1. A tumor composed of spindle-shaped cells in the delicate supporting connective tissue of nerve cells.
2. Rare mixed tumors of the brain and rarely the spinal cord which contain malignant neuroectodermal (glial) and mesenchymal components, including spindle-shaped fibrosarcoma cells.

These tumors are highly aggressive and present, primarily in adults, as rapidly expanding mass lesions. They may come up in tissue that has been previously irradiated.