Aldosterone-Producing Adenomas

Abstract

Primary aldosteronism is the most common form of secondary hypertension and is present in about 8% to 10% of patients with hypertension. In primary aldosteronism, aldosterone secretion is excessive and relatively autonomous of the normal regulatory mechanisms.1,2 It was originally described by Jerome Conn from the University of Michigan3 and is thought to be due to an aldosterone-producing adenoma (APA) causing hypertension and hypokalemic alkalosis. Primary aldosteronism is now recognized to include a spectrum of disorders from unilateral APA to bilateral zona glomerulosa (ZG) hyperplasia, or idiopathic hyperaldosteronism. The diagnosis of all forms of primary aldosteronism is based on the finding of elevated levels of aldosterone and suppressed renin secretion.1 Differentiation between unilateral and bilateral aldosteronism is done by a combination of adrenal imaging (computed tomography or MRI) and bilateral adrenal sampling.1,2 Diagnosis of an APA is attractive because surgical therapy with unilateral adrenalectomy should cure the disease, and mechanistically, APA would suggest a single etiology of a benign neoplastic transformation of cells of the ZG producing aldosterone, regardless of the molecular mechanism. However, the histological characteristics of most adrenal tumors classified as APA are heterogeneous when one considers the surrounding adrenal cortex4 and include varying proportions of 4 different types of cells: clear cells with large vacuolated lipid–laden cytoplasm and central round nuclei similar to zona fasciculata cells; lipid-poor ZG-like cells; compact eosinophilic cells similar to those of the zona reticularis; and cells with cytological features of both ZG and zona fasciculata cells, designated hybrid cells.4 The lipid-laden fasciculata-like cells usually predominate, giving the tumors a characteristic golden yellow color, but some have more glomerulosa-like characteristics.4 However, the histological picture is far more complex, as most patients with APA also have hyperplasia of the rest of the adrenal ZG (40%) or hyperplastic …