Caseating granuloma: the histology of tuberculosis

What it is

The histology in TB is the caseating granuloma. A typical tuberculous granuloma consists of a well-defined cluster of epithelioid cells with central caseous necrosis and Langhans giant cells, and that is what the figure of it shows on H&E at 100X. The word caseating is what separates it from sarcoidosis, which gives non-caseating granulomas, in the upper and middle lobes, with bilateral hilar lymphadenopathy. The same histology names TB outside the lung. A 40-year-old with vague long-standing abdominal pain and constitutional symptoms, with a palpable intra-abdominal mass in the RLQ, who underwent surgical resection of an ileocecal mass, is diagnosed by the histopathology slide: a caseating granuloma makes it abdominal TB. The peritoneal fluid there shows SAAG < 11.1 g/L, that is not portal hypertension related, with exudative features of a high fluid to serum LDH and protein, lymphocyte predominance, and AFB seen; and the mode of transmission is hematogenous spread from a pulmonary focus, TB itself being airborne.