Thyroidectomy with Parathyroid Implantation: Is It an Easy Technique?

Background: Feline hyperthyroidism is the most common endocrine disorder in cats. Cats may not reach the disease control and/or have side effects with medical therapy. Thyroidectomy is a definitive treatment and the only option when radioactive iodine is not available. Extracapsular thyroidectomy with transplantation of the external parathyroid gland is the surgical technique that minimizes the risk of postoperative hypocalcemia when it is compared to others. The aim of this study is report the difficulty in visualizing parathyroid gland during extracapsular thyroidectomy with transplantation of the external parathyroid gland technique in hyperthyroid cats. Materials, Methods & Results: Thirty hyperthyroid cats were evaluated and submitted to extracapsular thyroidectomy with transplantation of the external parathyroid gland. Blood samples were collected to hematologic, biochemical and hormonal (total thyroxine) analysis. On physical examination, at least one cervical thyroid lobe was palpable. Cats were treated with methimazole. Thyroidectomy was recommended when adverse effects of medication occurred or medical hormonal stabilization was not achieved. The excised thyroid and a sample of external parathyroid gland were histologically examined. Thirteen castrated males and seventeen spayed female cats in age ranging from eight to nineteen years (mean age 13.3 years) were indicated to surgery. Twenty three cats were Brazilian domestic short hair, six were Siamese and one was Oriental. Thyroid palpable cervical nodule was unilateral in eight cats and bilateral in twenty two cats. The reasons for surgery included adverse effects of methimazole (14/30), difficulty in medicating, owners’ interest in surgical treatment (6/30) and inability to stabilize with medical management (10/30). None developed any anesthetic or postoperative complications. The parathyroid gland was implanted in sixteen cats, because it wasn`t identified in the other fourteen cats during surgery. Twenty-six cases were diagnosed as thyroid adenoma and four as thyroid hyperplasia. Discussion: The extracapsular thyroidectomy with transplantation of the external parathyroid gland was the chosen technique because it minimizes the risk of postoperative parathyroid failure resulting in life threatening hypocalcemia. Staging thyroidectomies reduce or prevent the incidence and duration of postoperative hypocalcemia, hospitalization, and further oral supplementation of calcium and calcitriol because transplanted parathyroid tissue returns to its normal function within twenty-one days of surgery. Therefore, hyperthyroid cats were submitted to this surgical technique. However, the major concern of this technique was the difficulty in identifying external parathyroid gland. Parathyroid gland autotransplantation was performed in only sixteen cats because it was not visible in the other fourteen cats. The difficulty in identifying the parathyroid gland during thyroidectomy was not previously reported. In most cats, the external parathyroid gland is on the cranial one-third of the thyroid lobe while in others, it is about mid thyroid level or even on the caudal pole. One cat of this study had external parathyroid gland localized on caudal pole. Probably, external parathyroid gland was cranial in thyroid lobe and not found in fourteen cats. The identification of the parathyroid is easier when it is located in the ventral part of the thyroid gland and difficult when located elsewhere. Although extracapsular thyroidectomy with transplantation of the parathyroid gland is an easy surgical technique, external parathyroid gland may not be identified during surgery. Cat must be hospitalized in the second surgery when the parathyroid gland is not reimplanted in the first surgery due to possibility of threatening hypocalcemia postoperatively.