Comparison of objective criteria and expert visual interpretation to classify benign and malignant hilar and mediastinal nodes on 18-F FDG PET/CT.

Background And Objective: There is widespread adoption of FDG-PET/CT in staging of lung cancer, but no universally accepted criteria for classifying thoracic nodes as malignant. Previous studies show high negative predictive values, but reporting criteria and positive predictive values varies. Using Endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) results as gold standard, we evaluated objective FDG-PET/CT criteria for interpreting mediastinal and hilar nodes and compared this to expert visual interpretation (EVI).

Methods: A retrospective review of all patients with lung cancer who had both FDG-PET/CT and EBUS-TBNA from 2008 to 2010 was performed. Scan interpretation was blinded to histology. Patients from 2008/2009 were used for the prediction set. The validation set analysed patients from 2010. Objective FDG-PET/CT criteria were SUVmax lymph node (SUVmaxLN), ratio SUVmaxLN/SUVmax primary lung malignancy, ratio SUVmaxLN/SUVaverage liver, ratio SUVmaxLN/SUVmax liver and ratio SUVmaxLN/SUVmax blood pool. A nuclear medicine physician reviewed all scans and classified nodal stations as benign or malignant.

Results: Eighty-seven malignant lymph nodes and 41 benign nodes were in the prediction set. All objective FDG-PET/CT criteria analysed were significantly higher in the malignant group (P < 0.0001). EVI correctly classified 122/128 nodes (95.3%). Thirty-four malignant nodes and 19 benign nodes were in the validation set. The new proposed cut-off values of the objective criteria from the prediction set correctly classified 44/53 (83.0%) nodes: 28/34 (82.4%) malignant nodes and 16/19 (84.2%) benign nodes. EVI had 91% accuracy: 33/34 (97.1%) malignant nodes and 15/19 (79.0%) benign nodes.

Conclusions: Objective analysis of 18-F FDG PET/CT can differentiate between malignant and benign nodes but is not superior to EVI.