Poorly differentiated oxyphilic (Hürthle cell) carcinoma arising in lingual thyroid: a case report and review of the literature.

Clinically significant lingual thyroid is an unusual developmental anomaly, and carcinoma arising in lingual thyroid, an extremely rare entity. Here we describe the cytologic, histologic, immunohistochemical, and ultrastructural findings of the first poorly differentiated oxyphilic (Hürthle cell) carcinoma described in lingual thyroid along with a review of the literature. Carcinoma arising in lingual thyroid was reported in 12 males and 21 females age 12 to 86 yr (mean age: 40). Because in nonneoplastic lingual thyroid there exists an intimate and irregular relationship of normal follicles with the surrounding skeletal muscle fibers, unequivocal infiltration, with desmoplastic response, and/or vascular invasion should be demonstrated before making a diagnosis of carcinoma. Immunostain for thyroglobulin is the most useful marker for the differential diagnosis. Although, in some older cases, the precise histologic type is difficult to determine, follicular carcinoma seems to be prevalent. This contrasts with the predominance of the papillary type in thyroglossal duct associated carcinoma. This fact is probably related to the history of hypothyroidism and compensatory hyperplasia secondary to the absence of the orthotopic gland, like that occurring in areas of endemic goiter.