Limited significance of asymmetric adrenal visualization on dexamethasone-suppression scintigraphy

To assess whether a single measurement of the adrenal uptake of 6 beta-[131I]-iodomethylnorcholesterol (NP-59) on constant dexamethasone suppression would allow discrimination of adenoma from normal and bilateral hyperplasia, the adrenal uptake of 6 beta-[131I]iodomethylnorcholesterol (NP-59) was determined in 50 patients with primary aldosteronism (30 adenoma, 20 hyperplasia) and in 13 with hyperandrogenism (six adenoma, seven hyperplasia). Bilateral adrenal NP-59 activity at 5 days was seen in 14 of 36 patients with adenoma (normal to adenoma ratio of greater than or equal to 0.5), whereas marked asymmetric uptake of NP-59 was seen in six of 27 patients with hyperplasia (uptake ratio of less than or equal to 0.5). Thus the level of adrenal NP-59 uptake does not alone serve to distinguish either adenoma from the normal, contralateral adrenal or the adrenal glands in bilateral hyperplasia in all cases. It appears that the pattern of adrenal imaging, early unilateral or early bilateral NP-59 activity (less than 5 days after NP-59 on 4 mg dexamethasone), best serves to separate adrenal adenoma from bilateral hyperplasia.