Spinal and Paraspinal Arteriovenous Lesions
2019; Lippincott Williams & Wilkins; Volume: 50; Issue: 8 Linguagem: Inglês
10.1161/strokeaha.118.012783
ISSN1524-4628
AutoresStéphanie Lenck, Patrick Nicholson, Rachel Tymianski, Christopher Alan Hilditch, Aurélien Nouet, Krunal Patel, Timo Krings, Michael Tymianski, Ivan Radovanovic, Vítor Mendes Pereira,
Tópico(s)Meningioma and schwannoma management
ResumoHomeStrokeVol. 50, No. 8Spinal and Paraspinal Arteriovenous Lesions Free AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplemental MaterialFree AccessReview ArticlePDF/EPUBSpinal and Paraspinal Arteriovenous LesionsUncovering Vascular Pathology of the Spine Stéphanie Lenck, MD, Patrick Nicholson, MB, BCh BAO, Rachel Tymianski, MS, Christopher Hilditch, MD, Aurélien Nouet, MD, Krunal Patel, MD, Timo Krings, MD, PhD, Michael Tymianski, MD, PhD, Ivan Radovanovic, MD, PhD and Vitor Mendes Pereira, MD, MSc Stéphanie LenckStéphanie Lenck From the Division of Neuroradiology, Department of Medical Imaging, Toronto Western Hospital, University Health Network and University of Toronto (S.L., P.N., C.H., T.K., V.M.P.), University Health Network, ON, Canada Division of Neuroradiology (S.L.), Groupe Hospitalier Pitié-Salpêtrière, Paris Sorbonne University, France , Patrick NicholsonPatrick Nicholson From the Division of Neuroradiology, Department of Medical Imaging, Toronto Western Hospital, University Health Network and University of Toronto (S.L., P.N., C.H., T.K., V.M.P.), University Health Network, ON, Canada , Rachel TymianskiRachel Tymianski Adelaide Medical School, University of Adelaide, Australia (R.T.) , Christopher HilditchChristopher Hilditch From the Division of Neuroradiology, Department of Medical Imaging, Toronto Western Hospital, University Health Network and University of Toronto (S.L., P.N., C.H., T.K., V.M.P.), University Health Network, ON, Canada , Aurélien NouetAurélien Nouet Division of Neurosurgery (A.N.), Groupe Hospitalier Pitié-Salpêtrière, Paris Sorbonne University, France , Krunal PatelKrunal Patel Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, University of Toronto, ON, Canada (K.P., M.T., I.R., V.M.P.). , Timo KringsTimo Krings From the Division of Neuroradiology, Department of Medical Imaging, Toronto Western Hospital, University Health Network and University of Toronto (S.L., P.N., C.H., T.K., V.M.P.), University Health Network, ON, Canada , Michael TymianskiMichael Tymianski Krembil Neuroscience Center (M.T., I.R.), University Health Network, ON, Canada Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, University of Toronto, ON, Canada (K.P., M.T., I.R., V.M.P.). , Ivan RadovanovicIvan Radovanovic Krembil Neuroscience Center (M.T., I.R.), University Health Network, ON, Canada Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, University of Toronto, ON, Canada (K.P., M.T., I.R., V.M.P.). and Vitor Mendes PereiraVitor Mendes Pereira Correspondence to Vitor Mendes Pereira, MD, MSc, Division of Neuroradiology, Toronto Western Hospital - 3MCL-436, 399 Bathurst St, Toronto, ON M5T 2S8. Email E-mail Address: [email protected] From the Division of Neuroradiology, Department of Medical Imaging, Toronto Western Hospital, University Health Network and University of Toronto (S.L., P.N., C.H., T.K., V.M.P.), University Health Network, ON, Canada Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, University of Toronto, ON, Canada (K.P., M.T., I.R., V.M.P.). Originally published10 Jun 2019https://doi.org/10.1161/STROKEAHA.118.012783Stroke. 2019;50:2259–2269Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: June 10, 2019: Ahead of Print Vascular lesions of the spine and spinal cord can be categorized into intramedullary and extramedullary lesions. These lesions are rare and comprise a heterogeneous spectrum of diseases. They were first reported in the 19th century with the autopsy-based classification of Virchow and Picard.1 However, it was in the 1970s, with the advent of selective spinal angiography, that they became better understood; thanks to the descriptions of Djindjian and Kricheff,2,3 Aminoff and Logue,4 and Di Chiro and Wener.5 Their identification and localization have progressed significantly with the development of imaging techniques.6,7 Several classification systems