Granulomatous Inflammation
- Form of chronic inflammation characterized by collections of activated macrophages, often with T lymphocytes, and sometimes associated with central necrosis.
- Granuloma formation is the cellular attempt to contain an offending agent that is difficult to eradicate.
- Strong activation of T lymphocytes - macrophage activation - injury to normal tissue.
- Epithelioid cells - activated macrophages with abundant cytoplasm, resembling epithelial cells.
- Multinucleate Giant cells are formed by fusing of activated macrophages.
- Foreign body granulomas:
- Incited by relatively inert foreign bodies (talc, sutures or other fibres), in the absence of T cell-mediated immune responses. Foreign body can usually be identified in the centre of granuloma (retractile under polarised light).
- Immune granulomas:
- Caused by agents that are capable of inducing persistent T cell-mediated immune response (inciting agent difficult to eradicate - persistent microbe or a self antigen). Macrophages activate T cells - produce cytokines (IL-2) which activates other T cells - perpetuate response. Also IFN - γ activates macrophages.
- In H&E preparation, activated macrophages have pink granular cytoplasm with indistinct cell boundaries ► epithelioid cells. Surrounded by a collar of lymphocytes; older granulomas have a rim of fibroblasts and connective tissue.
- Langhans giant cells - multinucleated giant cells (40-50 μm in dia). Large mass of cytoplasm.
- In certain infections (most classically Mycobacterium tuberculosis), a combination of hypoxia and free radical-mediated injury leads to a central zone of necrosis. Grossly - caseous Microscopically - amorphous, structure less, eosinophilic, granular debris, with complete loss of cellular details.
- Granulomas in Crohn disease, sarcoidosis and foreign body reactions - no necrotic centres ► noncaseating.
| Disease | Cause | Tissue Reaction |
| Tuberculosis | Mycobacterium tuberculosis |
Caseating granuloma (tubercle) |
| Leprosy | Mycobacterium leprae |
Noncaseating granulomas |
| Syphilis | Treponema pallidum | Gumma |
| Cat-scratch disease | Gram-negative bacillus |
Rounded or stellate granuloma |
| Sarcoidosis | Unknown etiology |
Noncaseating granulomas |
| Crohn's disease | Intestinal bacteria | Occasional noncaseating granulomas |
Robbins & Cotran Pathologic Basis of Diseases, South Asia, 9e, pg. no. 97