A case of malignant myxoma (myxosarcoma) of the maxilla.

A centrally located maxillary myxoma with malignant histologic appearance and aggressive clinical course is reported in a 40-yr-old man. The gelatinous polypoid tumor mass was diagnosed as a myxoma in the first biopsy. The tumor recurred rapidly (within 3 wk) eroding the bony structures of the maxillary sinus and the hard palate and infiltrating the adjacent soft tissues. In repeated biopsy (as well as reassessment of the first biopsy) the tumor was found to be composed of plump stellate cells, some of which were pleomorphic with atypical and bizarre mitotic figures. The amorphic myxoid matrix contained acid mucopolysaccharides and was completely devoid of lipids. Electron microscopy demonstrated that the tumor cells were identical to fibroblasts, which is consistent with the appearance of myxoma cells. When radiotherapy was unsuccessful, we removed the left maxilla with orbital excenteration and reconstructed the jaw. Three years later the patient died accidentally. At autopsy, no recurrence of myxoma or distant metastases were found. Due to the malignant histologic appearance and the aggressive clinical course, this tumor can be called an odontogenic myxosarcoma and should be added to the WHO classification as a malignant variant of odontogenic myxoma.