The endocrine system consists of several glands located throughout the body that produce various hormones to control body functions. The pituitary and adrenal glands play roles in regulating cortisol in the body, a hormone that has an effect on many organs. A dog can develop a tumor of either the pituitary or the adrenal glands, resulting in excess cortisol production and leading to a condition known as Cushing’s syndrome.
The pituitary gland is a small gland located at the base of the brain. It produces several hormones, but one of its primary roles is controlling the production of cortisol by the adrenal glands by releasing adrenocorticotropic hormone,or ACTH. The adrenal glands are small glands, located just above the left and right kidney, responsible for directly releasing cortisol after stimulation from ACTH hormone.
If a tumor forms in the pituitary gland, it causes too much ACTH production and signals the adrenal glands to produce excess cortisol. Tumors of the adrenal gland almost always form in either the left or right gland, not both. When an adrenal tumor forms, it stimulates the affected gland to produce excess cortisol directly. Regardless of how the excess cortisol is produced, the resulting symptoms are the same. The most common symptoms of Cushing’s syndrome include an increased appetite, increased thirst with resulting increase in urination, a thin hair coat and a pot-bellied appearance. It is a condition that primarily affects middle-age or older dogs and can lead to effects on almost any organ including the heart, lungs, kidneys, liver or brain.
The majority of cases of Cushing’s syndrome result from benign tumors in the pituitary gland. However, you must perform diagnostics to determine where the excess hormone is being generated, because the treatment for each location is different. Blood tests that evaluate certain hormone levels can help determine if the pituitary gland or an adrenal gland is the cause of the problem. These tests are not always definitive, so additional testing may be at hand. A common test used to aid in diagnosis of Cushing’s syndrome is an abdominal ultrasound, which can identify an adrenal tumor or identify enlargement of both adrenal glands, as occurs with a pituitary tumor. An MRI or CT scan of the brain is the most accurate way to evaluate the pituitary gland and search for tumors in this location.
Tumors of the adrenal gland are more likely to be malignant, so surgery is one of the recommendations for treatment. Given that pituitary tumors are almost always benign, surgery is not commonly performed. In most cases of pituitary tumors and with fewer adrenal tumors, medication is administered to block the production of the excessive hormone, resulting in decreased cortisol levels. In rare cases, pituitary tumors will grow large enough to cause neurological symptoms such as confusion, blindness and seizures. The best treatment for these large tumors is radiation therapy. As you can see, it is important to determine if the pituitary gland or an adrenal gland is the root of the problem, because effective treatment for each location is quite different.