Abstract
A small subgroup of primary aldosteronism due to aldosteronoma, named aldosterone-producing renin-responsive adenoma (AP-RA), has been reported to masquerade as idiopathic hyperaldosteronism (IHA) because of the responsiveness of the plasma aldosterone concentration (PAC) to upright posture (UP). We found two patients with AP-RA in 19 patients with aldosteronoma who were examined by UP stimulation and were treated surgically. In 17 patients with typical aldosterone-producing adenoma (APA), PAC decreased or increased only slightly (less than 200% of the basal level); in contrast, it increased to over 300% of the basal level in two patients with AP-RA. The two groups were comparatively studied as to their hormonal levels, adrenal computed tomography (CT) scan and histological findings in order to clarify the characteristics of AP-RA. Basal PAC was within the normal range (11.1 and 13.0ng/dl) in AP-RA but in APA it ranged from 14.8 to 58.1ng/dl with a mean of 32.3± 2.7ng/dl. The diameters of the adenoma in AP-RA were apparently smaller (6 and 9mm) than those in APA ranged from 10 to 25mm with a mean of 15.5±1.1mm. After a contrast medium was injected at CT scan, the density of the normal adrenal gland adjacent to the adenoma increased but that of the adenoma did not in APA, making a clear distinction between the adenoma and the gland. On the other hand, the density of the adenoma and gland increased to almost the same degree in AP-RA. Thus, in AP-RA it was difficult to detect adrenal tumor by CT scan because of its size and because of the response to the contrast medium. Adenomas in both groups were mainly composed of clear cells, and no histological difference was found between the two groups. In summary, AP-RA was rarely present in primary aldosteronism and should be carefully diagnosed as primary aldosteronism because of normal PAC. Its PAC increased over to 300% of the basal level. It was showed that AP-RA are difficult to distinguish from IHA not only because of the similar responsiveness of PAC to UP but also because of difficulties in detecting adrenal tumor by adrenal CT scanning.
