A simplified arteriovenous malformation model in sheep: feasibility study.

BACKGROUND AND PURPOSE: Recently, a swine model of a cerebral arteriovenous malformation (AVM) has been developed that closely resembles a human AVM of the brain. The creation of such a model requires sophisticated neurointerventional techniques. The purpose of this study was to develop a simple and cost-effective AVM animal model that does not require additional endovascular techniques. METHODS: A surgical anastomosis was created in seven sheep between the common carotid artery and the ipsilateral jugular vein, followed by ligation of the jugular vein above the anastomosis and of the proximal common carotid artery below the anastomosis. The anastomosis was created on the left side in four animals and on the right side in three. Cerebral angiography from the contralateral carotid artery was performed before and immediately after surgery to delineate the relevant cerebral vascular anatomy and to determine the direction of blood flow. RESULTS: An angiographic appearance simulating an AVM was found in all the animals. The ramus anastomoticus and arteria anastomotica functioned as the feeding vessels to the rete mirabile, which represented the nidus in our model, and to the jugular vein, which represented the draining vein from the malformation. Extensive collateral flow through the rete mirabile into the distal segment of the external carotid artery above the ligature was observed angiographically, with retrograde flow through the surgical anastomosis into the jugular vein. CONCLUSION: A simple surgically created experimental model for cerebral AVMs was developed in sheep without the need for additional complex endovascular catheter manipulations of intracranial branches. Such an animal model can substantially reduce the cost of research and training in the neurointerventional or radiosurgical management of AVMs.     

Acute and chronic swine rete arteriovenous malformation models: hemodynamics and vascular remodeling

BACKGROUND AND PURPOSE: An acute and a chronic arteriovenous malformation (AVM) model were developed by using the swine rete to study hemodynamics and vascular remodeling. The models were also used to study in vivo polymerization kinetics and the distribution of various N-butyl 2-cyanoacrylate (NBCA) and Lipiodol mixtures. METHODS: In the acute swine AVM model, retrograde flow through the left side of the rete was created by the placement of an endovascular shunt through the ipsilateral ascending pharyngeal artery. In the chronic model, flow was redirected retrograde through the left side of rete and ascending pharyngeal artery by creating an arteriovenous fistula between the ipsilateral jugular vein and the common carotid artery. After a period of at least 6 months, the entire head with the rete was connected to a perfusion loop driven by a peristaltic pump. A total of 30 swine were used for both the acute (n = 23) and chronic groups (n = 7). Hemodynamic parameters, including the flow and pressure drop across the rete, were recorded before NBCA embolization. Image processing was used on high-resolution radiographs of the explanted retia to measure the total rete length. Measurements of rete vessel calibers were based on histology. RESULTS: The pressure gradients across retia were higher in the chronic model than in the acute model, but they did not reach the level of statistical significance (23.7 +/- 12.0 mm Hg vs 15.4 +/- 1.4 mm Hg). The rete blood outflow was significantly higher in the chronic model compared with the acute one (139.9 +/- 100.3 mL/min vs 32.5 +/- 17.6; P = .03). The rete length in the chronic model was significantly higher than in the acute model (593.1 +/- 39.9 vs 401.3 +/- 65.2 pixel; P < .001). The average vessel diameter of the rete in the chronic group was 520 microm and 320 microm in the control animals. CONCLUSION: Increased pressure gradients and flow in the chronic swine rete AVM model may be related to increased size and decreased impedance. The resulting hemodynamic changes reflect a true flow-induced vascular remodeling rather than a simple change related to aging and size of the animal.     

