We previously reported a patient with a diaphragmatic neurilemmoma and reviewed five similar cases from the English-language medical literature [1]. Recently, our patient was found to have another tumor within the pleural cavity. Thoracotomy showed a tumor, arising from the parietal pleura of the right anterior hemithorax, that was far removed from the site of the previously resected diaphragmatic tumor. Extensive histopathologic study and review yielded a final diagnosis of solitary fibrous tumor of the pleura. CD34 immunohistochemical staining was positive and S-100 protein was negative. The previously reported diaphragmatic tumor was also reviewed by our panel of pathologists; the diagnosis was changed to solitary fibrous tumor of the pleura. CD34 staining was not routinely used at the time of our previous report.
Solitary fibrous tumors are mesenchymal tumors that can arise in many tissues and organs. The pleural cavity is the commonest location, and most tumors are benign. These tumors can pose diagnostic problems for pathologists. Their morphologic appearances can be quite variable, and they do not have distinctive ultrastructural characteristics [2]. Until recently, they did not have distinc-tive immunohistochemical characteristics either [2,3]. CD34 monoclonal antibody testing now provides a positive marker that helps to distinguish solitary fibrous tumors from other spindle cell neoplasms such as neurilemmomas [3]. Our case raises a question about the accuracy of pathologic diagnosis in the other five reported patients with diaphragmatic neurilemmoma.