Hypophysectomy in Cats

Hypophysectomy is a surgical procedure used to treat tumors of the pituitary gland. This will involve removing the pituitary gland. It is a highly complex procedure that is currently available at only one specialist veterinary institution in the United States. Hypophysectomy is not generally the first line of treatment for pituitary tumors. Radiation and medical therapy are usually the treatment of choice for pituitary tumors.

Hypophysectomy is complex because surgeons enter the skull through the mouth. The approach may vary based on the expertise of and tools available to the surgeon. The general procedure steps for hypophysectomy are listed below.

1. Prior to surgery, extensive diagnostic testing will be conducted. This includes CT scan, complete blood count and blood chemical profile, and suppression tests.
2. On the morning of the surgery, cats with diabetes mellitus may need to take only half a dose of insulin.
3. General anesthesia and analgesics are then administered intravenously. The surgeon will place a breathing tube and administered gaseous anesthesia as well. Vital signs are monitored carefully throughout surgery.
4. The surgeon will incise the soft palate, followed by the mucoperiosteum, exposing the sphenoid bone.
5. Using a specialized bone burr and/or punches, the surgeon will drill through the bone and visualize the pituitary fossa.
6. The dura mater is then incised.
7. The pituitary gland is removed and the wound closed.
8. Hydrocortisone and atipamezole are administered.
9. The cat will then be hospitalized for up to seven days, and the pituitary gland will be sent to a pathology lab for examination. 

Although it is a very complex procedure, hypophysectomy is generally very effective for treating pituitary tumors. Hypophysectomy will usually reverse signs of diabetes. Roughly 70% of cats experience diabetic remission within the first three weeks following surgery. The remaining 30% do not require as much insulin as they did prior to surgery. However, because the surgery is complex, the mortality rate is relatively high at 20%. There is also a 20% tumor recurrence rate.

During hospitalization, the cat’s vital signs are monitored carefully. Plasma sodium and potassium levels are measured before surgery, and again eight, twenty-four, and forty-eight hours after surgery. Hydrocortisone, analgesics, and fluids are administered intravenously at regular intervals. Cats will be encouraged to drink water as soon as they recover from the effects of the anesthesia. Once the cat is conscious, oral cortisone acetate therapy will begin, and will act as a replacement for the growth hormone.

On the return home, owners should explicitly follow their surgeon’s postoperative care instructions. Cortisone acetate therapy should be continued for four weeks or as instructed by the surgeon. The dosage should decrease gradually throughout the recovery period. An antibiotic regimen will be prescribed after surgery and should be continued for at least fourteen days. It is imperative that owners monitor their cat’s drinking behavior and record their water intake each day. If excessive urination occurs, owners should consult their veterinarian immediately.

A follow-up appointment will be scheduled within eight to twelve weeks after surgery to monitor healing and ensure the condition has not recurred. During this appointment, a CT scan will be performed and the cat’s plasma chemistry profile, in addition to blood and urine samples, will be taken.

The cost of hypophysectomy may vary depending on standards of living and additional costs incurred. The cost of hypophysectomy ranges from $2,000 to $5,000.

With most brain surgeries, complications can occur and are often very serious. Complications associated with hypophysectomy may include, but are not limited to:

• Development of neurological abnormalities
• Delayed healing of the soft palate
• Development of oronasal fistula
• Wound rupture
• Loss of tear production in the eyes
• Hypoglycemia
• Hypernatremia: High sodium levels in the blood
• Recurrence of the condition
• Death due to unrelated disease

The surgeon will inform the owner of all possible complications of this surgery. In some studies, cats treated by hypophysectomy suffered from undiagnosed concurrent disease which ultimately caused mortality. These concurrent diseases were masked by the pituitary condition. This is a more common occurrence in cats than dogs diagnosed with pituitary masses.

It is difficult to prevent pituitary tumors in cats as they are often a geriatric condition. If owners notice any signs of diabetes mellitus in their cats, they should contact their veterinarian immediately.