Sclerosing fibrous tumor of the cauda equina: a fibroblastic variant of peripheral nerve tumors?

The case of a 43-year-old man with an unusual mesenchymal tumor of the cauda equina is presented. A well-circumscribed firm tumor was found in the lower spinal canal at L1 level. Although a nerve root was involved, the adjacent dura mater or filum terminale was unrelated to the tumor. Microscopically, the tumor was rich in collagen and made up of irregularly intertwining fascicles of fibroblastic spindle cells lacking in nuclear atypia or mitotic activity. Partial broad hyalinization of collagen was another histological feature of the tumor. Histological and immunohistochemical studies failed to reveal any findings that suggested known fibrous neoplasms, such as schwannoma, neurofibroma and meningioma, originating in the nervous system. Ultrastructural features of the tumor cells were consistent with those of fibroblasts. Hence, the present tumor is regarded as a unique pure fibroblastic tumor (fibroma) derived from the interstitium of a nerve root in the cauda equina.