GENERAL SCIENTIFIC SESSION 2 GENERAL SCIENTIFIC SESSION 2
Spinal Dural Arteriovenous Fistulas: How, When, and Why Matthew R. Sanborn, MD R. Webster Crowley, MD Timothy Uschold, MD Min S. Park, MD Felipe C. Albuquerque, MD Cameron G. McDougall, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona Correspondence: Cameron G. McDougall, MD, c/o Neuroscience Publications, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013. E-mail: [email protected] Copyright © 2014 by the Congress of Neurological Surgeons.
S
pinal dural arteriovenous fistulas (SDAVFs) are traditionally underdiagnosed lesions that, if left untreated, can result in paralysis; loss of bowel, bladder, and sexual function; and considerable pain. In recent years, major strides have been made in the imaging, understanding, and treatment of these lesions. These advances have led to earlier, more reliable recognition of SDAVFs and have provided treating physicians with low-risk options for the eventual treatment of SDAVFs. The nomenclature describing SDAVFs can be confusing. Although there are multiple pathologically distinct entities involving fistulous connections in or around the spinal cord, this article focuses on a relatively homogeneous group, most recently classified as intradural dorsal spinal arteriovenous fistulas.1 Previously, these lesions have most commonly been referred to as type I spinal arteriovenous fistulas.2 They have also been called dorsal extramedullary arteriovenous malformations and angioma racemosum.3 In these malformations, an abnormal connection is present between 1 or more branches of a radicular artery and a single medullary vein.4 The fistulous connection is intradural at the level of the dural sleeve of the nerve root (Figure 1) and results in arterialization of the coronal venous plexus draining the spinal cord. Symptoms ranging from myelopathy to paralysis generally occur as a result of congestive venous hypertension. SDAVFs exhibit a male predominance, with symptoms most often presenting in patients . 60 years of age. Although abrupt clinical deterioration from hemorrhage has been described, it is extremely rare. More typically, presentation is with a gradual onset of symptoms that result from venous hypertension.5 This insidious onset often leads to a delay in diagnosis, with a median time of 11 to 18 months between symptom onset and
The 2013 CNS Annual Meeting presentation on which this article is based is available at: http://bit.ly/1r8NtXI.
6 | VOLUME 61 | NUMBER 1 | AUGUST 2014
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.neurosurgery-online.com).
diagnosis.6 Aminoff and Logue7 first described the natural history of SDAVFs and noted a stepwise deterioration that led to 50% of patients having a severe disability by 3 years after diagnosis. The most common initial symptom is gait disturbance (34%), followed by numbness (24%) and paresthesias (21%). By the time patients present for clinical attention, however, most exhibit signs of bladder dysfunction (80%) and leg weakness (78%).8 A high index of suspicion is required to make a timely diagnosis. Imaging findings on routine magnetic resonance (MR) imaging can be subtle and include engorgement of the perimedullary veins and less specific findings such as T2 prolongation within the spinal cord and intramedullary enhancement. There are reports of angiographically proven SDAVFs in which no perimedullary veins were evident on initial MR imaging, complicating the diagnosis.9 Conversely, there are reported cases of incidental angiographically proven asymptomatic SDAVFs with engorged perimedullary veins but without edema of the spinal cord.10,11 The gold standard for the evaluation and characterization of spinal vascular malformation, including SDAVF, is catheter-based spinal digital subtraction angiography (DSA). However, DSA is not without attendant risks, including neurological injury, radiation exposure, and contrast nephropathy.12 When the level of shunt is not known, diagnostic angiography must encompass all potential vessels that could contribute to a fistula. This often requires individual catheterization of the vertebral, costocervical, and thyrocervical trunks, as well as all intercostal and iliolumbar arteries.13 Unless one serendipitously encounters the fistula early in the angiographic exploration, this results in lengthy procedures with significant exposure to radiation and contrast. Unfortunately, routine MR findings such as cord edema are not helpful in predicting the level of the pathological shunting.13 Advances in noninvasive imaging, however, such as computed tomography or MR angiography have made dynamic imaging possible. This greatly enhances the ability to correctly diagnose spinal cord vascular pathology
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SPINAL DURAL ARTERIOVENOUS FISTULAS
FIGURE 1. Artist’s rendering of a spinal dural arteriovenous (AV) fistula. Note the site of the fistulous connection (arrow) and the venous hypertension evident in the coronal venous plexus. Used with permission from Barrow Neurological Institute.
