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Ventral Cord Herniation

Summary

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  • Rare condition characterised by anterior herniation of the spinal cord through a dural defect, most commonly occurring in the thoracic spine
  • Presents with progressive myelopathy, often with Brown-Séquard-like syndrome or asymmetric motor and sensory deficits
  • MRI demonstrates focal anterior displacement of the cord with characteristic "C-shaped" configuration on axial images and obliteration of the anterior CSF space1

Pathophysiology

  • Etiology remains unclear with multiple proposed mechanisms:
    • Congenital dural defect theory
    • Acquired defect from trauma, inflammation, or disc herniation erosion
    • CSF pressure gradients causing progressive herniation
  • Pathologic process:
    • Ventral dural defect allows cord herniation
    • Tethering and strangulation of cord at defect edges
    • Progressive myelopathy from chronic compression and ischaemia
    • Associated adhesions between cord and ventral dura
  • Classification:
    • Type K: focal herniation with kink/angulation
    • Type D: diffuse smooth ventral displacement
    • Type P: associated with ventral pseudomeningocele

Demographics

  • Incidence:
    • Extremely rare condition
    • Less than 200 cases reported in literature
  • Age:
    • Middle-aged adults (40-60 years)
    • Mean age at diagnosis: 50 years
  • Gender:
    • Female predominance (F:M ratio approximately 2:1)
  • Location:
    • Mid-thoracic spine most common (T3-T7)
    • Rarely cervical or lumbar

Diagnosis

  • Clinical presentation:
    • Insidious onset of progressive myelopathy
    • Brown-Séquard syndrome (most common)
    • Asymmetric motor weakness
    • Sensory level deficit
    • Spasticity and hyperreflexia below lesion
    • Bowel/bladder dysfunction (late finding)
  • Physical examination:
    • Upper motor neuron signs
    • Asymmetric weakness
    • Dissociated sensory loss
    • Positive Babinski sign
  • Differential diagnosis:
    • Arachnoid cyst
    • Intradural disc herniation
    • Spinal cord tumour
    • Transverse myelitis
    • Anterior spinal artery syndrome

Imaging

  • MRI (modality of choice):
    • T2:
    • Focal anterior displacement of spinal cord
    • "C-shaped" or "boomerang" configuration on axial images
    • Obliteration of anterior subarachnoid space
    • Possible cord signal hyperintensity (myelomalacia/oedema)
    • Widened dorsal subarachnoid space
    • T1:
    • Anterior displacement of cord
    • Loss of normal anterior CSF signal
    • Cord may appear adherent to vertebral body
    • T1+C:
    • No enhancement typically
    • May show enhancement if associated inflammation
    • Sagittal imaging:
    • Focal kink or angulation of the cord with anterior displacement (the "scalpel sign" of a sharp dorsal indentation instead suggests a dorsal arachnoid web)
    • Axial imaging:
    • Characteristic C-shaped cord configuration
    • Cord adherent to posterior vertebral body/disc
    • CISS/FIESTA sequences:
    • Better delineation of dural defect
    • Improved visualization of arachnoid adhesions
  • CT Myelography:
    • Historical importance, largely replaced by MRI
    • Shows ventral filling defect
    • Cord displacement anteriorly
    • May demonstrate dural defect
  • Plain radiographs:
    • Usually normal
    • May show associated spinal deformity

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  • A 45-year-old patient experienced a long progressive history of numbness and mild weakness in both legs.
  • MRI showed the cord displaced anteriorly against the ventral theca.
  • There were also ventral epidural collections indicating a CSF leak and herniation of the cord into the defect.

Treatment

  • Surgical reduction and dural defect repair for progressive myelopathy; stable cases may be observed
  • The focal C-shaped anterior cord displacement with an effaced ventral CSF space and widened dorsal space is the key, and must be distinguished from a dorsal arachnoid web (which indents the cord dorsally)

Differential diagnosis

Differential diagnosis Differentiating feature
Arachnoid cyst Cyst appears as CSF-filled space posterior to cord; cord displaced anteriorly rather than herniated through dura
Spinal cord infarction Acute onset of symptoms; T2 hyperintensity within cord parenchyma; no anterior displacement or herniation
Multiple sclerosis Multiple lesions in space and time; plaques within cord substance rather than herniation; brain lesions often present
Syringomyelia Fluid-filled cavity within the cord parenchyma; cord may be expanded rather than herniated
Spinal arteriovenous malformation/fistula Flow voids on MRI; serpentine vessels along cord surface; cord oedema without herniation
Spinal cord tumour Mass effect with cord expansion; enhancement with contrast; no ventral herniation through dural defect
Transverse myelitis Acute inflammatory process; long segment T2 hyperintensity; cord swelling without herniation
Spinal cord atrophy Diffuse cord thinning without focal anterior displacement; no dural defect
Epidural lipomatosis Excessive epidural fat causing cord compression; no dural defect or cord herniation
Disc herniation with cord compression Disc material visible; cord compressed posteriorly rather than herniated anteriorly

  1. Buntting et al. Scalpel sign: Dorsal thoracic arachnoid web, thoracic arachnoid cyst and ventral cord herniation. 2022. Radiology case reports - Open in new tab. ↩