Cartilaginous tumors and chordomas of the cranial base.

Chordomas and chondrosarcomas are uncommon skull base tumors. They are locally aggressive. Chordomas arise from the clivus with the epicenter in the midline of the skull base. Chondrosarcomas, in contrast, usually arise along the petro-occipital fissure; occasionally, a chondrosarcoma may reveal a midline location and then cannot be differentiated from chordoma. Chordomas rarely calcify, whereas calcification is not an uncommon finding in chondrosarcomas. Following radiation, calcifications also increase in area and diameter in both chondrosarcomas. Both chondrosarcomas and chordomas reveal a low signal intensity on T1-weighted MR images and medium to increased signal intensity on T2-weighted images. They commonly enhance significantly but heterogeneously, because of the presence of necrosis, calcification, and mucinous materials. Occasionally, chondrosarcomas and chordomas reveal a low degree if enhancement. The prognoses of chordomas and chondrosarcomas vary. Long-term survival is usually seen with chondrosarcomas but is still considerably compromised with chordomas.