and, in many cases of SDAVF, to correctly pinpoint the level of interest (Figure 2).14 Routine use of contrast-enhanced MR angiography to guide spinal angiography catheterizations allows a reduction in the patient’s exposure to radiation and contrast. Several groups have demonstrated that MR angiography is both sensitive and specific in the detection and characterization of arteriovenous fistulas in the spine.15-17 Luetmer et al18 found that using MR angiography to guide subsequent angiography resulted in a 50% reduction in fluoroscopy time and contrast volume. When reviewing our experience with 11 consecutive angiographically proven SDAVF patients at Barrow Neurological Institute (Phoenix, Arizona), we found that MR angiography identified the correct side in all cases and the correct level in 9 of the 11 cases. In the remaining 2 cases, the MR angiography was within 2 levels (Table). All patients underwent endovascular embolization or surgical clip ligation of the fistula using the results of the MR angiography to target the lesion. Radiographic follow-up was available in 8 of the 11 cases and demonstrated resolution of dilated veins and either resolution of or improvement in intrinsic T2 cord signal. Clinical follow-up was available in 10 of 11 patients, of whom 9 demonstrated an improvement in symptoms and 1 remained stable. Of note, there was 1 patient in whom the arteries supplying the fistula arose from the iliac arteries. Without adequate noninvasive imaging, this would have certainly resulted in a full exploratory spinal angiogram; however, it was detected by MR angiography, which allowed a much more focused angiogram for the atypical lesion.
CLINICAL NEUROSURGERY
From these results, when a spinal DSA is performed to better characterize and possibly treat a SDAVF, we now typically catheterize 2 levels above and below the vessel of interest, as identified by MR angiography, bilaterally. It should be emphasized that, although noninvasive imaging is improving dramatically, the gold standard remains DSA. MR angiography is useful to target DSA, but DSA provides necessary and sometimes critical additional information that may help revise MR angiography findings and ultimately avoid technical misadventures during surgery.19 Although most fistulas arise from a single segmental feeding artery, there are occasional instances in which there are $ 2 segmental feeding arteries. This is a potential issue if DSA is targeted to fistulas identified on MR angiography and the MR angiography fails to identify all involved arteries. It is also possible for a single patient to have . 1 SDAVFs with the separate, unrelated lesions occurring at different levels. A high index of suspicion and a low threshold to perform full spinal DSA are necessary in cases with no clinical or radiographic improvement after treatment. SDAVFs may be treated by endovascular embolization or surgical ligation.20 Surgery entails a laminectomy followed by dural opening and ligation of the draining vein at the nerve root sleeve (Video 1, Supplemental Digital Content 1, http://links. lww.com/NEU/A632 [used with permission from Barrow Neurological Institute]).21 Video 1 shows MR angiography demonstrating an SDAVF arising from the left T7 radicular artery accompanied by dilation of the coronal venous plexus in a 49-year-old man with myelopathy and leg weakness. DSA confirmed the location of the fistulous connection. Onyx embolization was attempted but failed to penetrate into the proximal draining vein. The patient subsequently underwent surgical clip ligation of his left T7 SDAVF. Preoperative MR imaging demonstrated dilated perimedullary veins and T2 signal change within the spinal cord. Postoperative MR imaging and MR angiography demonstrated resolution of the perimedullary venous dilation, along with a reduction in T2 signal within the spinal cord. The patient’s myelopathy and leg weakness improved, leaving him with only mild lower-extremity numbness. A meta-analysis by Steinmetz et al22 demonstrated 98% successful surgical fistula obliteration, with 55% of patients showing some improvement postoperatively and 34% remaining stable. Up to 33% of patients showed some improvement in micturition. With the advancement of endovascular techniques and embolysates, endovascular treatment has gained traction as a safe and effective treatment of SDAVFs.23 The goal of endovascular embolization is to occlude both the arteriovenous shunt and the proximal portion of the medullary draining vein (Figure 3).24,25 Before embolization, a microcatheter is positioned as closely as possible to the fistula, and the embolization is then typically performed with n-butyl cyanoacrylate (Codman Neurovascular, Raynham, Massachusetts) or Onyx (eV3 Neurovascular, Irvine, California). Endovascular treatment is contraindicated if the arterial pedicle supplying the SDVAF also supplies the anterior spinal
