Spinal tumours are conveniently divided into extradural and intradural growths, the latter being further divided into those arising outside the spinal cord (extramedullary tumours) and those from within the cord (intramedullary tumours).
- 20% of spinal tumours are primarily extradural,
- 60% extramedullary,
- 20% intramedullary.
Although some involve more than one location. Extradural tumours have been dealt with in the preceding sections on vertebral neoplasms.
The most common extramedullary, intradural tumours are meningiomas and neurofibromas. Published figures of relative incidence vary, but meningiomas seem to be slightly more common than neurofibromas (Alter 1975), while the two together are between two and three times more common than spinal intramedullary gliomas.
The thoracic cord is the most common site of extradural and extramedullary tumours. Approximately two-thirds of extramedullary tumours are situated on the dorsal or dorsolateral aspects of the cord and approximately one-third on the ventral or ventrolateral aspects.
Neurofibromas usually arise from the spinal roots, the posterior more frequently than the anterior. They may be single or multiple, and may or may not be associated with generalized neurofibromatosis. Exceptionally, an extramedullary neurofibroma grows out through the intervertebral foramen, thus adopting a dumb-bell shape. The extraspinal portion may be palpable. Meningiomas may arise from arachnoid covering the roots or the cord. While neurofibromas develop at any level of the spinal canal and occur equally in the two sexes, meningiomas almost always lie in the thoracic region and affect females much more often than males. Sarcomatous changes in spinal meningiomas and primary extramedullary sarcomas are rare.
Lipomas occasionally occur, but usually in relation to occult spina bifida and spinal dysraphism. Other developmental anomalies, not strictly tumours, but which may mimic growths in causing cord compression, include dorsal neurenteric cysts and congenital extradural cysts (intraspinal meningoceles). It has been suggested that intraspinal epidermoid cysts may follow several years after lumbar puncture due to implantation if fragments of epidermis into the spinal canal. Chordomas are rare malignant tumours arising from a remnant of the notochord. Spinal chordomas are almost invariably situated in the sacrococcygeal region. Dermoid cysts and other forms of teratomatous growth may also develop within the spinal canal.
Both sexes are equally liable to spinal tumour (except for meningioma, which is much more common in elderly females), and tumour may develop at any age, although in over 80% symptoms first appear between the ages of 20 and 60. There is no significant difference in incidence in different races, but meningiomas are relatively rare in childhood, as indeed are all spinal neoplasms in comparison to intracranial neoplasms.
Intramedullary spinal tumours
Ependymomas were most common, accounting for 42% of tumours. The next most common intramedullary tumour is astrocytoma. Other tumour types include medulloblastoma, oligodendroglioma, ganglioneuroma, haemangioblastoma, and, rarely, intramedullary carcinoma metastases.
Leukaemic and lymphoma deposits may sometimes occur in the cord, as may tuberculomas. Systemic metastases from primary spinal neoplasm are rare, but have been described in ependymoma of the filum terminale. By contrast, intra- and extramedullary spinal deposits resulting from intracranial gliomas, especially medulloblastomas, are not uncommon, particularly in children.
MRI is the investigation of choice for the diagnosis of all forms of spinal tumour. Neurofibromas are usually hyperintense on T2-weighted images. Meningiomas may be isointense with respect to the spinal cord on T1- and T2-weighted images, but display prominent gadolinium enhancement. Lipomas produce a characteristic high signal on unenhanced T1-weighted images. As a rule, intramedullary tumours display swelling of the cord and gadolinium enhancement.
Benign extramedullary tumours causing cord compression, resulting in a progressive spastic paraplegia, should be removed surgically, and a generally good prognosis can be expected if the diagnosis is made promptly and the presurgical deficit is not severe.
Intramedullary gliomas or ependymomas may be extremely indolent, with a history evolving over many years or even decades. Surgical debulking of ependymomas may be possible in some instances and some cases of intramedullary glioma may benefit from radiotherapy.