have been proposed over time to describe vascular lesions of the spine.3,5,8–11 One of the classifications, from the Bicêtre group, categorizes spinal arteriovenous shunts (AVSs) according to their genetic and developmental features, distinguishing genetic hereditary lesions (type I), genetic nonhereditary lesions (type II), and focal (sporadic) lesions (type III).10 Although comprehensive, this classification is not widely used in clinical practice as most spinal AVSs belong to the third group, while a precise stratification of focal or sporadic lesions is necessary for the clinical and therapeutical management of the patients. In addition, recent studies have shown somatic activating mutations in the KRAS pathway in brain arteriovenous malformations (AVMs), opening new horizons in understanding the genetic patterns of arteriovenous lesions, particularly the nonhereditary and focal ones.12 Spetzler et al9 proposed a broader classification based on the type of vascular malformation and included neoplastic lesions, cavernomas, spinal aneurysms, arteriovenous fistula (AVF), and AVM. However, spinal AVS lesions share common pathophysiological mechanisms and clinical presentations, whereas nonshunting vascular lesions with a venous phenotype such as telangiectasias and cavernomas, as well as vascular tumors and idiopathic spinal artery aneurysms, represent different diseases with specific pathophysiology. Here, we focus only on the spinal AVS lesions and propose a systematic classification based on their anatomic relationship with the spinal cord and surrounding spinal structures. A brief introduction to the vascular anatomy of the spinal cord is detailed in the online-only Data Supplement.Pathophysiology of AVSs Involving the SpineAn AVS is defined as one or multiple abnormal communications between arteries and veins without the interposition of capillary vessels.13 Hemodynamically, this phenomenon results in high nonresistive flow in the feeding arteries and increased pressure in the draining veins. The transition between the feeding artery(s) and the vein(s) can be through an arteriolo-venular network (a nidus), and these AVSs are commonly named AVMs. Alternatively, when there is a direct communication between one (or several) main arterial feeder(s) and a single draining vein, these lesions are named AVF.13 A fistula usually carries a direct single draining vein, whereas the number of feeding arteries may vary.The clinical and radiological manifestations of spinal AVS are related to their venous drainage and to the vascular remodeling induced by hemodynamic stress over time. The chronic remodeling may affect both the arterial and venous components.14 Therefore, the feeding arteries and the draining veins of an AVS are often more fragile, dilated, and tortuous, with subsequent formation and enlargement of venous pouches and arterial aneurysms, which may rupture or compress the spinal cord or nerve roots. In addition, the AVS may impair the venous drainage of the spinal cord and lead to venous congestive myelopathy. Therefore, AVSs involving the spinal cord may present as follows.HemorrhageDepending on the anatomy of the lesion, spinal AVS (or their related aneurysms) may rupture into the spinal cord (hematomyelia), the subarachnoid space (subarachnoid hemorrhage [SAH]), rarely intracranially, and even more rarely into the epidural space.10,11 Because of their locations, intradural AVSs are more likely to present with hematomyelia or SAH than dural or epidural AVS. An associated aneurysm should be thoroughly looked for in patients presenting with spinal hemorrhage because, when present, it usually corresponds to the weak points of the malformation and may be the main focus of the treatment.15 Rarely, spinal AVS may have an intracranial venous drainage and may cause intracranial and SAH.16,17 Finally, epidural hematomas have been described as rare presentations of dural and epidural AVS.18,19Venous CongestionCongestive myelopathy is primarily a consequence of impaired venous outflow of the cord, which can be directly caused by reflux of the fistula into the perimedullary veins and indirectly by an obstruction of the spinal cord venous drainage. Anatomically, the lower thoracic spine has relatively fewer venous