)
Only 4% recurrence after wide local excision/superficial parotidectomy
Multiple recurrences can lead to seeding of surgical field

2. Malignant Transformation - Carcinoma Ex Pleomorphic Adenoma

Most serious complication
Risk of malignant change increases with duration:
- < 5 years: ~2% risk
- 15 years: ~10% risk
Malignant transformation usually takes the form of adenocarcinoma or undifferentiated carcinoma
Highly aggressive - mortality 30-50% at 5 years
Clinical clue: sudden rapid growth, pain, facial nerve palsy in a long-standing parotid mass

Diagnosis

Investigation	Finding
FNAC (Fine Needle Aspiration Cytology)	Biphasic pattern - epithelial/myoepithelial cells in myxoid/chondromyxoid background; diagnostic
USG	Well-defined hypoechoic mass
MRI / CT	Well-encapsulated mass; MRI shows bright signal on T2
Histopathology (post-excision)	Confirmatory - biphasic morphology as described above

FNAC is the investigation of choice pre-operatively; incision biopsy is contraindicated (risk of seeding and facial nerve damage).

Treatment

Superficial parotidectomy with preservation of the facial nerve - procedure of choice for parotid pleomorphic adenoma
Simple enucleation is not recommended (high recurrence)
For minor salivary gland tumors: wide local excision with clear margins
No radiotherapy for benign disease (unless recurrent/unresectable)

Summary Table

Feature	Pleomorphic Adenoma
Type	Benign
Most common salivary gland tumor	Yes (~60% of parotid tumors)
Cell of origin	Myoepithelial / ductal reserve cells
Key molecular change	PLAG1 overexpression; HMGA2 mutation
Gross	Encapsulated, bosselated; gray-white + myxoid/chondroid areas
Microscopy	Biphasic: epithelial/myoepithelial cells + chondromyxoid stroma
Clinical	Slow-growing, painless, mobile mass
Recurrence risk	25% (enucleation); 4% (parotidectomy)
Malignant change	Carcinoma ex pleomorphic adenoma (2-10% risk)
Treatment	Superficial parotidectomy

Sources: Robbins & Kumar Basic Pathology (p. 543) | Robbins, Cotran & Kumar Pathologic Basis of Disease (pp. 697-698) | Cummings Otolaryngology Head & Neck Surgery

Viral hepatitis

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Viral Hepatitis - Pathology Essay

Definition

Viral hepatitis is inflammation of the liver caused by a group of hepatotropic viruses - designated A, B, C, D, and E - each with distinct virology, transmission routes, clinical course, and outcomes. It ranges from acute self-limited illness to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC).

The Five Hepatitis Viruses - Comparative Features

Feature	Hep A (HAV)	Hep B (HBV)	Hep C (HCV)	Hep D (HDV)	Hep E (HEV)
Genome	ssRNA	Partially dsDNA	ssRNA	Circular defective ssRNA	ssRNA
Family	Picornaviridae	Hepadnaviridae	Flaviviridae	Deltaviridae	Hepeviridae
Transmission	Fecal-oral (food, water)	Parenteral, sexual, perinatal	Parenteral, IVDU	Parenteral (requires HBV)	Fecal-oral (water-borne)
Incubation Period	2-6 weeks	2-26 weeks	4-26 weeks	Same as HBV	4-5 weeks
Chronicity	Never	5-10%	>80%	10% co-infection; 90-100% superinfection	Immunocompromised only
Fulminant hepatitis	Rare (<0.1%)	Rare (0.1-1%)	Very rare	High risk with HBV	20% mortality in pregnancy
HCC risk	No	Yes	Yes	Yes (with HBV)	No
Diagnosis	Serum IgM anti-HAV	HBsAg, anti-HBc antibodies; HBV DNA PCR	ELISA anti-HCV; HCV RNA PCR	IgM/IgG anti-HDV; HDV RNA	IgM anti-HEV; HEV RNA
Vaccine available	Yes	Yes	No	Prevented by HBV vaccine	Yes (some countries)

Robbins, Cotran & Kumar - Table 18.3, p. 777

Pathogenesis

Liver injury in viral hepatitis is primarily immune-mediated, not directly cytopathic (except possibly HCV):

HBV/HCV: CD8+ cytotoxic T cells recognize viral antigens on infected hepatocytes and destroy them. CD4+ helper T cells amplify the response. This cell-mediated immune attack on hepatocytes is the main mechanism of liver damage.
HAV/HEV: Similar CD8+ T-cell cytolytic responses; viral shedding precedes liver injury.
Extrahepatic manifestations (HBV): Immune complex (HBsAg-anti-HBs) deposition causes vasculitis (polyarteritis nodosa), glomerulonephritis, and cryoglobulinemia.
HCV chronicity: Rapid mutation rate → viral quasispecies diversity → evades host immune containment. Also blocks type 1 interferon responses (NS3-4A protease).

