Spinal dural arteriovenous fistulas

Abstract

Spinal dural arteriovenous (AV) fistulas are the most commonly encountered vascular malformation of the spinal cord and a treatable cause for progressive para- or tetraplegia. They most commonly affect elderly men and are classically found in the thoracolumbar region. The AV shunt is located inside the dura mater close to the spinal nerve root where the arterial blood from a radiculomeningeal artery enters a radicular vein. The increase in spinal venous pressure leads to decreased drainage of normal spinal veins, venous congestion, and the clinical findings of progressive myelopathy. On MR imaging, the combination of cord edema, perimedullary dilated vessels, and cord enhancement is characteristic. Therapy has to be aimed at occluding the shunting zone, either by superselective embolization with a liquid embolic agent or by a neurosurgical approach. Following occlusion of the fistula, the progression of the disease can be stopped and improvement of symptoms is typically observed.

Fig 1.

Ventral epidural AV fistulas in 2 different patients. A and B, Early and late phases of an injection into a segmental artery with a shunt into the ventral epidural space (white arrows) with no reflux toward the cord. These shunts are classically asymptomatic. C−H, Enhanced CT (C), the bone window (D), axial (E) and sagittal (F) T2-weighted scans, and early (G) and late (H) phases of the iliac artery injections in an 18-year-old woman who had constant lumbago for the previous 2 years. A ventral epidural (or osteodural) shunt is demonstrated, which, despite its high-flow nature (usuration of the bone), does not lead to reflux toward the cord because the shunting vessels are related to structures developed from the notochord.

Fig 2.

T2-weighted (A−C) and T1-weighted images following contrast enhancement (D−F) in 3 different patients demonstrate the spectrum of characteristic findings of SDAVFs on routine sequences. A centromedullary edema and perimedullary dilated vessels are the hallmark findings. However, even in the absence of edema (B) or in the absence of pathologic vessels on T2-weighted scans (C), the suspicion of an SDAVF is raised due to the coiled vessels seen on T1-weighted scans after contrast enhancement. While a missing edema might indicate a DAVF picked up early in the course of the disease, the missing flow voids on T2-weighted scans indicate a slow-flowing shunt.

Fig 3.

When comparing a routine T2 TSE (A) sequence and a heavily T2-weighted (FIESTA, 3D T2 TSE, or CISS) sequence (B), the former depicts the cord edema better (arrow, A), whereas the latter is better suited to demonstrate the perimedullary flow voids (arrow, B), as seen in this patient.

Fig 4.

Following contrast enhancement, not only are the dilated perimedullary vessels depicted but sometimes (especially in the later stages of the disease) diffuse enhancement may be seen within the cord as a sign of chronic venous congestion with breakdown of the blood−spinal cord barrier.

Fig 5.

First-pass contrast-enhanced MRA can clearly demonstrate the early venous filling and thereby confirm the presence of a shunt in equivocal cases. A and B, On T2-weighted scans (A), the perimedullary flow voids indicate an SDAVF, which is confirmed on coronal spinal MRA (B). C, In addition, as indicated in this patient, MRA helps to demonstrate the level of the shunt, thereby directing the subsequent spinal DSA.

Fig 6.

In patients with spinal AV shunts, the venous return after injection into the ASA is delayed due to the arterialized pressure in the spinal cord veins. Therefore, stasis following injection into the segmental artery from which the ASA originates is seen as in this patient. A, The arrow demonstrates the hairpin curve of the ASA visible in the early arterial phase. B, The late venous phase still demonstrates contrast material within the ASA, which should have been washed out by this time under physiologic conditions (arrowheads). C, The reason for the delayed washout is a DAVF at a different level, leading to massive venous congestion.

Fig 7.

Endovascular therapy in DAVFs in 2 different patients (A−C and D−F, respectively). A and D demonstrate the global injections verifying that no supply to the spinal cord is present from the pedicle from which the spinal DAVF is fed. The superselective injections demonstrated on B and E show the feeding artery (black arrow), the shunting zone (asterisk), and the proximal draining vein (white arrow). For an embolization to be effective, the glue has to penetrate from the artery via the shunting zone into the vein. C and F, Respective glue casts in both patients: While in the first patient (C) the glue cast did not reach the vein, in the second patient, the glue is visible within the proximal vein. The first patient will necessarily demonstrate recanalization with neurologic deterioration following a period of transient improvement of symptoms, due to the vast collaterals present in the dura, which will reconstitute the fistula. We would, therefore, strongly recommend early surgery (ie, in the same hospital setting). The patient seen in the lower row, though, is completely cured.

Fig 8.

Images of this patient with the classic MR imaging findings of a DAVF on T1-weighted contrast-enhanced (A) and T2-weighted (B) scans demonstrate a vast network of dural collateral arteries in the shunting zone. Although the main supply to the shunt is derived from the radiculomeningeal artery originating from the injected segmental artery (arrowhead), there is an additional supply ascending from a lower segmental artery (small arrow) that is filled via longitudinal collaterals. The shunting zone is denoted by an asterisk. Only if the liquid embolic agent penetrates into the draining veins will this patient be cured; a proximal occlusion will invariably lead to refilling of the shunt via dural collaterals.

Fig 9.

In rare cases, the anterior spinal artery (black arrow) may arise from the same pedicle as the feeder to the shunt (shunting zone, asterisk; draining vein, white arrow). The anterior spinal artery can be identified by the following: 1) its ascending course along the nerve root, 2) its hairpin course at the midline, and 3) the straight course once it reaches the midline of the cord. The vein does not reach the midline via the ascending nerve root but instead via a horizontal and more tortuous course. Embolization in patients with this condition is extremely dangerous, and surgical options may be considered a safer approach.