Equine Carcinoma Hemithyroidectomy

Abstract

Background: In horses, the thyroid gland is located slightly caudal to the larynx and dorsolaterally between the third and sixth tracheal ring, adjacent to the thyroid, there are four small glands called parathyroid glands. In the clinical routine of horses, thyropathies are difficult to be diagnosed, as they have a silent evolution. Thyroid neoplasia is the most common finding in horses, usually unilateral and normally present in older animals. The present study reports a case of equine thyroid carcinoma and its systemic clinical effects, which was successfully treated by means of hemitieroidectomy. 

Case: A 12-year-old male mixed breed horse weighing 436 kg, was admitted to the Veterinary Medical Teaching Hospital of the FZEA/USP    with the main complaint of volume increase in the right ventrolateral region of the neck, difficulty in swallowing, significant weight loss and weakness of the pelvic limbs. On inspection, there was an increase in volume in the topographic region of the thyroid gland and on palpation, there was a firm mass, with delimited edges, with a smooth, mobile surface, without increasing the temperature and without pain. The animal was sent for ultrasound examination, which revealed a delimited mass, with an apparent capsule around it, differentiated and disorganized cellularity with small hypoechoic points of liquid inside the structure, with no apparent vascularization inside the mass. These findings, associated with the anatomical location of the mass, were consistent with thyroid tissue. The clinical signs commonly observed in thyroid neoformations are respiratory stridor, decreased performance, difficulty in swallowing and suffocation. As there was a compromised diet and weight gain, as well as athletic performance, he chose to have a hemithyroidectomy. After surgery, histopathology of the tissue was performed and thyroid carcinoma was diagnosed. Postoperatively, the animal was medicated with antibiotics, anti-inflammatory and anti-tetanus serum, after 10 days the stitches were removed and the animal was discharged. 

Discussion: Neoplasia is the most frequent cause of progressive thyroid growth and in case of suspicion of thyroid disorders, thin needle aspiration (FNAB) is recommended and, later, histopathological examination, which is considered the gold standard for diagnosis pathologies of the thyroid gland. In the present case, no FNAB or preoperative histopathological examination was performed due to the time required to obtain the result, associated with difficulty in swallowing and significant weight loss, which required immediate removal of the mass. Considering that the ultrasound examination revealed the absence of noble structures or important vascularization very close to or adhered to the mass, its removal prior to the histopathological examination was indicated. As there was compromised feeding and weight gain, he opted for hemithyroidectomy, the recommended treatment for unilateral tumors in horses. When performing a hemithyroidectomy, it should be remembered that the parathyroid glands accompany the thyroid and are located in its posterior portion, in the pre tracheal region, with its variable final position. With this variation in topography, the identification of parathyroid glands becomes challenging and, consequently, after thyroidectomy, a portion of parathyroid glands stops operating, and this fact is marked clinically by hypocalcemia and its consequences. In this case described, in which the animal had a tumor in thyroid tissue, possibly the parathyroid functions were also altered, which probably reflected in the lameness in the pelvic limbs. It is concluded that partial hemithyroidectomy in horses is an easy procedure to perform and has favorable results in relation to prognosis and quality of life. 

Keywords: carcinoma, hemithyroidectomy, thyroid. 

Título: Hemitireoidectomia por carcinoma em equino

Descritores: carcinoma, hemitireoidectomia, tireóide.