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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 enhancement1

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)

panels-1

  • 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 embolisation or surgical disconnection of the fistula; early treatment prevents irreversible myelopathy
  • The combination of central cord T2 oedema with dorsal perimedullary flow voids is the key imaging clue to this frequently missed, treatable cause of myelopathy

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

  1. C Koch. Spinal dural arteriovenous fistula. 2006. Current opinion in neurology - Open in new tab. ↩