Abstract
A 12-y-old, 654-kg, Santa Gertrudis cow was presented to the veterinary hospital with acute abdominal distension and a large mass on the left side of the neck. Upon presentation, the patient was bright and alert, with a corticosteroid stress leukogram, hyperglycemia, and mildly increased blood urea nitrogen and creatine kinase activity. A firm, 15 x 10-cm, non-painful left-sided proximal cervical mass and ruminal tympany were appreciable. A fine-needle aspirate of the mass was performed, and cytological findings were consistent with a neuroendocrine neoplasm. Given the large size of the mass and poor prognosis, the owner elected euthanasia. At autopsy, a firm 15 x 12 x 8-cm mass effaced the left lobe of the thyroid gland. Histological examination confirmed a thyroid follicular-compact carcinoma with metastasis to the deep cervical lymph nodes. Neoplastic cells showed immunolabeling for thyroglobulin, 10% of the neoplastic cells exhibited immunolabeling for thyroid transcription factor 1 (TTF1), and none of the neoplastic cells showed immunolabeling for synaptophysin. Although the cytological features were typical of neuroendocrine neoplasia, immunohistochemistry excluded a thyroid medullary neoplasm. Unlike C-cell and ultimobranchial neoplasms, thyroid follicular carcinomas are rarely reported in cattle. The thyroid follicular-compact carcinoma described herein was associated with acute tympany.