Quantitative imaging characterization of hypersecreting or nonhypersecreting adrenal adenomas: comparison between iodine-131 norcholesterol uptake and magnetic resonance signal intensity ratios.

Objective: To compare nor-cholesterol (nor-Chol) uptake and magnetic resonance (MR) signal intensity ratios (SIRs) in characterizing adrenal adenomas to differentiate hypersecreting from non-hypersecreting lesions. Methods: We studied 34 patients (14 M and 20 F, mean age 47±15 years) with hypersecreting (n=19) or non-hypersecreting (n=15) adrenal adenomas; all patients underwent iodine-131 nor-Chol scintigraphy and MR studies. Pathology (n=26) or follow-up data (n=8) were obtained. Imaging studies were qualitatively evaluated to calculate diagnostic accuracy of each test; radionuclide studies were also semi-quantitatively evaluated using a 4-point score to measure nor-Chol uptake, while MR scans were quantitatively assessed measuring SIRs of adrenal lesions; imaging data were then compared between hypersecreting and non-hypersecreting adenomas. Results: The diagnostic accuracies of nor-chol (100%) and MR (95%) scans to identify adrenal adenomas were similar; however, while a significantly (p=0.01) higher nor-chol uptake was observed in hypersecreting (2.8+0.5) adenomas compared to non-hypersecreting (2.2+0.6) lesions, no significant differences in SIRs were found in this comparative analysis; in this regard, no significant difference in tumor size (cm) occurred between hypersecreting (2.7+0.5) and non-hypersecreting (3.1+0.9) adenomas. Conclusion: Adrenal scintigraphy using nor-chol and MR are both able to accurately identify cortical adenomas; however, while semi-quantitative analysis of nor-chol uptake is effective to differentiate between hypersecreting and non-hypersecreting adenomas, SIRs evaluation is not useful for this purpose; in particular, the lower nor-chol uptake observed in non-hypersecreting adenomas might reflect the normal hormone synthesis status of these lesions and, thus, regular secretion; this finding could also reflect initial adrenal dysfunction responsible of sub-clinical disorders.