Compression of the spinal cord by a metastatic tumor in the vertebral column is a common occurrence in many types of cancers. Primary tumors of the spinal cord are considerably less frequent. In the Mayo Clinic series of 8,784 primary tumors of the CNS, only 15 percent were intraspinal (Sloof et al). In contradistinction to brain tumors, the majority of intraspinal ones is benign and produces effects mainly by compression of the spinal cord rather than by invasion. Thus, a proportion of intraspinal tumors are amenable to surgical removal, and their early recognition, before irreversible neurologic changes have occurred, becomes a matter of utmost importance.
General Considerations of Neoplastic Compression of the Cord (See Also Chap. 30)
Neoplasms and other space-occupying lesions within the spinal canal can be divided into two groups: (1) those that arise within the substance of the spinal cord, either as a primary neural neoplasm or as a metastasis, and invade and destroy tracts and central gray structures (intramedullary) and (2) those arising outside the spinal cord (extramedullary), either from vertebral bodies and epidural tissues (extradural) or in the leptomeninges or roots (intradural). In a general hospital, the relative frequency of spinal tumors in these different locations is approximately 5 percent intramedullary, 40 percent intradural–extramedullary, and 55 percent extradural, the majority of the latter being metastatic cancers, as already mentioned. This percentage of extradural lesions is higher than that encountered in more specialized neurosurgical services (e.g., Elsberg’s figures of 7, 64, and 29 percent, respectively), probably because the latter do not include as many patients with extradural lymphomas, metastatic carcinomas, and the like, as are seen in general hospitals.
Intraspinal tumors The most common primary extramedullary tumors are the neurofibromas and meningiomas, which together constitute approximately half of all intraspinal neoplasms. They are more often intradural than extradural. Neurofibromas have a predilection for the lumbar and thoracic region, whereas meningiomas are more evenly distributed over the vertical extent of the cord (Fig. 42-10). The other primary extramedullary tumors are sarcomas, vascular tumors, chordomas, and epidermoid and similar tumors, in that order of frequency.
Primary intramedullary tumors of the spinal cord have the same cellular origins as those arising in the brain (Chap. 30), although the proportions of particular cell types differ. Ependymomas, some of which arise from the filum terminale, make up 60 percent of the spinal cord cases and astrocytomas make up approximately 25 percent. The astrocytoma is the most common intramedullary tumor if one excludes tumors arising in the filum terminale (Fig. 42-11). Oligodendrogliomas are much less common. The remainder (approximately 15 percent) consists of a diverse group of nongliomatous tumors: lipomas, epidermoids, dermoids, teratomas, hemangiomas, hemangioblastomas, chordomas, schwannomas, and intraspinal metastatic carcinomas. The cavernous hemangioma may be a source of spontaneous hematomyelia. As indicated further on, there is a frequent association between intramedullary tumors (both gliomatous and nongliomatous) and syringomyelia. The basis of this relationship remains obscure.