The diagnostic role of radionuclide imaging in evaluation of patients withnonhypersecreting adrenal masses

The aim of this study was to evaluate the role of radionuclide imaging in t he characterization of nonhypersecreting adrenal masses. Methods: A total o f 54 patients (19 men, 35 women; mean age, 50 +/- 16 y) with nonhypersecret ing unilateral adrenal tumors that had been originally detected on CT or MR I underwent adrenal scintigraphy using different radiotracers. None of the patients showed specific symptoms of adrenal hypersecretion. Screening test s for excess cortical and medullary products showed normal adrenal hormone levels. Radionuclide studies (n = 73) included I-131-norcholesterol (n = 24 ), I-131-metaiodo-benzylguanidine (MIBG) (n = 23), and F-18-FDG PET (n = 26 ) scans. Results: Histology after surgery (n = 31) or adrenal biopsy(n = 23 ) was obtained. Adrenal lesions were represented by 19 adenomas, 4 cysts, 1 myelolipoma, 1 neurinoma, 2 ganglioneuromas, 5 pheochromocytomas, 4 pseudo tumors, 6 carcinomas, 2 sarcomas, and 10 metastases (size range, 1.5- to 5- cm diameter; mean, 4.9 +/- 3.1 cm). For norcholesterol imaging, diagnostic sensitivity, specificity, and accuracy were 100%, 71%, and 92%, respectivel y; the positive predictive value (PPV) of the norcholesterol scan to charac terize an adrenal mass as an adenoma was 89%, whereas the corresponding neg ative predictive value (NPV) to rule out this type of tumor was 100%. For M IBG imaging, diagnostic sensitivity, specificity, and accuracy were 100%, 9 4%, and 96%, respectively; the PPV of the MIBG scan to characterize an adre nal mass as a medullary chromaffin tissue tumor was 83%, whereas the corres ponding NPV to rule out this type of tumor was 100%. For FDG PET, diagnosti c sensitivity, specificity, and accuracy were 100%, 100%, and 100%, respect ively; the PPV of FDG PET to characterize an adrenal mass as a malignant tu mor was 100%, whereas the corresponding NPV to rule it out was 100%. Furthe rmore, in 7 patients with malignant adrenal tumors, FDG whole-body scanning revealed extra-adrenal tumor sites (n = 29), allowing an accurate diagnosi s of the disease's stage using a single-imaging technique. Conclusion: In p atients with nonhypersecreting adrenal masses, radionuclide adrenal imaging , using specific radiopharmaceuticals such as norcholesterol, MIBG, and FDG , may provide significant functional information for tissue characterizatio n. Norcholesterol and MIBG scans are able to detect benign tumors such as a denoma and pheochromocytoma, respectively. Conversely, FDG PET allows for r ecognition of malignant adrenal lesions. Therefore, adrenal scintigraphy is recommended for tumor diagnosis and, hence, for appropriate treatment plan ning, particularly when CT or MRI findings are inconclusive for lesion char acterization.