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Medical Term:

tubercle

Pronunciation: tu'ber-kel

Definition:

  1. A nodule, especially in an anatomic, not pathologic, sense.
  2. A circumscribed, rounded, solid elevation on the skin, mucous membrane, surface of an organ, or the surface of a bone, the latter giving attachment to a muscle or ligament.
  3. dentistry a small elevation arising on the surface of a tooth.
  4. A granulomatous lesion due to infection by Mycobacterium tuberculosis. Although somewhat variable in size (0.5–3 mm in diameter) and in the proportions of various histologic components, tubercle's tend to be fairly well circumscribed, spheroid, firm lesions that usually consist of three irregularly outlined but moderately distinct zones: 1) an inner focus of necrosis, coagulative at first, which then becomes caseous; 2) a middle zone that consists of a fairly dense accumulation of large mononuclear phagocytes (macrophages), frequently arranged somewhat radially (with reference to the necrotic material) resembling an epithelium, and hence termed epithelioid cells; multinucleated giant cells of Langhans type may also be present; and 3) an outer zone of numerous lymphocytes, and a few monocytes and plasma cells. In instances in which healing has begun, a fourth zone of fibrous tissue may form at the periphery. Morphologically indistinguishable lesions may occur in diseases caused by other agents; many observers use the term nonspecifically, with reference to any such granuloma; other clinicians use tubercle only for tuberculous lesions, and then designate those of undetermined causes as epithelioid-cell granulomas.

Synonym(s): tuberculumTA

[L. tuberculum, dim. of tuber, a knob, a swelling, a tumor]

© Copyright 2016 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.
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