Diagnostic performance of unenhanced computed tomography and 18 F-fluorodeoxyglucose positron emission tomography in indeterminate adrenal tumours.

Abstract

Evidence on the diagnostic performance of adrenal imaging is limited. We aimed to assess the diagnostic performance of unenhanced computed tomography (CT) and 18 F-fluorodeoxyglucose (18 FDG) positron emission tomography (PET)/CT imaging in a high-risk population for adrenal malignancy using an optimal reference standard. Retrospective cohort study. Imaging studies of patients with adrenal nodules who underwent adrenal biopsy and/or adrenalectomy between 1994 and 2014 were reviewed and compared to the reference standard of histology. Eighty % of patients presented with known or suspected extra-adrenal malignancy. Unenhanced abdominal CT was performed in 353 patients with adrenal lesions; median size was 3 (0.7-15) cm and median radiodensity was 33 (-21-78) Hounsfield units (HU). Radiodensity of >10HU diagnosed malignancy with a sensitivity of 100%, specificity of 33%, positive predictive value (PPV) of 72% and negative predictive value (NPV) of 100%. 18 FDG-PET/CT was performed in 89 patients; median tumour size was 2.1 (0.7-9.2) cm. Maximum standardized uptake (SUV max) was higher in malignant lesions when compared to benign lesions (median=10 [2.3-29.4] vs 3.7 [1.4-24.5], respectively, P<.0001). Similarly, median SUV max lesion to SUV max liver ratio (ALR) in malignant lesions was higher than in benign lesions (median=3 [0.74-13.4] vs 1.2 [0.5-6.6], respectively, P<.0001). 18 FDG-PET/CT ALR >1.8 diagnosed malignancy with a sensitivity of 87%, specificity of 84%, PPV of 85% and NPV of 86%. Noncontract CT radiodensity of ≤10HU excludes malignancy even in a high-risk population. For indeterminate adrenal lesions, given a superior specificity, 18 FDG-PET/CT could be considered as a second stage imaging study.