#00066344

A well-formed granulomatous structure composed of aggregates of epithelioid histiocytes with elongated, pale nuclei and indistinct cell borders, often surrounded by a rim of lymphocytes. The central area shows caseous necrosis, appearing as amorphous, granular, eosinophilic, acellular debris with loss of normal tissue architecture. Multinucleated giant cells (Langhans-type or foreign body-type) may be present, with nuclei arranged peripherally or haphazardly. The surrounding marrow may show inflammatory infiltrate and fibrosis. The defining feature is the presence of central caseation within an organized granulomatous response, most commonly associated with infectious etiologies such as tuberculosis.