Malignant mesotheliomas are almost always associated with asbestos exposure. Whereas the benign form may be cured by surgical resection, the malignant tumor is aggressive, spreading by local extension, and usually encasing the lung and mediastinum. Surgery is not possible in this case, and chemotherapy and radiation have been unsuccessful. Prognosis is very poor with a median survival of one year. CT is helpful in establishing the extent of the tumor.
Malignant mesothelioma appears as an irregular or nodular pleural thickening surrounding the lung.
The tumor is usually visible along the lateral chest wall, however, mediastinal or concentric pleural thickening may be seen in extensive disease. Associated fluid collections, which may be difficult to distinguish from mesothelioma, may be visualized by using contrast and by performing the CT scan with the patient in the prone or decubitus position. Benign mesothelioma is distinct is that it usually appears as localized, solitary lesions arising from the visceral pleural. It more commonly involves the costal pleural surface but may occur within a fissure. On the other hand, pleural thickening associated with asbestos-related pleural disease usually involves the parietal pleura and appears on the inner costal and vertebral surfaces.