outflow channels compared with the cervical spine, and this helps explain why the thoracic spinal cord is more vulnerable to venous congestion than the cervical cord.13 Because of this, the venous congestive edema is likely to extend in a caudocranial direction throughout the spinal cord. This may explain why the first symptoms of congestive myelopathy usually reflect dysfunction of the conus medullaris, although the shunt is located remotely. Congestive myelopathy is seen on magnetic resonance imaging as a poorly defined T2-weighted hyperintensity within the cord, often extending over multiple segments.20 The association of spinal cord edema and dilated tortuous perimedullary vessels is highly suggestive of a spinal or rarely paraspinal AVS.20Spinal or Radicular CompressionSpinal cord compression may occur in high-flow AVS, and the compression is usually caused by venous dilatations and pouches21–23 and more rarely by spinal artery aneurysms.24 Anatomically, the spinal cord can also be compressed by epidural or intradural vascular structures, whereas the nerve roots are usually compressed by epidural dilated veins.23Vascular Steal and High-Output Heart FailureVascular steal of the spinal cord has been reported as a possible mechanism for neurological deterioration in patients with high-flow fistulae.25,26 Although vascular steal is well-described in brain AVS, it remains a rare phenomenon in spinal AVS.27 In children, high-output heart failure may occur in large- or high-flow AVS.28Anatomic Classification of Spinal and Paraspinal AVSThe proposed Toronto classification of spinal AVS is summarized in the Table. Table I in the online-only Data Supplement highlights the clinical features and therapeutic considerations of spinal AVS. Table II in the online-only Data Supplement, meanwhile, compares our classification with those described previously.Table. Toronto Classification of Arteriovenous Malformations of the SpineVascular LesionsTopography of the ShuntSpinal cord AVMIntradural intramedullaryPial AVFIntradural pial Microfistula MacrofistulaDural AVFDuralEpidural AVFEpiduralParaspinal AVFParaspinal spaceSAMSMultipleAVF indicates arteriovenous fistulae; AVM, arteriovenous malformation; and SAMS, spinal arteriovenous metameric syndrome.AVS Located in the Spinal Canal: Intradural AVSsIntradural AVS account for 20% to 30% of all vascular malformations of the spine11,29 and include spinal cord AVM and pial AVF.30,31 Spinal cord AVMs are more frequent than pial AVF in both adults (85% versus 15%) and children (70% versus 30%).13 Intradural AVSs have been associated with several genetic syndromes caused either by a germinal (eg, hereditary hemorrhagic telangiectasias [HHT], capillary malformation-AVM syndrome) or somatic mutations (eg, Cobb; Klippel-Trenaunay-Weber; and congenital lipomatous overgrowth, vascular malformations, and epidermal nevi syndromes).13,32–34 If the syndrome is related to a germinal mutation, multifocal vascular lesions may occur along the spinal cord and in the brain. A complete magnetic resonance imaging evaluation of the spine and the brain is required at presentation in those patients to detect multifocal lesions, as well as life long clinical and radiological follow-up to detect de novo lesions.Spinal Cord AVMSpinal cord AVMs are nidus-type AVMs and may have a compact or a diffuse nidus, which can be exclusively intramedullary or may have both subpial and intramedullary components (Figure 1).30 While the primary vascular supply is usually from the anterior spinal artery (ASA), they may be also be fed by the radial arteries of the vasocorona arising from the posterior spinal arteries (PSA). Approximately half of the lesions are located at the thoracic level, whereas 30% and 20% are located at the cervical and at the level of the conus, respectively.35 Spinal cord AVMs occur equally in women and men with a mean age of presentation of 30 years.35 Because of the interposition of a nidus between arteries and veins, the flow in the malformation is usually low compared with a pial fistula, and the intranidal vessels are often small and fragile.31 This may explain why most patients present with hematomyelia and SAH, while congestive myelopathy occurs in only 20% of patients.31,35 The hemorrhage