Few prospective studies have evaluated the role of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) in the characterization of adrenal masses.

To assess the performance of ¹⁸F-FDG PET/CT in the malignancy diagnosis of adrenal masses in noncancer patients.

Prospective multicenter study.

The study population consisted of 87 patients (87 adrenal masses) referred to endocrine surgeons: 56 with mass diameter ≥40 mm and 31 with a diameter <40 mm and of indeterminate nature based on unenhanced and washout CT attenuation densities. Fourteen patients had hypercortisolism. Adrenal masses were characterized by ¹⁸F-FDG PET/CT. Histology was the gold standard for the diagnosis of malignancy. In the absence of pathological proof (n = 23), the nature of the lesion was based on the 12-month imaging follow-up.

Fifteen adrenal masses were classified as malignant (including 11 adrenocortical carcinomas) and 72 as benign. Compared with benign lesions, malignant lesions were larger in size (P = 0.003), had higher unenhanced densities (P = 0.002), lower relative washout values (P = 0.007), and higher ¹⁸F-FDG uptake parameters (P < 10⁻³). The optimal threshold value of (Tumor SUV_max:Liver SUV_max) the ratio for malignancy was >1.5 with sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 86.7%, 86.1%, 56.5%, 96.9%, and 86.2%, respectively.

Our results show that ¹⁸F-FDG PET/CT complements adrenal washout CT in the evaluation of adrenal masses and should be recommended in the evaluation of large and/or indeterminate adrenal masses.