SAT-172 FDG PET/CT in Benign vs. Malignant Adrenocortical Tumors

(18)F-fluorodeoxyglucose positron emission tomography computed tomography (FDG PET/CT) is frequently used for evaluation of indeterminate adrenal nodules. The objective of this study was to evaluate the diagnostic performance of FDG PET/CT in distinguishing benign adrenocortical adenomas (ACA) from adrenocortical carcinoma (ACC). We identified 139 patients in our institution who completed both FDG PET/CT and adrenal biopsy or adrenalectomy from 2001 to 2019 using the institutional Electronic Medical Record Search Engine (EMERSE). Patients with adrenal pathology revealing non-adrenocortical tumors were excluded. The imaging characteristics of ACAs were compared with ACCs. Sixteen patients with ACAs and 50 patients with ACC were identified; of the latter, 30 were excluded, because FDG PET/CT imaging was completed after adrenalectomy. The average age of the ACC vs. ACA group was 48±14 and 52±17 years, respectively, with a gender composition of 35% and 25% men, respectively. All 20 patients with ACC had FDG avid lesions, defined by imaging report and increased ratio of adrenal tumor maximum standardized uptake value (SUVmax) to hepatic parenchymal average SUV (SUVmean) of greater than 2.5. Among those with ACAs, 11 had positive, 1 had mildly positive, 3 had indeterminate, and 1 had negative FDG PET/CT findings according to the report. Ratio of adrenal SUVmax to hepatic SUVmean was greater in ACC compared to ACA (13.5 versus 1.6, respectively, p = 0.13), but did not reach statistical significance, likely due to the small sample size and unavailability of SUV ratios for all lesions. Our study identified a large number of ACAs that were deemed FDG avid but without adrenal SUVmax to hepatic SUVmean ratio of greater than 2.5. Although the sensitivity, and therefore the negative predictive value, of FDG PET/CT scan is excellent for the diagnosis of ACC, our data does not allow for the calculation of specificity. This is due to the selection bias inherent in our patient population referred for evaluation of unusual adrenal masses, and the fact that ACAs with negative FDG PET/CT often do not undergo surgery or biopsy, and therefore pathology results are not available. Despite this limitation, our findings show that calculation of the ratio of adrenal SUVmax to hepatic SUVmean, rather than lesion SUVmax alone, helps for characterization of adrenal lesions as malignant vs. benign, and that a negative FDG PET/CT is valuable in excluding ACC.