The Role of 18F-FDG PET/CT Integrated Imaging in Distinguishing Malignant from Benign Pleural Effusion

Abstract

Objective: The aim of our study was to evaluate the role of 18F-FDG PET/CT integrated imaging in differentiating malignant from benign pleural effusion.

Methods: A total of 176 patients with pleural effusion who underwent 18F-FDG PET/CT examination to differentiate malignancy from benignancy were retrospectively researched. The images of CT imaging, 18F-FDG PET imaging and 18F-FDG PET/CT integrated imaging were visually analyzed. The suspected malignant effusion was characterized by the presence of nodular or irregular pleural thickening on CT imaging. Whereas on PET imaging, pleural 18F-FDG uptake higher than mediastinal activity was interpreted as malignant effusion. Images of 18F-FDG PET/CT integrated imaging were interpreted by combining the morphologic feature of pleura on CT imaging with the degree and form of pleural 18F-FDG uptake on PET imaging.

Results: One hundred and eight patients had malignant effusion, including 86 with pleural metastasis and 22 with pleural mesothelioma, whereas 68 patients had benign effusion. The sensitivities of CT imaging, 18F-FDG PET imaging and 18F-FDG PET/CT integrated imaging in detecting malignant effusion were 75.0%, 91.7% and 93.5%, respectively, which were 69.8%, 91.9% and 93.0% in distinguishing metastatic effusion. The sensitivity of 18F-FDG PET/CT integrated imaging in detecting malignant effusion was higher than that of CT imaging (p = 0.000). For metastatic effusion, 18F-FDG PET imaging had higher sensitivity (p = 0.000) and better diagnostic consistency with 18F-FDG PET/CT integrated imaging compared with CT imaging (Kappa = 0.917 and Kappa = 0.295, respectively). The specificities of CT imaging, 18F-FDG PET imaging and 18F-FDG PET/CT integrated imaging were 94.1%, 63.2% and 92.6% in detecting benign effusion. The specificities of CT imaging and 18F-FDG PET/CT integrated imaging were higher than that of 18F-FDG PET imaging (p = 0.000 and p = 0.000, respectively), and CT imaging had better diagnostic consistency with 18F-FDG PET/CT integrated imaging compared with 18F-FDG PET imaging (Kappa = 0.881 and Kappa = 0.240, respectively).

Conclusion: 18F-FDG PET/CT integrated imaging is a more reliable modality in distinguishing malignant from benign pleural effusion than 18F-FDG PET imaging and CT imaging alone. For image interpretation of 18F-FDG PET/CT integrated imaging, the PET and CT portions play a major diagnostic role in identifying metastatic effusion and benign effusion, respectively.

Fig 1. The diagnostic criteria of ¹⁸F-FDG PET/CT integrated imaging in the differential diagnosis of pleural effusion.

Fig 2. ¹⁸F-FDG PET/CT integrated imaging of 54-year old woman with left lung cancer and malignant pleural effusion.

Axial CT (A) shows effusion in left pleural cavity, and axial ¹⁸F-FDG PET (B, arrow) and axial fused ¹⁸F-FDG PET/CT (C, arrow) display nodular ¹⁸F-FDG uptake (SUVmax of 3.0) in left-posterior pleural region. Pathology from thoracentesis confirmed malignant pleural effusion caused by metastatic adenocarcinoma.

Fig 3. ¹⁸F-FDG PET/CT integrated imaging of 72-year old man with tuberculous pleural effusion.

Axial CT (A) shows effusion in right pleural cavity and diffuse light smooth thickening of the pleura. Axial ¹⁸F-FDG PET (B) and axial fused ¹⁸F-FDG PET/CT (C) display diffuse ¹⁸F-FDG uptake in right pleural region (SUVmax of 7.9).