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FIGURE 2. Magnetic resonance (MR) angiography demonstrating a spinal dural arteriovenous fistula (SDAVF) arising from the left T7 radicular artery (A) accompanied by dilation of the coronal venous plexus (B) in a 49-year-old man with myelopathy and leg weakness. Digital subtraction angiography (C) confirmed the location of the fistulous connection. Onyx embolization was attempted but failed to penetrate into the proximal draining vein. The patient subsequently underwent surgical clip ligation of his left T7 SDAVF. Preoperative MR imaging (D) demonstrated dilated perimedullary veins and T2 signal change within the spinal cord. Postoperative MR imaging (E) and MR angiography (F) demonstrated resolution of the perimedullary venous dilation, along with a reduction in T2 signal within the spinal cord. The patient’s myelopathy and leg weakness improved, leaving him with only mild lower-extremity numbness. Also see Video 1 (Supplemental Digital Content 1, http://links.lww.com/NEU/A632), which demonstrates the surgical exposure and ligation of this fistula, along with indocyanine green angiography before and after fistula ligation. Used with permission from Barrow Neurological Institute.
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SPINAL DURAL ARTERIOVENOUS FISTULAS
TABLE. Magnetic Resonance Angiography and Spinal Angiographya Patient 1 2 3 4 5 6 7 8 9 10 11 a
Age, y
MRA Level/Side
DSA Level/Side
Actual Level/Side
Vessels Catheterized
69 64 50 64 72 46 66 67 68 78 71
Left L1 Left T5 Left T7 Median sacral or iliac Left T7 Right T10 Left T11 Right T10 Left T 10 Right T8 Left T7
Left L1/T12 Left T5 Left T7 Bilateral iliac Left T7 and T6 Right T10 Left T11 Right T10 Left T12 Not performed Left T7
Left T12 Left T5 Left T7 Bilateral iliac Left T7 and T6 Right T10 Left T11 Right T10 Left T12 Right T8 Left T7
2 (and 3-D spin) 5 8 2 6 4 9 4 13 N/A 12
DSA, digital subtraction angiography; MRA, magnetic resonance angiography; N/A, not applicable; 3-D, 3-dimensional.
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FIGURE 3. A 72-year-old man presented with 4 years of progressive lower-extremity weakness, myelopathy, and loss of sexual function. T2-weighted magnetic resonance (MR) imaging (A) demonstrates intrinsic spinal cord signal change and prominent dorsal flow voids. Bolus contrast MR angiography (B) demonstrated a likely fistula at the T7 pedicle. Digital subtraction spinal angiography (C) confirmed the site of the fistula. Onyx cast (D) after embolization showed good penetration of the proximal draining vein. At 13 months after embolization, T2-weighted MR imaging (E) demonstrated complete resolution of the intrinsic cord signal change. The patient had a return of strength but persistent sensory symptoms. Used with permission from Barrow Neurological Institute.
artery, posterior spinal artery, or a radiculomedullary artery.26 Inadequate access to the proximal medullary draining vein is also a contraindication to endovascular therapy. In these cases, surgery is the preferred treatment. Recurrence after embolization is possible, even with penetration into the draining vein.23,27,28 Postoperative imaging findings may be difficult to interpret; improvement in the MR imaging appearance of spinal cord abnormalities may be slow and incomplete and may not correlate with clinical outcomes.29 It is not uncommon, however, to see resolution of the intrinsic spinal cord T2 prolongation or resolution of the dilated perimedullary veins on follow-up imaging. Lack of clinical or radiographic improvement should prompt a search for residual or recurrent fistula and may indicate that the fistula is possibly fed from multiple arteries. SDAVFs are a cause of progressive paralysis but may be preventable if diagnosed and treated early. A high index of suspicion, even in atypical cases such as spinal cord edema without prominent flow voids, is necessary to avoid delays in diagnosis. MR angiography is a valuable aid in diagnosis and can help direct DSA, but it is not a replacement for catheter angiography. Once diagnosed, treatment with either endovascular embolization or surgical ligation is indicated. Identification and permanent obliteration of the fistula, together with the proximal medullary vein, are key to successful treatment. Disclosure Dr McDougall is a consultant for Covidien (eV3), Terumo (Microvention), and Codman. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.
