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PA2.8 | Cell Injury Morphology — Practical — SDL Guide (Part 3)

The 2×2 Comparison Grid: Four Necrosis Patterns at a Glance

The four main necrosis patterns are best learned side-by-side. The following composite photomicrograph (H&E, all panels at equivalent magnification ~10×) displays one pattern per panel:

Panel A — Coagulative necrosis (kidney infarct): ghost tubular outlines, eosinophilic, karyolysis, hyperaemic rim
Panel B — Liquefactive necrosis (brain abscess): cystic cavity, neutrophils, no residual architecture
Panel C — Caseous necrosis (TB lymph node): amorphous eosinophilic debris, epithelioid granuloma, Langhans cell
Panel D — Fat necrosis (peripancreatic fat): ghost adipocytes, basophilic Ca²⁺ deposits, foam cells

For each panel: (1) name the dominant staining colour; (2) state whether architecture is preserved or destroyed; (3) name the key diagnostic cell or structure.

A 2×2 histology comparison grid shows coagulative, liquefactive, caseous, and fat necrosis with key H&E features and diagnostic labels. — **Panel A:** Coagulative necrosis in kidney infarct: ghost tubules, ghost glomeruli, eosinophilic cytoplasm, karyolysis, hyperaemic rim, preserved architecture. **Panel B:** Liquefactive necrosis in brain abscess: cystic cavity, neutrophils, necrotic fluid, complete loss of residual architecture. **Panel C:** Caseous necrosis in TB lymph node: amorphous granular eosinophilic caseous debris, epithelioid granuloma, Langhans giant cell. **Panel D:** Fat necrosis in peripancreatic adipose tissue: ghost adipocytes, basophilic Ca2+ soap deposits, foam cells or macrophages.

SELF-CHECK

In the 2×2 grid above, Panel D (fat necrosis) differs from all three other panels in one specific staining characteristic. What is it?

A. It is the only panel showing predominantly basophilic (blue) deposits rather than eosinophilic material

B. It is the only panel with nuclear pyknosis rather than karyolysis

C. It is the only panel that retains recognisable tissue architecture with ghost outlines

D. It is the only panel that shows infiltrating neutrophils as the primary cell

Reveal Answer

Answer: A. It is the only panel showing predominantly basophilic (blue) deposits rather than eosinophilic material

Calcium soaps formed by saponification stain basophilic (blue/purple) on H&E — the only necrosis pattern where basophilia is a primary diagnostic feature. All other types produce eosinophilic debris. Ghost adipocyte outlines are present but the key staining signature is the basophilic calcification, not the outlines.

Gross Specimen Recognition: Infarcts and Gangrene

Six-panel medical diagram comparing pale and red infarcts, dry and wet gangrene, microscopy correlation, and caseous tuberculous lymph nodes. — **Panel A:** Kidney cut section; pale-tan wedge-shaped infarct; base toward capsule; apex toward hilum; hyperaemic rim; coagulative necrosis correlation.. **Panel B:** Lung cut section; dark red-black haemorrhagic wedge infarct; soft haemorrhagic area; collateral or dual blood supply; reperfusion into necrotic zone.. **Panel C:** Simplified H&E correlation; coagulative necrosis with preserved cell outlines; haemorrhage with red blood cells; necrotic tissue zone.. **Panel D:** Dry gangrene of toes; dry black shrunken mummified tissue; sharply demarcated line of separation; viable proximal tissue.. **Panel E:** Wet gangrene; swollen moist greenish-black tissue; bacterial infection; liquefactive component; poorly defined margin; sepsis or gas gangrene risk.. **Panel F:** Matted tuberculous lymph nodes; pale-tan cheese-like caseous center; firm fibrotic capsule; calcification flecks..

