Pheochromocytoma

TL;DR. Pheochromocytoma is an uncommon adrenal gland tumor in dogs and cats that secretes excess stress hormones, causing dangerous spikes in blood pressure, weakness, and heart complications.

The adrenal glands are located just ahead of each kidney and are responsible for producing vital hormones.

What is it?

A pheochromocytoma is an uncommon tumor that originates in the adrenal glands, which are small, cap-like organs located just ahead of each kidney. Specifically, this tumor develops within the chromaffin cells of the adrenal medulla—the inner core of the gland responsible for producing "fight-or-flight" hormones, collectively known as catecholamines. These hormones include epinephrine (adrenaline) and norepinephrine.

Under normal circumstances, the adrenal medulla releases tiny, controlled amounts of catecholamines to help your pet respond to stress, exercise, or excitement. However, when a pheochromocytoma develops, these tumor cells synthesize, store, and secrete massive, unpredictable surges of catecholamines into the bloodstream. This flooding of hormones forces the body into a state of chronic or episodic hyper-arousal, causing blood vessels to constrict severely, the heart to beat dangerously fast, and the blood pressure to spike to life-threatening levels.

While these tumors primarily affect the adrenal glands, related tumors can occasionally arise from chromaffin cells located outside the adrenal medulla, typically near the sympathetic nerve ganglia. These extra-adrenal tumors are known as paragangliomas, and they are exceptionally rare in both dogs and cats.

To understand the cellular nature of this disease, veterinary specialists refer to the fundamental pathology of these tissues:

"Pheochromocytoma is a tumor of the chromaffin cells of the adrenal medulla. These cells synthesize, store, and secrete cat[echolamines]..." — Small Animal Critical Care Medicine, p. 414

Because these hormones affect almost every major organ system, a pheochromocytoma can cause a wide array of seemingly unrelated symptoms, making it a highly complex and challenging condition to manage.

Causes & risk factors

The exact underlying cause of pheochromocytomas in dogs and cats remains unknown. Like many endocrine tumors in veterinary medicine, they are generally considered spontaneous, meaning they develop without a clear environmental or genetic trigger.

These tumors are primarily diagnosed in older pets. There are currently no documented breed predispositions for pheochromocytomas in dogs or cats within standard veterinary clinical records. Any senior dog or cat can develop this condition, regardless of breed or mix. Because of their slow-growing but highly invasive nature, these tumors are often present for a significant period before they cause noticeable clinical signs or are detected during routine veterinary diagnostics.

Signs to watch for

The clinical signs of a pheochromocytoma can be highly variable and frequently occur in episodes, or "spells," corresponding to sudden releases of hormones from the tumor. Between these episodes, your pet may appear completely normal, which can make early detection difficult.

Common Signs

• Generalized weakness: Your pet may suddenly seem too weak to stand or walk, often recovering after a brief period of rest.
• Episodic collapse: Sudden, temporary fainting or falling over, which can easily be mistaken for a seizure or a primary heart attack.
• Excessive panting and rapid breathing (tachypnea): Panting that occurs without physical exertion or high environmental temperatures.
• Agitation and nervous behavior: Unexplained restlessness, pacing, or anxiety, driven by the constant surge of adrenaline.
• Abnormally fast heart rate (tachycardia): A racing heart that your vet will detect during an examination, or that you may feel through your pet's chest wall.
• Muscle wasting: Progressive loss of muscle mass, particularly along the spine and hindquarters, caused by the chronic metabolic stress of the disease.
• High blood pressure (systemic hypertension): Severely elevated blood pressure, which can damage delicate blood vessels throughout the body.
• Protein in the urine (proteinuria): High blood pressure damages the filtering units of the kidneys, causing protein to leak into the urine.

