I-131 nor-cholesterol nuclear imaging in patients with hypersecreting or non-hypersecreting adrenal adenomas.

Background. The aim of this study was to evaluate the diagnostic accuracy of nor-cholesterol radionuclide imaging in patients with adrenal tumors detected by CT or MR imaging studies. Methods. 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. Pathology examinations (n=26) or CT follow-up studies (n=15) were obtained. Adrenal lesions were represented by 34 adenomas, 2 cysts, 1 myelolipoma, 1 pheochromocytoma, 1 carcinoma and 2 metastases. Radionuclide studies were qualitatively evaluated and the corresponding results were classified as true-positive (TP), true-negative, false-positive (FP) and false-negative. Diagnostic sensitivity, specificity and accuracy as well as positive (PPV) and negative (NPV) predictive values were calculated. In addition, nor-cholesterol uptake was semi-quantitatively compared between hypersecreting and non-hypersecreting adenomas using a four-point scoring. Results. The diagnostic values of nor-cholesterol scintigraphy to identify adrenal adenomas were: sensitivity 100%, specificity 71%, accuracy 95%, PPV 94% and NPV 100%; of note, 2 FP cases were observed represented by a pheochromocytoma and a myelolipoma, while no FN findings occurred. A significantly (p=0.01) higher nor-cholesterol uptake was observed in hypersecreting (n=19) adenomas compared to non-hypersecreting (n=15) lesions; however, no significant difference in tumor size was found in this comparative analysis. Conclusion. In the large majority of cases, adrenal scintigraphy using nor-cholesterol was able to characterize specific lesions as cortical adenomas. These findings show relevant clinical impact particularly in patients with non-hypersecreting adenomas; in this setting, laboratory data are not helpful for lesions characterization, while radionuclide abnormalities allow tumor-type identification. However, rare as well as unusual findings of adrenal scintigraphy may be observed since nor-cholesterol uptake was also found in two non-adenoma tumors (a myelolipoma and a pheochromocytoma). Finally, the lower nor-cholesterol uptake of non-hypersecreting adenomas might suggest a normal hormone synthesis of these lesions and, thus, regular secretion.