Thyroid Tumor Surgery in Cats

 

Thyroid Tumor Surgery in Cats

Did you know that cats can have a hyperactive thyroid gland? Also known as hyperthyroidism, it’s a fairly common condition in older cats. In fact, the vast majority of affected cats are older than 10 years of age. Most of the time, the reason is either a benign tumor or benign enlargement of the thyroid gland(s).

What is hyperthyroidism?

Hyperthyroidism is when thyroid glands work overtime and produce too much thyroid hormone. Because this hormone controls many organs, it can lead to multiple consequences:

• Weight loss, despite an increase in appetite
• Vomiting and/or diarrhea
• Irritable or aggressive behavior
• Increased drinking and urination
• Increased heart rate
• A heart murmur
• Poor hair coat
• Increased activity

Occasionally, a chubby couch potato kitty with gorgeous hair may turn into a skinny old cat with a rough hair coat, running around the house like a maniac.

How is hyperthyroidism diagnosed?

Since some of the signs of hyperthyroidism can be similar to other diseases, it’s important to perform a full workup. This starts with a thorough physical exam. A small nodule on the thyroid can often be felt by your veterinarian.

Blood work, including measurement of the thyroid hormone level, is the next logical step. The increased metabolic rate of hyperthyroidism can hide kidney issues and cause heart complications, so both should be monitored before and after treatment has been started. This requires blood work, X-rays, and ultrasound.

How is hyperthyroidism treated?
There are several treatment options:

• Methimazole is a medication that fights hyperthyroidism. It is usually given by mouth, every single day. Methimazole can also be compounded into a cream that is applied to the skin of the ear daily (transdermal application). This is a life-long treatment.
• I know about at least one special diet that is very low in iodine and was introduced a few years ago. If your veterinarian recommends this option, this is the only food your cat should eat for good results.
• Veterinary endocrinologists consider IV radioactive iodine treatment as the gold standard for hyperthyroidism.
• Surgery to remove the tumor is an option, although it is less and less common. It’s a delicate surgery but in good hands, it is highly successful.

What are the risks of thyroid surgery?

In addition to the risks of anesthesia [see common anesthesia myths here], one of the main risks of surgery is damage or accidental removal of the parathyroid glands. There are two parathyroid glands on each side: one inside each thyroid gland, and one just outside of each thyroid gland. When we remove the thyroid gland, we remove the “internal” parathyroid gland. If we remove both thyroid glands, then we remove both internal parathyroid glands. So there are only two external parathyroid glands left. If they are removed accidentally, along with a large thyroid mass, or if they are damaged during surgery, then three or even all four parathyroid glands might be removed.

As a consequence, the cat may have a complication called hypocalcemia, which means that the calcium levels in the bloodstream are dangerously low.

What medications are needed after thyroid surgery?
Besides the usual pain medications and antibiotics, hypocalcemia (low calcium) needs to be managed if it develops. This is typically done by giving calcium supplements and/or vitamin D. Their dosages are slowly tapered over time as the body slowly takes over. In addition, calcium is provided once the cat eats enough food.

What is the outcome of hyperthyroidism treatment?
Thyroid cancer (adenocarcinoma) is an aggressive tumor but thankfully very rare. The outcome for that is usually poor.

Benign tumors (adenomas) and benign enlargement of the thyroid gland are much more common and have a much better outcome. However, the outcome also depends on whether complications occur with the kidneys or the heart. Most cats live years after the initial diagnosis.

As with any disease, the sooner you address it, the more options you have and the better the outcome. If your cat is acting out of sorts in any way, please see your veterinarian as soon as possible.

Questions to ask your vet if your cat has a thyroid mass:

• What is the best treatment for my cat?
• What are the risks of anesthesia?
• What are the risks of surgery?

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.

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Thyroidectomy in Cats

What is Thyroidectomy?

Thyroidectomy is a surgical procedure that involves removing one or both thyroid glands. Thyroidectomy is used to treat hyperthyroidism, a common condition in older cats in which the thyroid glands produce extra amounts of thyroid hormones. Thyroidectomy is also used to treat select cases of thyroid cancer. The surgery has a high success rate, although postoperative complications are possible.

