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Define granuloma. Describe its components, types and causes.

Pathology · 2nd Professional — Para-Clinical

Definition

A granuloma is a microscopic focus of chronic inflammation consisting of an aggregation of activated macrophages transformed into epithelioid cells, usually surrounded by a collar of lymphocytes, and often containing multinucleate giant cells.

It is an attempt to wall off an agent that cannot be eliminated
Not to be confused with granulation tissue, which is the vascular fibroblastic tissue of healing

Components

Component	Description
Epithelioid cell	An activated macrophage with abundant pale pink cytoplasm and an elongated vesicular nucleus; secretory rather than phagocytic
Giant cells	Formed by fusion of 20 or more epithelioid cells
Lymphocytes	A peripheral collar; chiefly CD4 T cells
Fibroblasts and collagen	In older lesions
Central necrosis	Present in tuberculosis (caseous); absent in sarcoidosis

Types

Feature	Immune (epithelioid) granuloma	Foreign body granuloma
Stimulus	Persistent, poorly degradable antigen	Inert material too large to phagocytose
T cell response	Present — essential	Absent
Mediator	IFN-gamma from TH1 cells	None required
Giant cell	Langhans type	Foreign body type
Examples	Tuberculosis, leprosy, sarcoidosis, Crohn disease, fungi	Suture, talc, splinter, keratin

Causes

Group	Diseases
Bacterial	Tuberculosis (caseating), leprosy, syphilitic gumma, cat-scratch disease
Fungal	Histoplasmosis, cryptococcosis
Parasitic	Schistosomiasis
Inorganic dust	Silicosis, berylliosis
Unknown cause	Sarcoidosis, CROHN disease, granulomatosis with polyangiitis
Foreign material	Suture, talc, oil, keratin

CLINICAL PEARL

The single most useful question about any granuloma is whether it caseates.
Caseating means tuberculosis until proved otherwise, particularly in India.
Non-caseating suggests sarcoidosis, Crohn disease, leprosy or a foreign body. Every granuloma deserves a Ziehl–Neelsen stain before anything else is considered.

Applied Aspects

Sarcoidosis gives "naked" non-caseating granulomas with a scanty lymphocyte collar; Schaumann and asteroid bodies may be present but are not diagnostic
Crohn disease shows non-caseating granulomas in only about half of cases, but their presence supports the diagnosis against ulcerative colitis
Anti-TNF therapy reactivates latent tuberculosis, because TNF is needed to maintain the granuloma — showing that it is an actively held structure, not a passive scar
Foreign material is often birefringent under polarised light, which identifies a foreign body granuloma at once
Granulomatous inflammation in a lymph node in India is tuberculosis in the great majority; culture and molecular testing should always accompany histology

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