Key Points

• Pheochromocytomas are catecholamine-secreting neuroendocrine tumors that originate in the adrenal medulla (85% of cases) or in any sympathetic ganglion (paragangliomas).

• Hypertension, tachycardia, pallor, palpitations, diaphoresis, and anxiety are common.

• Paroxysmal hypertension often occurs, even in normotensive persons, and may result in hypertensive emergencies.

• Plasma and urine catecholamines and metanephrines are measured to diagnose pheochromocytoma.

• CT, MRI, and 123I-MIBG may be helpful for tumor localization.

Pheochromocytomas are catecholamine-secreting neuroendocrine tumors arising from chromaffin cells of neural crest origin. About 80% to 85% of pheochromocytomas originate in the adrenal medulla, and 15% to 20% are extra-adrenal (paragangliomas). Pheochromocytomas are rare tumors, with an incidence of 1 to 2 per 100,000 adults per year. Sporadic forms of pheochromocytoma are usually diagnosed in individuals age 40 to 50 years, whereas hereditary forms are diagnosed earlier, most often before age 40. The traditional "rule of 10" for pheochromocytomas (10% bilateral, 10% extra-adrenal, 10% familial, 10% malignant) is now challenged by advances in diagnosis and genetics. Hereditary pheochromocytomas occur in MEN-II, von Hippel-Lindau syndrome, neurofibromatosis type 1, and familial paragan-gliomas. Pheochromocytoma is rare in children but, when found, are often extra-adrenal, multifocal, and associated with hereditary syndromes (Lenders et al., 2005).

Clinical Presentation

Paroxysmal signs and symptoms caused by the episodic secretion of catecholamines provide clues to the diagnosis of pheochromocytoma. The presentation can vary greatly, and therefore the pheochromocytoma is often referred to as the "great mimic." Anesthesia and tumor manipulation are the most well-known stimuli to elicit a catecholaminergic crisis. Hypertension, tachycardia, pallor, palpitations, diaphoresis, headache, and feelings of panic or anxiety are common. The hypertension is often paroxysmal and may occur in patients with hypertension or in normotensive persons. The hypertensive episodes can be severe, resulting in hypertensive emergencies. Persons with paragangliomas may have normal BP or hypotension. Orthostatic hypotension (a result of hypovolemia), fever, nausea, flushing, leukocytosis, and polycythemia are less common findings. Metabolic abnormalities may be present and include hyperglycemia, lactic acidosis, and weight loss.

Laboratory Evaluation

All patients with suspected pheochromocytoma should undergo biochemical testing. Traditional tests include measurements of urinary and plasma catecholamines, urinary metanephrines (normetanephrine and metanephrine), and urinary vanillylmandelic acid (VMA). Measurement of plasma-fractionated metanephrines (normetanephrine and metanephrine) is a newer test. Plasma and urine metaneph-rine measurements are the most sensitive tests for diagnosis but do not always indicate a pheochromocytoma. Many physiologic stimuli (e.g., stress), drugs (e..g, phenoxybenza-mine, tricyclic antidepressants), and clinical conditions (e.g., hyperthyroidism, heart failure, stroke) may cause an increase in circulating catecholamines and metabolites and lead to false-positive results. The use of clonidine or glucagon to suppress catecholamine release from the sympathoadrenal system provides a dynamic pharmacologic test to distinguish increased catecholamine release due to sympathetic activation from increased release due to a pheochromocytoma.

If there is biochemical evidence for pheochromocytoma, tumor localization by CT scan of the entire abdomen (and pelvis), with and without contrast, should be performed. MRI with gadolinium has similar diagnostic sensitivity (90%-100%) and specificity (70%-80%) and is usually the preferred modality, especially for extra-adrenal lesions. Iiodine-123 metaiodobenzylguanidine (123I-MIBG) isotope scanning has increased specificity (95%-100%) over CT and MRI and is more appropriate for patients with extra-adrenal, metastatic, multifocal, or recurrent disease.

Treatment

Preoperatively phenoxybenzamine, prazosin, doxazosin, or urapidil can be used for the blockade of alpha adrenoceptors. Phenoxybenzamine is often preferred because it blocks alpha adrenoceptors noncompetitively. Alternative drugs for preoperative management are labetalol or calcium channel blockers, either alone or in combination with a-adrenergic receptor blockers. Treatment must be initiated 10 to 14 days preoperatively and is titrated until mild orthostasis (systolic BP should not fall below 90 mm Hg in standing position) is present. Blockade of beta adrenoceptors should never be initiated before blockade of alpha adrenoceptors. Laparo-scopic removal of intra- and extra-adrenal pheochromocy-tomas is the preferred surgical approach. All patients should be followed up every year for at least 10 years after surgery. BP and catecholamines should be monitored indefinitely in patients with extra-adrenal or familial pheochromocytoma to detect possible recurrence. For malignant disease, radical surgical removal is recommended, but survival remains poor (~50%). Treatment with 131I-MIBG or combination chemotherapy has shown disappointing results.

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