Neurosurgery notes/Spine/CSF spine diseases/Cord herniation

Cord herniation

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CSF spine diseases

General

  • A rare condition.
  • Aka
    • Anterior Thoracic Spinal Cord Herniation (ATSCH)
    • Idiopathic spinal cord herniation (ISCH)
  • The condition was first described in 1974.

Definition

  • Prolapse of the thoracic spinal cord through a defect in the anterior or anterolateral dura mater.

Epidemiology

  • Prevalence: 0.08% of cases.
  • A rare cause of progressive myelopathy.
  • It typically affects middle-aged adults, with an average age of 51 years.
  • The condition is more common in females.

Clinical Features

  • The characteristic symptom is a progressive Brown-Séquard-like deficit.
    • This may progress to paraparesis (weakness in the lower limbs).
  • Other common features include:
    • Back pain.
    • Sensory level changes.
    • Spasticity and muscle atrophy in the lower limbs.
    • Sexual and sphincter dysfunction.

Pathophysiology

  • The exact origin of the dural defect is unknown but there are several theories
    • Congenital Disorders:
      • A congenital dural defect could lead to an extradural arachnoid cyst or pseudomeningocele. Some theories suggest the cord herniates into a duplication of the dura mater.
    • Acquired Defects:
      • Possible causes include trauma, disc herniation, inflammation, or pressure erosion of the dura.
    • Anatomical Factors:
      • The natural forward curve (kyphosis) of the thoracic spine places the spinal cord in an anterior position, which may facilitate herniation through a ventral dural defect.
    • Dynamic Forces:
      • Repetitive minor trauma from cardiac, pulmonary, and cerebrospinal fluid (CSF) pulsations against a weakened dura may contribute to the herniation.

Investigation

  • MRI:
      • This is the most accurate diagnostic tool.
      • Features
        • Thinning of the spinal cord.
        • Adherence of the cord to the anterior spinal canal.
        • A visible "gap" in the anterior dura on T2-weighted images.
          •  
      notion image
  • CT Myelography:
    • This can also be a useful diagnostic modality.

Classification

  • A classification system based on MRI findings has been proposed to categorise the herniation:
    • Sagittal Classification:
      • Type K: Shows an obvious ventral "kink" in the spinal cord.
      • Type D (Discontinuous): The spinal cord appears to completely disappear at the site of herniation.
      • Type P (Protrusion): The anterior subarachnoid space disappears, but there is almost no focal kink in the cord.
    • Axial Classification:
      • Location: Classified as central (Type C) or lateral (Type L).

Management

Conservative Management

  • Indications
    • Asymptomatic

Surgical Management

  • Indications:
    • Neurological progression
    • Severe neurological deficit
  • Aim
    • Halt neurological deterioration.
  • Surgical goals:
    • De-tether the cord
    • Reduce the herniation
    • Implement measures to prevent re-herniation.
  • Approach:
    • Posterior approach via a laminectomy or laminoplasty.
      • Most common approach
    • Thoracotomy
      • Less preferred due to trans-thoracic complications
  • Surgical Techniques:
    • 2 techniques to repair the dural defect
      • Widening of the Dura Defect (WDD):
        • This involves cutting the inner dural layer along the herniated cord to enlarge the defect, making it wider than the spinal cord's diameter to prevent re-herniation.
        • This technique avoids additional manipulation in front of the vulnerable spinal cord.
      • Anterior Dura Patch (ADP):
        • This technique involves covering the dural defect with a patch (Duragen, muscle or fascia)
          • Suture the patch to the surrounding tissue to prevent drifting of patch down
    • Choice of Technique:
      • In a direct comparison, WDD was associated with more patients showing improvement than ADP.
        • However, in a more complex multivariate analysis, the pre-operative presence of a Brown-Séquard-like deficit was the most dominant factor influencing outcomes, and a clear statistical preference for WDD could not be established.
        • Despite this, the authors of the meta-analysis favour WDD as the surgical technique of choice, considering it an effective and safe method for spinal cord release and prevention of re-herniation.
  • Use intraoperative Neurophysiologic Monitoring (IONM)

Prognosis and Outcomes:

  • Surgical results are generally favourable, with a high percentage of patients (75.2%) experiencing postoperative improvement.
  • The strongest predictor of postoperative motor improvement is the presence of a Brown-Séquard-like deficit before surgery, as compared to patients with paraparesis.
  • Prognosis is worse for patients with more severe pre-existing deficits like established paraplegia and spasticity.