Pituitary Tumors: Frequently Asked Questions

About 85% of dogs with Cushing’s have the pituitary dependent form of the disease, which is caused by a tumor on the pituitary gland. Below are answers to frequently asked questions about pituitary tumors.

What causes pituitary tumors?

Pituitary tumors develop from the abnormal growth of cells within the pituitary gland, which is a small gland located at the base of the brain. The exact cause of this abnormal growth is not known.

How do pituitary tumors bring about Cushing’s disease?

The pituitary gland is responsible for producing ACTH, a hormone that tells the adrenal glands to produce cortisol. When a pituitary tumor develops, it causes the gland to release excessive ACTH, which stimulates the adrenal gland to produce excessive cortisol, resulting in Cushing’s disease.

Can pituitary tumors cause neurological issues?

In addition to Cushing’s, pituitary tumors can cause neurological issues if they grow large. Pituitary tumors larger than 10 mm in diameter are called macroadenomas. A pituitary tumor may not be a macroadenoma at the time Cushing’s disease is diagnosed but may grow over the years.

Macroadenoma can compress brain structures and cause a variety of symptoms. These symptoms range from subtle changes, like mental dullness and poor appetite, to neurological issues such as pacing, seizures, and repetitive circling. If the tumor puts pressure on the optic nerve, it can cause vision problems.

How are pituitary tumors diagnosed?

If a dog shows signs of Cushing’s disease, a veterinarian will run specialized tests to make a diagnosis. Once the disease is confirmed, additional tests and imaging could be needed to determine whether it is caused by a pituitary tumor or an adrenal tumor.

Are pituitary tumors cancerous?

The vast majority of pituitary tumors are non-cancerous. Malignant pituitary tumors are possible but extremely rare.

How quickly do pituitary tumors grow?

Pituitary tumors are generally tiny, slow growing masses but some expand more rapidly. About 10 to 20 percent of dogs with pituitary-dependent Cushing’s eventually develop a tumor that is large enough to put pressure on the brain. In many cases, large tumors only cause subtle symptoms, such as decreased appetite or lack of energy. Other dogs develop obvious neurological issues that can include pacing, excessive circling, walking difficulties, and seizures. A veterinarian can confirm the size of a pituitary tumor through a CT scan or MRI.

What are the treatment options for pituitary tumors?

Symptoms of Cushing’s disease, from a pituitary tumor, can usually be controlled with a prescription drug called Vetoryl (trilostane). The active ingredient in Vetoryl is an enzyme inhibitor called trilostane, which blocks the excessive production of cortisol by the adrenal glands.

Lysodren (mitotane) can also be used to treat Cushing’s, but it is prescribed much less commonly than Vetoryl. This drug reduces cortisol levels by eroding the cortisol-producing layers of the adrenal glands.

In some cases, radiation therapy can be used to shrink pituitary tumors. For dogs with neurological issues, the goal is to reduce the tumor’s size enough to take pressure off the brain and alleviate symptoms. Radiation is usually administered a couple of times a week for four to six weeks. As with all medical treatments, there are potential side effects to be aware of when your dog is undergoing radiation. These side effects can include damage to the skin and hearing loss.

Can pituitary tumors be cured?

Removal of the pituitary gland is the only way to completely eliminate a pituitary tumor. This procedure is called hypophysectomy and consists of surgically removing the pituitary gland through the roof of the dog’s mouth. Unfortunately, hypophysectomy is a complex operation that’s only performed by a handful of specialized surgeons around the world.

References

Pituitary Macroadenoma in Cushing’s Syndrome, by Wendy Brooks, DVM

Pituitary-Dependent Cushing’s Disease Treatments, by University of Missouri

Neurologic signs can be subtle, by Johnny D. Hoskins, DVM, PhD

Vet Guide 2025: Pituitary Macroadenoma, by Dr. Duncan Houston