¹⁸F-FDG PET/CT imaging in differential diagnosis of exudative pleural effusions

Objectives: To investigate the value of ¹⁸F-FDG PET/CT imaging in differentiating malignant from benign exudative pleural effusions.

Methods: 224 patients with CT scan and pleural effusion puncture examination evidence of moderate or massive exudative pleural effusions entered the study to evaluate the accuracy of ¹⁸F-FDG PET/CT in differential diagnosis between malignant and benign exudative pleural effusions. Image analysis of PET/CT was performed both with visual interpretation and using a quantitative method on coronal, sagittal and axial reconstructions. The results of PET/CT imaging were compared to cyto- or histological data and at least one year follow-up results if diagnose as benign.

Results: Ninety-three patients with exudative pleural effusion were confirmed as benign according to cyto- or histological data and at least one-year follow-up results. 114 patients with pleural effusion were caused by metastasis, and primary tumor was found in 99 patients using PET/CT. 12 patients were caused by mesothelioma and 5 patients wer caused by hematological cancer. There is significant difference of the pleural FDG activity grades between the benign and malignant pleural effusion (P<0.001). PET/CT parameters including the pleural SUVmax and thickness were found to be significant different in differentiating malignant from benign pleural effusion. A cut-off value of 2.6 for SUVmax gave the best accuracy for distinguishing between benign and malignant pleural effusion, reaching 68% with 84.0%, 55.9%, 72.8%, 71.2% respectively, for sensitivity, specificity, NPV and PPV. And the cut-off value of 6.95mm for pleural thickness gave the best accuracy reaching 75.4% with 76.3%, 74.2%, 80.6%, 69.0% respectively, for sensitivity, specificity, NPV and PPV. Further study showed the pleural SUVmax and thickness of the subgroups of the malignant pleural effusion (caused by metastasis or mesothelioma or hematological cancer) were both higher than the benign group (tuberculosis or other specific inflammatory) (P<0.001).

Conclusions: ¹⁸F-FDG PET/CT imaging is valuable in ruling out the malignant origin of a pleural effusion or thickening. The pleural SUVmax has a higher sensitivity than thickness with a lower specificity, tuberculosis or specific inflammatory can lead to false positive results, and invasive procedure is not avoidable in these patients.