Occasional Signs

• Lethargy and depression: General sluggishness and a lack of interest in normal activities.
• Increased thirst (polydipsia) and increased urination (polyuria): Drinking and urinating much more frequently than normal.
• Gastrointestinal upset: Occasional vomiting, diarrhea, and abdominal distention.
• High blood sugar (hyperglycemia): Elevated glucose levels caused by the hormone surges interfering with normal insulin function.
• Nosebleeds (epistaxis): Sudden bleeding from the nose, often caused by blood vessels rupturing under the strain of extreme high blood pressure.
• Eye complications: Bleeding within the eye (retinal hemorrhage) or sudden blindness caused by the retina detaching from the back of the eye (retinal detachment) due to severe hypertension.
• Irregular heartbeats (cardiac arrhythmias): Disruptions in the heart's normal rhythm, which can be life-threatening.

Severe high blood pressure caused by a pheochromocytoma can lead to retinal hemorrhage and sudden blindness.

Many of these symptoms are shared with other common endocrine disorders, which requires a thorough diagnostic investigation to differentiate them:

"The most common clinical signs and physical examination abnormalities involve the respiratory, cardiovascular, and musculoskeletal systems and include generalized weakness, episodic collapse, agitation, nervous behavior, excessive panting, tachypnea, and tachycardia. Excess catecholamine secretion may also cause severe systemic hypertension, resulting in nasal and retinal hemorrhage, retinal detac[hment]" — Internal Medicine 5th p.889

How vets diagnose it

Diagnosing a pheochromocytoma is a multi-step process. Because the symptoms are often episodic and mimic more common conditions, such as Cushing's disease (hyperadrenocorticism), your vet must systematically rule out other causes.

"... panting, weakness) and blood pressure alterations seen in dogs with hyperadrenocorticism (common) are similar to those observed in dogs with pheochromocytoma (uncommon). In addition, both pheochromocytoma and adrenocortical carcinoma invade adjacent structures and cause tumor thrombi in the phrenicoabdominal vein and caudal vena cava. It is important to rule out adrenal-dependent hyperadrenocort[icism]" — Internal Medicine 5th p.890

To reach a diagnosis, your vet will utilize several key diagnostic tools:

• Blood pressure monitoring: Since systemic hypertension is a hallmark of this disease, repeated blood pressure measurements are crucial. Your vet will look for sustained or highly fluctuating spikes in blood pressure.
• Abdominal ultrasound: This imaging technique allows your vet to visualize the adrenal glands directly. An ultrasound can identify an adrenal mass and, critically, evaluate whether the tumor has invaded adjacent structures, such as the phrenicoabdominal vein or the caudal vena cava (the main vein returning blood to the heart). Finding a tumor thrombus (a clot made of tumor tissue) in these vessels is highly suggestive of an invasive adrenal tumor.
• Electrocardiogram (ECG) or Holter monitoring: An ECG helps detect and characterize cardiac arrhythmias. A Holter monitor—a portable ECG worn by your pet at home for 24 to 48 hours—can capture episodic arrhythmias that occur outside the clinic.
• Measurement of urinary catecholamines: Testing your pet's urine for catecholamines or their breakdown products (metabolites) can provide non-invasive evidence of excessive hormone secretion.
• Histopathologic evaluation [GOLD STANDARD]: While imaging and hormone tests can strongly point to a pheochromocytoma, a definitive diagnosis can only be made by analyzing the tumor tissue under a microscope after it has been surgically removed.

"As a result, the antemortem definitive diagnosis of a pheochromocytoma ultimately relies on histologic evaluation of the surgically excised adrenal mass." — Internal Medicine 5th p.891

Abdominal ultrasound is a vital tool for detecting adrenal masses and checking for blood vessel invasion.

Treatment options

Managing a pheochromocytoma requires a carefully coordinated, two-phase treatment plan: medical stabilization followed by surgical removal of the tumor.

