Definition
Adrenal tumors, often associated with hyperadrenocorticism or Cushing’s Disease, are lumps on one or both of the adrenal glands, located in the abdomen just above the kidneys. What causes adrenal tumors is not well-understood. In dogs, these tumors are split fairly equally between benign adenomas and malignant adenocarcinomas. Nonfunctional tumors don’t affect the adrenal glands’ secretion of hormones and rarely cause any problems. Functional adrenal tumors, whether benign or malignant, make dogs feel lousy, because their adrenal glands are secreting excessive amounts of steroid hormones into their bloodstream without any regulation. Dogs with functional adrenal tumors become weak, listless and lethargic. They aren’t hungry and they lose weight. They also become extremely thirsty. If malignant functional adrenal tumors are not treated or removed, they usually are fatal. It’s important for owners to recognize the signs of adrenal tumors so that they can get appropriate medical attention for their canine companion.
Causes of Adrenal Tumors
As with other types of cancer, the causes of adrenal gland tumors are not well understood. In companion dogs, adrenal tumors are split fairly equally between adenomas, which are benign or non-malignant masses, and adenocarcinomas, which are malignant. A malignant tumor is one that tends to progressively worsen with time and, if not treated or removed, usually will result in death of the affected animal. Malignant masses typically are highly invasive, meaning nearby tissue is affected, and metastatic, which means that the cancerous cells spread from one part of the body to others.
Adenomas can be either functional or non-functional. Non-functional adenomas do not affect the production or release of adrenal steroid hormones. However, functional adenomas, and almost all adenocarcinomas, stimulate unregulated release of corticosteroids from the adrenal cortex – most commonly cortisol, a glucocorticoid hormone. They can cause over-production of other steroids, as well. Functional tumors cause the adrenal glands to keep releasing adrenal hormones regardless of the presence or absence of normal pituitary gland adrenocorticotropic hormone (ACTH) stimulus and regulation. Functional adrenal tumors basically keep the affected gland or glands “turned on” all the time, as they are constantly being bombarded with copious amounts of ACTH. The unregulated overabundance of corticosteroids in circulation is a condition called hyperadrenocorticism, also commonly known as “Cushing’s Disease.”
Functional adenomas and/or adenocarcinomas can develop on one or both of the adrenal glands. In dogs, the right and left adrenal glands seem to be affected by both types of adrenal tumors with equal frequency. When a functional mass affects only one of the glands, the other – referred to as the “contralateral” adrenal gland - starts to shrivel and decreases dramatically in size. This happens because the overload of circulating corticosteroids from the functional tumor signals the pituitary gland to stop releasing ACTH. This, in turn, shuts down the cortex of the contralateral adrenal gland, leaving it with nothing to do. It basically withers away from disuse.
Prevention of Adrenal Tumors
Veterinary science does not yet fully understand the causes of adrenal gland adenomas and adenocarcinomas. As a result, there is no realistic way to describe a sound preventative protocol.
Special Notes
Adenocarcinomas are much more serious even than functional adenomas, because they are malignant and prone to be progressive, highly invasive and metastatic. When an adrenal tumor is suspected, most general practitioners will refer the owner and her dog to a veterinary teaching hospital or other highly-specialized referral center, where the newest and most advanced diagnostic and treatment options are available.
Initial Evaluation
Masses on the adrenal glands are a mystery to most people, including veterinarians. Fortunately, adrenal tumors can be diagnosed and treated, or at least medically managed, most of the time. Nonfunctional adrenal tumors rarely cause harm to, or symptoms in, the affected animal. When a veterinarian sees a dog showing signs consistent with abnormally high secretion of adrenal corticosteroid hormones, she will perform a thorough physical examination of the animal. She will also take a complete history from the dog’s owner about its health, vaccination status, access to potential toxins and access to unvaccinated animals, among a number of other things. The dog’s history and physical examination results will guide the next diagnostic steps.
Diagnostic Procedures
Most veterinarians evaluating a dog showing non-specific signs that might suggest hyperadrenocorticism will recommend taking blood and urine samples for a complete blood count (CBC), a serum biochemistry panel and a urinalysis. Those results may or may not suggest an adrenal tumor. However, if there is a functional tumor on one or both of the adrenal glands, the test results usually will be abnormal.
Radiographs (X-rays) can be taken to look for any spread (metastasis) of malignant tumors. X-rays can also reveal abnormally sized or shaped abdominal organs and/or enlarged, shrunken or mineralized adrenal glands. An abdominal ultrasound can also help the doctor assess the size and structure of each adrenal gland in greater detail. The veterinarian will be looking for enlargement or irregularity of one of the adrenals and a shrunken or smaller contralateral gland, which would strongly suggest a functional adrenal tumor.
Once a functional tumor is identified, a number of diagnostic tests are available to determine whether mineralocorticoids, glucocorticoids or sex hormones are being secreted by the adrenal cortex. Abdominal computed tomography (CT scan), and/or magnetic resonance imaging (MRI), can be quite helpful to detect any local or remote tissue invasion or spread by a metastatic adrenal mass.
Some adrenal tumors can be biopsied or removed surgically as part of making a definitive diagnosis. The removed tissue will be submitted to a diagnostic laboratory, where it will be analyzed under a microscope. This is the most accurate way to determine whether the tumor is malignant or not.
Special Notes
While arriving at a definitive diagnosis of adrenal tumors can be somewhat time-consuming, almost all of these tumors ultimately can be identified and treated or at least medically managed. There is no easy way to distinguish functional adenomas from adenocarcinomas unless the affected adrenal glands are removed and analyzed by a pathology laboratory. Adenocarcinomas do tend to be a bit larger than adenomas, which sometimes can be detected using radiograph (X-ray) or ultrasound techniques.
