What parameters from 18F-FDG PET/CT are useful in evaluation of adrenal lesions?

Prior studies have suggested that F-18-FDG PET/CT can help characterize adrenal lesions and differentiate adrenal metastases from benign lesions. The aim of this study was to assess the value of F-18-FDG PET/CT for the differentiation of malignant from benign adrenal lesions. This retrospective study included 85 patients (47 men and 38 women, age 63.8 +/- 10.8 years) who had undergone F-18-FDG PET/CT (60 min after injection 300 - 370 MBq F-18-FDG; Biograph 64 scanner) for evaluation of 102 nonsecreting adrenal masses. For semiquantitative analysis, the maximum standardized uptake value (SUVmax), adrenal to liver (T/L) SUVmax ratio, mean CT attenuation value and tumour diameter were measured in all lesions and compared with the pathological findings. Malignant adrenal tumours (68 % of evaluated tumours) had a significantly higher mean SUVmax (13.0 +/- 7.1 vs. 3.7 +/- 3.0), a higher T/L SUVmax ratio (4.2 +/- 2.6 vs. 1.0 +/- 0.9), a higher CT attenuation value (31.9 +/- 16. 7 HU vs. 0.2 +/- 25.8 HU) and a greater diameter (43.6 +/- 23.7 mm vs. 25.6 +/- 13.3 mm) than benign lesions. The false-positive findings were tuberculosis and benign phaeochromocytoma. Based on ROC analysis, a T/L SUVmax ratio > 1.53, an adrenal SUVmax > 5.2, an attenuation value > 24 HU and a tumour diameter > 30 mm were chosen as the optimal cut-off values for differentiating malignant from benign tumours. The areas under the ROC curves for the selected cut-off values were 0.96, 0.96, 0.88 and 0.77, respectively. A multivariate logistic regression model revealed that the T/L SUVmax ratio was an independent prognostic factor for malignancy (p < 0.001); a CT attenuation value of > 25 HU and a tumour diameter > 30 mm had no additional individual importance in the diagnosis of malignancy. Using a T/L SUVmax ratio > 1.53 and an adrenal SUVmax > 5.2 in F-18-FDG PET/CT led to high diagnostic sensitivity, specificity and negative predictive value for characterizing adrenal tumours. The diagnostic accuracies of the two parameters were comparable, but T/L SUVmax ratio was an independent predictor of malignancy.