Hypothyroidism resulting from follicular‐compact thyroid carcinoma in a dog

Abstract A 13‐year‐old, spayed, female beagle, weighing 21 kg, was presented with a cervical nodule that had appeared about 15 days earlier. On palpation, a firm, slightly mobile mass measuring approximately 4 cm in diameter was detected in the thyroid region. The topography of the left thyroid gland, the cervical ultrasound, and the computed tomography revealed a well‐defined, rounded, space‐occupying lesion measuring 2.9 × 2.8 × 2.8 cm and 4.33 × 3.09 × 3.24 cm, respectively. A unilateral thyroidectomy was performed, and the sample was submitted for histopathology, which confirmed the diagnosis of compact follicular thyroid carcinoma. Postoperatively, the dog received levothyroxine (synthetic T4) supplementation and, after 3 months, returned for follow‐up with clinical improvement and no signs of tumour recurrence.