Pheochromocytoma

Pheochromocytoma is a rare endocrine tumor derived from chromaffin cells. It is the most common neoplasm of the adrenal gland in dogs and cattle. The tumor can be unilateral or bilateral, and has no reported breed or sex predilection. Pheochromocytomas in dogs are usually benign, however, occasionally, they are malignant with metastasis to the liver, regional lymph nodes, and lungs. Affected dogs are usually older, with a mean age of 11 years.

Signs

Clinical signs associated with pheochromocytoma are often vague and intermittent, and may mimic more common disorders such as hyperadrenocortisism, diabetes mellitus, liver disease, kidney failure, and various tumors. Most common signs include weakness, collapse, lethargy, anorexia, vomiting, panting, weight loss, anxiety, restlessness, increased thirst and urination, diarrhea, abdominal distention, hind limb swelling, nosebleeds, seizures, and acute blindness. The signs are generally associated with catecholamine excess and high blood pressure. Elevation of blood pressure induced by sudden release of catecholamines can cause acute congestive heart failure, pulmonary edema, myocardial infarction, ventricular fibrillation and cerebral bleeding.

Pheochromocytomas occasionally result in secondary conditions including thrombosis of the vena cava, aortic thromboembolism, spontaneous rupture of the tumor, paresis secondary to spinal cord compression, arrhythmias, cardiac hypertrophy, arteriolar sclerosis, systemic hypertension, and hyperadrenocortisism. About 15-38% of pheochromocytomas develop in the inferior vena cava, causing clinical signs of ascites, hind limb edema, and distention of epigastric veins.

Aortic thromboembolism is fairly uncommon in dogs. Rarely, pheochromocytomas may rupture spontaneously and cause abdominal bleeding. Systemic hypertension occurs in 43-70% of canine patients with pheochromocytoma, and concurrent hyperadrenocortism has been found in 12% of reported cases.

Treatment

The treatment of choice for canine pheochromocytoma is surgical removal of the tumor. Medical therapy can be used for nonresectable or metastatic disease, or to stabilize the patient prior to surgery. Medical therapy is generally aimed at correcting systemic hypertension and cardiac arrhythmias. The prognosis is guarded; however, survival of up to one year has been reported in 50% of dogs with uncomplicated cases following surgical removal of the tumor. Pheochromocytoma is considered in cases which have vague clinical signs and concurrent hypertension. Perhaps with more awareness of this condition, it can be diagnosed and managed more successfully.

References

1. Jones TC, BD Hunt and NW King: 1997. Veterinary Pathology. Baltimore: Williams and Wilkens.
2. Jubb KVF, PC Kennedy, N Palmer (Eds): 1993. Pathology of Domestic Animals, 4th ed. San Diego: Academic Press, 1993.
3. Locke-Bohannon LG and GE Mauldin: 2001. Canine Pheochromocytoma: diagnosis and management. 'Compendium on Continuing Education for the Practicing Veterinarian 23: 807-814.
4. McGavin MD, WW Carlton, JF Zachary: 2001. Thompson's Special Veterinary Pathology, 3rd ed. St. Louis: Mosby
5. Santamarina et al: 2003. Aortic Thromboembolism and Retroperitoneal Hemorrhage Associated with 'a Pheochromo-cytoma in a Dog. J Vet Int Med. 17(6): 917-922.
6. Williams JE and SG Hackner: 2001. Pheochromocytoma Presenting as Acute Retroperitoneal Hemorrhage in a Dog. J Vet Emerg and Critical Care.

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