REFERENCES 1. Kim LJ, Spetzler RF. Classification and surgical management of spinal arteriovenous lesions: arteriovenous fistulae and arteriovenous malformations. Neurosurgery. 2006;59(5 suppl 3):S195-S201. 2. Di Chiro G, Ommaya AK. Selective arteriography of arteriovenous malformations. Prog Neurol Surg. 1971;4:329-354. 3. Wyburn-Mason R. The Vascular Abnormalities and Tumors of the Spinal Cord. London, UK: H. Klimpton; 1943. 4. McCutcheon IE, Doppman JL, Oldfield EH. Microvascular anatomy of dural arteriovenous abnormalities of the spine: a microangiographic study. J Neurosurg. 1996;84(2):215-220. 5. Aminoff MJ, Barnard RO, Logue V. The pathophysiology of spinal vascular malformations. J Neurol Sci. 1974;23(2):255-263. 6. Fugate JE, Lanzino G, Rabinstein AA. Clinical presentation and prognostic factors of spinal dural arteriovenous fistulas: an overview. Neurosurg Focus. 2012;32(5):E17.
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7. Aminoff MJ, Logue V. The prognosis of patients with spinal vascular malformations. Brain. 1974;97(1):211-218. 8. Jellema K, Canta LR, Tijssen CC, van Rooij WJ, Koudstaal PJ, van Gijn J. Spinal dural arteriovenous fistulas: clinical features in 80 patients. J Neurol Neurosurg Psychiatry. 2003;74(10):1438-1440. 9. Miller TR, Eskey CJ, Mamourian AC. Absence of abnormal vessels in the subarachnoid space on conventional magnetic resonance imaging in patients with spinal dural arteriovenous fistulas. Neurosurg Focus. 2012;32:E15. 10. Sato K, Terbrugge KG, Krings T. Asymptomatic spinal dural arteriovenous fistulas: pathomechanical considerations. J Neurosurg Spine. 2012;16(5): 441-446. 11. van Rooij WJ, Nijenhuis RJ, Peluso JP, Sluzewski M, Beute GN, van der Pol B. Spinal dural fistulas without swelling and edema of the cord as incidental findings. AJNR Am J Neuroradiol. 2012;33(10):1888-1892. 12. Forbes G, Nichols DA, Jack CR Jr, et al. Complications of spinal cord arteriography: prospective assessment of risk for diagnostic procedures. Radiology. 1988;169(2):479-484. 13. Krings T, Mull M, Gilsbach JM, Thron A. Spinal vascular malformations. Eur Radiol. 2005;15(2):267-278. 14. Mull M, Nijenhuis RJ, Backes WH, Krings T, Wilmink JT, Thron A. Value and limitations of contrast-enhanced MR angiography in spinal arteriovenous malformations and dural arteriovenous fistulas. AJNR Am J Neuroradiol. 2007; 28(7):1249-1258. 15. Ali S, Cashen TA, Carroll TJ, et al. Time-resolved spinal MR angiography: initial clinical experience in the evaluation of spinal arteriovenous shunts. AJNR Am J Neuroradiol. 2007;28(9):1806-1810. 16. Bowen BC, Fraser K, Kochan JP, Pattany PM, Green BA, Quencer RM. Spinal dural arteriovenous fistulas: evaluation with MR angiography. AJNR Am J Neuroradiol. 1995;16(10):2029-2043. 17. Saraf-Lavi E, Bowen BC, Quencer RM, et al. Detection of spinal dural arteriovenous fistulae with MR imaging and contrast-enhanced MR angiography: sensitivity, specificity, and prediction of vertebral level. AJNR Am J Neuroradiol. 2002;23(5):858-867. 18. Luetmer PH, Lane JI, Gilbertson JR, Bernstein MA, Huston J III, Atkinson JL. Preangiographic evaluation of spinal dural arteriovenous fistulas with elliptic centric contrast-enhanced MR angiography and effect on radiation dose and volume of iodinated contrast material. AJNR Am J Neuroradiol. 