Spinal Vascular Malformations

Patient Selection

Treatment of patients with spinal arteriovenous malformations (AVMs) carries a risk of paraplegia or quadriplegia. Therefore, before treatment is recommended, the natural history of the lesion must be weighed against the risks of therapy. Once neurological symptoms appear, most patients with dural arteriovenous fistulas (AVFs) become progressively disabled, and many are confined to bed or a wheelchair within months. The risk of treatment is low so these patients should be treated promptly. In contrast, the intradural AVMs, AVFs, and cavernous malformations have a less predictable natural history, the risk of treatment is higher, and there is less likelihood of complete obliteration of the lesion. Therefore, treatment decisions need to be individualized in these cases. If the patient has hemorrhaged, usually treatment is delayed until the hemorrhage resolves.

Successful treatment requires: (1) diagnosis of the AVM before irreversible cord injury occurs; (2) determination of the site and the type of AVM and delineation of the vascular anatomy of the AVM and of the vessels supplying the spinal cord in the vicinity of the AVM; (3) coupling the goals of surgery with the mechanism of cord injury, which differs in the different types of spinal vascular malformations; and (4) successful execution of the planned surgery. The goal of treatment is safe, complete, permanent obliteration of the lesion.

30.1.1 Classification of Spinal Vascular Malformations

There are three main types of vascular abnormalities of the spinal cord. Dural AVFs are embedded in the dura of the proximal portion of the nerve root sleeve and adjacent spinal dura. Intradural AVMs have a nidus in the spinal cord or on the surface of it and are further categorized into AVMs of the spinal cord, juvenile and glomus AVMs, and pial AVFs, in which a direct arterial to venous transition occurs (usually on the surface of the spinal cord) without an intervening glomus of abnormal vessels. Cavernous malformations of the spine are located within the parenchyma of the spinal cord.

30.2 Preoperative Preparation

A spinal catheter angiogram is generally done for all spinal AVMs and AVFs. In the past, patients with suspected spinal vascular lesions often underwent exploratory angiograms of the entire spine to locate the lesion. However, recent improvements in magnetic resonance angiography and computed tomography angiography have largely obviated the need for full spinal angiograms, as they are quite effective at identifying vascular lesions, as well as the specific level and side of associated feeding arteries. A formal arteriogram is still recommended; however, in combination with available noninvasive imaging, the arteriogram can be targeted to the suspected levels. This greatly reduces the patient’s exposure to radiation and contrast. Imaging at a rapid rate (6–10 frames/s) is recommended. With the intradural AVMs and AVFs, preoperative embolization performed during arteriography 1 to 2 days before surgery reduces the blood flow through the lesion and facilitates manipulation of the vessels during surgery. High-dose glucocorticoid therapy is administered just before, during, and for 24 to 48 hours after surgery or embolization. Intravenous heparin is administered for 48 hours when embolic occlusion is complete.

30.3 Operative Procedure

30.3.1 Dural Arteriovenous Fistulas

The options for treatment include surgery to interrupt the vein draining the AVF as it penetrates the inner layer of dura ( ▶ Fig. 30.1, ▶ Fig. 30.2, ▶ Fig. 30.3, Video 30.1) or endovascular embolization. Embolic occlusion with particulate materials, such as polyvinyl alcohol, does not permanently obliterate the nidus and therefore is typically not used for fistulas. Conversely, embolization with polymerizing liquid embolic agents such as Onyx or n-butyl cyanoacrylate may provide a durable occlusion, and an increasing number of centers are now preferentially treating dural AVFs using endovascular methods. Just as the goal of surgical ligation is to interrupt the draining vein as it enters the dura, an endovascular cure requires penetration of the embolysate to the point of fistula, and often into the venous side of the fistula. This is not always safe or feasible due to a number of factors such as the tortuosity of the arterial supply to the fistula, or the involvement or proximity of medullary arteries that supply the normal spinal cord such as the Artery of Adamkiewicz. Even in cases where embolization is felt to be a possibility, the embolysate may not penerate to the fistula, which typically results in an incomplete occlusion. Lastly, recanalization of a presumably cured fistula has been reported. Surgery, on the other hand, is often fairly straightforward, and most of these factors that make embolization difficult do not impact surgical treatment. For these reasons, a substantial percentage of spinal DAVFs remain best managed surgically.

