The type IV AVF represents a direct fistula from the anterior spinal artery to the coronal venous plexus (Figure 16.2). Radiculopial supply may also be involved. The intradural arteriovenous fistula has three subtypes, A, B, and C. These lesions can be seen anywhere along the spine.
Subtype A (also classified as Merland subtype I) represents a small shunt, with moderate venous hypertension. There is no enlargement of the anterior spinal artery (ASA) and only minimal dilatation of the ascending draining vein.1,7 The fistula is located at the point that a vessel caliber change is seen.8 The ASA is the only feeder, and the AVF is typically located along the anterior aspect of the conus medullaris or proximal filum terminale.9
Subtype B (Merland subtype II) represents a moderate-sized shunt with moderate enlargement of the feeding artery or arteries and the draining veins. The location of the fistula is marked by venous ecta-sia.8 There are several abnormally dilated feeding arteries, composed
Figure 16.2. Schematic illustration of a pial arteriovenous malformation (AVM type IV). 1, lumbar artery; 2, longitudinal pretransverse anastomosis; 3, nerve root sleeve; 4, dor-sospinal branch; 5, dural artery; 6, radicu-lomedullary artery; 7, dorsal somatic artery; 8, anterior spinal artery; 9, coronal venous plexus; 10, anterior median vein; 11, arteriovenous fistula between anterior spinal artery and the anterior median vein.
of the ASA and one or two arteries from the dorsolateral pial network [posterior spinal artery (PSA)], all of which converge on the fistula. These are typically located at the level of the conus. Venous drainage is into tortuous and dilated ascending perimedullary veins.9
Subtype C represents a giant fistula with one or more very large arterial feeders from the ASA and dorsolateral pial network (PSA) converging into the fistula and draining directly into a giant venous ecta-sia, often embedded within the substance of the cord. These fistulas are rare,8 although in at least one large series they represented the largest subtype of ventral intradural AVFs.9 The location of the fistula is more difficult to ascertain because of the giant ectatic draining vein.8 The giant ectatic draining vein usually drains into the local metameric efferent veins, which are also dilated.9 These lesions are typically located at the thoracic or cervical levels.9
Signs and symptoms may be due to vascular steal (more so with higher flow), venous hypertension, mass effect (with venous enlarge-ment/aneurysms), and hemorrhage (SAH).1 The clinical signs and symptoms almost always appear before age 40 and often present during the first decade (mean age at diagnosis being between 11.5 and 13.5 years). Subarachnoid hemorrhage is the presenting sign in approximately 40% of patients in one series, but according to some authors, only type C fistulas present with hemorrhage.8,10 Occasionally, hematomyelia has also been reported. Paraparesis or paraplegia is the most common sign, with progressive deterioration over time. Radicu-lomyelopathy or radiculopathy can also be present, presumably due to the mass effect from dilated venous structures.
These lesions can be seen anywhere along the spine. While the fistula is often ventrolateral, a posterolateral location may also occur when there is significant involvement of the dorsolateral pial network (PSA).
In subtype A, the blood supply generally occurs through a minimally dilated anterior spinal artery with slow flow, and thus endovascular obliteration remains difficult. Frequently, superselective catheteriza-tion for an AVF obliteration may be hazardous. Surgical obliteration is frequently the only choice. In case the fistula is located in the ventral surface of the spinal cord and surgical access is difficult, a PVA particle embolization from a proximal catheter position may be considered. Subtype B shows higher flow within one or multiple dilated pial arteries; thus, an endovascular approach is feasible, with curative obliteration of the arteriovenous fistula by means of NBCA. In the case of a complex AVF, intraoperative transvenous embolization has been described.11 In subtype C, the AVF is large and the feeding arteries extremely dilated. Detachable balloons or fibered coils have been used in the past for a permanent obliteration. Under flow control, NBCA may be used safely for a complete closure.10
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...