2005;26: 711-718. 19. Sharma AK, Westesson PL. Preoperative evaluation of spinal vascular malformation by MR angiography: how reliable is the technique: case report and review of literature. Clin Neurol Neurosurg. 2008;110(5):521-524. 20. Andres RH, Barth A, Guzman R, et al. Endovascular and surgical treatment of spinal dural arteriovenous fistulas. Neuroradiology. 2008;50(10):869-876. 21. Afshar JK, Doppman JL, Oldfield EH. Surgical interruption of intradural draining vein as curative treatment of spinal dural arteriovenous fistulas. J Neurosurg. 1995; 82(2):196-200. 22. Steinmetz MP, Chow MM, Krishnaney AA, et al. Outcome after the treatment of spinal dural arteriovenous fistulae: a contemporary single-institution series and meta-analysis. Neurosurgery. 2004;55(1):77-87. 23. Gemmete JJ, Chaudhary N, Elias AE, et al. Spinal dural arteriovenous fistulas: clinical experience with endovascular treatment as a primary therapy at 2 academic referral centers. AJNR Am J Neuroradiol. 2013;34(10):1974-1979. 24. Jellema K, Sluzewski M, van Rooij WJ, Tijssen CC, Beute GN. Embolization of spinal dural arteriovenous fistulas: importance of occlusion of the draining vein. J Neurosurg Spine. 2005;2(5):580-583.
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SPINAL DURAL ARTERIOVENOUS FISTULAS
25. Sivakumar W, Zada G, Yashar P, Giannotta SL, Teitelbaum G, Larsen DW. Endovascular management of spinal dural arteriovenous fistulas: a review. Neurosurg Focus. 2009;26(5):E15. 26. Doppman JL, Di CG, Oldfield EH. Origin of spinal arteriovenous malformation and normal cord vasculature from a common segmental artery: angiographic and therapeutic considerations. Radiology. 1985;154(3):687-689. 27. Adamczyk P, Amar AP, Mack WJ, Larsen DW. Recurrence of “cured” dural arteriovenous fistulas after Onyx embolization. Neurosurg Focus. 2012; 32(5):E12. 28. Blackburn SL, Kadkhodayan Y, Ray WZ, et al. Onyx is associated with poor venous penetration in the treatment of spinal dural arteriovenous fistulas [published online ahead
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of print August 13, 2013]. J Neurointerv Surg. 2013. doi: 10.1136/neurintsurg-2013010779. Available at: http://jnis.bmj.com/content/early/2013/08/13/neurintsurg-2013010779.long. Accessed April 11, 2014. 29. Kaufmann TJ, Morris JM, Saladino A, Mandrekar JN, Lanzino G. Magnetic resonance imaging findings in treated spinal dural arteriovenous fistulas: lack of correlation with clinical outcomes. J Neurosurg Spine. 2011;14(4):548-554.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.neurosurgery-online.com).
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Spinal Dural Arteriovenous Fistulas: How, When, and Why Matthew R. Sanborn, MD R. Webster Crowley, MD Timothy Uschold, MD Min S. Park, MD Felipe C. Albuquerque, MD Cameron G. McDougall, MD Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona Correspondence: Cameron G. McDougall, MD, c/o Neuroscience Publications, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013. E-mail: [email protected] Copyright © 2014 by the Congress of Neurological Surgeons.
