SAT-157 Diagnostic Performance of 18F-fluorodeoxyglucose Positron Emission Tomography in Indeterminate Adrenal Tumors

Evidence on the diagnostic performance of 18F-fluorodeoxyglucose(18FDG) positron emission tomography(PET)/CT imaging of adrenal lesions is limited. We aimed to assess the diagnostic performance of this diagnostic modality in a high risk population for adrenal malignancy using an optimal reference standard. We included 21 patients operated in our clinic during 2019 for whom 8FDG PET was performed before adrenalectomy. 3 patients with pheochromocytoma were later excluded from statistical analysis, they were sent to PET before increased urine metanephrines were received. Unenhanced abdominal CT was performed in all the patients; median size was 4,5 (2.3-10) cm and median radiodensity was 32 (-7 to 43) Hounsfield units (HU). All patients with adrenocortical carcinoma and metastasis to adrenals from other organs had radiodensity of >10 HU. Maximum standardized uptake (SUV max) was higher in malignant lesions when compared to benign lesions (median = 10,9 [5.4-29.6] vs 4.1 [2.6-7.22], respectively, P=.003). Similarly, median SUV max lesion to SUV max liver ratio (ALR) in malignant lesions was higher than in benign lesions (median = 2,18 [1.41-5.53] vs. 1.29 [0.67-2.13], respectively, P=.017).18FDG- PET/CT SUV max lesion > 6.7 diagnosed malignancy with a sensitivity of 83,3%, specificity of 91,7%. Conclusion: Noncontract CT radiodensity of ≤10 HU excludes malignancy even in a high risk population. For indeterminate adrenal lesions, given a superior specificity, 18FDG PET/CT could be considered as a second stage imaging.