Endovascular Treatment of Spinal Arteriovenous Malformations

190 Endovascular Treatment of Spinal Arteriovenous Malformations
Marc L. Otten, Matthew C. Garrett, and Philip M. Meyers

Contraindications

Depends on the anatomic features of the specific vascular malformation
Provocative anesthetic testing during the angiographic and endovascular treatment procedure demonstrating unexpected neurologic deficits may preclude transcatheter therapy. For instance, vascular supply to the malformation that is integral to the vascular supply to the spinal cord parenchyma or nerve roots.
Coagulation disorders and adverse reactions to heparin or contrast (relative)
Renal insufficiency or failure (relative)

♦ Preoperative

Operative Planning

Define vertebral levels radiographically to provide landmark for surgeon if open procedure needed and to look for anatomic anomalies.

Diagnostic angiography should be performed with specific intent to fully evaluate all arterial feeding vessels, the vascular nidus (if appropriate to the type of lesion), and the venous drainage pattern both for the malformation and the normal spinal cord. A complete understanding of normal spinal vascular anatomy, variant anatomy, and pathologic anatomy is mandatory for successful evaluation and treatment.

Slow fluoroscopic and imaging frame rates (~1 frame/sec) should be used when possible to limit patient and operator radiation exposure until pathologic vascular anatomy is identified. Then, imaging at more rapid frame rates may be necessary to further evaluate high flow or shunt-type vasculature.

The choice of embolic material depends upon the overall treatment plan. If embolization is preoperative/adjunctive, then a permanent embolic material may not be necessary. Certain liquid embolic agents may offer more durable and complete occlusion of a malformation but require great precision of delivery to achieve acceptable results and may present a greater risk of procedural complications.
Like brain AVMs, spinal vascular malformations and dural fistulas may have multiple sources of vascular supply and venous drainage. Complete endovascular evaluation requires a complete knowledge of vascular pathology to ensure adequate angiographic evaluation without exposing patient and operator to excessive radiation or the patient to excessive iodinated contrast.

Special Equipment

As for retrograde percutaneous femoral artery puncture
5 to 7 French (F) sheath
There are many types of angiographic catheters used to perform spinal arteriography depending on the vascular anatomy. Many patients requiring spinal angiography are elderly and have significant atherosclerotic disease in the thoracoabdominal aorta.
0.035-inch guide wire and 5F catheter for diagnostic study
1.3 to 2.3F microcatheters and micro”guide wires (0.008- to 0.018-inch)
Flow-directed or over the wire microcatheters (if pathology dictates)
Many choices for embolization material exist (e.g., coils, polyvinyl alcohol, gelatin spheres, ethanol, n-butyl-2-cyanoacrylate (NBCA), or ethylene vinyl alcohol copolymer)
Protamine should be readily available if intraoperative hemorrhage occurs.

Anesthetic Issues

Monitored anesthetic care can be used to allow provocative clinical testing prior to embolization of a feeding vessel, although awake anesthesia is performed at the expense of significant motion artifact.
Many interventionalists perform diagnostic spinal angiography under general anesthesia to ensure optimal imaging; a patient with a negative diagnostic angiogram will likely not be retested.
General anesthesia is used with somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) for provocative testing; many interventionalists perform all AVM embolizations under general anesthesia to ensure optimal imaging.

Monitoring

Provocative testing is performed with amobarbital (10 to 50 mg) and 2% cardiac lidocaine (5 to 10 mg) injections of the feeding vessels through the microcatheter to determine that embolization will not result in a neurologic deficit.
SSEPs and MEPs are used in patients under general anesthesia or clinical testing in awake patients to detect deficits prior to embolization.

♦ Intraoperative

Positioning

The patient is placed in the supine position.

Intravenous antibiotics, if needed, are given.

A Foley catheter is placed.
The proper radiation shielding is placed on the patient.
Both inguinal areas are shaved and prepped with iodine solution.
A sterile drape is placed over the prepped areas.
The head is positioned in neutral position and gently taped in place.

Technique

Femoral artery puncture is performed and a 5 to 7F sheath inserted as described
An angiogram of the vessels is performed.
Angiography of the spinal AVM must delineate all feeding arteries. Multiple feeding pedicles are often present and anterior and posterior spinal arteries must be visualized both caudal and cephalad to the lesion. For surgical planning, the location of the nidus or fistula must be defined (right, left, anterior, or posterior to spinal cord).
The patient may be heparinized (activated clotting time ~2.5 times baseline) for superselective spinal artery catheterization if embolization is planned.
Under roadmap guidance, the microcatheter is advanced to one of the major parent vessels (e.g., anterior or posterior spinal artery) and maintained at continuous heparinized saline flush.
The microcatheter is navigated through the feeding artery to the margin of the AVM nidus distal to any vessels supplying normal parenchyma; this may require gentle manipulation of the microcatheter with normal saline flushes if a flow directed catheter is used.
A superselective angiogram of this branch is obtained and the transit time is evaluated (reflecting the speed of blood flow through the lesion).
Microcatheter (in the feeding artery) pressure and simultaneous measurement of systemic arterial pressure may be measured for research purposes.
If provocative testing is performed in an awake patient, anesthesia is lightened: baseline neurologic function prior to and after amobarbital and lidocaine are injected through the microcatheter; in a sleeping patient, MEP/SSEP are evaluated before and after anesthetic administration; if there is no change in neurologic function or evoked potentials, then the vessel may be embolized at the present site of the microcatheter tip; should deficits occur with testing, the microcatheter is advanced further along the vessel and repeat testing performed.
After considering the transit time in the feeding vessel, the NBCA is mixed with ethiodized oil with or without tantalum or tungsten powder; the amount of ethiodized oil and NBCA varies (10 to 50% NBCA to 50 to 90% ethiodized oil).
The microcatheter is flushed with 6 to 9 mL of 5% dextrose (ionic solutions will cause polymerization of the NBCA in the catheter, as contact with anion is the mechanism of coagulation).
The NBCA is injected under subtraction angiography, usually using the singlecolumn technique (usually between 0.2 and 0.7 mL); the objective is to fill the nidus and obliterate the connection with the feeding vessel without any significant glue entering the draining veins; the experienced interventionalist can vary the setting time of the glue material and deliver the embolic agent in a safe, controlled fashion.
The microcatheter is then rapidly removed during aspiration to prevent further injection of embolic material.
A postembolization angiogram is then performed to confirm occlusion of the target vessel, preservation of venous drainage, and that all other vessels remain patent; surrounding levels and other identified feeding arteries must be evaluated.