In histopathological examination of a lymph node from a patient with primary TB, the central area of the granuloma shows structureless eosinophilic material. What is the correct term for this necrosis and which cell is characteristically central to the granuloma in TB?

• A Liquefactive necrosis; neutrophil is central
• B Coagulative necrosis; foreign body giant cell at the centre
• C Fibrinoid necrosis; CD8+ cytotoxic T-lymphocyte at the periphery
• D Caseous necrosis; Langhans giant cell peripherally with epithelioid macrophages ✓

Explanation

The characteristic histopathological lesion of TB is the caseating granuloma with central caseous necrosis — a cheese-like, amorphous, eosinophilic, acellular area resulting from incomplete cell death of macrophages. Surrounding the caseous centre are epithelioid macrophages (modified, abundant pale cytoplasm), and at the periphery are Langhans giant cells (peripheral horseshoe or ring arrangement of nuclei) derived from fusion of macrophages. A rim of CD4+ T lymphocytes surrounds the granuloma. This structure is the hallmark of type IV (delayed) hypersensitivity response to M. tuberculosis antigens.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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