Detection of minute pleural fluid in the pleural retracted space associated with peripheral lung cancer: evaluation with MR imaging

PURPOSE: To evaluate the efficacy of magnetic resonance imaging (MRI) in detecting minute pleural fluid in the pleural retracted space (PRS) associated with peripheral lung cancer. MATERIALS AND METHODS: Our subjects were 20 patients with peripheral lung cancer in whom thin-section CT in the lung window setting demonstrated lesions adjacent to the pleural surface, and who were referred for MR imaging. The imaging findings were retrospectively evaluated and correlated with the histopathologic specimens. Pleural fluid was aspirated for cytology under ultrasound (US) guidance in six patients. RESULTS: STIR MR images revealed water SI areas beneath the chest wall associated with the lung cancer, whereas, on CT images, lung cancer and minute pleural fluid in the PRS showed similar soft-tissue density without enabling easy differentiation. Two of the six patients who underwent aspiration cytology showed malignancy. All histopathologic specimens obtained from 18 patients who underwent surgery showed pleural retraction corresponding to the water SI areas on STIR images. Histopathological study revealed that the fibrotic focus of the tumor tended to occur more intensively when the shape of pleural retraction was thinner and deeper. CONCLUSION: Water SI areas on STIR images were thought to suggest pleural fluid retention in the PRS. MRI was sensitive in detecting minute pleural fluid in the PRS and may help to avoid overdiagnosis of chest wall invasion induced from peripheral lung cancers.