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February 2009 Case of the Month
Compiled by: Malcolm Shupeck, M.D.
History: An 83-year-old male with progressive gait disturbance, lower extremity weakness, and urinary retention
Images:
Image 1: Axial T1 fat suppression post-contrast. Arrow highlights enhancing dilated pial vein.
Image 2: Sagittal T1 fat suppression post-contrast. Arrows highlight enhancing pial vessels and patchy parenchymal enhancement.
Image 3: Sagittal inversion recovery. Arrow highlighting tapering flame shaped edema pattern and abnormal pial vessels
Image 4: Axial GRE demonstrating abnormal cord configuration and subtlety of findings on this sequence.
Image 5: Sagittal T2. Arrow highlights widened edematous cord.
Image 6: T1 axial with arrow highlighting dilated pial veins.
Figure 1
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Figure 2
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Figure 6
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Diagnosis: Spinal dural arteriovenous fistula (Type I spinal arteriovenuous malformation)
Discussion: Spinal arteriovenous malformation is an uncommon cause of progressive lower extremity and sphincter dysfunction. Spinal AVMs are classified into four types:
| 1. Type I: Spinal dural Arteriovenous fistula extra dural AVF without intramedullary nidus |
| 2. Type II: Intramedullary glomus type AVF forming compact nidus witin the cord similar to brain AVM |
| 3. Type III: Juvenile type. Large complex intra- and extramedullary with extra spinal extension; Rarest 7% |
| 4. Type IV: Intradural extra-perimedullary fistula adjacent to the cord |
Spinal dural arteriovenous fistula (Type I spinal AVM) is the most common form, representing approximately 70% of spinal AVMs. Males predominate by approximately 5:1, with typical onset in middle age. Presenting symptoms include ascending progressive gait disturbance, leg weakness, and sphincter dysfunction. Symptoms may worsen with erect posture or Valsalva.
The condition is presumed to be acquired with thrombosis of extradural veins contributing to the development of an arteriovenous fistula draining into the coronal venous plexus. Absence of valves within this plexus allows transmission of elevated pressure to intramedullary radial veins. Venous hypertension results in venous congestion and ultimately venous thrombosis. Venous hypertension results in a decreased A-V gradient and reduced spinal cord perfusion and congestive myelopathy. As the process progresses from venous congestion to thrombosis the spinal cord sustains increasingly irreversible neural injury, which may ultimately lead to spinal-cord necrosis. Necrotic myelopathy secondary to dural AVF is known as the “syndrome of Foix and Alajouanine.”
Therapy is directed at interruption of the fistulous communication by endovascular intervention or open spinal surgery. Early diagnosis is critical, because good treatment response may often be obtained if intervention takes place prior to irreversible parenchymal injury.
MRI findings classically include an enlarged spinal cord with T1 hypointensity and abnormal enhancing vessels on the pial surface. T2 hyperintensity is reportedly the most sensitive sign. Cord edema is characteristically flame-shaped, with tapering margins superiorly and inferiorly, and spares the cord periphery. Multiple small abnormal vessel flow voids are evident on the pial surface. Contrast images often demonstrate enhancing serpentine vessels on the cord surface and patchy enhancement within the cord.
Findings are distinguishable from demyelination by the length and absence of skip areas. Inferior vena cava should be inspected to exclude vena caval occlusion with collateral venous flow. Spinal AVM (Types II-IV) generally have differing morphology and a more acute presentation, often featuring hemorrhage. Additional differential considerations include vasculitis, polyarteritis nodosa, and porhyria, which differ in clinical presentation, laboratory correlates, and lack of findings of venous obstruction. B12 deficiency generally affects the posterior columns preferentially.
Spinal angiography is the gold standard for confirming the diagnosis and localizing the level of the A-V shunt. Gadolinium-enhanced MR angiography with 3D TOF may also permit localization of the fistula in a majority of cases.
References:
1. Ross J, et al. Diagnostic Imaging.Spine (First Edition). Amirsys, 2005; Section V, 6-18.
2. Thorpe JW, et al. Neuroradiology 1994; 36:522-529.
3. Kataoka H, et al. Neurosurgery; 48(6):1224-1230.
4. Farb,RI, et al. Radiology. 2002; 222:843.
5. Jellema,K, et al. Journal of Neurology ,Neurosurgery and Psychiatry 2003; 74:1438-1440.
6. Bowen, BC, et al. AJNR 1995, Vol. 16; 10:2029-2043. | 
