Pleural fibroma (Benign fibrous mesothelioma)This is the primary benign lesion of pleura. The tumor is often attached to the pleural surface by a pedicle. These tumor do not usually produce a pleural effusion and have no relationship to asbestos exposure (in contrast to malignant mesothelioma). They consist of dense fibrous tissue with occasional cysts filled with viscid fluid. Microscopically, the tumors show whorls of reticulin and collegen fibers among which are interspersed spindle cells resembling fibroblasts. The tumor cells are CD 34 (+)ve and keratin negative by immunostaining. This feature can be diagnostically useful in distinguishing these lesions from malignant mesothelomas which is CD34 (-)ve and keratin positive.