General Description

Spinal vascular malformations, including arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs), are rare lesions that are believed to account for 10% of all spinal cord lesions. Symptoms tend to present after a spontaneous hemorrhage or in a more progressive slow fashion, resulting in spinal cord dysfunction. The natural history of these lesions tends to be that 10% hemorrhage, 19% lead to progressive motor weakness within 6 months of diagnosis, and 71% have a slower progression over time. Understanding the angioarchitecture of these lesions becomes paramount to understanding high-risk characteristics for treatment planning, patient selection, and risk assessment. The etiology of symptom progression tends to focus around intramedullary hemorrhage, arterial steal caused by high-flow lesions, venous hypertension likely from dural arteriovenous fistulas (dAVFs), and mass effect.

Evidence for Treatment

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  Endovascular treatment for dAVFs leads to gait improvement in 80% of moderately disabled patients and 65% of severely disabled patients.

  
  
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  Intradural perimedullary fistulas are classified based on Merland’s initial description. Type 1 lesions tend to be surgically accessible and high risk for endovascular therapy. Type 2 lesions, located on the dorsal surface of the spinal cord, can be effectively embolized. Type 3 lesions are high-flow dilated vessels likely needing presurgical endovascular therapy. Antonietti et al reported improvement in symptoms for patients after embolization in 26% of type 1 lesions, 27% of type 2 lesions, and 62% of type 3 lesions.

  
  
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  38 of 47 intramedullary AVMs were treated with N-butyl-2-cyanoacrylate (n-BCA), resulting in obliteration of the lesion in 53% with an overall complication rate of 11%.

Classification and Indications

Rosenblum et al ¹ classified AVMs into four types. Type 1 lesions are dAVFs. These lesions can be cured by focusing on achieving successful embolization distal to the arterial-to-venous connection. An embolic plug placed endovascularly in the venous channel significantly improves patient outcomes and decreases risk of hemorrhage and venous hypertension. Type 2 lesions are intramedullary spinal AVMs that are potentially resectable. Angioarchitecture plays a critical role in understanding the indications for treatment. Focused embolization for high-risk features such as intranidal aneurysms can decrease the risk of subsequent hemorrhage and clinical deterioration as well as serve as a preoperative adjunct. Type 3 lesions are juvenile AVMs that have not been associated with high rates of complete obliteration postoperatively. Indications for treatment include high-risk features that require embolization for palliation of symptoms. Type 4 lesions are perimedullary AVFs without an intervening nidus. Several small series have demonstrated successful embolization of these lesions through a transarterial route.

Neuroendovascular Anatomy

Spinal vascular malformations typically arise from segmental vessels off the aorta. An understanding of the origin of the artery of Adamkiewicz as well as the typical vascular loop noted at the conus and higher cervical and subclavian branches that anastomose at the level of the spine is important to appreciate the angioarchitecture of a spinal vascular malformation. Lesions in the spinal cord tend to arise 1 or more vertebral segments from the nidus. They are usually supplied by anterior and posterolateral radiculomedullary arteries with high-flow–low-resistance shunts. Fistulous components and dAVFs occur primarily in the lower thoracic and upper lumbar spine. These malformations consist of a small collection of dural vessels draining into a single intradural vein. They are supplied most often from radicular artery branches, smaller segmental branches, and/or meningoradicular branches. An understanding of the anatomy of perimedullary venous drainage is important. Radiculomedullary venous drainage with retrograde flow into the spinal perimedullary veins must be appreciated. Hairpin loops of vessels typically originate below the pedicle of the vertebra and can lead to malformations several segmental levels away.

Specific Technique and Key Steps

(Video 34.1, Video 34.2, Video 34.3)

Spinal angiography can be challenging and determining the angioarchitecture of these lesions before approaching them can be even more daunting. A step-by-step method to diagnose the lesion, find major spinal cord arterial pedicles (also referred to as “feeding” pedicles or feeders), and develop a plan for embolization is important. Key steps are as follows (Fig. 34.1–34.3, Video 34.1–34.3):

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   A 6 French (F) sheath is placed into the right common femoral artery.

