Malignant granular cell tumor of the posterior mediastinum with dissemination.

A 66-year-old man presented with severe back pain. Imaging studies revealed a well-circumscribed mass in the left posterior mediastinum. Because of pleural dissemination observed at thoracotomy, palliative resection was performed to relieve his back pain. Histologically, the tumor was composed of cells with large eosinophilic and granular cytoplasm, which were strongly positive for S-100. Mediastinal malignant granular cell tumor with pleural dissemination is extremely unusual.