SPINAL CORD AND ROOTS

Disorders localised to the spinal cord or nerve roots are detailed below, but note that many diffuse neurological disease processes also affect the cord (see Section V, e.g. multiple sclerosis, Friedreich’s ataxia).

SPINAL CORD AND ROOT COMPRESSION

As the spinal canal is a rigidly enclosed cavity, an expanding disease process will eventually cause cord and/or root compression.

Causes

Manifestations of cord or root compression depend upon the following:

Site of lesion within the spinal canal: an expanding lesion outside the cord produces signs and symptoms from root and segmental damage.

ROOT – lower motor neuron (l.m.n.) and sensory impairment appropriate to the distribution of the damaged root.

Lesions within the cord (intramedullary) produce segmental signs and symptoms.

SPINAL CORD AND ROOT COMPRESSION

Level of the lesion: a lesion above the L1 vertebral body may damage both the cord and its roots. Below this, only roots are damaged.

Vascular involvement: neuronal damage from mechanical stretching is of less importance than the vascular effects. At first venous obstruction leads to vasogenic oedema, but eventually impaired arterial flow causes irreversible spinal cord infarction. Clinical findings may suggest cord damage well beyond the level of compression, implying a distant ischaemic effect from vessel compromise at the lesion site.

Speed of onset: speed of compression effects the clinical picture. Despite producing upper motor neuron damage, a rapidly progressive cord lesion often produces a ‘flaccid paralysis’ with loss of reflexes and absent plantar responses. This state is akin to ‘spinal shock’ seen following trauma. Several days or weeks may elapse before tone returns accompanied by the expected ‘upper motor neuron’ signs.

SPINAL CORD AND ROOT COMPRESSION – NEUROLOGICAL EFFECTS

LATERAL COMPRESSIVE LESION

Root/segmental damage

MUSCLE WEAKNESS in groups supplied by the involved root and segment with LOWER MOTOR NEURON (l.m.n.) signs: – wasting; – loss of tone; – fasciculation; – diminished or absent reflexes. N.B. motor deficit is seldom detected with root lesions above C5 and from T2 to L1.

SENSORY DEFICIT of all modalities or hyperaesthesia in area supplied by the root, but overlap from adjacent roots may prevent detection.

Long tract – signs and symptoms Partial (Unilateral) cord lesion

(Brown-Séquard syndrome)

MOTOR DEFICIT – dragging of the leg. In high cervical lesions weakness of finger and hand movements are noted on the side of the lesion.

UPPER MOTOR NEURON (u.m.n.) signs (maximal on side of lesion):

– weakness in a ‘pyramidal’ distribution, i.e. arms – extensors predominantly affected; legs – flexors predominantly affected.

– increased tone, clonus; – increased reflexes;

– extensor plantar response.

SENSORY DEFICIT – numbness may occur on the same side as the lesion and a burning dysaesthesia on the opposite side.

– joint position sense and accurate touch localisation (two point discrimination) impaired on side of lesion.

– Pinprick and temperature sensation impaired on opposite side.

In practice, cord damage is seldom restricted to one side. Usually a mixed picture occurs, with an asymmetric distribution of signs and symptoms.

Damage to sympathetic pathways in the T1 root or cervical cord causes an ipsilateral Horner’s syndrome (page 145).

BLADDER symptoms are infrequent and only occur when cord damage is bilateral. Precipitancy or difficulty in starting micturition may precede retention.

Long tract damage – complete cord lesion

MOTOR DEFICIT: the speed of cord compression affects the clinical picture. Slowly growing lesions present with difficulty in walking; the legs may ‘jump’ at night. Examination reveals u.m.n. signs often with an asymmetric distribution. Rapidly progressive lesions produce ‘spinal shock’ – the limbs are flaccid, power and reflexes diminished or absent and plantar responses absent or extensor.

SENSORY DEFICIT: involves all modalities and occurs up to the level of the lesion.

BLADDER: patient first notices difficulty in initiating micturition. Retention follows, associated with incontinence as automatic emptying occurs. Constipation is only noticed after a few days. Some patients develop priapism (painful erection).

CENTRAL CORD LESION

Segmental damage: A central lesion initially damages the second sensory neuron crossing to the lateral spinothalamic tract; pain and temperature sensations are impaired in the distribution of the involved segment – a suspended sensory loss. As the lesion expands, anterior horn cells are also involved and a l.m.n. weakness occurs.

Long tract effects: further lesion expansion damages the spinothalamic tract and corticospinal tracts, the most medially situated fibres being involved first. With a lesion in the cervical region, the sensory deficit to pain and temperature extends downwards in a ‘CAPE’-like distribution. As the sacral fibres lie peripherally in the lateral spinothalamic tract, SACRAL SPARING can occur, even with a large lesion. Involvement of the corticospinal tracts produces u.m.n. signs and symptoms in the limbs below the level of the lesion. The bladder is usually involved late.

In the cervical cord, sympathetic involvement may produce a unilateral or bilateral Horner’s syndrome.

LOWER CORD (CONUS) CAUDA EQUINA LESIONS

VERTEBRAL COLUMN

If a spinal cord or root lesion is suspected look for:

SPINAL CORD AND ROOT COMPRESSION – INVESTIGATIONS

MRI

This is now the investigation of choice for spinal disease, whether this lies within or outwith the dura or the spinal cord. Clinical examination and straight X-rays may suggest the level of the lesion, but for suspected metastatic disease, a sagittal MRI should cover the whole spine since more than one site may be involved and the site of compression may lie many segments higher than the clinical signs indicate. The examination must involve both T1 and T2 weighted images, the former often repeated with gadolinium enhancement.