   
   
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   Either a reverse curve-shaped guide catheter (such as a Simmons 1) is navigated directly into the aorta and used to select the segmental vessels of choice or a diagnostic spinal catheter such as a Mikaelson (Soft-Vu) or Cobra (Cook) catheter is used to identify the correct pedicle and a 0.035-inch Glidewire (Terumo) is used to exchange out the diagnostic catheter for a 5F or 6F guide catheter system.

   
   
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   The guide catheter is left at the ostia of the segmental vessel and a microcatheter placed over a microwire (Headway DUO, MicroVention over a Synchro 2, Stryker) microwire is advanced into the segmental vessel (Fig. 34.1–34.3, Video 34.1–34.3).

   
   
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   Microcatheter runs are performed to help guide treatment and define the angioarchitecture of the lesion.

   
   
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   Under roadmap guidance, the microcatheter is navigated distally.

   
   
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   An intermediate catheter may be required to provide support to the microcatheter delivery in robust segmental arteries (Distal Access Catheter, Stryker).

   
   
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   Wada provocative testing can potentially be helpful in identifying vascular territories that provide en passant vessels or supply the spinal cord.

   
   
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   Identification of the artery of Adamkiewicz is crucial to avoiding spinal cord vascular injury.

   
   
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   Onyx (Medtronic) or small particles of n-BCA (Trufill, DePuy Synthes) can be used for embolization, depending on the flow rate as well as the size of the pedicle and distal nidus (Fig. 34.1–34.3, Video 34.1–34.3).

   
   
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    Postembolization runs are performed through the guide catheter to confirm obliteration of the vascular malformation.

    
    
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    The guide catheter is removed from the ostia of the segmental vessel.

Device Selection

In the authors’ and editors’ practice, the following are common setups and devices used for spinal angiography proceeded by endovascular embolization:

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  5 or 6F sheath.

  
  
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  6F guide catheter or 5F multipurpose access catheter (Cordis) after selection with a Mikaelson or Cobra catheter.

  
  
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  0.035-inch angled Glidewire.

  
  
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  Intermediate catheter in robust segmental arteries (e.g., distal access catheter).

  
  
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  Synchro 2 or Synchro 10 microwire (Stryker).

  
  
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  Marathon (Medtronic) or Headway DUO microcatheters.

  
  
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  n-BCA for smaller particle embolizations (Fig. 34.1, Video 34.1).

  
  
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  Onyx 18 or 34 (Fig. 34.2, Video 34.2).

  
  
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  Coils (Fig. 34.3, Video 34.3).

Pearls

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  In patients with dAVFs, the feeder and anterior and posterior spinal arteries, including the artery of Adamkiewicz, arise from the same segmental artery. Therefore, identification and navigation into the correct feeder and navigation into the distal vessel becomes paramount to avoid occlusion of a vessel supplying normal spinal cord.

  
  
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  Embolization with n-BCA has shown a 55% rate of improvement in gait for patients with dAVF and a 15% recanalization rate. Onyx can be used depending on the anatomy of the lesion.

  
  
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  Coils placed distally can be used to prevent embolization of muscular branches, primarily for the patient’s comfort (Fig. 34.2, Video 34.2).

  
  
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  Slow, small particle embolization of intramedullary lesions with provocative testing helps in achieving a safe embolization. Serial pressure measurements from the microcatheter can indicate when to stop embolization when pressures exceed 90%; however, these measurements are not obtained routinely.

  
  
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  Electrophysiological monitoring for intramedullary lesions with somatosensory-evoked potentials and motor-evoked potentials during general anesthesia is very helpful, especially when navigating the convoluted angiographic anatomy of the spine.

  
  
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  Frequent “puffing” of contrast material from the guide catheter during the embolization procedure, even while navigating the microcatheter, can help ensure that the guide catheter has maintained purchase in the segmental vessel ostia.

  
  
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  To help maintain guide catheter position at the ostia of the segmental vessel, a buddy wire (a second 0.014-inch microwire that provides additional support to the system) can be used to allow the catheter to stay in place during micronavigation.