Gross pattern recognition is tested in the spotting practical and in viva. Know these cold:

Pale (anaemic) infarct:
• Organs: kidney, heart, spleen (solid, end-arterial)
• Gross: firm, pale-tan or yellow-white, wedge-shaped with apex toward the hilum, base toward capsule
• Hyperaemic rim at boundary (reactive vasodilation)
• Correlates with: coagulative necrosis on H&E

Red (haemorrhagic) infarct:
• Organs: lung (dual blood supply), bowel (reperfusion), testis (loose parenchyma)
• Gross: dark red-black, soft, haemorrhagic, wedge-shaped
• Mechanism: blood re-enters necrotic zone from collateral or dual supply
• Correlates with: coagulative necrosis + haemorrhage on H&E

Dry gangrene:
• Ischaemic coagulative + mummification; toes/foot in diabetic/atherosclerotic ischaemia
• Gross: dry, black, shrunken, sharply demarcated line of separation from living tissue

Wet gangrene:
• Superimposed bacterial infection → liquefactive component
• Gross: swollen, moist, putrid, greenish-black, foul-smelling, no clear line
• Emergency: risk of sepsis, gas gangrene (Clostridium)

Caseous nodes (TB):
• Matted lymph nodes, pale-tan soft cheese-like centre, firm fibrotic capsule, may be calcified

SELF-CHECK

A surgeon excises a gangrenous toe from a 68-year-old with longstanding type 2 diabetes and peripheral artery disease. The amputated toe is dry, black, shrunken, with a sharply demarcated line of separation. What is the MOST accurate pathological classification?

A. Wet gangrene with superimposed Clostridium infection

B. Dry gangrene — ischaemic coagulative necrosis with mummification, no secondary infection

C. Liquefactive necrosis following arterial embolism

D. Caseous necrosis due to atypical mycobacterial infection in a diabetic

Reveal Answer

Answer: B. Dry gangrene — ischaemic coagulative necrosis with mummification, no secondary infection

Dry gangrene is coagulative necrosis caused by gradual ischaemia (atherosclerosis, diabetes) without superimposed infection. The tissue mummifies — loses moisture, shrivels, turns black due to haemoglobin breakdown products. The sharp line of demarcation is characteristic. Wet gangrene is moist, swollen, malodorous and lacks a clear margin because of bacterial invasion.

Apoptotic Bodies, Pigments and Dystrophic Calcification on H&E

Three additional H&E findings complete the practical checklist for cell injury:

Apoptotic bodies:
• Small, round, deeply eosinophilic cytoplasmic fragments with condensed nuclear material (pyknotic fragments)
• Scattered individually — no surrounding inflammatory response (key distinction from necrosis)
• Membrane-bound: content is phagocytosed by neighbouring cells → no 'leakage'
• Seen in: viral hepatitis (Councilman bodies = apoptotic hepatocytes), graft rejection, ischaemia

Common pigments on H&E:
• Haemosiderin — golden-brown granular intracellular pigment; Perls' Prussian Blue stain confirms iron
• Lipofuscin — yellow-brown granular 'wear-and-tear' pigment; perinuclear in cardiac/liver cells
• Melanin — brown-black, in melanocytes and melanophages
• Bile (bilirubin) — green-brown intracanalicular or intracytoplasmic plugs in cholestasis

Dystrophic calcification:
• Basophilic (blue/purple) granular or laminated deposits in areas of necrosis or old inflammatory foci
• Occurs in dead or dying tissue at normal serum calcium levels
• Examples: TB caseous foci, atherosclerotic plaques, old infarcts, psammoma bodies in papillary carcinoma
• Distinguish from metastatic calcification (same appearance, but in viable tissue, due to hypercalcaemia)

A four-panel H&E comparison grid showing coagulative, liquefactive, caseous, and fat necrosis with diagnostic histological features labeled. — **Panel A:** Coagulative necrosis in kidney infarct: ghost tubular outlines, eosinophilic cytoplasm, karyolysis, hyperaemic rim.. **Panel B:** Liquefactive necrosis in brain abscess: cystic cavity, neutrophils, necrotic debris, destroyed architecture.. **Panel C:** Caseous necrosis in TB lymph node: amorphous eosinophilic caseous debris, epithelioid granuloma, Langhans giant cell, lymphocytes.. **Panel D:** Fat necrosis in peripancreatic fat: ghost adipocytes, basophilic calcium deposits, foam cells, inflammatory cells..

