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

Objective: To compare norcholesterol uptake and magnetic resonance (MR) signal intensity ratios (SIRs) in characterizing adrenal adenomas to differentiate hypersecreting from nonhypersecreting lesions. Methods: We studied 34 patients (14 males and 20 females, mean age: 47±15 years) with hypersecreting (n=19) or nonhypersecreting (n=15) adrenal adenomas; all patients underwent iodine-131 norcholesterol 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 semiquantitatively evaluated using a four-point score to measure norcholesterol uptake, whereas MR scans were quantitatively assessed for measuring SIRs of adrenal lesions. Imaging data were then compared between hypersecreting and nonhypersecreting adenomas. Results: The diagnostic accuracies of norcholesterol (100%) and MR (95%) scans to identify adrenal adenomas were similar; however, while a significantly (P=0.01) higher norcholesterol uptake was observed in hypersecreting (2.8±0.5 cm) adenomas compared with nonhypersecreting (2.28±0.6 cm) lesions, no significant differences in SIRs were found in this comparative analysis; in this regard, no significant difference in tumor size (centimeter) occurred between hypersecreting (2.7±0.5 cm) and nonhypersecreting (3.1±0.9 cm) adenomas. Conclusion: Adrenal scintigraphy using norcholesterol and MR are both able to accurately identify cortical adenomas; however, while semiquantitative analysis of norcholesterol uptake is effective to differentiate between hypersecreting and nonhypersecreting adenomas, SIRs evaluation is not useful for this purpose; in particular, the lower norcholesterol uptake observed in nonhypersecreting adenomas might reflect the normal hormone synthesis status of these lesions and, thus, regular secretion; this finding could also reflect initial adrenal dysfunction responsible for subclinical disorders.