## Distinguishing Caseating from Non-Caseating Granulomas ### Key Pathological Difference **Key Point:** Central caseous (cheese-like) necrosis is the hallmark feature that separates tuberculosis (caseating granuloma) from sarcoidosis (non-caseating granuloma). ### Comparative Histology | Feature | Tuberculosis | Sarcoidosis | |---------|--------------|-------------| | **Central necrosis** | Caseous (caseating) | Absent (non-caseating) | | **Epithelioid cells** | Present | Present | | **Langhans giant cells** | Present | Present | | **Lymphocytic rim** | Present | Present | | **Acid-fast bacilli** | Demonstrable (Ziehl-Neelsen) | Absent | ### Why Central Necrosis Matters **High-Yield:** The presence of caseous necrosis (central acellular debris with amorphous, eosinophilic material) is the single most reliable histological discriminator between TB and sarcoidosis. TB granulomas are **caseating**; sarcoid granulomas are **non-caseating**. **Clinical Pearl:** While both conditions produce epithelioid granulomas with Langhans giant cells and lymphocytic infiltration, only TB shows the characteristic central caseous necrosis. This necrosis results from the mycobacterial cell wall component (cord factor) triggering tissue destruction. ### Mechanism of Caseous Necrosis in TB The mycobacterial lipid-rich cell wall activates macrophages and T cells, leading to: 1. Release of hydrolytic enzymes and reactive oxygen species 2. Focal tissue necrosis with loss of cellular architecture 3. Accumulation of lipid-rich debris ("cheese-like" appearance) **Warning:** Do not confuse the presence of necrosis with the *type* of necrosis. TB shows caseous necrosis; other infections may show suppurative necrosis (pus formation).
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