On displaying an abnormality at a particular site, coronal views and axial views at selected levels may provide additional information.

MRI differentiates a syrinx (page 401) or a cystic swelling within the spinal cord from a solid intramedullary tumour (page 400).

SPINAL CORD AND ROOT COMPRESSION

METASTATIC TUMOUR

Occurs in 5% of all cancer patients and accounts for 50% of adult acute myelopathies.

Primary site: Usually breast, lung, prostate, kidney or myeloma (see below).

Metastatic site: Thoracic vertebrae most often involved, but metastasis may occur at any site and may be multiple.

Clinical features: Bone pain and tenderness are common features usually preceding limb and autonomic dysfunction.

Investigations: Plain radiology may be diagnostic as osteolytic lesions or vertebral collapse are present in most cases. MRI will identify extradural compression and help exclude or confirm multiple level disease.

Management

In earlier years, numerous patients were subjected to a ‘decompressive’ laminectomy followed by radiotherapy. Since metastatic tumour usually involves the vertebral body and pedicles, removal of the spinous processes and lamina increases instability. Not surprisingly results were extremely poor and led to a swing towards radiotherapy alone. A recent randomised trial in patients with radioresistant tumours affecting one site comparing decompressive surgery plus radiotherapy against radiotherapy alone showed that surgery increased the percentage of patients who remained ambulant and who regained the ability to walk. This has led to a revival of decompressive procedures in such patients. Surgical treatment aims to establish a histological diagnosis, to decompress the spinal cord and to provide stability if instability causes pain.

Techniques

Major operative treatment is inappropriate in the elderly, when paraplegia persists for > 48 hours and in those with a dismal prognosis. In such patients, if medication fails to control pain, a palliative course of radiotherapy may help.

Prognosis: Outcome depends on the nature of the primary tumour. Median survival is 3–6 months. Early diagnosis is important to ensure that the majority of patients remain ambulant. Good prognostic factors include – ambulant before or after treatment, a radiosensitive tumour and only one level of involvement.

MYELOMA

This malignant condition usually affects older age groups. It is often multifocal, involving the vertebral bodies, pelvis, ribs and skull, but solitary tumours may occur (‘plasmacytoma’). Spinal cord compression occurs in 15% of patients with myeloma and rarely without vertebral body involvement due to intradural deposits. If suspect, look for characteristic changes in the plasma immunoglobulins and for Bence-Jones protein in the urine. An isotope bone scan may be less informative than a radiological skeletal survey. Bone marrow shows infiltration of plasma cells. Serum calcium levels may be high.

Management is as for metastatic tumour with additional chemotherapy. The prognosis is variable but patients may survive many years with a solitary plasmacytoma.

MENINGIOMA

Spinal meningiomas tend to occur in elderly patients and are more common in females than in males. They usually arise in the thoracic region and are almost always intradural. Slow growth often permits considerable cord flattening to occur before symptoms become evident. MRI or CT myelography will identity the lesion.

The operative aim is complete removal. Results are usually good, but if the tumour arises anteriorly to the cord, excision of the dural origin is difficult, if not impossible, and recurrence may result.

SCHWANNOMA/NEUROFIBROMA

Schwannomas are slowly growing benign tumours occurring at any level and arising from the posterior nerve roots. They lie either entirely within the spinal canal or ‘dumbbell’ through the intervertebral foramen, on occasions presenting as a mass in the thorax or posterior abdominal wall.

Neurofibromas are identical apart from their microscopic appearance (page 304) and their association with multiple neurofibromatosis (Von Recklinghausen’s disease NF1 – see page 561) – look for café au lait patches in the skin.

Schwannomas tend to occur in the 30–60 age group. Typically they present with root pain. Root signs and/or signs of cord compression may follow.

MRI or CT myelography identifies an intradural/extramedullary lesion. Axial views will delineate any extraspinal extension (see page 395). Complete operative removal is feasible but the nerve root of origin is inevitably sacrificed. Overlap from adjacent nerve roots usually minimises any resultant neurological deficit.

INTRAMEDULLARY TUMOURS

Intrinsic tumours of the spinal cord occur infrequently. In adults, ependymomas occur more frequently, but in children low grade astrocytomas are by far the most common. Cystic cavities may lie within the tumour or at the upper or lower pole. Benign lesions include haemangioblastoma, lipoma, epidermoid, tuberculoma and cavernous angioma.

Clinical features

The onset is usually gradual. Segmental pain is common. Interruption of the decussating fibres of the lateral spinothalamic tract causes loss of pain and temperature sensation at the level of the involved segments.

Tumour expansion and involvement of the anterior horn cells produces a lower motor neuron weakness of the corresponding muscle groups; corticospinal tract involvement produces an upper motor neuron weakness below the level of the lesion. The sensory deficit spreads downwards bilaterally, the sacral region being the last to become involved.

EPENDYMOMA OF THE CAUDA EQUINA

Over 50% of spinal ependymomas occur around the cauda equina and present with a central cauda equina syndrome (page 394). Operative removal combined with radiotherapy usually gives good long-term results, although metastatic seeding occasionally occurs through the CSF.

SPINAL CYSTIC LESIONS

SYRINGOMYELIA

Syringomyelia is the acquired development of a cavity (syrinx) within the central spinal cord. The lower cervical segments are usually affected, but extension may occur upwards into the brain stem (syringobulbia, see page 381) or downwards as far as the filum terminale.

The cavitation appears to develop in association with obstruction:

The syrinx may obliterate the central canal leaving clumps of ependymal cells in the wall. In contrast HYDROMYELIA is the congenital persistence and widening of the central canal.

Syringomyelia should be distinguished from cystic intramedullary tumours, although both pathologies may coexist.