Thyroidectomy Procedure in Cats

There are a few different surgical techniques veterinary surgeons can use to remove the thyroid gland(s). The technique used will depend on whether or not both glands need to be removed. The procedure steps for both single (unilateral) thyroid removal and total (bilateral) thyroid removal will be discussed below. These techniques carry the lowest risk of complication and the highest rate of success.

Preoperative Preparations

1. For a few weeks prior to surgery, cats will be required to take oral medications to help them gain weight, lower their heart rate, and prepare them for the general anesthetic.
2. The surgeon may take blood tests prior to surgery to confirm kidney function.
3. The cat will first be anesthetized.

Unilateral Thyroidectomy

1. The surgeon will make the initial entry incision and identify the enlarged thyroid or tumor.
2. The thyroid capsule is then cut, and the surgeon will take care to avoid damaging the parathyroid gland.
3. The external parathyroid gland and surrounding thyroid capsule will then be dissected, or separated, from the tumor.
4. The blood supply to the tumor will be cut off using bipolar cautery.
5. Once the blood supply has been ligated, the tumor will be removed along with the surrounding thyroid capsule.
6. The thyroid capsule surrounding the parathyroid gland will be left in place to ensure proper blood flow and prevent complications from parathyroid damage.
7. The surgeon will ensure all diseased portions of the thyroid have been removed before suturing the wound closed with absorbable sutures.
8. The initial entry site will then be sutured

Bilateral Thyroidectomy

1. The surgeon will repeat the steps listed above to remove the other thyroid gland.
2. Some surgeons may suggest that the removal of the second thyroid gland take place three to four weeks following the removal of the first. However, this is may not be ideal, particularly because the disease is more common in older cats that are susceptible to complications associated with general anesthesia.

Efficacy of Thyroidectomy in Cats

The efficacy of the surgical procedure will depend on the underlying condition. While there are some valid concerns about administering general anesthesia to older cats, the surgery is short and typically cures hyperthyroidism in the majority of cats. For cases of thyroid cancer, the prognosis is usually guarded due to the condition of the heart at the time of surgery.

Thyroidectomy Recovery in Cats

Owners should ensure that cats rest during the recovery period and drink plenty of water. Cats that have undergone thyroidectomy will usually be prescribed anti-inflammatory medications and analgesics for pain management. Cats may be required to wear an Elizabethan collar to prevent them from irritating the surgery site. Owners should check the surgery site daily to ensure no bleeding, pus, or swelling has developed. Follow-up appointments will typically be scheduled for a few days following surgery, and again two to three weeks following surgery to monitor healing and remove sutures.

Cost of Thyroidectomy in Cats

The cost of thyroidectomy will vary based on other costs incurred, such as medications and supportive care. The cost of thyroidectomy on its own can range from $900 to $1,200.

Cat Thyroidectomy Considerations

Though the surgery is generally curative in most cases, complications after surgery are possible. If one thyroid gland is removed, the other thyroid gland may become diseased over time and will also have to be removed. The condition may recur in the same thyroid gland because a small amount of thyroid capsule tissue is not removed. In some cases, surgery reveals problems with kidney function, which is why surgeons will generally attempt to assess kidney function prior to surgery. 

There is also a chance that thyroidectomy will cause damage to the parathyroid gland. This can cause calcium levels to drop, which can lead to serious complications such as tremors and seizures. Damage to the parathyroid gland is generally managed with calcium and vitamin D supplementation, which is usually successful. For cases of thyroid cancer, there is a chance that the condition can recur following surgery.

Thyroidectomy Prevention in Cats

Hyperthyroidism has been linked to pollutants in the environment, such as:

• BPA: A chemical used to make certain plastics
• PBDE: A flame-retardant chemical used in foam and plastics
• Soy isoflavones: A plant derivative often found in commercial cat food 

Owners are encouraged not to use plastic food or water bowls as these may contain toxic chemicals known to cause hyperthyroidism. Certain cat litter may also contain harmful chemicals that cause hyperthyroidism. Fish-based commercial diets may also play a role in the development of hyperthyroidism. Diets that are also incredibly low or high in iodine should be avoided.

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