Case Description—A 14-year-old castrated male domestic shorthair cat was evaluated because of a large fluid-filled mass on the ventral aspect of the neck that failed to resolve after repeated draining.

Clinical Findings—Radiography and computed tomography revealed a fluid-filled mass 13 cm in diameter extending from the level of the first cervical vertebra to the manubrium. No evidence of metastasis was seen. Cytologic examination of the fluid revealed it to be a transudate with a T₄ concentration considered to be normal. Incisional biopsy of the cyst wall was performed and led to a diagnosis of thyroglossal duct cyst.

Treatment and Outcome—The cyst was excised, and no recurrence was observed 15 months after surgery. Aside from temporary seroma formation, no complications developed after the surgery. A distinct tract through the hyoid apparatus to the base of the tongue, as has been described in humans, was not identified.

Clinical Relevance—Thyroglossal duct cyst should be considered as a differential diagnosis in cats with masses on the ventral aspect of the neck. Complete excision appeared to be curative in the cat of this report.