Low-grade myxoid chondrosarcoma of the base of the skull: CT, MR, and histopathology.

A retrospective CT, MR, and histopathologic study was performed in five patients with histologically verified low-grade myxoid chondrosarcoma of the base of the skull. In four patients, the tumor originated off the midline and was associated with bone destruction at the petrous apex near the petrooccipital fissure. Tumor extent included the cerebellopontine angle in three patients and the parasellar area in two patients. The fifth tumor originated on the midline and was associated with destruction at the dorsum sellae. Three tumors contained calcifications, whereas two lesions were mostly isodense with brain on CT scan. All tumors were hypointense on T1-weighted MR images and very intense on T2-weighted images except for areas of signal void consistent with calcifications. Light microscopy revealed islands of mature hyaline cartilage in an abundant myxoid ground substance. Histology and immunocytochemical analysis were consistent with a low-grade myxoid chondrosarcoma. The CT and MR features of low-grade myxoid chondrosarcoma are comparable with those of chordoma. Chordoma usually arises from the midline, but cases with origin from the lateral portion of the clivus or the petrous apex have been described. Low-grade myxoid chondrosarcoma has distinct histologic and immunocytochemical features and includes lesions formerly called "chondroid chordomas."