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.