"A period of medical therapy intended to reverse the effects of excessive adrenergic stimulation, followed by surgical removal of the tumor, is the treatment of choice for pheochromocytoma." — Internal Medicine 5th p.891

Phase 1: Medical Stabilization (First-Line Therapy)

Before surgery can be safely performed, your pet must undergo a period of medical therapy (typically lasting several weeks) to block the dangerous effects of the hormone surges and stabilize their blood pressure.

• Phenoxybenzamine (Alpha-Adrenergic Blocker): This is the primary medication used to prepare pets for surgery. It works by blocking alpha-receptors on blood vessels, preventing catecholamines from causing severe constriction. This relaxes the blood vessels, lowers blood pressure, and significantly reduces the risk of life-threatening blood pressure spikes during anesthesia and surgical manipulation of the tumor.
• Phenylpropanolamine (Sympathomimetic): In specific clinical scenarios, your veterinarian may incorporate this medication as part of a highly tailored protocol to help manage vascular tone and clinical signs.

Phase 2: Surgical Removal (Adrenalectomy)

Once your pet's blood pressure is stabilized, surgical removal of the affected adrenal gland (adrenalectomy) is performed. This is a highly complex, high-risk surgery that is ideally performed by a board-certified veterinary surgeon. The surgery is challenging because touching the tumor can trigger a massive release of catecholamines, causing sudden, extreme blood pressure swings and heart arrhythmias. Furthermore, if the tumor has invaded the caudal vena cava, the surgeon must carefully extract the tumor thrombus from the vein, which carries a risk of severe hemorrhage.

Phase 3: Postoperative and Intensive Care (Second-Line Therapy)

Immediately following the removal of the tumor, your pet's body may experience a sudden drop in hormone levels, leading to dangerously low blood pressure (hypotension).

• Vasopressin (Hormone / Antidiuretic / Vasopressor): In the intensive care unit, your veterinary team may use vasopressin to help support and stabilize your pet's blood pressure and fluid balance during this critical transition period.

Prognosis

The prognosis for pets with a pheochromocytoma is generally guarded, but it can vary significantly depending on whether the tumor has spread or invaded local blood vessels.

About 50% of these tumors are malignant. However, some veterinary oncology resources recommend treating all pheochromocytomas as malignant due to their highly invasive local behavior and potential to metastasize (spread) to distant sites, including the liver, lungs, regional lymph nodes, bone, and central nervous system:

"Pheochromocytoma should always be considered a malignant tumor in dogs and cats. Distant sites of metastasis include the liver, lung, regional lymph nodes, bone, and CNS." — Internal Medicine 5th p.889

If the tumor has already metastasized or extensively invaded major blood vessels at the time of diagnosis, the long-term prognosis is significantly poorer. However, for pets that successfully survive the surgery and the immediate, critical postoperative period, long-term survival times and quality of life can be excellent.

Prevention

Because the exact cause of pheochromocytomas is unknown, there are no specific preventative measures, lifestyle changes, or genetic tests available to prevent this disease.

The best defense is early detection. Routine wellness examinations for senior pets—including regular blood pressure checks, routine blood work, urinalysis to check for protein, and screening abdominal ultrasounds—can help identify adrenal masses before they cause severe, life-threatening clinical signs.

When to call your vet

A pheochromocytoma is a serious, progressive condition that requires urgent veterinary attention. You should contact your veterinarian immediately if you observe any of the following red-flag symptoms in your pet:

• Any episode of sudden collapse, fainting, or extreme weakness
• Sudden onset of blindness, dilated pupils, or bleeding within the eye
• Unexplained, sudden nosebleeds
• Severe, persistent panting or difficulty breathing
• Extreme restlessness, pacing, or inability to settle down
• A noticeably racing or pounding heartbeat

If your pet collapses or experiences sudden blindness, treat this as a medical emergency and transport them to the nearest emergency veterinary hospital immediately.

Sources

• Internal Medicine, 5th Edition, pages 889, 890, 891.
• Small Animal Critical Care Medicine, 2nd Edition, page 414.

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