risk of an unruptured spinal cord AVM is around 4% per year, while it increased to 10% per year for the previously ruptured ones.35 Spinal cord AVM-associated hemorrhage may also be caused by associated aneurysms. These can be prenidal or intranidal and are mainly located at the cervical level.36 Prenidal aneurysms involve the ASA in most cases.36Download figureDownload PowerPointFigure 1. Spinal cord arteriovenous malformation (AVM). A and B, Anatomic 3-dimensional (A) and axial (B) representations of a spinal cord AVM, showing the intramedullary nidus fed by the sulcal and radial branches of the anterior spinal artery (ASA) or posterior spinal artery (PSA). C, Three-dimensional reconstruction of a selective angiogram of the right T8 intercostal artery. Note the injection of the ASA (blue arrow) and of both right (red arrow) and left PSA through the arterial basket of the conus. D, Selective spinal angiogram, with injection of the right T8 intercostal artery, which gives rise to the Adamkiewicz artery and thus to the thoracic ASA (blue arrow). The AVM is mainly fed by the branches of the PSAs (black arrow) through the arterial basket of the conus with some indirect feeding arteries arising from the ASA.Spinal cord AVMs are the most challenging arteriovenous lesions of the spine as the nidus is usually nestled within the spinal cord and fed by functional sulcal and radial arteries arising from the ASA and PSA. Given the risks of microsurgery and endovascular therapy, unruptured spinal cord AVMs are usually managed conservatively. Conversely, given their hemorrhagic risks, treatment is indicated in most cases of ruptured spinal cord AVM.35 Two strategies can be used: complete resection or embolization, or partial embolization targeting the weak point of the malformation. Conservative treatment can also be a reasonable option even for a ruptured AVM if the risks of surgery or endovascular therapy are considered too high.Safe surgical resection of a spinal cord AVM is feasible in AVM with a specific favorable angioarchitecture, that is, posterolaterally located AVMs that are fed by radial arteries arising from the PSA (Figure 1). For these AVMs, the pial resection technique allows to safely resect the pial component, while avoiding resection of the intramedullary component. Unlike brain AVM, a subtotal surgical devascularization of a spinal cord AVM may secondarily lead to a complete obliteration of the lesion without haemorrhage.37,38 However, intramedullary spinal cord AVMs are usually located within the spinal cord, and they are rarely suitable for microsurgery given the high risk for neurological impairment related to the dissection of the spinal cord. Unlike brain AVM, partial embolization of spinal AVM seems to reduce the hemorrhage rate and thus improve long-term clinical outcome.15,35 The purpose of endovascular treatment is to target embolization toward the weak point of the malformation (prenidal or intranidal aneurysms).35 Embolization of spinal cord AVM is especially challenging given the small size and the eloquence of the feeding arteries. The embolic agents may be polyvinyl alcohol particles,39 N-butyl cyanoacrylate,40–42 and more recently, ethylene vinyl alcohol–based agents.43,44 Embolization with ethylene vinyl alcohol–based agents remains controversial and is not used in our institution given the necessity of refluxing to make a plug and thus the high risk of occluding functional arteries.Pial AVFPial AVFs are shunts located superficially of the cord in the subpial space (Figure 2).9,30 Depending on the location of the shunt and on its flow, they are directly fed by the ASA and more rarely the PSA and drain directly in the anterior or posterior perimedullary veins. Those pial AVFs have been previously called perimedullary AVF, fistulous type AVMs, or type IV spinal AVF.31,45–48 Filum terminale AVF may be grouped into this category as the filum terminale is covered by the pia mater and the shunt occurs between the artery of the filum terminale, which is the continuation of the ASA, and the vein of the filum terminale, which is the continuation of the anterior spinal perimedullary vein.49,50 Congestive myelopathy is the most common presentation of pial AVFs (60% of patients),31,47 whereas 