Characterization of hypersecreting or non-hypersecreting adrenal adenomas: comparison between iodine-131 nor-cholesterol scintigraphy and magnetic resonance imaging.

The aim of this study was to compare the results of nor-cholesterol scintigraphy and those of magnetic resonance imaging (MRI) in characterizing adrenal adenomas and differentiating between hypersecreting and non-hypersecreting lesions. We studied 41 patients (18 M and 23 F, mean age 47±15 years) with hypersecreting (n=19) or non-hypersecreting (n=22) unilateral adrenal tumors; all patients underwent iodine-131 nor-cholesterol adrenal scintigraphy and MRI studies. Pathology examinations (n=26) or follow-up data (n=15) were obtained showing 34 adenomas, 2 cysts, 1 myelolipoma, 1 pheochromocytoma, 1 carcinoma and 2 metastases. Imaging studies were qualitatively evaluated and the corresponding results were classified as true-positive, true-negative, false-positive and false-negative calculating diagnostic accuracy of each test. Imaging studies were also quantitatively assessed comparing nor-cholesterol uptake and MRI signal intensity ratios (SIRs) in hypersecreting and non-hypersecreting adenomas. The diagnostic accuracies of nor-cholesterol scintigraphy (95%) and MRI (93%) to identify adrenal adenomas were comparable; however, while a significantly (p=0.01) higher nor-cholesterol uptake was observed in hypersecreting (n=19) adenomas compared to non-hypersecreting (n=15) lesions, no significant differences in MRI SIRs were found in this comparative analysis; furthermore, no significant difference in tumor size occurred between hypersecreting and non-hypersecreting adenomas. In conclusion, adrenal scintigraphy using nor-cholesterol and MRI are both able to accurately identify cortical adenomas; in particular, while quantitative analysis of nor-cholesterol uptake is effective to differentiate between hypersecreting and non-hypersecreting adenomas, MRI SIRs evaluation is not useful for this purpose. These findings have relevant clinical implications particularly in patients with non-hypersecreting adenomas; in such patients, laboratory data are not helpful for lesion diagnosis, while imaging findings allow tumor characterization; in particular, the lower nor-cholesterol uptake observed in non-hypersecreting adenomas might reflect the normal hormone synthesis status of these lesions and, thus, regular secretion.