The value of scintigraphy and computed tomography for the differential diagnosis of primary hyperaldosteronism

Adrenocortical adenoma is the most common cause of primary hyperaldosteronism. Most tumours are small, less than 2 cm in diameter and, therefore, their localization may be difficult. We have compared two different methods, adrenal scintigraphy (AS) and computed tomography (CT) in the differential diagnosis of 12 patients with primary hyperaldosteronism. AS was performed using either [131I]cholesterol or 6-iodomethyl-19-norcholesterol during dexamethasone suppression. Of the patients, five showed a normal CT and symmetrical uptake of the isotope as AS. They were considered representative of bilateral hyperplasia. All showed good therapeutic response to spironolactone. Seven patients had an adrenocortical adenoma verified at operation. The CT finding indicated a tumour in five patients. This was correct in four, but in one patient the adenoma was found in the contralateral adrenal gland. In two patients with an adenoma, CT was considered normal. AS correctly indicated the tumour in all seven patients. The uptake was unilateral in six, and bilateral but clearly asymmetrical in one patient. The results indicate that AS is superior to CT in the pre-operative localization of aldosteroma. Although CT remains the primary method for the investigation of these patients, AS should be applied always when CT does not unequivocally indicate the presence and localization of an adrenal tumour.