Morphology

A. Acute Viral Hepatitis

Gross:

Liver may be normal, enlarged (due to inflammation), or shrunken (in fulminant hepatic necrosis/"acute yellow atrophy")

Microscopy - General (all types):

Feature	Description
Panlobular infiltration	Predominantly lymphocytes; plasma cells and eosinophils variably present
Hepatocyte injury	Necrosis and apoptosis; pigmented macrophages scavenging debris
Ballooning degeneration	Swollen, pale hepatocytes with cleared cytoplasm
Councilman (apoptotic) bodies	Acidophilic, shrunken, rounded hepatocytes = apoptotic hepatocytes (pyknotic nucleus + eosinophilic cytoplasm) - key feature
Kupffer cell hyperplasia	Reactive hyperplasia of sinusoidal macrophages
Mitotic figures / Rosette formation	Evidence of hepatocyte regeneration
Reticulin framework preserved	In uncomplicated acute hepatitis
Variable cholestasis	Bile plugs in canaliculi

Patterns of necrosis in severe disease:

Confluent necrosis - groups of hepatocytes
Bridging necrosis - necrosis connecting portal tracts to central veins, or central vein to central vein (condensed reticulum + inflammatory debris = "bridge") - poor prognosis marker
Panlobular/panacinar necrosis - entire lobule necrosed
Massive hepatic necrosis (Fulminant hepatitis) - small, shrunken, soft liver; massive dropout of hepatocytes; extensive reticulin collapse

B. Chronic Viral Hepatitis

Defining feature: Portal lymphocytic (lymphoplasmacytic) inflammation with fibrosis

Inflammatory cells cross the limiting plate → injury of periportal hepatocytes = "Interface hepatitis" (piecemeal necrosis)
Fibrosis progression: portal/periportal → bridging fibrosis (portoportal) → cirrhosis

Virus-specific microscopic features:

Virus	Distinctive Histological Feature
HBV	"Ground-glass" hepatocytes - ER swollen, filled with HBsAg; identified by Orcein or Aldehyde fuchsin stain; seen in chronic (not acute) HBV
HCV	Prominent lymphoid aggregates / lymphoid follicles in portal tracts; steatosis (especially genotype 3); focal bile duct injury
HDV	Microvesicular steatosis (occasional)
HEV	Marked cholestasis

Diagrammatic representation showing morphologic features of acute (lobular inflammation, hepatocellular injury) and chronic hepatitis (dense portal inflammation, fibrosis, bridging necrosis)

Fig. 18.14 - Diagrammatic representation of morphologic features of acute and chronic hepatitis - Robbins Cotran Kumar

Serological Markers of HBV (Most Tested in Exams)

Marker	Significance
HBsAg	Hepatitis B surface antigen - first marker to appear; indicates infection (acute or chronic)
Anti-HBs	Antibody to HBsAg - indicates recovery and immunity; also appears after vaccination
HBcAg	Core antigen - found in liver (not routinely in serum)
Anti-HBc IgM	Acute HBV infection (appears early, short-lived)
Anti-HBc IgG	Past or chronic infection
HBeAg	Viral replication marker - indicates high infectivity
Anti-HBe	Seroconversion from HBeAg - indicates decreasing infectivity
HBV DNA	Most sensitive marker for active viral replication
"Window period"	HBsAg gone, Anti-HBs not yet appeared - only Anti-HBc IgM is positive

Clinicopathologic Syndromes

1. Acute Symptomatic Hepatitis (4 Phases)

Phase	Features
Incubation period	Virus-dependent (see table above); peak infectivity at end of this phase
Pre-icteric (prodromal)	Fever, malaise, anorexia, nausea, vomiting, RUQ pain, arthralgias (serum-sickness in HBV)
Icteric phase	Jaundice, dark urine, pale stools, hepatomegaly, ↑↑ ALT/AST
Convalescence	Gradual resolution of symptoms over weeks

2. Acute Asymptomatic Infection with Recovery

Subclinical; diagnosed by elevated transaminases or presence of antibodies
Common with HAV and HBV

3. Chronic Hepatitis

Defined as hepatitis persisting >6 months
HBV: 5-10% of adults; HCV: >80% of all cases
Progresses: chronic hepatitis → cirrhosis → HCC

4. Acute Liver Failure (Fulminant Hepatitis)

Massive hepatic necrosis ("acute yellow atrophy")
Encephalopathy, coagulopathy, jaundice
HBV and HDV superinfection most common viral causes
HEV: 20% mortality in pregnant women
Pathology: small, shrunken liver; massive dropout of hepatocytes

5. Carrier State

Persistent HBsAg positivity >6 months without active disease
High-risk source of transmission

Clinical Features of Acute Hepatitis

Constitutional: Fever, malaise, fatigue, anorexia, weight loss
GI: Nausea, vomiting, abdominal pain (RUQ), diarrhea
Jaundice: Icteric sclera, yellow skin
Dark urine (bilirubinuria) and pale stools (reduced urobilinogen)
Hepatomegaly - tender
Raised ALT > AST (hepatocellular pattern)

Complications

Complication	Virus
Chronic hepatitis	HBV, HCV, HDV
Cirrhosis	HBV, HCV (most common)
Hepatocellular carcinoma (HCC)	HBV (via HBx protein; integration), HCV (via chronic inflammation)
Fulminant hepatic failure	HBV, HBV+HDV, HEV in pregnancy
Extrahepatic: polyarteritis nodosa, GN	HBV
Extrahepatic: cryoglobulinemia, vasculitis	HCV
Aplastic anemia	HAV (rare)

Summary - "ABCDE" Mnemonic

Hepatitis	Key Fact
A	Acute only; fecal-oral; never chronic; vaccine available
B	Blood-borne; ground-glass cells; 5-10% chronic; HCC risk; vaccine available
C	Most common cause of chronic hepatitis (>80%); lymphoid aggregates + steatosis; no vaccine
D	Delta virus - defective; needs HBV; worst outcome in superinfection
E	Enteric (fecal-oral); deadly in pregnancy (20%); no chronicity in immunocompetent

Sources: Robbins, Cotran & Kumar Pathologic Basis of Disease (pp. 777-779, Table 18.3) | Harrison's Principles of Internal Medicine 22nd Edition (pp. 2691-2694)

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