S
pinal dural arteriovenous fistulas (SDAVFs) are traditionally underdiagnosed lesions that, if left untreated, can result in paralysis; loss of bowel, bladder, and sexual function; and considerable pain. In recent years, major strides have been made in the imaging, understanding, and treatment of these lesions. These advances have led to earlier, more reliable recognition of SDAVFs and have provided treating physicians with low-risk options for the eventual treatment of SDAVFs. The nomenclature describing SDAVFs can be confusing. Although there are multiple pathologically distinct entities involving fistulous connections in or around the spinal cord, this article focuses on a relatively homogeneous group, most recently classified as intradural dorsal spinal arteriovenous fistulas.1 Previously, these lesions have most commonly been referred to as type I spinal arteriovenous fistulas.2 They have also been called dorsal extramedullary arteriovenous malformations and angioma racemosum.3 In these malformations, an abnormal connection is present between 1 or more branches of a radicular artery and a single medullary vein.4 The fistulous connection is intradural at the level of the dural sleeve of the nerve root (Figure 1) and results in arterialization of the coronal venous plexus draining the spinal cord. Symptoms ranging from myelopathy to paralysis generally occur as a result of congestive venous hypertension. SDAVFs exhibit a male predominance, with symptoms most often presenting in patients . 60 years of age. Although abrupt clinical deterioration from hemorrhage has been described, it is extremely rare. More typically, presentation is with a gradual onset of symptoms that result from venous hypertension.5 This insidious onset often leads to a delay in diagnosis, with a median time of 11 to 18 months between symptom onset and
The 2013 CNS Annual Meeting presentation on which this article is based is available at: http://bit.ly/1r8NtXI.
6 | VOLUME 61 | NUMBER 1 | AUGUST 2014
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.neurosurgery-online.com).
diagnosis.6 Aminoff and Logue7 first described the natural history of SDAVFs and noted a stepwise deterioration that led to 50% of patients having a severe disability by 3 years after diagnosis. The most common initial symptom is gait disturbance (34%), followed by numbness (24%) and paresthesias (21%). By the time patients present for clinical attention, however, most exhibit signs of bladder dysfunction (80%) and leg weakness (78%).8 A high index of suspicion is required to make a timely diagnosis. Imaging findings on routine magnetic resonance (MR) imaging can be subtle and include engorgement of the perimedullary veins and less specific findings such as T2 prolongation within the spinal cord and intramedullary enhancement. There are reports of angiographically proven SDAVFs in which no perimedullary veins were evident on initial MR imaging, complicating the diagnosis.9 Conversely, there are reported cases of incidental angiographically proven asymptomatic SDAVFs with engorged perimedullary veins but without edema of the spinal cord.10,11 The gold standard for the evaluation and characterization of spinal vascular malformation, including SDAVF, is catheter-based spinal digital subtraction angiography (DSA). However, DSA is not without attendant risks, including neurological injury, radiation exposure, and contrast nephropathy.12 When the level of shunt is not known, diagnostic angiography must encompass all potential vessels that could contribute to a fistula. This often requires individual catheterization of the vertebral, costocervical, and thyrocervical trunks, as well as all intercostal and iliolumbar arteries.13 Unless one serendipitously encounters the fistula early in the angiographic exploration, this results in lengthy procedures with significant exposure to radiation and contrast. Unfortunately, routine MR findings such as cord edema are not helpful in predicting the level of the pathological shunting.13 Advances in noninvasive imaging, however, such as computed tomography or MR angiography have made dynamic imaging possible. This greatly enhances the ability to correctly diagnose spinal cord vascular pathology
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SPINAL DURAL ARTERIOVENOUS FISTULAS
FIGURE 1. Artist’s rendering of a spinal dural arteriovenous (AV) fistula. Note the site of the fistulous connection (arrow) and the venous hypertension evident in the coronal venous plexus. Used with permission from Barrow Neurological Institute.
