Spinal dural arteriovenous fistula (SDAVF) is the most common spinal vascular malformation, accounting for 60-80% of all spinal vascular malformations. Also classified as Type I spinal AVM. Pathologically, there is an abnormal direct connection (fistula) between a dural artery and a perimedullary (radiculomedullary) vein — typically located at the spinal nerve root exit point (dural sleeve). This fistula causes arterialized venous blood flow: perimedullary veins dilate, venous pressure increases, and cord venous drainage is impaired. The result is chronic venous congestion → cord edema → progressive myelopathy (Foix-Alajouanine syndrome). Two cardinal MRI findings: (1) diffuse cord T2 hyperintense signal (central edema) and (2) serpentine flow voids on cord surface (dilated perimedullary veins). Thoracolumbar level (75-80%) is the most commonly affected region. Progressive lower extremity weakness, urinary retention, and sexual dysfunction are typical clinical presentations. Conventional spinal angiography (DSA) is the gold standard for diagnosis. Treatment is by endovascular embolization or surgical fistula ligation.
Age Range
40-80
Peak Age
60
Gender
Male predominant
Prevalence
Rare
The fundamental pathophysiology of SDAVF is based on the venous congestion mechanism. Under normal conditions, spinal cord venous drainage flows through low-pressure perimedullary veins to the epidural venous plexus and then to the systemic venous system. When a fistula forms, the dural artery delivers arterialized blood directly into the perimedullary vein — venous pressure rises to arterial levels. This high pressure causes dilation of perimedullary veins (flow voids on MRI). More importantly, increased venous pressure creates a gradient that impedes cord intramedullary venous drainage — venous outflow from cord parenchyma is impaired. Venous congestion reduces perfusion pressure at the capillary level, causing cord hypoxia and ischemia. Simultaneously, capillary permeability increases and vasogenic edema develops — T2 hyperintensity on MRI reflects this edema. Chronic ischemia leads to accumulated neuronal damage and irreversible myelopathy (Foix-Alajouanine syndrome). Gadolinium enhancement indicates disrupted blood-cord barrier. Flow voids on MRI result from signal loss of fast-flowing blood — in spin-echo sequences, fast flow prevents protons from receiving both the 90° and 180° pulses, resulting in signal loss (flow void).
Multiple signal-void structures with serpentine, tortuous course on the spinal cord surface. Correspond to dilated perimedullary veins carrying arterialized blood. Pathognomonic for SDAVF — spinal angiography is indicated when this finding is present. These structures appear bright on contrast series.
Tortuous, serpentine signal-void structures (flow voids) are observed on the dorsal and ventral cord surface. These structures correspond to dilated perimedullary veins carrying arterialized blood. On sagittal T2, they create a 'string of beads' or 'snake-like' appearance on the cord surface. This finding is pathognomonic for SDAVF and is the most important distinguishing feature from other myelopathy causes.
Report Sentence
Multiple serpentine flow voids on the spinal cord surface corresponding to dilated perimedullary veins, consistent with spinal dural arteriovenous fistula.
Diffuse T2 hyperintense signal in the cord center extending over a long segment (typically >5-6 vertebral segments). Edema usually extends cranially from the conus region. Central gray matter predominant involvement may be seen on axial. Signal intensity is homogeneous or mildly heterogeneous. This edema develops through a vasogenic mechanism due to venous congestion.
Report Sentence
Diffuse T2 hyperintense signal in the spinal cord extending over [X] vertebral segments from [level], corresponding to venous congestive myelopathy (SDAVF).
Post-gadolinium patchy cord parenchymal enhancement and enhancement of dilated veins on the cord surface are observed. Cord enhancement reflects disrupted blood-cord barrier. Vein enhancement creates bright appearance of tortuous, serpentine structures — 'unmasking' of flow voids on contrast series is typical.
Report Sentence
Patchy cord parenchymal enhancement and enhancement of dilated tortuous vascular structures on the cord surface on post-contrast series, consistent with SDAVF.
Contrast-enhanced MR angiography (MRA) or time-resolved MRA can localize the fistula point. Early arterial phase shows abnormal filling of the dural artery and early venous drainage. Fistula is usually at thoracolumbar level (T6-L2), at a unilateral nerve root exit. MRA reduces the invasiveness of DSA by narrowing the fistula level and guiding DSA.
Report Sentence
Abnormal venous enhancement in early arterial phase at [level] on MR angiography, consistent with dural arteriovenous fistula; confirmation with conventional spinal angiography recommended.
CT myelography (after intrathecal contrast) may show irregular, serpentine filling defects or dilated vascular structures outlined by contrast on the cord surface. CT myelography is an alternative diagnostic method when MRI is contraindicated or unavailable. Cannot directly show cord edema but can detect cord swelling and surface vascular abnormalities.
Report Sentence
Serpentine filling defects consistent with dilated vascular structures on the cord surface on CT myelography; spinal dural AVF should be investigated.
Criteria
Dural artery → perimedullary vein. Single fistula point. Thoracolumbar level. Low-flow.
Distinct Features
Most common type (75-80%). Treated with embolization or surgery. Usually single feeding artery.
Criteria
Fistula in epidural space. May be high-flow. Prominent epidural venous dilation.
Distinct Features
Rarer. More aggressive clinical course. Endovascular treatment may be more challenging.
Criteria
Fistula on cord surface (intradural). Anterior spinal artery → perimedullary vein. High-flow.
Distinct Features
In younger patients. Giant perimedullary venous ectasia. Higher risk of hemorrhagic complications.
Distinguishing Feature
Flow voids are ABSENT on cord surface in transverse myelitis — this is the most critical differentiating point. Myelitis has acute/subacute onset; SDAVF shows progressive chronic course. Enhancement in myelitis is patchy but surface vein enhancement is not expected. AQP4-IgG/MOG-IgG antibodies support myelitis.
Distinguishing Feature
Spinal astrocytoma forms a focal expansile mass with heterogeneous enhancement. SDAVF shows diffuse cord edema and surface flow voids. Astrocytoma in younger patients; SDAVF common in >40-year-old males. Flow voids not expected in astrocytoma.
Distinguishing Feature
Ependymoma forms a central focal mass with intense homogeneous enhancement, may show polar cysts and hemosiderin cap sign. SDAVF has no focal mass effect, edema is diffuse and surface flow voids are distinguishing. Ependymoma in young-middle age; SDAVF in older age.
Urgency
urgentManagement
interventionalBiopsy
Not NeededFollow-up
specialist-referralSDAVF is a treatable cause of progressive myelopathy — neurological deficits may be partially or fully reversible with early diagnosis and treatment. Delayed diagnosis leads to permanent paraplegia. Conventional spinal angiography (DSA) is the gold standard for diagnosis — precisely localizes the fistula point. Treatment options: (1) endovascular embolization — closing the fistula's draining vein connection with acrylic glue (NBCA/Onyx), success rate 60-80%; (2) surgical ligation — intradural ligation of the draining vein, success rate 90-95%, very low recurrence rate. Post-treatment MRI follow-up is performed — regression of cord edema and disappearance of flow voids indicate successful treatment. Neurological recovery depends on treatment timing — with early intervention, motor function improvement is 60-80%, urinary function improvement is more limited.
SDAVF is a treatable cause of progressive myelopathy — delayed diagnosis leads to permanent paraplegia. Conventional spinal angiography (DSA) is the gold standard. Treated by endovascular embolization (with acrylic glue) or surgical ligation to close the draining vein. Neurological deficits may be reversible with early diagnosis.