Malignant Mesothelioma Versus Metastatic Carcinoma of the Pleura: A CT Challenge

BACKGROUND: Malignant pleural mesothelioma (MPM) is a rare malignant neoplasm of the pleura that typically affects individuals occupationally exposed to asbestos through a variety of industries. MPM presents with several CT features similar to more common pleural diseases such as metastatic pleural malignancy. OBJECTIVES: The aim of this study is to differentiate malignant pleural mesothelioma from metastatic carcinoma of the pleura by pathological and radiological assessment in order to investigate accuracy of CT scan in this regard and to compare CT features of these two malignancies. PATIENTS AND METHODS: Chest CT scans of 55 pleural malignancy patients including MPM and metastatic pleural malignancy were evaluated in this retrospective study. The pathologist made the definite diagnosis based on immunohistochemistry. A chest radiologist unaware of the pathology diagnosis observed all CT scans. Several parameters including pleural thickening, pleural effusion, thickening of inter lobar fissure, contralateral extension, contraction of involved hemithorax, parenchymal involvement (infiltration, nodules, fibrosis), pleural mediastinal involvement, lymphadenopathy, extrapleural invasion (hepatic, chest wall, diaphragm, intraperitoneal), and pericardial involvement were checked. Data analysis was carried out using SPSS version 16, and the ability of CT scan to differentiate malignant pleural mesothelioma and metastatic pleural diseases was investigated. RESULTS: Totally 29 males and 26 females were assessed in this study. Based on pathology, 17 MPM and 38 metastatic pleural malignancies were diagnosed. According to CT study, about 82% of the patients with MPM and about 79% of the patients with metastatic pleural diseases were correctly diagnosed by a radiologist. The most common findings suggestive of MPM were pleural thickening (88.2%), loculated effusion (58.8%), and thickening of the interlobar fissure (47.1%). Whereas free pleural effusion (71.7%), parenchymal infiltration (65.8%) and pleural thickening (63.2%) were most prevalent parameters among metastatic cases. CONCLUSION: CT scan is highly accurate in differentiating malignant pleural mesothelioma and metastatic pleural diseases. Pleural thickening and thickening of interlobar fissure lead us to the diagnosis of MPM and massive free pleural effusion is more commonly seen in metastatic pleural malignancy.