Cystic ectopic lingual thyroid tissue in a male cat.

CASE DESCRIPTION-A 6-year-old neutered male cat was examined because of a 4-week history of abnormal sounds while drinking and a previously noted mass at the base of the tongue. CLINICAL FINDINGS-Oral examination revealed a 1-cm-diameter midline cystic mass on the dorsal aspect of the base of the tongue at the junction of the rostral two-thirds and caudal third of the tongue. Complete blood count and serum biochemical analysis revealed no clinically relevant abnormalities, and serum total thyroxine and free thyroxine (determined by equilibrium dialysis) concentrations were within the reference range. TREATMENT AND OUTCOME-The fluid in the cystic mass was aspirated, and the remaining deflated mass was marsupialized. Histologic and immunohistochemical examination of sections of the excised mass revealed ectopic thyroid tissue. The cat recovered uneventfully from the surgery, clinical signs resolved, and the cat remained euthyroid with no recurrence of the mass as of 8 months after surgery. CLINICAL RELEVANCE-This is the first known reported case of ectopic lingual thyroid tissue in a male cat. In humans, the most common site of ectopic thyroid tissue is at the base of the tongue and the condition is disproportionately found in females, compared with males. In humans with ectopic lingual thyroid tissue, the patient often lacks any other functional thyroid tissue. However, the cat of this report remained euthyroid after mass resection.