Adrenal Tumors: Types and Symptoms

Approximately 15% of dogs with Cushing’s disease have the adrenal-dependent form of the disease, caused by an adrenal tumor. This article discusses common types of adrenal tumors, their symptoms, and diagnosis.

About the Adrenal Glands

The adrenal glands are two small, but critically important, glands located in front of the kidneys. A dog’s adrenal glands produce essential hormones, such as cortisol, which help to regulate blood pressure, metabolism, response to stress, the immune system, and several other bodily functions.

The adrenal glands are divided into two parts: the cortex and the medulla. The cortex is the outer layer of the adrenal glands. Its main function is to produce steroid hormones, such as cortisol and aldosterone.

The medulla is at the center of each adrenal gland, surrounded by the cortex, and primarily secretes adrenaline and noradrenaline. These are “fight or flight” hormones released by the body in response to stress. In short, the adrenal glands are essential to life.

A tumor can develop in any part of the adrenal glands. There are several types of adrenal tumors, including:

Cortisol-secreting tumor

It’s common for adrenal tumors to produce cortisol, causing adrenal-dependent Cushing’s disease. Symptoms may include increased thirst, increased hunger, excessive urination or incontinence, potbelly, and hair loss. These tumors can either be benign (adrenal adenoma) or malignant (adrenal carcinoma).

Pheochromocytoma

This type of adrenal tumor is rare. They typically release bursts of excessive adrenaline, causing unpredictable symptoms that occur “off and on.” Common symptoms include high blood pressure, increased heart rate, increased thirst/urination, anxiety/pacing, weakness, occasional collapse, and loss of appetite. Pheochromocytomas can be benign or malignant and has the potential to invade the vena cava, a major blood vessel in the abdomen.

NOTE: Most pheochromocytomas do not produce cortisol and do not cause Cushing’s disease. However, in a small percentage of cases, pheochromocytomas release ACTH and trigger the adrenal gland to release excessive cortisol, which can lead to Cushing’s symptoms. This is called Ectopic Cushing’s syndrome.

Sex hormone tumor

Some adrenal tumors produce sex steroid hormones, such as progesterone and estrogens. This type of tumor can cause atypical Cushing’s disease, a condition in which a dog’s cortisol levels are normal, but sex steroid hormones are elevated. For more information, see our All About Atypical Cushing’s Disease article.

Non-functional tumor

Non-functional adrenal tumors do not produce hormones. These tumors usually cause no clinical signs, unless they are large or have spread beyond the adrenal glands.

Diagnosis of Adrenal Tumors

Dogs with cortisol-secreting adrenal tumors will show symptoms of Cushing’s disease, which your veterinarian will confirm with diagnostic tests. In most cases, the Low-Dose Dexamethasone Suppression Test will be used.

The presence of an adrenal tumor is usually confirmed through an ultrasound or CT scan. Since a normal adrenal gland is less than a half centimeter thick and hidden in fat, it is usually necessary for a board-certified radiologist to find an adrenal tumor.

In dogs with Cushing’s disease caused by an adrenal tumor, it’s common for the adrenal gland with the tumor to be enlarged and the gland without the tumor to be smaller than normal.

Is the Tumor Benign or Malignant?

50 percent of dogs with adrenal-dependent Cushing’s have a benign adrenal tumor; the other 50 percent have a malignant adrenal tumor.

Certain characteristics can point to whether an adrenal tumor is benign or malignant. As multiple studies show, adrenal tumors greater than 20 mm (2 cm) in diameter are more likely to be malignant. Malignant tumors also grow more quickly than benign tumors and have the potential to metastasize to other organs. The most common places for malignant adrenal tumors to spread are the liver and lungs; your veterinarian can perform an ultrasound or x-rays of the chest and abdomen to check for this.

Please note: lack of tumor spread beyond the adrenal glands does not necessarily mean that the tumor is benign. While up to 50 percent of malignant adrenal tumors metastasize, many will not have done so at the time of initial diagnosis or may have only metastasized microscopically.

References

Adrenal Masses or Tumors, by Veterinary Specialty Center (Illinois)

Adrenal Gland Tumors in Dogs, by Lauren Jones, VMD

Adrenal Treatment, by Mar Vista Animal Medical Center