Follicular carcinoma with clear cell change arising in lingual thyroid.

A case of follicular carcinoma arising in the lingual thyroid of a 23-year-old woman is added to the 22 previous reports. The embryology and the clinical and pathologic differential diagnoses are discussed. Histologic criteria useful in diagnosing follicular malignancy in this area include local and vascular invasiveness, hypercellularity, mitotic activity, and necrosis. The use of the immunohistochemical marker thyroglobulin and electron microscopy are described for the first time and confirm a thyroid follicular cell origin.