Adrenal masses: the value of additional fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) in differentiating between benign and malignant lesions

Objective  To investigate whether integrated fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) can differentiate benign from adrenal malignant lesions on the basis of maximum standardized uptake value (SUV_max), tumor/liver (T/L) SUV_max ratio, and CT attenuation value (Hounsfield Units; HU) of unenhanced CT obtained from FDG-PET/CT data. Methods  We studied 30 patients with 35 adrenal lesions (16 adrenal benign lesions, size 16 ± 5 mm, in 15 patients; and 19 adrenal malignant lesions, 24 ± 12 mm, in 15 patients) who had confirmed primary malignancies (lung cancer in 23 patients, lymphoma in 2, esophageal cancer in 2, hypopharyngeal cancer in 1, prostate cancer in 1, and 1 patient in whom lesions were detected at cancer screening). All patients underwent PET/CT at 1 h post FDG injection. Diagnosis of adrenal malignant lesions was based on interval growth or reduction after chemotherapy. An adrenal mass that remained unchanged for over 1 year was the standard used to diagnose adrenal benign lesions. Values of FDG uptake and CT attenuation were measured by placing volumetric regions of interest over PET/CT images. Adrenal uptake of SUV_max ≥ 2.5 was considered to indicate a malignant lesion; SUV_max < 2.5 was considered to indicate a benign lesion. In further analysis, 1.8 was employed as the threshold for the T/L SUV_max ratio. Unenhanced CT obtained from PET/CT data was considered positive for adrenal malignant lesions based on a CT attenuation value ≥ 10 HU; lesions with a value < 10 HU were considered adrenal benign lesions. Mann–Whitney’s U test was used for statistical analyses. Results  SUV_max in adrenal malignant lesions (7.4 ± 3.5) was higher than that in adrenal benign lesions (2.1 ± 0.5, p < 0.05). The CT attenuation value of adrenal malignant lesions (27.6 ± 11.9 HU) was higher than that of adrenal benign lesions (10.1 ± 12.3 HU, p < 0.05). In differentiating between adrenal benign and malignant lesions, a CT threshold of 10 HU corresponded to a sensitivity of 57%, specificity of 94%, accuracy of 74%, positive predictive value of 92% and negative predictive value of 65%. An SUV_max cut-off value of 2.5 corresponded to a sensitivity of 89%, specificity of 94%, accuracy of 91%, positive predictive value of 94% and negative predictive value of 88%. The T/L SUV_max ratio was 1.0 ± 0.2 for adrenal benign lesions and 4.5 ± 3.0 for adrenal malignant lesions. And T/L SUV_max ratio cut-off value of 1.8 corresponded to a sensitivity of 85%, specificity of 100%, accuracy of 91%, positive predictive value of 100% and negative predictive value of 83%. Conclusions  FDG-PET/CT with additional SUV_max analysis improves the diagnostic accuracy of adrenal lesions in cancer patients.