Adrenal Gland Tumors in Dogs

What Are Adrenal Gland Tumors in Dogs?

Adrenal glands are two small glands in your dog’s abdomen, just in front of the kidneys, and any part of these glands can develop tumors. Not all adrenal tumors are cancer. Some are benign, or noncancerous. Benign tumors within the adrenal glands may still be hormonally active, causing various symptoms.

A dog’s adrenal glands are crucial in regulating heart rate, blood sugar, blood pressure, and secretion of hormones during physical and emotional stress. The glands are divided into two parts: the outer area, called the cortex, and the middle area, the medulla.

The cortex is divided into three layers and secretes the following steroid hormones: 

• Mineralocorticoids (such as aldosterone), which help control sodium and potassium electrolytes

• Glucocorticoids (such as cortisol), which have a role in metabolism, reducing inflammation, and helping the immune system

• Sex hormones, such as estrogen, progesterone, and testosterone

The medulla secretes catecholamines, which are important hormones during stress and fight-or-flight responses. In addition, the medulla releases epinephrine (also known as adrenaline) and norepinephrine.

The most common disease caused by adrenal tumors is adrenal-dependent hyperadrenocorticism, also known as Cushing’s disease. Dogs with Cushing’s disease most notably have excessive thirst, urination, and appetite. Cushing’s is very common in dogs, but most acquire the disease from dysfunction within their pituitary gland, not the adrenals. Only around 20% of dogs with Cushing’s disease have an adrenal tumor.

Other rare tumors of the adrenal glands may secrete aldosterone and cause a disorder called hyperaldosteronism, which may cause weakness and lethargy. More serious rare adrenal gland tumors can invade major vessels in the body and cause arrhythmias and clots while severely increasing blood pressure.

The most common adrenal tumors in dogs are:

• Adrenal adenoma: A tumor that may be functional (secrete hormones) or nonfunctional (does not secrete hormones). Adenomas commonly secrete cortisol, causing Cushing’s disease, or aldosterone, causing hyperaldosteronism.

• Adrenal carcinoma: a tumor that is malignant and can also secrete cortisol or aldosterone, causing Cushing’s disease or hyperaldosteronism. These metastasize, or spread, in up to 50% of cases. Metastasis sites are usually the liver and the lungs.

• Pheochromocytoma: A rare tumor in the medulla that secretes epinephrine, norepinephrine, or both.

• Paraganglioma: A rare tumor coming from the nerves that can secrete catecholamines.

Most adrenal gland tumors occur in middle-aged to older dogs, but there are no breed predispositions. Larger dogs may be at higher risk of functional tumors secreting cortisol, causing Cushing’s disease.

Symptoms of Adrenal Gland Tumors in Dogs

Symptoms of adrenal gland tumors in dogs vary, based on the type of tumor. Most commonly, tumors secrete cortisol, which is a steroid. Overproduction of steroids leads to:

• Increased thirst

• Increased urination

• Increased hunger

• Weight gain

• Pot-belly appearance

• Skin issues

• Urinary tract infections

• Hair loss

More serious tumors, called pheochromocytomas, secrete fight-or-flight hormones like adrenaline. These symptoms may be vague, and wax and wane. At times, the dog may even seem normal, but these types of tumors have profound cardiac and other manifestations, such as:

• Abnormal heart rate and rhythm leading to weakness and collapse

• Increased blood pressure leading to behavior changes or blindness

• Increased thirst and urination

• Weight loss and decreased appetite

• Seizures

• Panting

• Fever

• Cough

• Gastrointestinal signs

Tumors secreting aldosterone result in high blood pressure and low potassium. Pet parents may notice:

• Weakness

• Blindness secondary to high blood pressure

• Lethargy

• “Dropped” legs in the back

• Abnormal neck flexion

• Collapse

Causes of Adrenal Gland Tumors in Dogs

Causes of adrenal gland tumors are mostly unknown. However, there may be a genetic predisposition to adrenal tumors and environmental, diet, or medication factors that make certain animals more prone to develop them. More studies and research are needed to better understand the cause of these diseases.

How Veterinarians Diagnose Adrenal Gland Tumors in Dogs

Most adrenal gland tumors are found with an ultrasound, which can assess size, shape, and structure. However, while ultrasound can confirm the presence of a tumor in the adrenals, it can only lead veterinarians to an educated guess about the type.

Benign adenomas are typically small and noninvasive. Carcinomas are usually bigger and can invade the surrounding tissue. Tumors typically only affect one, not both, adrenal glands. A biopsy is required for a definitive diagnosis, although not all dogs are candidates for this procedure.

Based on the clinical signs and severity of the disease, other important tests to diagnose adrenal tumors include:

• Routine blood chemistry and complete blood count

• Blood pressure measurements

• X-rays of the chest and abdomen to evaluate for cancerous spread

• Cardiac consultation to rule out heart failure

• Advanced imaging to determine the extent of invasive tumors

• Hormone testing

• Endocrine testing, such as an ACTH Stimulation test or Low-Dose Dexamethasone Suppression Test

Treatment of Adrenal Gland Tumors in Dogs

Removal of the affected adrenal gland (adrenalectomy) is the treatment of choice. However, surgery may not be an option if the tumor has invaded major blood vessels or other organs or spread to distant sites (metastasis). An adrenalectomy is a serious surgery and should be performed by a surgical specialist at a 24-hour facility, as complications during and after surgery are common.

For dogs who are not candidates for surgery, medical management may be beneficial for a period of time. However, fatal complications, such as blood clots and arrhythmias, may occur at any time.

• Dogs with adrenal-dependent Cushing's disease may improve clinically on the drugs mitotane or trilostane, which work to suppress cortisol.

• Dogs with nonresectable pheochromocytomas may benefit from drugs to treat their clinical signs, such as blood pressure or cardiac arrhythmias.

• Dogs with nonresectable adrenal tumors secreting aldosterone may benefit from drugs like spirinolactone that help block the receptors for aldosterone.

Supportive care may be required during acute crises. Many dogs need to stay in a veterinary hospital on IV fluids, medications, and supplements.

Recovery and Management of Adrenal Gland Tumors in Dogs

Dogs with benign, nonfunctional tumors have the best prognosis, followed by dogs with benign, functional tumors. Hyperaldosteronism is rare, and the prognosis is usually uncertain.

Cushing’s disease, caused by a benign tumor, is commonly well-managed by surgery or medications followed by periodic exams and testing. Prognosis is good for these animals if symptoms are controlled.

Dogs with malignant tumors causing Cushing’s disease have a worse prognosis, with relatively high metastatic rates. Some of these dogs may live for a few years after diagnosis and adrenal removal, and just over a year if managed with medication alone.

Dogs with pheochromocytomas have a guarded to poor prognosis, as these are typically invasive and metastatic, with many severe side effects causing a poor quality of life. About 20-30% of dogs may not survive the surgery to remove the tumor. Dogs that do survive surgery have an average survival of around 1 year, with less than 60% surviving longer than 3 years. Survival time decreases as the tumor size increases.