Pheochromocytoma

Biochemical screening for pheochromocytoma is best done by measurement of plasma or 24-hour urine catecholamines and metanephrines. This test should be done on an annual basis. If this test is negative, no further workup is necessary until the next year. If the test is positive or borderline, imaging is needed to determine if a pheochromocytoma is present. Almost all patients with MEN types IIA and

Figure 17-8. Adrenal computed tomographic scan showing a large left adrenal pheochromocytoma in a patient with multiple endocrine neoplasia type IIA.

Figure 17-8. Adrenal computed tomographic scan showing a large left adrenal pheochromocytoma in a patient with multiple endocrine neoplasia type IIA.

IIB have some degree of adrenal medullary hyper-plasia and may have borderline elevations of urinary catechols without a definite pheochromocytoma.

Adrenal computed tomography (CT) or magnetic resonance imaging (MRI) can detect tumors 1 cm or larger (Figure 17-8). Opposed-phase chemical shift MRI may distinguish a pheochromocytoma from an adrenal adenoma, which occurs in up to 9% of normal patients.17 Radioactive iodine (131I)-metaiodobenzyl-guanidine scanning is useful in detecting extra-adrenal pheochromocytomas, although extra-adrenal tumors are extremely rare in patients with MEN types IIA and IIB.

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