Risk stratification of adrenal masses by [¹⁸ F]FDG PET/CT: Changing tactics

[¹⁸ F]FDG PET/CT improves adrenal tumour characterization. However, there is still no consensus regarding the optimal imaging biomarkers of malignancy.

To assess the performance of Tumour standardized uptake value (SUV)_max :Liver SUV_max for malignancy-risk and to build and evaluate a prediction model.

The cohort consisted of consecutive patients with adrenal masses evaluated by [¹⁸ F]FDG PET/CT. The gold standard for malignancy was based on histology or a multidisciplinary consensus in nonoperated cases. The performance of the previously reported cut-off for Tumour SUV_max :Liver SUV_max (>1.5) was evaluated in this independent cohort. Additionally, a predictive model of malignancy was built from the training cohort (previous study) and evaluated in the validation cohort (current study).

Sixty-four patients were evaluated; 28% of them had a Cushing's syndrome. Fifty-four adrenal masses were classified as benign and 10 as malignant (including 7 adrenocortical carcinomas). Compared to benign masses, malignant lesions were larger in size, had higher unenhanced densities and higher [¹⁸ F]FDG uptake. CT-derived anthropometric parameters did not differ between benign and malignant masses. A tumour SUV_max :Liver SUV_max  > 1.5 showed a good diagnostic performance: Se = 90.0%/Sp = 92.6%/PPV = 69.2%/NPV = 98.0% and accuracy = 92.2%. A predictive model based on tumour size and tumour-to-liver uptake SUV_max ratio for malignancy-risk was validated and provides a complementary approach to the ratio.

Tumour SUV_max :Liver SUV_max uptake ratio is a useful biomarker for diagnosis of adrenal masses. Another tactic would be to calculate with the model an individual risk of malignancy and integrate this information into a shared decision-making process.