35% of patients will present with hemorrhage.47 A flow-related aneurysm is found in 10% of pial AVF.47Download figureDownload PowerPointFigure 2. Pial arteriovenous fistula (AVF). A and B, Anatomic 3-dimensional (A) and axial (B) representations of an anterior pial AVF, showing the direct communication between the anterior spinal artery (ASA) and the anterior perimedullary vein at the anterior surface of the spinal cord. C, Selective angiogram of the left T8 intercostal artery showing a thoracic pial AVF in an 8-y-old patient with hereditary hemorrhagic telangiectasia. The main feeding artery is the left posterior spinal artery (PSA; green star) with a contribution from the right PSA (orange star). The ASA (blue star) originates from the left T8 intercostal artery and anastomoses with the right PSA (orange star) through a circumferential anastomosis (blue arrow). The ASA and both PSA anastomose through the arterial basket of the conus (red arrow) to feed the pial fistula mainly through the left PSA (green star). Note the venous pouch that is the primary venous collector of the fistula (white arrow). D, Selective angiogram of the left T11 intercostal artery feeding the left PSA (green star). The shunt is direct between the left PSA and the venous pouch of the fistula (white arrow).Pial AVF can be categorized into microfistulae and macrofistulae.10 Di Chiro and Wener5 previously classified pial AVF into 3 subtypes. They defined type IVa as simple extramedullary fistulae fed by a single arterial branch; type IVb as intermediate-sized fistulae with multiple dilated arterial feeders; and type IVc as giant multipediculated fistulae. We propose to classify the Di Chiro type IVa as a specific group called pial AVF with microfistula, while bringing the types IVb and IVc together into a group called pial AVF with macrofistula.51 Pial AVF with microfistulae occur more frequently in older males around 50 years old and are usually idiopathic or traumatic.45–47 Otherwise, pial AVFs with macrofistulae affect younger patients and children and are often associated with genetic conditions such as HHT and less frequently Klippel-Trenaunay-Weber; capillary malformation-AVM syndrome; congenital lipomatous overgrowth, vascular malformations, and epidermal nevis; or Cobb syndromes.32–34 Pial AVF with macrofistulae is a classical cause of neurological presentation of HHT in children.52 HHT is a genetic autosomal dominant disease with 2 main genotypes (HHT-1 and HHT-2), corresponding to mutations in ENG and ACVRL1, respectively. Pial AVFs associated with HHT are usually high-flow lesions, which are usually fed by the PSA and located at the posterior surface of the cord.52Given the subpial location of the shunt and the simple angioarchitecture of pial AVF, the results of both microsurgery and endovascular therapy are better than for spinal cord AVMs. The complete obliteration rate after microsurgery or endovascular therapy is ≈80%, but this depends on the size of the fistula.47 The therapeutic goal of treatment is the disconnection of the fistula, while preserving the feeding artery. Microsurgical disconnection and endovascular transarterial embolization with N-butyl cyanoacrylate and coils or detachable balloon for high-flow fistulas may be considered.47 Endovascular therapy is usually the preferred approach if a microcatheter can be navigated to the fistulous point. The long-term outcome after treatment is usually good with improvement of the symptoms in 75%.47AVS Located in the Spinal Canal: Dural and Epidural AVFDural AVFSpinal dural AVFs (DAVFs) account for ≈70% of all vascular spinal malformations (Figure 3).20,53 Spinal DAVF is an acquired lesion, which usually becomes symptomatic in elderly men.20 Approximately 90% of spinal DAVFs are located at the thoracic level.6 The feeding artery is the radiculomeningeal branch of a radicular artery, which may also contribute to the spinal cord as ASA or PSA. The draining vein is a radicular vein, and the shunt usually occurs within 1 cm of its dural portion,13 at the dorsal surface of the root sleeve in the intervertebral foramen, located underneath the pedicle of the vertebral body.20,54 They are usually low-flow and high-pressure lesions.55 Congestive myelopathy is the most common and