Interruption of the vein that carries blood from the dural AVF to the coronal venous plexus cures almost all of these patients ( ▶ Fig. 30.1, ▶ Fig. 30.2, ▶ Fig. 30.3, Video 30.1). During the preoperative arteriogram a marker placed on the patient’s back, or a detachable coil placed endovascularly within the segmental artery at the level of the fistula, can provide a useful radiographic landmark for localizing the AVF at surgery. The lamina of the neural arches, one level above and below the AVF, are removed widely. The dura is opened in the midline, the arachnoid is separated from the underlying vessels, and the dura and arachnoid are retracted laterally with dural sutures. Correlation of the vascular anatomy as seen on preoperative arteriography with that displayed intraoperatively permits identification of the site of dural penetration of the medullary vein carrying arterial blood to the dilated, tortuous coronal venous plexus on the surface of the spinal cord ( ▶ Fig. 30.2, ▶ Fig. 30.3, Video 30.1). Indocyanine green (ICG) microscopy is useful to confirm identification of the target vessel. This arterialized vein is then coagulated with bipolar forceps and sharply divided as it enters the dura. This simple procedure provides effective, permanent therapy for almost all patients.

Fig. 30.1 The vascular anatomy of a spinal dural arteriovenous fistula (AVF). The AVF is supplied by a dural artery and drained by a medullary vein. Arterial input into the valveless intradural venous system increases venous pressure within the coronal venous plexus and causes myelopathy. Treatment is to coagulate and divide the arterialized draining vein at the site of the intradural penetration of the AVF.

Fig. 30.2 (a) Selective spinal arteriogram of a spinal dural arteriovenous fistula (AVF) embedded in the root sleeve of the ninth right thoracic nerve root. The nidus of the AVF (arrows) is typically in the intervertebral foramen and the lateral aspect of the spinal canal and drains into dilated, tortuous intradural veins on the cord surface. (b) Subtraction arteriogram with the image reversed to correspond to (c–f) the view at surgery with the patient prone. The upward-pointing arrowheads in (b) and (c) indicate the caudal loop of the medullary vein draining the dural AVF. The left pointing arrowhead in (c) indicates the right T9 sensory root, and the arrow points to the site of dural penetration of the vein draining the AVF and the sensory root. In (d) the forceps grasp the dura (asterisk). This intra and extradural view shows the AVF imbedded in the dura (to the right of the dura in the image) and the site of intradural penetration of the medullary vein draining the AVF intradurally (arrow). In (e) and (f) the dura (asterisk in e) is retracted laterally, revealing the relationship of the nerve root and the dural penetration of the arterialized medullary vein that drains the blood from the fistula intradurally to the spinal venous system.

(a, d, and e reproduced with permissions from Oldfield E, DiChiro G, Quindlen E, et al. Successful treatment of a group of spinal cord arteriovenous malformations by interruption of dural fistula. J Neurosurg 1983:59:1019.)

Fig. 30.3 Selective spinal arteriogram in a 36-year-old male with a spinal dural arteriovenous fistula (AVF) at the left seventh thoracic nerve root. (a) The seventh left thoracic intercostal artery provides a common origin of the arterial supply to the dural AVF (arrow) and the artery of Adamkiewicz (arrowheads pointing to the left of the image). Note the medullary vein draining the AVF intradurally (arrowhead pointing upward) takes a horizontal course initially. (b–d) Surgical view (patient prone) after the dura (asterisk) and arachnoid have been opened. (b) The medullary vein draining the AVF enters the dura (arrow) just dorsal to the left seventh thoracic sensory root (arrowheads). (c) Medullary vein draining the dural AVF has been coagulated and divided (arrows) as it enters the subdural space (upper arrow). Note the dural penetration of the sensory root just deep to the site of intradural entry of the vein (lower arrowhead). (d) The artery of Adamkiewicz (arrows) is identified by its straight course and rostral direction immediately after penetrating the dura just deep to the dural penetration of the left seventh thoracic nerve root (arrowheads). The forceps retract the denticulate ligament (white) medially. (e) Postoperatively the dural fistula no longer opacifies. The arrow designates the abrupt termination of the vessel previously supplying the AVF, and the arrowheads indicate the patent artery of Adamkiewicz and anterior spinal artery.