The two-in-one model: a new variation of the arteriovenous malformation model in swine

We report a new variation of the well-established experimental arteriovenous malformation (AVM) model in swine. To provide high flow through the rete mirabile (nidus, RM) and thereby to reduce the rate of spontaneous thrombosis of the AVM, we performed an end-to-end anastomosis of the left common carotid artery (CCA) and the external jugular vein (EJV) microsurgically in three micropigs. After 1 and 4 months the animals underwent angiograms of the CCA and vertebral artery (VA). In all cases the diversion of the blood through the RM was patent, up to the 4 months follow-up. We observed an arteriovenous fistula (arteriovenous pseudomalformation, pAVF) between the VA and the EJV in each case at both 1 and 4 months. This modification of the well-known AVM model in the micropig could be used to monitor long-term changes after embolisation, avoiding the naturally high rate of spontaneous thrombosis. This two-in-one model is thus well suited for preclinical testing of embolic materials. Received: 2 December 1999 Accepted: 31 August 2000     

Complete obliteration of intracranial arteriovenous malformation with endovascular cyanoacrylate embolization: initial success and rate of permanent cure

BACKGROUND AND PURPOSE: Endovascular treatment with cyanoacrylate embolization is an option when complete obliteration of the nidus of an intracranial arteriovenous malformation (AVM) is the goal. Our purpose was to evaluate the rates of initial success and permanent cure of such treatment in a Chinese population. METHODS: Twenty-seven consecutive patients with an intracranial AVM underwent endovascular embolization with cyanoacrylate between June 1995 and May 1997. Twenty-six patients had cerebral AVMs and one had a cerebellar AVM. Curative embolization was attempted in 10 patients in whom 1) the nidus was not larger than 3 cm, 2) the number of feeders did not exceed three, and 3) the nidus was accessible with the tip of the catheter. We used a flow-directed microcatheter and a 20-25% mixture of cyanoacrylate in contrast medium. Long-term outcomes were observed angiographically and clinically. RESULTS: Complete embolization was achieved in six patients. No procedure-related complications occurred during attempted curative embolization. Follow-up angiography performed at 17-32 months showed complete obliteration of the AVM nidus in the six patients after initial embolization. These patients remained asymptomatic 5-7 years after treatment. The rate of permanent cure of the initially complete embolization was 100% (six of six). The success rate of endovascular cure for patients treated with curative intent was 60% (six of 10). The overall cure rate was 22% (six of 27). CONCLUSION: The overall initial cure rate of intracranial AVM with cyanoacrylate embolization was 22%. Initial angiographic evidence of complete embolization indicated permanent cure in these patients.     

Three-dimensional dynamic magnetic resonance angiography for the evaluation of radiosurgically treated cerebral arteriovenous malformations

We assessed the value of three-dimensional (3D) dynamic magnetic resonance angiography (MRA) for the follow-up of patients with radiosurgically treated cerebral arteriovenous malformations (AVMs). Fifty-four patients with cerebral AVMs treated by radiosurgery (RS) were monitored using conventional catheter angiography (CCA) and 3D dynamic MRA with sensitivity encoding based on the parallel imaging. Cerebral AVM was qualitatively classified by two radiologists into one of five categories in terms of residual nidus size and persistence of early draining vein (I, >6 cm; II, 3–6 cm; III, <3 cm; IV, isolated early draining vein; V, complete obliteration). 3D MRA findings showed a good agreement with CCA in 40 cases (κ=0.62). Of 23 nidus detected on CCA, 3D dynamic MRA showed 14 residual nidus. Of 28 occluded nidus on 3D dynamic MRA, 22 nidus were occluded on CCA. The sensitivity and specificity of 3D dynamic MRA for the detection of residual AVM were 81% and 100%. 3D dynamic MRA after RS may therefore be useful in association with MRI and can be repeated as long as opacification of the nidus or early venous drainage persists, one CCA remaining indispensable to affirm the complete occlusion at the end of follow-up.     

