Takao Obara, MD ■ Yukio Ito, MD ■ Masatoshi Iihara, MD

Hyperaldosteronism occurs in primary and secondary forms. In this chapter, we describe the characteristic features of primary hyperaldosteronism and discuss the rational surgical management of this disorder. Primary hyperaldosteronism is characterized by excessive secretion of aldosterone from the adrenal gland associated with suppression of plasma renin activity (PRA), which usually results in hypertension and hypokalemia. Conn first described this syndrome in 1954.1 Primary hyperaldosteronism is an uncommon but potentially curable cause of hypertension. The development of simplified testing and improvement of localization studies have allowed this condition to be diagnosed accurately and the tumor removed more precisely. Nevertheless, the most appropriate diagnostic approach for selecting surgically curable forms of primary hyperaldosteronism remains a matter of controversy.

There are several subtypes of primary hyperaldosteronism. Aldosterone-producing adrenocortical adenoma and idiopathic hyperaldosteronism (bilateral adrenal hyperplasia) are the two most common subsets and account for 95% of all cases.2'3 An aldosterone-producing adenoma is usually treated by unilateral adrenalectomy, whereas idiopathic hyperaldosteronism does not respond to surgical treatment and is best managed medically. Uncommon forms of primary hyperaldosteronism include primary adrenal hyperplasia,4,5 aldosterone-producing carcinoma,6,7 and glucocorticoid-suppressible hyperaldosteronism.8,9 Primary adrenal hyperplasia is morphologically similar to idiopathic hyperaldosteronism but mimics aldosterone-producing adenoma in response to biochemical tests and unilateral adrenalectomy. Glucocorticoid-suppressible aldosteronism (familial hyperaldosteronism type 1) is familially inherited in an autosomal fashion and is caused by the presence of a chimeric gene, consisting of the regulatory region of a gene coding for the enzyme 1 l(3-hydroxylase (CYP11B1), adrenocorti-cotropin (ACTH), and the coding region of the gene for aldosterone synthesis (CYP11B2).8 Hence, aldosterone synthesis is primarily regulated by ACTH, resulting in excessive aldosterone production. This condition can be controlled by glucocorticoid administration. Familial hyperaldosteronism type 2 refers to the familial occurrence of aldosterone-producing adenoma, adrenal hyperplasia, or both.1011 The appropriate treatment of primary hyperaldosteronism depends on the correct differential diagnosis of these subtypes.

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