and, in many cases of SDAVF, to correctly pinpoint the level of interest (Figure 2).14 Routine use of contrast-enhanced MR angiography to guide spinal angiography catheterizations allows a reduction in the patient’s exposure to radiation and contrast. Several groups have demonstrated that MR angiography is both sensitive and specific in the detection and characterization of arteriovenous fistulas in the spine.15-17 Luetmer et al18 found that using MR angiography to guide subsequent angiography resulted in a 50% reduction in fluoroscopy time and contrast volume. When reviewing our experience with 11 consecutive angiographically proven SDAVF patients at Barrow Neurological Institute (Phoenix, Arizona), we found that MR angiography identified the correct side in all cases and the correct level in 9 of the 11 cases. In the remaining 2 cases, the MR angiography was within 2 levels (Table). All patients underwent endovascular embolization or surgical clip ligation of the fistula using the results of the MR angiography to target the lesion. Radiographic follow-up was available in 8 of the 11 cases and demonstrated resolution of dilated veins and either resolution of or improvement in intrinsic T2 cord signal. Clinical follow-up was available in 10 of 11 patients, of whom 9 demonstrated an improvement in symptoms and 1 remained stable. Of note, there was 1 patient in whom the arteries supplying the fistula arose from the iliac arteries. Without adequate noninvasive imaging, this would have certainly resulted in a full exploratory spinal angiogram; however, it was detected by MR angiography, which allowed a much more focused angiogram for the atypical lesion.
CLINICAL NEUROSURGERY
From these results, when a spinal DSA is performed to better characterize and possibly treat a SDAVF, we now typically catheterize 2 levels above and below the vessel of interest, as identified by MR angiography, bilaterally. It should be emphasized that, although noninvasive imaging is improving dramatically, the gold standard remains DSA. MR angiography is useful to target DSA, but DSA provides necessary and sometimes critical additional information that may help revise MR angiography findings and ultimately avoid technical misadventures during surgery.19 Although most fistulas arise from a single segmental feeding artery, there are occasional instances in which there are $ 2 segmental feeding arteries. This is a potential issue if DSA is targeted to fistulas identified on MR angiography and the MR angiography fails to identify all involved arteries. It is also possible for a single patient to have . 1 SDAVFs with the separate, unrelated lesions occurring at different levels. A high index of suspicion and a low threshold to perform full spinal DSA are necessary in cases with no clinical or radiographic improvement after treatment. SDAVFs may be treated by endovascular embolization or surgical ligation.20 Surgery entails a laminectomy followed by dural opening and ligation of the draining vein at the nerve root sleeve (Video 1, Supplemental Digital Content 1, http://links. lww.com/NEU/A632 [used with permission from Barrow Neurological Institute]).21 Video 1 shows MR angiography demonstrating an SDAVF arising from the left T7 radicular artery accompanied by dilation of the coronal venous plexus in a 49-year-old man with myelopathy and leg weakness. DSA confirmed the location of the fistulous connection. Onyx embolization was attempted but failed to penetrate into the proximal draining vein. The patient subsequently underwent surgical clip ligation of his left T7 SDAVF. Preoperative MR imaging demonstrated dilated perimedullary veins and T2 signal change within the spinal cord. Postoperative MR imaging and MR angiography demonstrated resolution of the perimedullary venous dilation, along with a reduction in T2 signal within the spinal cord. The patient’s myelopathy and leg weakness improved, leaving him with only mild lower-extremity numbness. A meta-analysis by Steinmetz et al22 demonstrated 98% successful surgical fistula obliteration, with 55% of patients showing some improvement postoperatively and 34% remaining stable. Up to 33% of patients showed some improvement in micturition. With the advancement of endovascular techniques and embolysates, endovascular treatment has gained traction as a safe and effective treatment of SDAVFs.23 The goal of endovascular embolization is to occlude both the arteriovenous shunt and the proximal portion of the medullary draining vein (Figure 3).24,25 Before embolization, a microcatheter is positioned as closely as possible to the fistula, and the embolization is then typically performed with n-butyl cyanoacrylate (Codman Neurovascular, Raynham, Massachusetts) or Onyx (eV3 Neurovascular, Irvine, California). Endovascular treatment is contraindicated if the arterial pedicle supplying the SDVAF also supplies the anterior spinal
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FIGURE 2. Magnetic resonance (MR) angiography demonstrating a spinal dural arteriovenous fistula (SDAVF) arising from the left T7 radicular artery (A) accompanied by dilation of the coronal venous plexus (B) in a 49-year-old man with myelopathy and leg weakness. Digital subtraction angiography (C) confirmed the location of the fistulous connection. Onyx embolization was attempted but failed to penetrate into the proximal draining vein. The patient subsequently underwent surgical clip ligation of his left T7 SDAVF. Preoperative MR imaging (D) demonstrated dilated perimedullary veins and T2 signal change within the spinal cord. Postoperative MR imaging (E) and MR angiography (F) demonstrated resolution of the perimedullary venous dilation, along with a reduction in T2 signal within the spinal cord. The patient’s myelopathy and leg weakness improved, leaving him with only mild lower-extremity numbness. Also see Video 1 (Supplemental Digital Content 1, http://links.lww.com/NEU/A632), which demonstrates the surgical exposure and ligation of this fistula, along with indocyanine green angiography before and after fistula ligation. Used with permission from Barrow Neurological Institute.
