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Spinal-Dural Arteriovenous Fistulas: A treatable cause of myelopathy frequently overlooked
December 14th, 2009 by Administrator

The author: Professor Yasser Metwally

http://yassermetwally.com


INTRODUCTION

December 14, 2009 — Spinal-dural arteriovenous fistulas are the most common variety of spinal cord AVM.[1] Spinal-dural arteriovenous fistulas are thought to be acquired lesions,[1] occur mainly in older adults (mean age of 51 years), and are found more often in men than women. Patients present with slowly progressive myelopathy and radiculopathy,[2,3] which, if left untreated, can progress to paraparesis or quadriparesis. (Click to download a case record in PDF format)  (Click to view all case records under the title “arteriovenous fistula” in http://yassermetwally.com)

The arteriovenous fistula is located in the dura itself. The feeding vessels are nonradicular branches of the spinal arteries, small, tortuous arterioles that originate from the dura. The feeding arteries are generally normal in caliber and flow through these lesions is exceptionally slow. A single draining radicular vein is often at the level of the spinal root foramina. The vein is dilated many times the size of the artery and flows retrograde into the anterior and posterior medullary veins and coronal venous plexus surrounding the spinal cord. Chronic venous hypertension and stagnation result in chronic medullary ischemia.[4]

Although phase contrast MR I [5] or dynamic gadolinium-enhanced MR I [6] may increase detection, in our experience these small connections can be easily missed even on excellent quality MRI images. Serpiginous flow voids around the cord may represent flow in dilated medullary veins. The spinal cord may also be enlarged, and intramedullary increased signal on T2-weighted images may represent edema or ischemia secondary to venous hypertension.

Slide show 1. MRI showing  dilated perimedullary veins (due to dural spinal arteriovenous fistula) and congestive myelopathy demonstrated as central cord edema (Central cord T2 hyperintensity) and spinal cord enlargement. The central cord hyperintensity is taking the shape of the central grey matter

Contrast myelography in both the supine position, which can best demonstrate the retromedullary veins, and the prone position reveals dilated and tortuous veins over the dorsum of the cord. If dilated veins are observed, complete spinal angiography is indicated. Image quality must be the best possible to delineate the origin of the shunt. Filming should continue into the late venous phase up to several seconds after the injection.

The majority of patients with the fistula in the thoracic and lumbar region have arterial supply independent of the supply to the spinal cord. Internal iliac artery supply was observed in 12.5% of cases.[7] Endovascular embolization with liquid adhesive can frequently cure these lesions. Initial apparently successful embolization was achieved in 90% of 20 patients in one study; the fistula recurrence rate (failure to occlude the draining vein) for N-butyl cyanoacrylate (NBCA) was 15% (3 patients). All patients who underwent embolization had either improved (55%) or unchanged (45%) gait disability at last follow-up.[8] Not infrequently, complete clinical cure can be achieved in cases presenting with a nonfixed, moderate, neurologic deficit. Recanalization has occurred in cases in which PVA was used as the primary therapy.[9] Open surgery is recommended if embolization fails to occlude the dural arteriovenous fistula.

Slide show 2. Spinal angiography (same patient as in slide show 1) Showing the spinal dural arteriovenous fistula before and after embolization


References

  1. Rosenblum B, Oldfield EH, Doppman JL, Di Chiro G. Spinal arteriovenous malformations: a comparison of dural arteriovenous fistulas and intradural AVM’s in 81 patients. J Neurosurg 1987;67:795-802
  2. Merland JJ, Riche MC, Chiras J. Intraspinal extramedullary arterio-venous fistulae draining into the medullar veins. J Neuroradiol 1980;7:271-320
  3. Koenig E, Thron A, Schrader V, Dichgans J. Spinal arteriovenous malformations and fistulae: clinical, neuroradiological and neurophysiological findings. J Neurol 1989;236:260-266
  4. Kataoka H, Miyamoto S, Nagata I, Ueba T, Hashimoto N. Venous congestion is a major cause of neurological deterioration in spinal arteriovenous malformations. Neurosurgery 2001;48:1224-1229; discussion 1229-1230
  5. Mourier KL, Gelbert F, Reizine D, et al. Phase contrast magnetic resonance of the spinal cord preliminary results in spinal cord arterio-venous malformations. Acta Neurochir (Wien) 1993;123:57-63
  6. Thorpe JW, Kendall BE, MacManus DG, McDonald WI, Miller DH. Dynamic gadolinium-enhanced MRI in the detection of spinal arteriovenous malformations. Neuroradiology 1994;36:522-529
  7. Larsen DW, Halbach VV, Teitelbaum GP, et al. Spinal dural arteriovenous fistulas supplied by branches of the internal iliac arteries. Surg Neurol 1995;43:35-40; discussion 40-41
  8. Song JK, Gobin YP, Duckwiler GR, et al. N-Butyl 2-cyanoacrylate embolization of spinal dural arteriovenous fistulae. AJNR Am J Neuroradiol 2001;22:40-47
  9. Nichols DA, Rufenacht DA, Jack CR Jr, Forbes GS. Embolization of spinal dural arteriovenous fistula with polyvinyl alcohol particles: experience in 14 patients. AJNR Am J Neuroradiol 1992;13:933-940
  10. Spinal dural arteriovenous fistula [Full text]
  11. Arteriovenous Malformations/Fistulas of the Cervical Spinal Cord [full text]
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