I-131 6-BETA-IODOMETHYLNORCHOLESTEROL SCINTIGRAPHY - AN ASSESSMENT OFITS ROLE IN THE INVESTIGATION OF ADRENOCORTICAL INCIDENTALOMAS

OBJECTIVE Most incidentally discovered adrenal adrenocortical adenomas . It has been suggested that I-131-6 beta-iodomethylnorcholesterol (IM C) scan could specify the degree of functional autonomy of such adenom as depending on whether they prevent contralateral adrenal tracer upta ke. Our purpose was to examine this hypothesis in a correlated scintig raphic and endocrine study. DESIGN Prospective study evaluating the pr evalence of unilateral IMC uptake (tumour uptake with no visualization of the contralateral adrenal gland) and bilateral uptake (uptake in b oth the tumoral and the contralateral adrenal glands) in patients with unilateral incidentaloma. Comparison of adrenocortical function and o f IMC scan after dexamethasone (DXM) in the two scintigraphic groups t hus defined. PATIENTS Thirty-five patients with a unilateral mass high ly suggestive of benign adrenocortical adenoma on CT scan. MEASUREMENT S The IMC scan was performed in basal conditions (baseline scan) and a fter DXM (suppression scan). Adrenocortical function assessment includ ed basal measurements of 11-deoxycortisol, 17 alpha-hydroxyprogesteron e (17-OHP), dehydroepiandrosterone sulphate (DHEAS), plasma cortisol a nd ACTH, urinary free cortisol (UFC), overnight and low-dose DXM suppr ession test, and CRH test. RESULTS The baseline scan showed 16 patient s (46%) with unilateral uptake (group A) and 19 (54%) with bilateral u ptake (group B). Patients in group A exhibited lower ACTH values at 08 00 h (P = 0.05) and higher cortisol values after an overnight DXM supp ression test (P = 0.02), than did patients in group B. In addition, 3 patients in group A failed the overnight and the low-dose DXM suppress ion tests. Adrenal masses were larger in group A than group B (P = 0.0 4) and an inverse correlation was found in the whole population betwee n tumour size and ACTH value at 0800 h (P = 0.05). On the suppression scan performed in 14 patients (7 in each group), patients in group A c ontinued to exhibit unilateral tumour uptake and bilateral uptake was suppressed in 72% of patients in group B. An adrenal mass was removed in 3 patients of group A with confirmed benign adrenocortical adenomas . In the post-surgical period, the contralateral gland was again visua lized in a baseline scan and the hormonal evaluation returned to the n ormal range. CONCLUSION Unilateral I-131-6 beta-iodomethylnorcholester ol tumour uptake is a frequent feature in benign adrenocortical adenom as. Hormonal data and scintigraphic profiles obtained after dexamethas one, as well as hormone-scintigraphic changes observed after surgery, provide evidence that unilateral uptake is related to functioning aden omas with various degrees of autononomy and suggest that the I-131-6 b eta-iodomethylnorcholesterol scan could be a valuable tool for screeni ng 'subclinical'' Cushing's adenomas.