Most pheochromocytomas are located in the adrenal glands (90% in adults and 70% in children), occurring more frequently on the right than on the left. In one series, right-sided pheochromocytomas have been described as producing paroxysmal hypertension more often than sustained hypertension, whereas the opposite is true for tumors arising from the left adrenal gland.18 Adrenal pheochromocytomas are bilateral in about 10% of adults and 35% of children. They may present at any age but are more common in the fourth and fifth decades.
In familial cases, pheochromocytomas typically are discovered at an earlier age, and about 70% of adrenal pheochromocytomas are bilateral when discovered; extra-adrenal paragangliomas are often also present concomitantly. Eventually, in familial cases, nearly all patients will develop bilateral pheochromocytomas or medullary hyperplasia.15
Most sporadic pheochromocytomas are circumscribed and encapsulated by either a true capsule or a pseudocapsule of the adrenal capsule. At surgery, pheochromocytomas are firm in texture. They are often opaque, with yellow areas of remaining adrenal cortex and brown areas of periadrenal fat. Hemorrhages within the tumor may impart a mottled or dark red appearance. Larger tumors frequently have large areas of hemorrhagic necrosis that undergo cystic degeneration (see Figure 9-1). Viable tumor may be found in the cyst wall. Calcification may be present. Pheochromocytomas may rarely invade adjacent tissue or the adrenal vein, extending into the vena cava and resulting in pulmonary emboli.2 Pheochromocytomas vary enor mously in size, ranging from microscopic to 3,600 g. The "average" pheochromocytoma weighs 100 g and is 4.5 cm in diameter.
Paragangliomas (extra-adrenal pheochromocy-tomas) account for about 10% of pheochromocytomas in adults and about 30% in children. These tumors arise from sympathetic ganglia. About 85% are intraabdominal, where they are typically located in the juxtarenal or para-aortic region, particularly in the perinephric, periaortic, and bladder regions. Retroperitoneal paragangliomas are more likely to be malignant (30 to 50%) and present with pain or a mass15; about 36% of such tumors are functional. Functional status is not known to affect survival.30 Nonfunctional paragangliomas frequently concentrate metaiodobenzyl-guanidine (MIBG) or cause increased serum levels of chromogranin A. Paragangliomas of the bladder cause symptoms on micturition. Large perinephric tumors can cause renal artery stenosis. Vaginal tumors can cause dysfunctional vaginal bleeding.
Paragangliomas may also arise in the anterior or posterior mediastinum or the heart.31 Central nervous system locations include the sella turcica, petrous ridge, and pineal region; cauda equina paragan-glioma can cause increased intracranial pressure.32 Nonchromaffin paragangliomas of neuroectodermal chemoreceptors are known as chemodectomas or glomus tumors; they are typically found in the head and neck, particularly near the carotid body, glomus jugulare, or jugulotympanic region or in the lung. Chemodectomas rarely secrete catecholamines.33
Carney's triad generally presents in women under age 40. It consists of the triad of multicentric para-
gangliomas, indolent gastric leiomyosarcomas, and pulmonary chondromas.
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