A 34-year-old man complains of sudden attacks of dizziness, blurred vision, and excruciating headaches of 4 months in duration. During one of these attacks, his blood pressure was 180/120 mm Hg. The patient's father had been treated for thyroid cancer about 15 years ago. Laboratory studies show normal serum levels of aldosterone, renin, and angiotensin. A 24-hour urinalysis reveals increased metanephrines. Episodic hypertension in this patient is most likely caused by a tumor in which of the following endocrine organs?

Pheochromocytoma is a rare tumor of chromaffin cells of the adrenal medulla thatsecretes catecholamines. Such tumors also originate in extra-adrenal sites, in which case they are termed paragangliomas. The clinical features associated with pheochromocytoma are caused by the release of catecholamines. Patients with pheochromocytoma come to medical attention because of (1) asymptomatic hypertension discovered on a routine physical examination, (2) symptomatic hypertension that is resistant to antihypertensive therapy; (3) malignant hypertension (e.g., encephalopathy, papilledema, proteinuria), (4) myocardial infarction or aortic dissection, or (5) convulsions. The other choices do not include tumors that lead to episodic hypertension.Diagnosis: Pheochromocytoma