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SPINAL DURAL ARTERIOVENOUS FISTULAS
TABLE. Magnetic Resonance Angiography and Spinal Angiographya Patient 1 2 3 4 5 6 7 8 9 10 11 a
Age, y
MRA Level/Side
DSA Level/Side
Actual Level/Side
Vessels Catheterized
69 64 50 64 72 46 66 67 68 78 71
Left L1 Left T5 Left T7 Median sacral or iliac Left T7 Right T10 Left T11 Right T10 Left T 10 Right T8 Left T7
Left L1/T12 Left T5 Left T7 Bilateral iliac Left T7 and T6 Right T10 Left T11 Right T10 Left T12 Not performed Left T7
Left T12 Left T5 Left T7 Bilateral iliac Left T7 and T6 Right T10 Left T11 Right T10 Left T12 Right T8 Left T7
2 (and 3-D spin) 5 8 2 6 4 9 4 13 N/A 12
DSA, digital subtraction angiography; MRA, magnetic resonance angiography; N/A, not applicable; 3-D, 3-dimensional.
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FIGURE 3. A 72-year-old man presented with 4 years of progressive lower-extremity weakness, myelopathy, and loss of sexual function. T2-weighted magnetic resonance (MR) imaging (A) demonstrates intrinsic spinal cord signal change and prominent dorsal flow voids. Bolus contrast MR angiography (B) demonstrated a likely fistula at the T7 pedicle. Digital subtraction spinal angiography (C) confirmed the site of the fistula. Onyx cast (D) after embolization showed good penetration of the proximal draining vein. At 13 months after embolization, T2-weighted MR imaging (E) demonstrated complete resolution of the intrinsic cord signal change. The patient had a return of strength but persistent sensory symptoms. Used with permission from Barrow Neurological Institute.
artery, posterior spinal artery, or a radiculomedullary artery.26 Inadequate access to the proximal medullary draining vein is also a contraindication to endovascular therapy. In these cases, surgery is the preferred treatment. Recurrence after embolization is possible, even with penetration into the draining vein.23,27,28 Postoperative imaging findings may be difficult to interpret; improvement in the MR imaging appearance of spinal cord abnormalities may be slow and incomplete and may not correlate with clinical outcomes.29 It is not uncommon, however, to see resolution of the intrinsic spinal cord T2 prolongation or resolution of the dilated perimedullary veins on follow-up imaging. Lack of clinical or radiographic improvement should prompt a search for residual or recurrent fistula and may indicate that the fistula is possibly fed from multiple arteries. SDAVFs are a cause of progressive paralysis but may be preventable if diagnosed and treated early. A high index of suspicion, even in atypical cases such as spinal cord edema without prominent flow voids, is necessary to avoid delays in diagnosis. MR angiography is a valuable aid in diagnosis and can help direct DSA, but it is not a replacement for catheter angiography. Once diagnosed, treatment with either endovascular embolization or surgical ligation is indicated. Identification and permanent obliteration of the fistula, together with the proximal medullary vein, are key to successful treatment. Disclosure Dr McDougall is a consultant for Covidien (eV3), Terumo (Microvention), and Codman. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.
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SPINAL DURAL ARTERIOVENOUS FISTULAS
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