Prior studies have suggested that 18F-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 18F-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 18F-FDG PET/CT (60 min after injection 300 – 370 MBq 18F-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 18F-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.