tuberkel

Tubercle, or tuberkel in some spellings, is a small nodular lesion that forms as part of a granulomatous inflammatory response, most notably in tuberculosis. In the lungs, a tubercle is a granuloma with a central area of caseous necrosis surrounded by activated macrophages (epithelioid cells) and Langhans-type multinucleated giant cells, encircled by lymphocytes and a fibrous capsule. The lesion may calcify over time and can appear on radiographs as a calcified nodule; in primary infection it is part of a Ghon focus, and calcified nodules with regional lymph node involvement form the Ranke complex.

Formation is driven by cell-mediated immunity (type IV hypersensitivity). Infected macrophages present mycobacterial antigens to CD4+ T helper 1 cells, which secrete interferon-gamma, activating macrophages to form the characteristic histology and to contain the bacilli.

Clinical significance: tubercles are a histopathologic hallmark of tuberculosis. They can remain clinically silent or progress to active disease. Tuberculous involvement can also occur in other organs, including lymph nodes, meninges, and bones.

Etymology: the term derives from Latin tuberculum, meaning a small swelling or bump; tuberkel is an alternative spelling used in some languages and older texts.

See also: tuberculosis; granuloma; Ghon complex; Langhans giant cell.