almost exclusive clinical presentation of spinal DAVF.20 Venous congestion occurs because of venous reflux from the radicular vein to the perimedullary vein, and ultimately, the occurrence of symptoms depends on the spinal cord venous outflow efficiency.56–58 Rarely, DAVF draining intracranially may present with intracranial hemorrhage.17 Finally, spinal DAVF may seldom cause symptomatic compression of the nerve root by a dilated radicular vein.6Download figureDownload PowerPointFigure 3. Dural arteriovenous fistula. A and B, Anatomic 3-dimensional (A) and axial (B) illustrations of a dural arteriovenous fistula, showing the shunt between the radicular artery and the radicular vein at the dorsal surface of the dural root sleeve in the intervertebral foramen located underneath the pedicle of the vertebral body. C, Cone-beam computed tomographic images showing the T5 radicular artery supplying the posterior spinal artery (PSA; blue arrow), as well as filling both the radicular vein (green arrow) and the perimedullary vein (orange arrow). Embolization of this fistula is contraindicated as the PSA (blue arrow) arises from the same radicular artery as the fistula. D, Direct open surgical view in the same plane, after opening of the dura. This shows the arterialization of the radicular vein corresponding to the primary venous collector (green arrow) and the dilatation of the posterior perimedullary veins (red arrow).Both microsurgery and endovascular therapy may be proposed for patients with DAVF. The microsurgical treatment consists of surgical disconnection of the intradural vein that receives the blood from the shunt zone. Endovascular therapy is performed using a liquid embolic agent after catheterization of the feeding radicular artery.20 The endovascular aim is for the liquid embolic agent to penetrate into the first portion of the draining vein, while avoiding occlusion of the perimedullary veins. If the primary draining vein is not occluded, it is highly likely that the fistula will recur by refilling via other arterial anastomoses.20 If the feeding radicular artery is an artery that supplies the spinal cord (ASA or PSA), selective embolization is contraindicated, given the risk of migration of embolic material into the spinal artery and of spinal cord ischemia. Three- dimensional selective rotational angiography of the feeding segmental artery is useful to exclude this anatomic configuration. In those cases, before referring the patient to neurosurgery, coils may be deployed in the corresponding intercostal artery to guide the neurosurgeon to the appropriate vertebral level with fluoroscopy.Epidural AVFSpinal epidural fistulas affect preferentially elderly men between 60 and 70 years of age and can be idiopathic or traumatic (Figure 4).6,59 Approximately 70% to 80% of the fistulas are located at the lumbar level.6,59 The shunt is located in the epidural space into the spinal canal, between the dura matter and the bone.6,59 In 90% of the cases, the shunt is located in the retrocorporeal space on the posterior surface of the vertebral body, and those fistulae are named ventral epidural AVF.60 More rarely, the fistula can be in the lateral or posterior epidural spaces. In ventral epidural AVF, the main feeding arteries are the dorsal somatic branches of the regional segmental arteries through the retrocorporeal arcade. In lateral and posterior AVF, the main feeding artery is the prelaminar artery.6,59 The primary draining vein is an epidural vein. From the epidural venous plexus, the fistula can drain into the paraspinal venous plexuses laterally or reflux into the perimedullary veins medially (through the duramatter) or both. The clinical presentation of epidural AVF depends on this venous drainage.6,59 The flow is significantly lower in epidural AVF with exclusively perimedullary venous reflux compared with epidural AVF with paraspinal venous drainage.59 This may be explained by the venous reflux-impeding mechanism embedded within the dura matter, which can restrict flow at the junction between the epidural venous plexus and the radiculomedullary vein. Meanwhile, the junction between the epidural venous plexus and the paraspinal veins is valveless with no flow restriction.61 Consequently, perimedullary venous