CLINICAL PEARL

'No inflammation' is the clinical and microscopic signature of apoptosis. When you see an isolated eosinophilic body with no surrounding neutrophils or macrophages, think apoptosis — not necrosis. This distinction matters in practice: necrosis triggers inflammation (and fever, raised CRP); apoptosis does not. In viral hepatitis, you may see both: scattered Councilman bodies (apoptosis) alongside focal necrosis and portal inflammation. Reporting both accurately changes the grade of hepatitis.

SELF-CHECK

A liver biopsy from a patient with acute hepatitis B shows scattered small, round, deeply eosinophilic bodies in the sinusoids with no surrounding inflammatory infiltrate. Nearby hepatocytes appear intact. These bodies are BEST described as:

A. Mallory-Denk bodies — indicative of alcoholic liver disease

B. Lipofuscin granules — age-related wear-and-tear pigment

C. Councilman bodies — apoptotic hepatocytes, confirmed by absence of perilesional inflammation

D. Haemosiderin deposits — iron overload from haemochromatosis

Reveal Answer

Answer: C. Councilman bodies — apoptotic hepatocytes, confirmed by absence of perilesional inflammation

Councilman (acidophil) bodies are the classical term for apoptotic hepatocytes seen in viral hepatitis. They are small, round, densely eosinophilic, membrane-bound fragments with condensed nuclear debris. The defining feature is the absence of surrounding inflammatory cells — because apoptotic contents do not 'leak' and do not trigger the DAMP/PAMP pattern-recognition cascade. Mallory-Denk bodies are irregular eosinophilic cytoplasmic inclusions in alcoholic hepatocytes, not rounded isolated fragments.

Putting It Together: A Diagnostic Checklist

A three-panel pathology infographic showing a checklist for diagnosing cell injury specimens, key microscopic necrosis patterns, and a viva-style conclusion workflow. — **Panel A:** Checklist rows for Architecture, Staining, Nuclear changes, Infiltrate, Gross correlate, and Special stain, with visual cues for coagulative, liquefactive, caseous, fat necrosis, apoptosis, and gangrene.. **Panel B:** Microscopic thumbnails showing preserved architecture and karyolysis, neutrophilic liquefaction, caseous debris with granuloma and Langhans giant cells, adipocyte ghosts with calcium deposits and foam cells, apoptotic bodies, and macrophages in late brain infarct.. **Panel C:** Viva conclusion workflow: identify pattern, name likely cause, correlate gross finding, and choose special stain such as ZN, Perls', PAS, or Oil Red O..

Use this checklist for any cell-injury specimen in the practical:

Feature	Ask yourself
Architecture	Preserved (coagulative) / Destroyed (liquefactive, caseous) / Absent — adipocytes only (fat necrosis)
Staining	Eosinophilic debris (most) / Basophilic deposits (fat necrosis calcification, dystrophic Ca²⁺)
Nuclear changes	Karyolysis dominant (coagulative) / No nuclei (caseous, fat necrosis) / Pyknotic fragments (apoptosis)
Infiltrate	Neutrophils (bacterial liquefactive) / Epithelioid granuloma + Langhans cells (caseous) / Foam cells + giant cells (fat necrosis) / None (apoptosis) / Macrophages (late brain infarct)
Gross correlate	Pale wedge (coagulative infarct) / Cystic (liquefactive brain) / Cheese-like (caseous TB) / Chalk-marks (fat necrosis) / Black dry/wet (gangrene)
Special stain if needed	ZN (TB) / Perls' (iron) / PAS (fungi, glycogen) / Oil Red O frozen (lipid)

In your write-up or viva: state (1) type of necrosis, (2) extent, (3) probable aetiology, (4) one special stain that would confirm.