A case of unilateral adrenal hyperplasia being difficult to distinguish from aldosterone-producing adenoma.

Unilateral adrenal hyperplasia (UAH) is very rare, and shows similar endocrine features to aldosterone-producing adenoma (APA). We report a case of UAH diagnosed preoperatively as APA. Pathological analysis showed that the adrenal mass did not contradict a diagnosis of APA. However, in situ hybridization and real-time PCR indicated that the hyperplastic zona glomerulosa cells rather than the adenoma cells demonstrated intense mRNA expression of steroidogenic enzymes necessary for production of aldosterone. UAH is believed to account for less than 1% of primary aldosteronism, but it is possible that some cases of UAH may be mistakenly considered to be APA, and that the actual frequency of UAH may thus be higher than presumed. Recently, partial adrenalectomy has been attempted. It should be borne in mind that cases exist in which it is difficult to differentiate between APA and UAH only by preoperative hormonal and radiologic investigations.