Pheochromocytoma is the most common neoplasm of the adrenal gland in dogs and cattle. It is derived from chromaffin cells and can affect one of both glands. Most canine pheochromocytomas are benign; however, occasionally, they become malignant with metastasis to the liver, regional lymph nodes, and lungs. Affected dogs are usually older, with a mean age of 11 years. Clinical signs associated with this type of tumor are often vague and intermittent, and may mimic more common disorders, such as hyperadrenocortisism, diabetes mellitus, liver disease, kidney failure, and various tumors. The signs are generally associated with catecholamine excess and high blood pressure and may include weakness, lethargy, panting, anorexia, vomiting, weight loss, anxiety, restlessness, increased thirst and urination, diarrhea, abdominal distention, hind limb swelling, nosebleeds, seizures, and sudden blindness. 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. About 15-38% of pheochromocytomas develop in the inferior vena cava, causing clinical signs of ascites, hind limb edema, and distention of epigastric veins.
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Occasionally, pheochromocytomas may be complicated by thrombosis of the vena cava, aortic thromboembolism, spontaneous rupture of the tumor, paresis due to spinal cord compression, arrhythmias, cardiac hypertrophy, arteriolar sclerosis, systemic hypertension, and hyperadrenocortisism. 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.
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.
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