Pheochromocytomas occur in 40 to 50% of patients with MEN types IIA and IIB, with the incidence increasing with age. Pheochromocytomas develop
from the catecholamine-secreting adrenal medullary cells. They are hormonally active and can present with classic signs and symptoms of excess catechol secretion: hypertension, headache, heart palpitations, anxiety, and tremulousness. Complications of unrecognized disease include malignant hypertension, stroke, myocardial infarction, and cardiac arrhythmias. There are frequent reports of sudden death in patients with known or unsuspected pheochromocytomas who have undergone unrelated surgical procedures or during childbirth.
Pheochromocytomas rarely precede the development of C-cell abnormalities in MEN type II syndrome as nearly all patients with pheochromocy-tomas have at least biochemical evidence of C-cell hyperplasia.4 Approximately 10% of MEN type II patients present with signs or symptoms of pheochromocytomas that precede those of MTC. As with the thyroid C cells, adrenal medullary cells undergo similar, predictable, morphologic changes in the development of a pheochromocytoma. Histologi-cally, the lesion progresses from diffuse hyperplasia to nodular hyperplasia, with nodules > 1 cm being defined as pheochromocytomas. In MEN type II, pheochromocytomas are often multifocal, with bilateral tumors occurring in more than half of those patients who develop pheochromocytomas. As opposed to the sporadic form of the disease, malignant and extra-adrenal pheochromocytomas are very rare within MEN type II populations. The frequency of development of pheochromocytomas varies among MEN type II kindreds, with some kindreds displaying the tumor as the dominant characteristic. In MEN type II patient populations, pheochromocy-tomas may be clinically silent in up to 60% of cases.5 However, multiple biochemical markers for this tumor exist, including epinephrine, norepinephrine, dopamine, vanillylmandelic acid, and metanephrines.
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