Spinal cord compression

The spinal cord lies within the vertebral canal from the foramen magnum to approximately the first lumbar vertebra, and thereafter continues as the nerve roots of the cauda equina. It is surrounded by the three meningeal layers of dura, arachnoid and pia. There is very little spare room within the vertebral canal and space-occupying pathological processes soon lead to spinal cord compression. To some extent the symptomatology depends on the vertebral level, the layer of meninges containing the pathological process and the speed of onset of compression - the faster the onset, the poorer the prognosis for recovery even with expeditious treatment, and the converse applies for slowly compressing lesions.

In the cervical region, compression expresses itself as sensory and motor symptoms and signs of numbness and weakness in the upper limbs, which may be flaccid or spastic depending on the level, and weakness of the trunk and lower limbs, which will have increased tone or even spasticity. If vertebrae are involved in the pathological process, there is often neck pain (or referred interscapular pain), but intradural lesions are often painless.

In the thoracic region if the bone is involved, there is often pain in the spine and girdle pain around the chest wall in the distribution of the appropriate intercostal nerve, unilaterally or bilaterally. The arms are unaffected but the legs develop weakness and increased tone, and there is usually a sensory level in the trunk and lower limbs distal to the affected level. Bladder function is often compromised.

In the lumbar region there is a motor and sensory para-paresis with bladder dysfunction, depending on the level of cord or cauda equina compression.

Neurological dysfunction of the bladder (the neurogenic bladder) is particularly important to recognize. In the early phases, there is failure fully to empty the bladder such that the bladder enlarges, eventually building up back pressure on the ureters and kidneys. Finally, the patient goes into urinary retention which is often painless due the involvement of the sensory pathways. In the male, neurogenic bladder is accompanied by failure of penile erection and ejaculation.

Causes

Vertebral column

Malignancy may be secondary or primary. Metastases occur most commonly in the thoracic spine and may weaken the bone leading to collapse. Malignant tissue may also spread into the extradural space as well as into the paraspinal tissues. The single commonest primary site is bronchogenic carcinoma but other sites are carcinomas of breast, prostate and kidney. Less commonly, other primary malignancies may metastasize to the spine. Malignancies from the reticuloendothelial system

Figure 21.8. Magnetic resonance scan of the thoracic spine in 60-year-old man with a pathological collapse fracture of vertebra (large arrow) and multiple vertebral body lesions (small arrow). The diagnosis was found by needle biopsy to be multiple myeloma.

and blood-forming tissues also occur, either as part of widespread disease or starting primarily in the spine; these include myeloma (Fig. 21.8), Hodgkin's and non-Hodgkin's lymphoma and reticulosarcoma (see Ch. 11).

Primary neoplasms occur in the spine and are similar to those occurring in bones elsewhere in the body such as osteogenic sarcoma, osteoclastoma, chondroma and chron-drosarcoma. In children, Ewing's sarcoma may occur in the vertebrae and neuroblastoma within the extradural space. In patients with osteoporosis, particularly in post-menopausal women, collapse fractures can occur spontaneously or with minimal trauma (pathological fractures). Such fractures may be single or multiple. Osteomalacia can also lead to pathological fractures (see Chapter 20).

The spine can be infected by tuberculosis or pyogenic bacteria such as staphylococci. As the infection takes hold, the bone is weakened although the intervertebral disc is more resistant (Figs 21.9 and 21.10). Pus may be formed and the abscess spreads both inwards into the extradural space and outwards into the paraspinal tissues.

Figure 21.9. Magnetic resonance scan of the thoracic spine in 40-year-old man showing collapse with abnormal signals of two contiguous vertebrae in mid-thoracic region (large arrow). Note some preservation of intervertebral disc. Note also spinal cord compression (small arrow).

A small proportion of defective intervertebral discs may protrude centrally and cause spinal cord or cauda equina compression often fairly acutely, although more chronic compression may develop from osteophytes in spondylosis of the spine.

Intradural lesions

Intradural lesions may be either in the subdural space but extrinsic to the spinal cord, or intrinsic within the spinal cord. The commonest subdural extrinsic neoplasms are menin-giomas and neurofibromas; the latter may also grow through an intervertebral canal and enlarge outside the spine (dumbbell tumour). The commonest intrinsic neoplasms are ependymomas and astrocytomas and both can compress and destroy the spinal cord from within outwards. Rarely, sub-dural pyogenic abscesses may form in the subdural space and can spread for quite long distances within the vertebral canal.

Figure 21.10. Same case as Fig. 21.8 with coronal images. Note paravertebral mass (arrows). The patient was explored and an abscess found with osteomyelitis due to Staphylococcus aureus.

Investigations

Recognition of acute spinal cord compression demands real urgency. Often patients have been previously well but primary malignancies elsewhere should be suspected. However, even if there is an antecedent proven malignancy elsewhere in the body, it is unwise to assume that cord compression is due to metastasis since there may be an alternative unrelated process in the spine.

Radiological tests play a key part in the investigation. Plain radiographs of the spine should be performed looking for destruction of bone and paraspinal masses. At the same time, a chest radiograph is mandatory to look for bronchogenic carcinoma. The spine must be imaged by MRI of the whole spine, or if this is not available then by myelography and CT of any areas of myelographic block or indentation.

Management

Emergency referral to a neurosurgeon is essential for consideration of decompression of the cord compression, usually by laminectomy and excision or drainage of the pathological process. The patient should have an indwelling urinary catheter inserted for free drainage of urine. In the case of metastasis, partial excision is all that can be effected, although this does have the additional merit of yielding a histological tissue diagnosis. If the cord compression is incomplete, needle biopsy of the spine can be performed under radiological guidance. Instability of the spine is treated by instrumented fixation with products now specifically designed for all parts of the spine. The treatment thereafter of a metastasis is usually radiotherapy of the affected portions of the spine and treatment of the primary malignancy. Abscesses require drainage and in the case of the thoracic spine, this is usually performed through a thoracotomy and an anterolateral approach to the spine.

The general care of patients with neurological deficits is as for patients with spinal injuries (see above), although special treatments may be necessary and obviously the prognosis will depend on various factors outlined above.

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