PHEOCHROMOCYTOMAS ARE pharmacologically volatile, potentially lethal catecholamine-containing tumors of chromaffin tissue.1 They are usually found in the adrenal medulla, but they may occur wherever chromaffin tissue is located. Chromaffin cells are associated with the celiac, mesenteric, renal, adrenal, hypogastric, testicular, and paravertebral sympathetic nerve plexus. The major sites where pheochromocytomas occur are the adrenal medulla (90%), the paraganglia cells of the sympathetic nervous system, and the organ of Zuckerkandl.2 Approximately 10% of sporadic and 50% of familial adrenal tumors are bilateral, and approximately 10% of pheochromocytomas are multiple in location at the time of presentation.3 Paragangliomas are derived from neural crest cells that migrate in close association with autonomic ganglion cells, and all paragangliomas have the capacity to secrete catecholamines.4,5 Functional paragangliomas that secrete norepinephrine can occur and present similarly to pheochromocytoma. The proportion of catecholamine-secreting paragangliomas is thought to be high for adrenal pheochromocytomas, intermediate for aorticosympathetic and visceroautonomic tumors, and low for paragangliomas of the head and neck, also known as glomus tumors.5 Paragangliomas may present as painless swellings in the neck overlying the carotid bifurcation. These are also called carotid body tumors or chemodectomas.5 Of paragangliomas, 10% are malignant, but they can be locally invasive and can cause cranial nerve palsies.4 The resection of a pheochromocytoma or biochemically active paraganglioma has great potential for intraoperative and postoperative complications owing to release of catecholamines during manipulation of the tumor. Significant hemodynamic and metabolic effects are associated with a sudden decrease in catecholamine levels after removal of a tumor.6 In a series of 138 patients undergoing resection of pheochromocytoma tumors in a variety of anatomic locations between 1926 and 1970, surgical mortality was 2.9%.7 Desmonts et al8 reported a 3.9% mortality rate in their series of 102 patients between 1964 and 1976. A more recent series of 143 patients who underwent pheochromocytoma or paraganglioma resection showed no mortality and the absence of perioperative myocardial infarctions or cerebrovascular accidents.9 Advances in localization techniques, medical management, and anesthetic management have resulted in improved surgical outcomes.10 PRESENTATION