Abnormalities of adrenal cortical and medullary function are important causes of hypertension in adults. Mineralocorticoid hypertension, characterized by spontaneous hypokalemia with excessive kaliuresis and low plasma renin activity, is most commonly caused by aldosterone-producing adenoma or, less frequently, by nonadenomatous adrenal hyperplasia. However, recent evidence indicates that this classification oversimplifies the pathophysiologic diversity of this syndrome. Advances in steroid biochemistry and molecular biology have improved our ability to identify patients with various forms of mineralocorticoid hypertension and also provide evidence that they are underdiagnosed. Pheochromocytomas are most commonly located in the adrenal medulla, where they may overproduce norepinephrine or epinephrine. Appropriate screening of norepinephrine, epinephrine, and their metabolites is essential because tumors that secrete epinephrine exclusively may not present with hypertension and, thus, can be overlooked. Extra-adrenal pheochromocytomas are more prevalent than previously considered and pose special problems because they may be multicentric, difficult to locate, and more likely to be malignant than are adrenal pheochromocytomas.
