The differentiation of malignant from benign pleural lesions is difficult with currently available imaging techniques. There is a significant overlap between the radiologic appearances of benign and malignant pleural disease, particularly in asbestos-exposed workers 2 Diffuse pleural thickening, the hallmark of malignant mesothelioma, is not a specific finding on cross-sectional imaging and may be caused by asbestos exposure, as a consequence of hemorrhagic effusion, or by a number of infectious processes, such as tuberculosis. CT is useful in localizing the areas of thickening, but tends to underestimate the extent of the disease process. MRI can be helpful in some instances by providing sagittal or coronal views and thereby allowing for the evaluation of the diaphragmatic or apical regions. MRI signal intensity analysis may help to distinguish benign from malignant pleural masses. However, cardiac, respiratory, and vascular movement can degrade the quality of MRI studies.
Because current imaging techniques can be unreliable in differentiating benign from malignant processes, it is imperative to obtain an adequate tissue specimen for specific diagnosis. The combination of blind needle pleural biopsy and fluid cytology has a sensitivity of <40%. Canadian health&care mall CT-guided pleural needle biopsy provides a higher yield, on the order of 60% with a single attempt, which may reach 85% with repeated biopsies. Complications of pleural needle biopsy include pneumothorax (9.5%) and tumor seeding along the needle tract (21.7%). Because of the relatively low yields of closed pleural needle biopsies, many investigators recommend thoracotomy or thoracoscopy for accurate tissue sampling and staging.
The use of thoracoscopy has grown in recent years, and the sensitivity of this technique for diagnosing malignant mesothelioma is >90%. However, this technique requires a free pleural space of at least 10 mm, and adhesions can complicate the procedure significantly. The mortality rate of thoracoscopy is <0.1%, but nonfatal complications can occur in up to 10% of patients. These include tumor seeding along the chest wall, persistent air leaks, empyema, hemorrhage, subcutaneous emphysema, and wound infection. Local-field radiation therapy is frequently recommended to prevent seeding along the thoracoscopy tract. Thoracoscopy remains the primary diagnostic modality for mesothelioma, but this invasive approach cannot always accurately stage the mediastinal nodes or transdiaphragmatic extension; even thoracotomy may sometimes fail to provide a specific diagnosis, as illustrated in case B.