reflux may lead to congestive myelopathy, whereas paraspinal venous drainage may lead to spinal cord or nerve root compression by dilated arterial and venous structures. Epidural AVF with reflux in both perimedullary and paraspinal veins may present with myelopathy and compressive symptoms. Finally, a large number of epidural AVFs, especially without perimedullary reflux, may be asymptomatic.62,63 Epidural hematoma has been reported as a rare manifestation of epidural AVF.18Download figureDownload PowerPointFigure 4. Epidural arteriovenous fistula. A and B, Anatomic anterior (A) and axial (B) representations of an epidural arteriovenous fistula showing the shunt between the posterior somatic branches and the epidural venous plexus at the dorsal surface of the vertebral body, in the epidural space. C, T2 axial view at the level of the L4-L5 foramina showing the compression of the dilated radicular vein (blue star) on the left L4 nerve root and the mild compression of the dilated epidural vein on the cauda equina. This radiological picture explained why the patient presented with a left L4 deficit. D, Three-dimensional reconstructions of an angiogram in a coronal anterior view after injection of the left L3 lumbar artery, showing an epidural arteriovenous fistula fed by the posterior somatic branch and multiple indirect arterial feeders and draining into the epidural venous plexus (green star). The venous drainage is from the epidural venous plexuses (green star) to the paravertebral venous plexuses (red star) through the radicular veins (blue stars). There is no reflux into the perimedullary veins, explaining the absence of congestive myelopathy.While asymptomatic epidural AVFs are usually managed conservatively, both microsurgery and endovascular therapy may be considered for patients with symptomatic epidural AVF. However, endovascular therapy is usually preferred to surgery.6,59 The surgical approach may be difficult in epidural AVF because the venous pouch is usually located at the ventral epidural space and, therefore, surgical access is restricted and may be hampered by diffuse epidural bleeding obscuring the field. The perioperative identification of the primary venous collector may also be difficult because all the draining veins of the fistula may be dilated. On the contrary, catheterization of the dorsal somatic branch is technically easy for an interventional neuroradiologist because it usually runs straight to the venous pouch. Unlike DAVF, there is a lower risk for migration of the liquid embolic agent into a spinal artery. The therapeutic goal is a complete occlusion of the draining vein. This may be straightforward if the primary draining vein is small, but it may be much more difficult in high-flow fistulas as the primary draining vein may be highly dilated. In those cases, combined approach of transarterial and transvenous embolizations may be used. Complete obliteration of epidural AVF after treatment varied from 59% to 100% in the literature.6,59AVSs Located Outside the Spinal Canal: Paraspinal FistulaeParaspinal AVFs are usually high-flow fistulas fed by adjacent segmental arteries that drain into the paraspinal venous plexuses (Figure 5). The most frequent location is the cervical level, where they are named vertebro-vertebral AVFs while thoracic and lumbar paraspinal AVF are rare.13,64 At the cervical level, they are usually the consequence of a traumatic or spontaneous dissection of the vertebral artery.64 Therefore, diseases such as collagen type III vasculopathies, fibromuscular dysplasia, and neurofibromatosis type 1 are associated with these fistulas as they can lead to spontaneous arterial dissections.13,65 These fistulas are rarely associated with neurologic symptoms unless the venous drainage secondarily involves the epidural plexuses. In those cases, spinal cord compression or more rarely congestive myelopathy may occur with the same pathophysiology as described for epidural AVF.66 Exceptionally, high-flow paraspinal fistulae can result in high-output heart failure and multiorgan dysfunction in children.67 In the cervical location, pulsatile tinnitus is the most frequent manifestation,64 and rarely, high-flow vertebro-vert
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