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Spinal Dural Arteriovenous Fistula (DAVF)

Summary

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  • Abnormal arteriovenous shunt between radiculomeningeal artery and radicular vein within dura mater, causing venous congestion and progressive myelopathy
  • Presents with progressive lower extremity weakness, sensory changes, and bowel/bladder dysfunction
  • MRI shows T2 hyperintense cord signal with perimedullary flow voids and cord enhancement

Pathophysiology

  • Acquired lesion with direct arteriovenous shunt typically at nerve root sleeve level
  • Arterial feeder (usually single radiculomeningeal artery) connects directly to radicular vein
  • Arterialized venous flow causes venous hypertension in coronal venous plexus
  • Venous congestion leads to:
    • Decreased arteriovenous pressure gradient
    • Reduced tissue perfusion
    • Chronic hypoxia and oedema
    • Progressive myelopathy (Foix-Alajouanine syndrome)
  • Most commonly located in thoracolumbar region (T6-L2)

Demographics

  • Most common spinal vascular malformation (60-80% of all spinal AVMs)
  • Male predominance (5:1 ratio)
  • Peak incidence: 5th-6th decade
  • Rare in patients under 30 years
  • Risk factors:
    • Previous spinal trauma
    • Prior surgery
    • Unknown in most cases (idiopathic)

Diagnosis

  • Clinical presentation:
    • Insidious onset with progressive symptoms
    • Ascending myelopathy
    • Lower extremity weakness (symmetric or asymmetric)
    • Sensory disturbances (paresthesias, numbness)
    • Bowel and bladder dysfunction
    • Erectile dysfunction in males
    • Symptoms may worsen with exercise (venous congestion)
  • Physical examination:
    • Upper motor neuron signs below lesion level
    • Hyperreflexia
    • Positive Babinski sign
    • Sensory level may be present

Imaging

  • MRI Spine:

    • T2: Hyperintense intramedullary signal (cord oedema), typically involving multiple segments with predominant central/centromedullary distribution
    • T2: Perimedullary flow voids (dilated veins) appearing as serpentine hypointense structures on dorsal cord surface
    • T1: Normal or slightly hypointense cord signal
    • T1+C: Patchy intramedullary enhancement (subacute cases), enhancement of perimedullary vessels
    • DWI: Usually normal (helps differentiate from acute infarction)
    • MRA: May demonstrate enlarged perimedullary vessels and early draining vein

  • CT Angiography:

    • Dilated perimedullary veins
    • May identify feeding artery level
    • Less sensitive than MRI for cord changes

  • Digital Subtraction Angiography (DSA):

    • Gold standard for diagnosis and treatment planning
    • Identifies:
    • Feeding radiculomeningeal artery
    • Fistula location
    • Draining radicular vein
    • Dilated coronal venous plexus
    • Prolonged venous phase
    • Absence of nidus (differentiates from AVM)

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  • A 50-year-old male presented with a 6 month history of progressively worsening spasticity and weakness in both legs.
  • MRI showed distal cord hyperintensity and many extramedullary flow voids.
  • Time-resolved MRA showed early arterial filling of a vessel running along the ventral cord.

Treatment

  • Endovascular embolization:

    • First-line treatment in accessible lesions
    • Liquid embolic agents (N-butyl cyanoacrylate, Onyx)
    • Goal: Complete obliteration of fistula
    • Success rate: 70-90%
    • Risk of incomplete occlusion or recanalization

  • Surgical ligation:

    • Indicated when:
    • Endovascular approach fails or not feasible
    • Feeding artery supplies anterior spinal artery
    • Recurrence after embolization
    • Interruption of intradural draining vein
    • Success rate: >95%
    • Lower recurrence rate than embolization

  • Post-treatment follow-up:

    • Clinical assessment for symptom improvement
    • MRI at 3-6 months to assess cord signal changes
    • DSA if clinical or MRI suspicion of recurrence

Differential diagnosis

Differential diagnosis Differentiating feature
Spinal cord tumour Intramedullary expansile mass with cord enlargement and heterogeneous enhancement; no perimedullary flow voids
Transverse myelitis Absence of perimedullary flow voids on MRI; cord swelling and enhancement; no serpiginous vascular structures
Multiple sclerosis Multiple periventricular and juxtacortical white matter lesions on brain MRI; short cord lesions without perimedullary flow voids
Spinal cord infarction Restricted diffusion on DWI with owl-eye or pencil-like pattern; absence of perimedullary flow voids; anterior cord predilection
Subacute combined degeneration (B12 deficiency) Dorsal column predominant signal change with inverted V sign on axial MRI; no perimedullary flow voids
Spinal arteriovenous malformation (AVM) Intramedullary nidus visible on angiography; multiple feeders rather than a single fistulous connection
Chronic inflammatory demyelinating polyneuropathy (CIDP) Nerve root enhancement on post-contrast MRI rather than cord signal change; no perimedullary flow voids
Radiation myelopathy T2 signal change and cord atrophy confined to the radiation treatment field; no perimedullary flow voids