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Tethered cord

Tethered spinal cord syndrome, also known as an occult spinal dysraphism sequence, is a neurological disorder caused by tissue attachments that limit the movement of the spinal cord within the spinal column.

Clinical presentation

The condition is closely linked to spina bifida, and as such presentation in childhood may be with the cutaneous stigmata of dysraphism (hairy patch, dimple, subcutaneous lipoma).

There may be associated foot and spinal deformities, leg weakness, low back pain, scoliosis and incontinence.

The condition may go undiagnosed until adulthood, with development of sensory and motor problems and loss of bowel and bladder control.

Pathology

Spinal cord tethering should be thought of as primary and secondary:

  • primary tethered cord syndrome occurs as an isolated anomaly
  • secondary tethered cord syndrome occurs in the setting of other abnormalities, e.g. myelomeningocoelefilum terminale lipoma, trauma 3

The spinal column develops at a greater rate than the spinal cord during fetal development, and abnormal attachments lead to abnormal stretching of the spinal cord.

Tethering may also develop after spinal cord injury and scar tissue can block the flow of fluids around the spinal cord.

Fluid pressure may cause cysts to form a syringomyelia

Radiographic features

Imaging features are of a low conus medullaris (below L2) and thickened filum terminale (> 2 mm).

Ultrasound 

Ultrasound may be a useful screening exam and may be of use in the paediatric population. The lack of ossification of the posterior arch of the spine in normal infants and the presence of a bony defect in patients with spina bifida permit sonographic examination.

MRI

MRI is useful in visualizing the conus medullaris, assessing the thickness of the filum terminale, identifying traction lesions, and evaluating associated bony dysraphisms.

In one study of 25 patients 1 in 84% the tip of the conus was below the level of the mid-L2 vertebral body.

Prone imaging may be useful in patients who have undergone tethered cord surgery or in those in whom clinical suspicion is high while supine MRI imaging demonstrated no abnormalities. Prone MRI imaging is however of little value when supine MRI has demonstrated the defect.

Treatment and prognosis

Untreated, tethered cord syndrome has a progressive course. Surgical release, in selected patients, can dramatically improve function 3


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