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The hypophysis, or pituitary gland as it is often called, is an endocrine gland located at the bottom of the brain. It is responsible for signalling the adrenal glands all through the body to produce cortisol. In dogs, it is not uncommon for growths to form on the pituitary gland, causing it to overproduce the signaling hormone, ACTH (adrenocorticotropic hormone). This leads to excess cortisol in the body, which causes high blood pressure, increased sugar levels, immunosuppression, imbalanced electrolytes, and an abnormal metabolism.
To treat this detrimental disorder, often an aggressive medical therapy is administered. This generally involves the use of chemotherapy, but has a high rate of condition recurrence. The surgical removal of the hypophysis, termed a hypophysectomy, is a newer treatment option that has a much higher success rate. As it is not yet an established technique, an ACVS board-certified veterinary surgeon who specializes in endocrine surgery is needed to perform the operation.
To confirm that the condition is being caused by tumors of the pituitary gland, an MRI or CT scan will be needed. With this advanced imaging, all tumors can be located and their size can be determined. Dogs with small to moderately sized growths are good surgical candidates for a hypophysectomy. Blood work is needed to determine if the dog is healthy enough to survive the use of general anesthesia.
The dog will be required to fast for several hours before the operation begins. It will then be sedated and intravenous tubes will be inserted. Various surgical approaches may be used, with a transsphenoidal (through the nose) entry being the most common. A videoscope is inserted to allow the surgical site to be visible and magnified for the duration of the procedure. The opening to the brain will need to be enlarged using a bone punch. All pituitary gland matter can then be excised using forceps. The hypothalamus (a lower part of the brain) should be clearly visible once all of the gland has been extracted. For the surgery to be effective, no remnants of the pituitary gland should be left.
The removal of the pituitary gland has been found to be an effective and permanent treatment of hyperadrenocorticism. Overall success depends on the size of the tumors present, with larger tumors being more difficult to treat. The anatomy of the dog can also complicate this procedure, with extremely short or long-nosed dogs providing a more difficult surgical approach.
Full remission from the disease is possible, with success rates ranging from 68% to 84%. An adenomectomy may be performed if possible, removing only the growths of the gland, however this is rarely possible due to the microscopic size of most pituitary tumors in dogs. Surgical treatment carries a better prognosis than medical therapy in most cases, as it treats the cause of the issue, while chemotherapy (using o,p’DDD) does not permanently relieve the problem.
The dog's vital functions and blood levels will need to be closely monitored in the hours following surgery. Drinking should be encouraged as soon as the dog has fully regained consciousness. Antibiotics and pain medication will also be administered at this time. A Schirmer Tear Test will be run shortly after the operation to see if the dog's tear production has been affected, if it has, treatment for this will be given.
The dog will be hospitalized for up to three days. It will be prescribed desmopressin for the following two weeks, at which time a follow-up appointment will be had. Urine will be collected and analyzed at this appointment, and then again at eight weeks, six months and one year to determine if the proper balance of hormone supplementation has been achieved. Oral administration of such hormones will be needed every six hours, tapering down to once every twelve hours for the remainder of the dog's life.
This procedure involves a very sensitive area of the body and requires a specialist to perform it. A surgeon with experience is needed to increase the likelihood of good results. As this surgery is not yet commonplace, it can cost in the range of $8,000 to $10,000. The alternative treatment method using chemotherapy is also quite costly, as it needs to be ongoing. Hormone replacement after surgery will need to continue for the rest of the dog's life, although this is less expensive than chemotherapy.
While most dogs who undergo a hypophysectomy experience a full remission from hyperadrenocorticism, complications can develop. Many dogs will suffer from a reduction of tear production after receiving this operation. Diabetes insipidus can also occur due to the imbalance of certain hormones. If hyperthyroidism develops, it will need immediate treatment to decrease the chance of further complications. There can be negative reactions to the general anesthesia during surgery. Hemorrhage during the operation is also a risk. If the growths in the pituitary gland are too large, removal may not be possible and palliative care should be sought instead.
Preventing Cushing's Disease in dogs can be difficult. Some breeds experience this condition more than others. Poodles, dachshunds, terriers and American Eskimo dogs are especially susceptible to this issue. The administration of prednisone for other health issues has also been linked to the development of hyperadrenocorticism in some cases.
The earlier this health problem is identified, the better chance of a good outcome for the affected dog. This is because small growths make the gland easier to remove than large growths. Signs of an overactive pituitary gland include thin skin, constant drinking, urinating, and panting, hair loss and weight gain. However, the most common symptom of hyperadrenocorticism is chronic infections that are difficult to eradicate. These can affect the eyes, urinary tract, gums, skin or ears of a dog. Take your dog in for examination if any of these issues are noticed.
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