Chordomas of the skull base. Radiologic and clinical evaluation.

Chordomas are uncommon skull base tumors, which are locally agressive and are usually not amenable to complete surgical resection. Proton beam irradiation, following surgery, is the preferred treatment modality. For diagnosis and determination of tumor site and extension, CT and MR imaging are the imaging modalities of choice. CT delineates bone destruction and the presence of calcifications and destroyed bone optimally. MR imaging is the modality of choice for better definition of the tumor margin from brain and other soft tissue structures (pharynx) and visualization of blood vessels. The signal intensities and enhancement pattern fail to differentiate chordoma from chondroid chordoma or chondrosarcoma. Chordomas arise from the clivus and therefore are located more centrally, whereas the majority of chondrosarcomas originate in the petroclival fissure and occur more laterally, although occasional overlap occurs in about one third of cases. Immunohistochemical methods allow differentiation of pure chordoma from chondroid chordoma and chondrosarcoma. Chordomas have a lower local control rate than chondrosarcomas.