Nuclear imaging to characterize adrenal tumors: Comparison with MRI

To describe the role of nuclear imaging modalities using nor-cholesterol, metaiodobenzylguanidine (MIBG) and fluorine-deoxy-glucose (FDG) in adrenal tumors for lesion characterization in comparison with magnetic resonance (MR).

Population was classified in group 1 consisting of 30 patients with non-hypersecreting unilateral adrenal masses, in group 2 consisting of 34 patients with hypersecreting (n = 19) or non-hypersecreting (n = 15) adrenal adenomas and in group 3 consisting of 18 patients with chromaffin-tissue tumors (CTT), of which 14 were pheochromocytomas while 4 were paragangliomas (n = 4). All patients underwent MR and nuclear studies (nor-cholesterol, MIBG and FDG). Pathology samples (n = 63) or follow-up data in adenomas (n = 19) were used as standard of reference for imaging studies interpretation.

In group 1, MR findings were not highly accurate for lesion characterization, while the results of nuclear scans showed abnormal nor-cholesterol, MIBG and FDG concentration in all cases of adenomas, pheos and malignant tumors, respectively. In group 2, no differences in MR parameters were found between hyperfunctioning and non-hyperfunctioning adenomas, while nor-cholesterol uptake was significantly higher in hyperfunctioning compared to non-hyperfunctioning lesions. In group 3, no differences in MR parameters were found between benign and malignant CCT, while MIBG uptake was significantly higher in malignant compared to benign tumors.

On the basis of our findings, nuclear imaging modalities using specific target agents are able to better characterize adrenal tumors, compared with MR. In particular, radionuclide techniques are able to identify the nature of adrenal incidentalomas and to differentiate between hypersecreting and non-hypersecreting adenomas as well as between benign and malignant CTT.