Dermoid cysts presenting as enlarged thyroid glands in a cat.

A 5-year-old spayed female cat was evaluated for hyperthyroidism based on an elevated free thyroxine (T(4)) measurement and bilaterally enlarged symmetric subcutaneous masses in the area of the thyroid glands. Physical examination revealed bilateral subcutaneous masses on either side of the cervical trachea. Blood was obtained for serum biochemical profile and thyroid function analysis. Mild hyperalbuminemia, mild hypercalcemia, and mildly increased alanine aminotransferase activity were identified. Serum concentrations of total and free thyroxine were within the reference interval. Cytologic analysis of fine-needle aspirates from one of the masses was suspicious for neoplasia. Nuclear scintigraphy revealed no abnormalities. Surgically obtained excisional biopsies of both masses were submitted for histopathology and diagnosed as bilateral dermoid cysts. After excisional biopsy, the patient recovered without incident. The histopathologic diagnosis of completely excised bilateral dermoid cysts indicated that no further medical or surgical intervention was required. This is the first report of a cat presenting with bilateral dermoid cysts in the area of the thyroid glands. Histopathologic examination was necessary to make a definitive diagnosis. Practitioners should include cysts in their list of differential diagnoses for ventral neck masses in cats.