Pheochromocytomas in Animals

Pheochromocytomas arise from the adrenal medullary chromaffin cells that normally synthesize and secrete the catecholamines epinephrine and norepinephrine.

Pheochromocytomas have been identified more often in dogs (uncommon) than in cats (rare), usually affect only one gland, and tend to occur in older animals. There is no breed predilection. Males may be overrepresented.

Pheochromocytomas are often locally invasive (may result in thrombus formation in the adjacent vena cava) and metastasize in ≥ 25% of cases. Extra-adrenal sites for related tumors (paragangliomas) have been reported in other tissues, including the heart.

Clinical signs of pheochromocytomas are nonspecific and may appear sporadically, possibly related to periodic or intermittent release of catecholamines. In addition, clinical signs may vary depending on which catecholamine predominates.

Clinical signs reported in most dogs include the following:

Dyspnea and tachycardia may occur, and hypertension is common.

Diagnosis of pheochromocytoma is challenging.

Indirect blood pressure measurement can help establish the diagnosis.

Diagnostic imaging modalities such as ultrasonography Ultrasonography in Animals Ultrasonography is the second most commonly used imaging format in veterinary practice. It uses ultrasonic sound waves in the frequency range of 1.5–15 megahertz (MHz) to create images of body... read more and CT are very useful in confirming a suspected adrenal mass. In any patient with a suspected adrenal tumor, thoracic radiography is recommended for detection of pulmonary metastases.

The much more common adrenal disorder hyperadrenocorticism Cushing Disease (Pituitary-dependent Hyperadrenocorticism) in Animals Cushing disease is hyperadrenocorticism caused by an ACTH-secreting tumor of the pituitary gland. Clinical signs include polyuria, polydipsia, alopecia, and muscle weakness. A low-dose dexamethasone... read more should be included as a differential diagnosis when an adrenal mass is identified. Other differential diagnoses for adrenal nodules and masses include adrenal cortical adenoma or adenocarcinoma, metastasis, and adrenal hyperplasia.

Immunohistochemical staining for chromogranin A can distinguish pheochromocytomas from adrenocortical tumors.

Although surgical removal is the treatment of choice, patients with pheochromocytoma have increased anesthetic risk secondary to the cardiovascular effects of the catecholamines. Surgery is further complicated by the tendency toward local invasion of these tumors and their proximity to large vessels.

The tyrosine kinase inhibitor toceranib phosphate may be useful in the treatment of nonresectable pheochromocytoma. 1 Reference Pheochromocytomas are rare tumors that originate from the adrenal medulla. They have been most commonly reported in dogs, horses, and cattle. Clinical signs associated with pheochromocytomas... read more

Note: toceranib phosphate has also been suggested as a potential treatment for other neuroendocrine tumors, including thyroid carcinoma, insulinoma, and chemodectoma.

Pretreatment with phenoxybenzamine (a noncompetitive alpha adrenergic receptor antagonist) for 1–2 weeks before surgery improves the perioperative mortality rate.

Dogs without metastatic disease have a good longterm prognosis.