When should endovascular embolization be used as first‑line treatment for symptomatic spinal arteriovenous malformations, and what are the key indications and procedural considerations (lesion accessibility, neurological baseline, AVM type and location, hemorrhage or progressive myelopathy, imaging requirements, and embolic agents such as ethylene‑vinyl alcohol copolymer (Onyx) or n‑butyl cyanoacrylate (n‑BCA))?

Endovascular Treatment of Spinal Arteriovenous Malformations

Primary Recommendation

Endovascular embolization should be used as first-line treatment for spinal AVMs when the lesion has favorable anatomy: small compact nidus (<1 cm), limited arterial feeders (1-2 vessels), accessible feeding arteries for superselective catheterization, and well-defined venous drainage without stenosis. 1, 2 For lesions with these characteristics, particularly pial arteriovenous fistulas and small glomus-type AVMs, endovascular therapy achieves complete obliteration rates of 95-100% with procedural morbidity of only 0-2.7%. 1, 2

Key Indications for First-Line Endovascular Treatment

Anatomic Criteria (Most Critical)

• Small lesions (<1 cm diameter) with compact architecture are ideal candidates, as they demonstrate the highest complete occlusion rates with endovascular therapy. 1
• Single arterial feeder lesions, such as those supplied by distal PICA or single radiculomedullary arteries, are optimal for transarterial embolization. 1
• Deep or eloquent location lesions (posterior fossa, intramedullary spinal cord) benefit most from endovascular approaches, as surgical access carries prohibitively high morbidity. 1
• Anterograde venous drainage into superficial veins without stenosis or reflux reduces hemorrhagic risk during embolization. 1

Clinical Presentations Favoring Endovascular Approach

• Acute hemorrhagic presentation requiring immediate protection from rebleeding, where endovascular therapy provides instant flow reduction. 3
• Progressive myelopathy from venous hypertension, where partial flow reduction through iterative particle embolization stabilizes symptoms in 57% and improves symptoms in 31% of cases. 4
• Surgically inaccessible lesions with high-risk features (deep perforator supply, eloquent location). 5

Procedural Considerations and Technical Approach

Pre-Procedural Imaging Requirements

• Digital subtraction angiography (DSA) with 2D, 3D, and reformatted cross-sectional views is mandatory for treatment planning, as it defines feeding arteries, nidus architecture, and venous drainage patterns. 3
• Identify associated aneurysms (present in 7-41% of cases), as these require treatment first if symptomatic or intranidal. 3

Embolic Agent Selection

For curative intent with favorable anatomy:

• Ethylene-vinyl alcohol copolymer (Onyx) is the preferred agent for transarterial embolization, allowing controlled, prolonged injections using the pressure cooker technique with DMSO-compatible balloon microcatheters to achieve complete nidal penetration. 1, 6, 7
• N-butyl cyanoacrylate (n-BCA) is an alternative permanent agent, though it requires faster injection and more precise timing. 3
• Curative embolization rates with Onyx and n-BCA range from 15-50% overall, but reach 95-100% for carefully selected small lesions with favorable anatomy. 3, 1

For palliative intent or complex lesions:

• Calibrated particle embolization as first-line therapy is safe for spinal cord AVMs with small, distal, multiple shunts, with zero neurological deterioration in particle-only cases versus 4 complications with cyanoacrylate (P<0.001). 4
• Iterative particle embolization (median 5 sessions) prevents rebleeding (0/322 patient-years with partial treatment vs. 4/14 patient-years without treatment, P=0.001), even without complete angiographic cure. 4

Critical Technical Execution

Catheter positioning:

• Position the microcatheter as distally as possible near the fistula point to ensure complete nidal obliteration and minimize complications. 2, 8
• Superselective catheterization of feeding arteries is mandatory; proximal occlusion without nidal penetration promotes collateral formation (16% recanalization rate) and eliminates future endovascular access. 1, 8

Injection technique:

• Achieve complete nidal obliteration in a single session when anatomically feasible to avoid collateral formation and treatment difficulties. 2, 8
• For particle embolization, use "one by one" injection technique with calibrated particles to maximize safety. 4

Expected Outcomes and Risk Profile

Efficacy

• Complete angiographic obliteration: 95-100% for small pial fistulas, 11% for nidal-type spinal AVMs, 63% for fistulous-type spinal AVMs. 1, 4
• Partial embolization prevents rebleeding (0/322 patient-years) even without complete cure in spinal cord AVMs. 4

Complications

• Hemorrhagic complications: 2-6% 3, 1
• New neurological deficits: 10-14% (transient in most cases) 3
• Permanent neurological deficits: 2-5% 3, 1
• Mortality: <1% 3, 1

Critical Pitfalls to Avoid

Never perform proximal feeding artery occlusion without nidal penetration, as this worsens the lesion by promoting collateral formation (16% recanalization with polyvinyl alcohol) and eliminates future endovascular access. 1, 8

Never occlude the draining vein before complete nidal obliteration, as this causes catastrophic hemorrhage from venous hypertension. 1, 2

Avoid partial embolization without intent to cure or palliate, as incomplete treatment without a defined endpoint increases hemorrhage risk and complicates subsequent therapy. 1, 8

Do not use particle embolization for large single shunts; cyanoacrylate or Onyx is required for these lesions, as particles cannot occlude high-flow fistulas. 4

Post-Procedural Management

Maintain strict blood pressure control targeting normotension with continuous monitoring for at least 24 hours to prevent hemorrhagic complications from flow redistribution and normal perfusion pressure breakthrough. 2, 8

Perform follow-up angiography to confirm complete obliteration, as delayed recanalization can occur even with permanent embolic agents. 8

Alternative Treatment Pathways

When Endovascular Therapy is Adjunctive (Not First-Line)

• Pre-surgical embolization for medium-to-large AVMs (>3 cm) to reduce operative time, blood loss, and surgical morbidity by targeting deep perforators and reducing nidus size. 3
• Adjunct to radiosurgery for large lesions to reduce target volume, though this adds cumulative risk from each modality. 3

When Surgery is Preferred Over Endovascular

• Intradural dorsal (dural) AVFs remain largely surgical due to lower recurrence rates with surgical disconnection, though recent data show equivocal outcomes with endovascular treatment. 9
• Extradural-intradural (juvenile) AVMs and conus AVMs remain difficult-to-treat lesions where multimodality therapy is often required. 9