In an adult presenting with progressive myelopathy, back pain or radiculopathy from a spinal arteriovenous fistula (type I dural or type II intradural perimedullary), what is the recommended first‑line endovascular embolisation protocol, including general anesthesia, systemic heparinisation (70–100 U/kg bolus to maintain activated clotting time 250–300 seconds), choice of embolic material (detachable coils, n‑butyl‑2‑cyanoacrylate (NBCA) mixed 1:1 with Lipiodol, or ethylene‑vinyl‑alcohol copolymer (Onyx)), postoperative steroid regimen, anticoagulation management, neuro‑intensive care monitoring, and follow‑up imaging schedule?

Endovascular Treatment of Spinal Arteriovenous Fistulas

Primary Treatment Recommendation

For spinal dural arteriovenous fistulas (Type I), microsurgical disconnection remains the definitive first-line treatment with superior long-term occlusion rates (100% vs 75-88% for endovascular), though endovascular embolization is a reasonable alternative for anatomically favorable lesions with experienced operators. 1, 2

When to Consider Endovascular Embolization First-Line

Endovascular embolization is most appropriate when:

• Single, easily accessible radicular feeding artery identified on diagnostic angiography with straightforward catheter navigation 1
• Proximal fistula location where the arteriovenous connection can be reached without tortuous vessel navigation 3
• Patient factors precluding surgery (medical comorbidities, anticoagulation requirements, patient preference for minimally invasive approach) 4

Critical caveat: Endovascular treatment should only be attempted when complete occlusion of both the fistula point AND the proximal draining vein can be achieved—partial embolization increases surgical difficulty and does not reduce hemorrhage risk. 3, 1

Endovascular Protocol Details

Anesthesia and Monitoring

• General endotracheal anesthesia is standard, though no evidence demonstrates superiority over conscious sedation for complication rates 5
• Direct arterial pressure monitoring via femoral sheath or guide catheter 5
• Pulse oximetry on ipsilateral foot to detect femoral artery compromise 5
• Bladder catheter for fluid management during prolonged procedures 5

Anticoagulation Management

• Systemic heparinization with 70-100 U/kg bolus to maintain activated clotting time 250-300 seconds during catheter manipulation 5
• This prevents thromboembolic complications during prolonged microcatheter positioning 5

Embolic Agent Selection

Liquid embolic agents (Onyx/EVOH or NBCA) are strongly preferred over coils or particles:

• Onyx (ethylene-vinyl-alcohol copolymer) achieves 83% complete occlusion rates in modern series, with no procedure-related complications and no recurrences when complete occlusion achieved 6
• NBCA (n-butyl cyanoacrylate) mixed 1:1 with Lipiodol provides superior penetration into the draining vein but requires faster injection technique 3, 6
• Polyvinyl alcohol particles demonstrate 16% recanalization rates and should be avoided 5
• Detachable coils alone are inadequate—they cause proximal arterial occlusion without nidal penetration, promoting collateral formation and eliminating future endovascular access 7, 8

The critical technical goal is penetration of embolic material through the fistula point into the proximal 1-2 cm of the draining vein—this is what differentiates curative from palliative embolization. 3, 6

Technical Execution

• Superselective microcatheter positioning as close to the fistula point as possible, ideally within the intradural segment of the radicular artery 7, 8
• Controlled, prolonged injection using pressure cooker technique with DMSO-compatible balloon microcatheters for Onyx to achieve complete nidal penetration 5
• Avoid proximal arterial occlusion without addressing the fistula itself—this worsens the lesion 7, 8

Post-Procedure Management

Immediate Post-Operative Care

• Strict blood pressure control to normotension for at least 24 hours to prevent hemorrhagic complications from flow redistribution 8
• Neurointensive care monitoring for 24 hours minimum to detect complications 9
• Maintain euvolemic, normotensive state—avoid hypotension which may worsen spinal cord perfusion 9

Steroid Regimen

No rigorous evidence supports routine corticosteroid use in spinal AVF embolization 5. Steroids may be considered if:

• Significant cord edema present on pre-procedure MRI
• Concern for inflammatory response to embolic material
• Post-procedure neurological deterioration

Anticoagulation Post-Procedure

• Discontinue heparin immediately after procedure completion 5
• No routine post-procedure anticoagulation unless other indication exists 3, 6
• Aspirin or antiplatelet therapy is not routinely indicated for spinal dural AVFs 5

Follow-Up Imaging Schedule

• Immediate post-procedure angiography to confirm complete fistula occlusion 6, 2
• MRI spine at 3-6 months to assess for regression of perimedullary varices and cord edema 6, 4
• Spinal angiography at 6-12 months if MRI shows persistent flow voids or clinical deterioration, as recurrence occurs in 12-13% of cases 4, 2
• Annual clinical follow-up indefinitely, as late recurrences can occur 4

Expected Outcomes

Angiographic Success Rates

• Complete occlusion with Onyx: 76-88% in modern series 6, 4
• Complete occlusion with NBCA: 70-90% 3
• Microsurgical occlusion: 96-100% 1, 2

Clinical Outcomes

• Clinical improvement or stabilization: 88-92% when complete occlusion achieved 6, 4
• Motor and gait improvement more likely than bladder function recovery 3
• Recurrence rate: 12-13% requiring repeat intervention 4, 2

Critical Pitfalls to Avoid

1. Partial embolization without venous penetration—this does not cure the fistula and complicates subsequent surgery by promoting collaterals 7, 8, 3

2. Proximal feeding artery occlusion with coils—this is the worst possible outcome, as it eliminates endovascular access while leaving the fistula patent 7, 1

3. Inadvertent venous occlusion before complete nidal obliteration—causes catastrophic hemorrhage from venous hypertension 7

4. Declaring success without confirming venous penetration—post-embolization angiography must demonstrate complete absence of arteriovenous shunting 6, 2

Salvage Strategy for Failed Embolization

When endovascular embolization fails to achieve complete occlusion (12-25% of cases), proceed directly to microsurgical disconnection rather than repeat embolization attempts. 1, 2

• Intraoperative micro-Doppler helps localize the fistula point 1
• Endovascular coil placement pre-operatively can mark the fistula location 1
• Surgical outcomes remain excellent even after failed embolization if the fistula point is correctly identified 2

Type II Intradural Perimedullary AVFs

These lesions have different anatomy and treatment considerations:

• More compact architecture with direct arterial-to-venous connection on the cord surface 7, 8
• Higher endovascular cure rates (95-100%) when single feeder and compact nidus present 7, 8
• Transvenous embolization may be advantageous for single draining vein lesions 5, 7
• Surgical access more challenging due to intramedullary location 5