Non-clinical sciences/Pathology · Inflammation

Granulomas

What it means

Aggregates of activated epithelioid macrophages ± multinucleate giant cells. Caseating (necrotic centre): TB (ZN-positive AFB), some fungi. Non-caseating: sarcoidosis, Crohn's, foreign-body reaction. Necrotising with vasculitis: GPA (c-ANCA).

Worked example

Caseating granuloma + acid-fast bacilli on Ziehl–Neelsen → TB; non-caseating + bilateral hilar lymphadenopathy + ↑ACE → sarcoidosis.

In the exam

A hilar node biopsy shows epithelioid macrophages around a central area of necrosis, with acid-fast bacilli on special staining.

What settles it

Caseating granuloma = TB (necrotic centre, AFB); non-caseating = sarcoid/Crohn's. Both are a type IV (delayed) response.

Classically confused with

Acute inflammation

Source: StatPearls — Granuloma