Differentiating adrenal adenomas from nonadenomas using 18F-FDG PET/CT:: Quantitative and qualitative evaluation

Rationale and Objectives. We sought to assess the ability of F-18-fluoro-2-deoxy-D-glucose (FDG) PET/CT to distinguish adrenal adenomas from nonadenomas in patients with suspected malignancy. Methods. Fifty-nine adrenal masses were evaluated with coregistered F-18-FDG PET (PET/CT). Two reviewers independently graded uptake of F-18-FDG by visual inspection of the adrenal mass in comparison to liver and background. CT attenuation value of the adrenal mass and the standardized uptake value (SUV) of the mass, liver, background, and primary neoplasm (when visible) were measured. Mean SUVs of the adrenal mass, liver, and background and ratios of the SUVs were calculated. Results. Of 47 adenomas, 43 measured < 10 HU on unenhanced CT. Of 12, 12 nonadenomas measured > 10 HU on unenhanced CT. Using qualitative assessment of FDG activity in the adrenal mass compared with liver, adenomas were less than, equal to, or more active than the liver in 51%, 38%, and 10%, respectively. Nonadenomas were less than, equal to, or more active than liver in 0%, 25%, and 75%, respectively. The mean SUV of adenomas (4.2) was significantly lower (P =.002) than that of their primary malignancies (9.2) but not that of liver (4.3). The mean SUV of adenomas was not significantly different than that of nonadenomas (5.2), but the mean adrenal/liver ratio (1.0) for the adenomas was significantly lower (P =.006) than that of the nonadenomas (2.1). Conclusion. Adrenal adenomas were better differentiated from nonadenomas using unenhanced CT measurements in combination with ratios of the SUVs. Adrenal mass activity, which was visibly less than liver, was more specific for adenoma, whereas adrenal mass activity visibly greater than liver was more specific for malignancy.