Surgeon's Corner: Feline Thyroidectomy
Howard B. Seim, DVM, DACVS, Colorado State University
Presentation
PresentationThis is a series of five cats that were diagnosed with hyperthyroidism. Each cat had a palpable thyroid mass and was subsequently scheduled for thyroidectomy. All cats are positioned in dorsal recumbency with the head toward the bottom of the screen.
Surgery
Feline thyroidectomy is approached through a ventral midline cervical incision, separating the sternohyoideus–thyroideus muscles of the neck and exposing the underlying trachea. Both thyroid glands are easily exposed via this midline approach. The surgeon should be able to evaluate the thyroid gland on both sides to determine unilateral versus bilateral involvement. The recurrent laryngeal nerve is visible in most cats. The surgeon should use caution to protect the recurrent laryngeal nerve.
Related Article: Feline Hyperthyroidism
The surgeon should attempt to preserve vascularized parathyroid gland; the mission of this case series is to identify methods by which this can be performed. In general, the thyroid gland dissection is begun at the caudal aspect of the gland. The caudal thyroid artery is identified and carefully isolated and either cauterized or ligated. The gland is then gently peeled away from the surrounding loose connective tissue taking care to maintain the integrity of the thyroid capsule. As the dissection progresses toward the cranial aspect of the thyroid gland, the surgeon will encounter the parathyroid gland, which typically appears as a whitish structure within the capsule of the thyroid gland. Utilization of cotton swabs during dissection can be very helpful when dissecting the parathyroid gland away from the thyroid tissue. The thyroid capsule is carefully opened using iris scissors or bipolar cautery, and the parathyroid is peeled away from the thyroid gland with an intact blood supply.
The second patient had a slightly different appearance to the parathyroid gland, involving much more of the thyroid gland than in the previous case. Dissection is done as previously described. The caudal thyroid artery is identified and either ligated (here with a hemoclip) or cauterized; the gland is gently dissected and thyroid gland capsule is removed until the parathyroid gland is observed. Once the parathyroid gland is observed, the surgeon can enter the capsule of the thyroid gland and gently remove the parathyroid gland from its intimate attachment to the thyroid gland. Care is taken to identify and ensure adequate blood supply to the parathyroid tissue. Bipolar cautery can be utilized to enter the capsule of the thyroid gland and allow removal of the parathyroid gland from within the capsule of the thyroid. In this example, the surgeon is touching the capsule with bipolar cautery right at the junction of the thyroid capsule and parathyroid gland. Iris scissors are used to incise through the capsule, and, frequently, liquid material will emerge from within the thyroid capsule. Care is taken to peel the parathyroid from thyroid and to maintain parathyroid blood supply. In this case, the surgeon has been successful in allowing parathyroid tissue to remain.
Related Article: Current Concepts on Diagnosing and Managing Thyroid Disease in Dogs and Cats
The opposite thyroid gland is carefully examined, and in this case the gland is of an unusually large size and the surgeon has elected to remove it. If possible, the parathyroid tissue is preserved on this side as well to ensure the presence of viable parathyroid tissue so that the patient can maintain calcium homeostasis. This thyroid gland is dissected and removed as before.
The third patient also had a readily visible, generously sized parathyroid gland. Bipolar cautery is utilized to enter the capsule at the junction between thyroid and parathyroid tissues. Care is taken to preserve the blood supply as well as try to ensure that all thyroid tissue is completely removed to help minimize recurrence. In this case, the patient was having difficulties during anesthesia and both the opposite thyroid and parathyroid glands were removed as an entire unit. No attempt was made to preserve the second parathyroid gland in this case.
The fourth patient had low platelets at the time of surgery causing bruising on his neck. Despite thrombocytopenia, this surgical approach causes minimal hemorrhage. The blood supply to the parathyroid and thyroid glands is readily identified in this patient. The generous piece of parathyroid tissue was readily dissected free from the thyroid gland while maintaining blood supply. Again, the opposite gland was removed as one unit and no attempt was made to preserve the parathyroid in order to shorten anesthetic time.
The fifth patient presented with a much larger tumor. On occasion, cats will present with very large tumors that may be attached to the surrounding connective tissue. These large tumors are often histologically identified as carcinomas. Surgical removal can be more difficult because of the size of the tumor and adhesions that can occur when the tumor is invading surrounding tissues. This tumor was confirmed to be a thyroid adenocarcinoma.
Outcome
All patients presented in this series were able to maintain calcium homeostasis after thyroidectomy. The first four cases presented were all confirmed thyroid adenomas. The large mass in the final case was confirmed to be a thyroid adenocarcinoma.
This video was authored by Howard B Seim III, DVM, DACVS. Other surgical videos are available through VideoVet.
Surgeon’s Corner is intended as a forum for those with specialized expertise to share their approaches to various techniques and procedures. As such, the content reflects one expert’s approach and is not subject to peer review.
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