The patient went on to have surgery. The tumor was found to be partially extradural, but with an intradural component protruding through a large dural defect which was repaired with dural substitute.

Histology

MICROSCOPIC DESCRIPTION: The sections show a chondroid lesion. It is mildly cellular, containing lobules of cartilage. The stroma is prominently myxomatous. Some of the matrix is mineralized. Occasional chondrocytes show mild nuclear enlargement and hyperchromasia. Binucleated forms are inconspicuous. There are no mitoses or necrosis. Some of the cartilage are surrounded by host bone. No invasion through the bone or soft tissue is seen.

There are no histological features to suggest a sarcoma. The lesional cells are S-100 and M2A positive. They are CAM5.2 negative, excluding a chordoma. The features are those of chondroma.

FINAL DIAGNOSIS: Osteochondroma.