Design and methodsWe have recently demonstrated that the adrenal cortices attached to aldosterone-producing adenoma (APA) contained microscopic subcapsular micronodules suggestive of active aldosterone production. In this study, we usedin situhybridization to investigate the mRNA expression of steroidogenic enzymes in the adrenal cortices attached to cortisol-producing adenoma (CPA) and clinically silent adenoma (non-functioning adenoma; NFA), in addition to APA.ResultsMicroscopic subcapsular micronodules, which were several hundreds of micrometers in size and spheroid in shape, were observed in the cortices attached to CPA and NFA, as well as APA, at high frequency. Most of the cortical nodules in zona fasciculata to zona reticularis showed a suppressed steroidogenesis in the cortices attached to adenoma, but some expressed intensely all necessary steroidogenic enzyme mRNAs for cortisol synthesis.ConclusionsIt is thus necessary to keep in mind, on the occasion of subtotal adrenalectomy, that lesions with the potential to later develop into functional adrenocortical nodules may be present in other parts of the ipsilateral or contralateral adrenal cortices.