Paper I — 2022 July (Supplementary) (2019 Scheme) — Q7
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Paper I
2022 July (Supplementary) (2019 Scheme) · 100 marks · 180 min
Question
Define granulomatous inflammation. Describe the pathogenesis and morphological
features of any one type of granuloma
Q78 marksShort Essays
Answer
Definition
Granulomatous inflammation is a distinctive pattern of chronic inflammation characterized by the formation of granulomas — focal collections of activated macrophages (often with an epithelioid appearance), typically triggered by persistent, poorly degradable antigens or by cell-mediated (Type IV) hypersensitivity reactions
Pathogenesis and morphology of tuberculous (caseating) granuloma
Pathogenesis
Following inhalation, Mycobacterium tuberculosis is phagocytosed by alveolar macrophages, which are unable to fully kill/degrade the organism due to its resistant cell wall (mycolic acid)
Persistent antigen presentation to CD4+ T helper cells activates a Th1 immune response, releasing IFN-γ, which activates macrophages
Activated macrophages transform into epithelioid cells (with abundant eosinophilic cytoplasm) and may fuse to form multinucleated Langhans giant cells
Surrounding lymphocytes (mostly T cells) form a peripheral rim; fibroblasts lay down a peripheral fibrous rim over time
Morphological features
Central area of caseous necrosis (granular, cheese-like, eosinophilic necrotic debris)
Surrounded by a rim of epithelioid macrophages
Langhans giant cells (multinucleated, with nuclei arranged peripherally in a horseshoe pattern)
Peripheral cuff of lymphocytes
Outer fibroblastic/fibrous rim (in older/healing granulomas)
Special stain (Ziehl-Neelsen) may demonstrate acid-fast bacilli within the granuloma
