Granulomatous Inflammation
Overview
A granuloma is a discrete focus of organising chronic inflammation consisting of a central collection of activated (epithelioid) macrophages, often fused into multinucleated giant cells, surrounded by a rim of lymphocytes and sometimes fibrosis. It represents the body's attempt to wall off and contain a persistent, non-digestible stimulus.
Types of Granulomas
- Caseating (Necrotising): Central cream-cheese necrosis (caseous necrosis). Granuloma contains dead macrophages and debris. Classic in Tuberculosis and some fungal infections.
- Non-Caseating: Compact granulomas without central necrosis. Classic in Sarcoidosis, Crohn's disease, leprosy (tuberculoid), and foreign body reactions.
- Suppurative: Pus-filled with PMN infiltration. Seen in bartonellosis (cat scratch disease) and Yersinia infections.
Common Granulomatous Diseases
- Tuberculosis: Caseating granulomas rich in Langhans' giant cells (nuclei arranged at periphery). Ghon complex on CXR (calcified primary focus + calcified hilar node).
- Sarcoidosis: Non-caseating granulomas along lymphatics. Bilateral hilar adenopathy + perilymphatic nodules on HRCT.
- Crohn's Disease: Non-caseating granulomas in the bowel wall and mesenteric lymph nodes — transmural inflammation is key.
- Hypersensitivity Pneumonitis: Poorly-formed non-caseating granulomas in the lung. Responds to antigen removal.
WarningTB vs Sarcoidosis on HRCT
TB and sarcoidosis both cause mediastinal/hilar lymphadenopathy. Key distinction: TB nodes typically show central low-density necrosis (caseation) with peripheral rim enhancement on CT. Sarcoid nodes are solid and homogeneously enhancing. Sarcoid nodules are perilymphatic; TB nodules are often centrilobular/random.
High Yield Facts
LightbulbFRCR / MD Prep Pearl
ACE (Angiotensin Converting Enzyme) is elevated in ~60% of active sarcoidosis — produced by epithelioid macrophages in granulomas. PET-CT is the most sensitive tool for detecting active sarcoidosis and monitoring treatment response (FDG-avid granulomas). Gallium-67 scan shows 'panda sign' (parotid + lacrimal) and 'lambda sign' (mediastinal + hilar uptake) in sarcoidosis.