Malignancy Risk Stratification in FDG-PET Avid Adrenal Lesions: Diagnostic Utility and Predictive Factors

Fluorodeoxyglucose positron emission tomography (^18FFDG PET) aids in assessing adrenal lesions, but variability in reporting and wide diagnostic standardised uptake value maximum (SUVmax) ranges hinder routine use. This study aimed to identify the utility of FDG_PET in guiding malignancy risk stratification and define diagnostic thresholds for FDG-avid adrenal lesions.

A multi-centre retrospective cohort study of adrenalectomies (2006-2024) was conducted. Of 1136 adrenalectomies, 138 had pre-operative FDG-PET. Clinicopathological and imaging data were reviewed. Imaging parameters, including unenhanced Hounsfield units (HU), SUVmax, SUVmean and total lesion glycolysis (TLG), were independently and blindly re-reported.

One hundred and four cases were included (53.8% male, median age 65, median lesion size 40 mm). Malignancy was confirmed in 65.4%. Mean SUVmax was 10.6 for malignant versus 4.7 for benign lesions (p < 0.001). An optimal SUVmax cut-off of 5.63 yielded 75% sensitivity and a 19.4% false-positive rate. In the sub-analysis excluding histologically confirmed RCC lesions, sensitivity increased to 82.5% at a SUVmax of 11.7. Multivariate analysis identified SUVmax ≥ 5.63 (OR 6.0, CI [1.1-33.7], p = 0.004) as independently predictive of malignancy. Additional predictors included ROC HU ≥ 37 (OR 9.3, CI [1.8-47.2], p = 0.001), current practice HU ≥ 20 (OR 22.8, CI [1.3-41.0], p = 0.003), and > 1 avid lesion (OR 5.4, CI [1.1-25.2], p = 0.003).

FDG-PET is a useful diagnostic adjunct in undifferentiated adrenal lesions, with defined thresholds (SUVmax ≥ 5.63 and HU ≥ 20) guiding malignancy risk stratification. FDG-PET should be considered in large, suspicious lesions or those with a history of malignancy.