Thyroidectomy in Dogs

Thyroidectomy in the dog is a surgical procedure to remove a cancerous thyroid gland. 

Dogs have two thyroid glands located either side of the trachea (windpipe) in the neck. The main disease linked to the thyroid glands in the dog is underactivity (hypothyroidism) however, a small percentage can suffer from a cancer of the thyroid gland. Unfortunately, around 90% of canine thyroid tumors are malignant and liable to spread. This makes early detection and removal the treatment of choice. Breeds most associated with thyroid carcinoma include the Golden retriever, Beagle, and Boxer.

Thyroidectomy in the dog can be problematic, due to invasion of major blood vessels. Therefore, this procedure is usually undertaken by a specialist surgeon. However if the cancer is detected early and remains small and encapsulated, a vet in general practice may attempt the surgery. 

The thyroid glands are located beside major blood vessels such as the jugular vein, and alongside the laryngeal nerve. Thyroid tumors may invade surrounding blood vessels, so the patient must be carefully screened for blood clotting disorders prior to surgery. 

It is also wise to fully stage the cancer, because if there is advanced metastatic spread already present in the lungs, then surgery to remove the thyroid is of limited use. 

Those dogs taken forward to surgery are given pre-emptive pain relief and general anesthesia induced. The dog rests on their back and the fur is clipped from the neck and throat region. Under aseptic conditions, the surgeon makes a linear incision longitudinally along the neck over the area of the windpipe. 

The muscles overlying the trachea and thyroid are carefully dissected away, taking care not to disturb the laryngeal nerve or damage blood vessels. The thyroid gland is dissected free and removed in its entirety. 

The muscles are then repaired and sutures placed in the skin. The dog is woken from the anesthetic and monitored for signs of swelling or hemorrhage. Most dogs are allowed home within 24 hours of surgery and return for a postoperative check two days later and suture removal after 10 to 14 days. 

The smaller the thyroid tumor the greater the chance of removing the gland in its entirety. However, the inverse is also true where the larger the tumor the less the chance of removing all the cancer cells and there is also a greater risk that metastasis (secondary spread) has already occurred. 

The long-term outlook depends how cleanly the thyroid was removed and whether spread has already happened on a microscopic level. The average survival time for canine patients after thyroidectomy for cancer is 20 months. 

For the majority of patients. early surgical removal is the treatment of choice. However, for large thyroid tumors or those that have invaded blood vessels then alternative treatments may help extend life. These options include radiotherapy or injection with radioactive iodine. These are unlikely to be curative. 

For successful, uncomplicated thyroidectomies, most dogs can recover at home and the sutures are removed after 10 to 14 days. During the recovery period, using a harness instead of a collar for restraint is advisable. 

Complications can and do occur. These include hemorrhage from blood vessels invaded by the thyroid, hypothyroidism (low levels of thyroid hormone in the blood), and low blood calcium levels. The latter can occur with the removal of the parathyroid glands which sit on top of the thyroid gland. 

Another complication is damage to the laryngeal nerve. This can lead to a narrowing of the larynx which interferes with the dog's ability to breathe and can make swallowing difficult. 

The workup for a thyroidectomy involves advanced imaging techniques such as an MRI or CT scan. This is liable to incur charges in the region of $1,500. Further tests to check lymph nodes and stage the cancer may cost around $500. The surgery itself ranges from relatively straightforward to very complex (if blood vessels are invaded). At a referral center, costs in the region of $2,500 to $3,000 should be anticipated. 

Surgery is most likely to be successful when the tumor measures less than 4 cm in diameter. For these cases when the whole thyroid gland is removed, and in the absence of secondary spread, there is a good chance of obtaining a surgical cure. 

However, for advanced or large tumors the chance of cure is reduced, and the risks and benefits should be carefully weighed up and discussed ahead of surgery. It may be that at best surgery extends survival time, rather than cures the dog. 

There are no known triggers for thyroid carcinoma, therefore prevention of its development is not possible.