Effects of Adrenal Tumors – From the Dog’s Point of View
If an adrenal gland tumor is not functional – which means that it is not causing the adrenal cortex to secrete abnormally large amounts of corticosteroid hormones into the dog’s bloodstream - the affected animal usually will have no noticeable symptoms of disease or discomfort. Benign nonfunctional adenomas rarely cause any significant consequences.
When a tumor is functional, however; it will cause the affected adrenal gland or glands to make and release unusually high amounts of adrenal hormones into circulation. Within a fairly short period of time, most dogs that have functional adenomas or adenocarcinomas will start to feel increasingly sick. They will feel weak, listless and lethargic. They won’t feel hungry and will lose their appetite, causing them to lose weight and feel even weaker. They will be excessively thirsty. Put plainly, they will feel lousy. These are fairly non-specific signs that can be caused by many other disorders, which makes adrenal gland tumors somewhat difficult to diagnose.
Symptoms of Adrenal Tumors – What the Owner Sees
Owners of dogs with nonfunctional adrenal tumors almost never notice any signs or symptoms of discomfort or distress. However, owners of dogs with functional adenomas or adenocarcinomas may observe one or more of the following signs, depending on which layer of the adrenal cortex is affected:
- Excessive water intake (polydipsia)
- Increased urine output (polyuria)
- Increased appetite and food intake (polyphagia; affected dogs are often ravenous)
- Weight gain, frequently to the point of obesity
- Abdominal enlargement (pendulous, distended abdomen; “pot-bellied” appearance)
- Hair loss (alopecia; usually patchy and symmetrical on both sides of the body)
- Darkening of skin (hyperpigmentation)
- Excessive panting; often when lying down and appearing to be resting quietly
- Skin bruising
- Clitoral enlargement in females (clitoral hypertrophy)
- Testicular enlargement in males (testicular hypertrophy)
- Loss of normal reproductive cycling in females (anestrus)
- Infertility (males and females)
- Weakness
- Lethargy, listlessness
- Exercise intolerance
- Muscle atrophy
- Thin, fragile skin that tears easily
- Poor coat condition
- Lack of coordination (ataxia)
- Neurological signs (circling, aimless wandering, pacing, bumping into walls or furniture, falling down for no apparent reason)
- Poor wound healing
Dogs at Increased Risk
Functional tumors of the adrenal glands most commonly afflict middle-aged and older dogs, regardless of whether the masses are benign adenomas or malignant adenocarcinomas. As a result, when they start to notice some of the above symptoms, many owners are fooled into thinking that their beloved companions are just going through the natural effects of aging, which is completely understandable. Females and large-to-giant breed dogs also seem to have an elevated risk of developing adrenal masses. According to some reports, German Shepherds, Labrador Retrievers, Dachshunds, Poodles and some breeds from the Terrier Group may be predisposed to adrenal gland tumors, although the reasons for these associations are not well-understood.
Treatment Goals
Nonfunctional adrenal tumors typically do not require treatment. The goals of treating functional tumors of one or both adrenal glands are to destroy or remove the affected glands if possible, and remove or destroy any sites where malignant tissue has spread. Other goals are to relieve the discomfort suffered by the dog and to restore and prolong its quality of life.
Treatment Options
The preferred treatment for dogs with functional adrenal gland tumors is to remove them surgically. X-rays and ultrasound examinations can show the precise location of the adrenal mass and can also reveal generalized enlargement of the adrenals or masses in other areas. Without surgery, there is no way to determine unequivocally whether an adrenal gland tumor is or is not malignant. Because the adrenal glands in dogs are so tiny, surgical removal of an adrenal mass requires removal of the entire affected gland. If surgery is hoped cure the dog’s hyperadrenocorticism, appropriate margins of healthy tissue surrounding the affected adrenal gland must also be removed.
Dogs with adrenal tumors will need to be stabilized medically in a veterinary hospital before they can be taken safely to surgery. Pre-surgical management will include administration of medication to inhibit the production and secretion of adrenal corticosteroids while the surgical procedure is taking place. Most dogs will need intravenous fluid support to keep them well-hydrated during and after the surgery. Other medical therapy may be necessary to reduce hypertension (high blood pressure), if it is present in the particular patient.
Medical management and supportive care are extremely important for dogs with adrenal gland tumors, whether or not surgical removal is attempted or entirely effective. If both adrenal glands are removed, or if only one is removed but the contralateral gland has atrophied to the point of being nonfunctional, the dog will have to be on oral corticosteroid replacement therapy for the rest of its life. Long-term steroid treatment can be as costly as, or even more expensive than, the cost of the surgery.
Prognosis
A dog with a functional adenoma or adenocarcinoma that has not spread to other parts of its body, and that recovers well following successful surgical removal of the affected glands, usually has a fairly good prognosis, as long as its owner follows the veterinarian’s steroid replacement therapy instructions to a tee. The average survival time for dogs in that circumstance is somewhere between 16 to 36 months following diagnosis and surgery. Unfortunately, malignant masses that have metastasized or become locally invasive carry a guarded to poor prognosis.
Special Notes
Surgical removal of the tiny adrenal glands is called an “adrenalectomy.” This is not a simple procedure, but it is done successfully with some frequency in veterinary medicine. Relatively non-invasive laparoscopic adrenalectomies are occasionally and increasingly being performed.
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