Histopathologic characteristics of a chronic arteriovenous malformation in a swine model: preliminary study

BACKGROUND AND PURPOSE: The experimental induction of histologic transformations in microvessels of similar caliber to those of nidus vessels of cerebral arteriovenous malformations (AVMs) has not been attempted previously. Our goal was to examine preliminarily the histopathologic characteristics of nidus vessels and the angiographic features of a chronic AVM model in swine. METHODS: AVM models were fashioned from bilateral carotid retia mirabilia of seven swine after the surgical formation of large unilateral carotid-jugular fistulas. One AVM model was made for immediate use, whereas in the other six, follow-up angiography was obtained at varying intervals (2 to 180 days) after model creation. Light and electron microscopy, immunohistochemistry (using monoclonal antibodies against smooth muscle actin and PC10 against proliferating cell nuclear antigen), and histometry were performed on the nidus vessels of three swine: one acutely created, one 2 months old, and one 6 months old. RESULTS: Vascular dilatation and tortuosity of the main arterial feeder and draining vein were evident angiographically as early as 4 days after AVM creation, and were maximal in the 6-month-old model. Compared with the acutely created nidus vessels, those in the two chronic models revealed disrupted and attenuated elastica and intimal hyperplasia that was focal ("cushions") or generalized, leading to luminal occlusion. Variable numbers of cells in the tunica media of chronic nidus vessels contained smooth muscle actin. PC10/proliferating cell nuclear antigen immunoreactivity was observed in the endothelium and subendothelial layers. Histometry showed increases in intimal hyperplasia and medial thickness in the chronic vessels. CONCLUSION: Nidus vessels in this chronic swine AVM model exhibited striking histologic changes similar to those seen in cerebral AVMs. The induced vessel growth seen angiographically and histologically in components of the chronic AVMs was consistent with the presence of persistently raised intravascular hemodynamic loads. This preliminary feasibility study suggests that the realistic histologic characteristics of this chronic AVM model are an attractive feature, and if confirmed in future, more comprehensive, studies would be of benefit in accurate histopathologic interpretation of the effects of superimposed experimental embolotherapy or radiosurgery. This model may provide a useful experimental tool to study the dynamic cellular and tissue events that dictate the development and natural history of AVMs.     

MR imaging in the management of supratentorial intracranial AVMs

The MR images, CT scans, and angiograms of 15 consecutive patients with intracranial, supratentorial arteriovenous malformations (AVMs) were studied retrospectively. The three imaging techniques were evaluated separately to assess their utility in defining the size, characteristics, and location of the AVM nidus, its arterial supply, and venous drainage. The studies were also evaluated for their ability to show associated parenchymal abnormalities, the presence of mass effect, and changes occurring after embolization. MR was superior to both CT and angiography in showing the exact anatomic relationships of the nidus, feeding arteries, and draining veins, as well as in demonstrating the extent of AVM nidus obliteration after embolization. MR was more sensitive than CT in revealing associated parenchymal abnormalities and subacute hemorrhage. Because of flow-related artifacts and low sensitivity in distinguishing calcification from rapid flow and/or hemosiderin, MR seemed to have a low sensitivity for detecting old hemorrhage within an AVM nidus. Angiography is still needed in the planning of either surgical or endovascular treatment of AVMs.     

出血性脑动静脉畸形的影像特点与血管内治疗

目的：探讨以出血发病的脑动静脉畸形的影像学特点与血管内治疗的技术操作。方法：经脑CT或MRI确认为脑实质内出血的56例病例，经DSA全脑血管造影证实为脑动静脉畸形(AVM)，根据AVM病灶的特点，行经血管内超选择应用α-氰基丙烯酸正丁酯栓塞或结合放射外科治疗。结果：56例在1-3次栓塞后，36例病灶完全消除；1例因AVM中有新生的动脉瘤及1例术后1年发生出血而行第2次栓塞治愈，1例在接受X-刀治疗后3个月再次出血，经手术后痊愈。结论：AVM病灶内或病灶旁存在动脉瘤和动脉囊样扩张、引流静脉细小和脑室内生长的AVM是引起脑出血的主要原因，而在栓塞中优先处理动脉瘤样病变对防止脑出血有重要意义。     

Endovascular treatment of arteriovenous malformations with selective intranidal occlusion by detachable platinum electrodes: technical feasibility in a swine model.

The technical feasibility of selective intranidal endovascular occlusion of experimental arteriovenous malformations with detachable superfine platinum electrodes was assessed in a swine model. The delivery and release of electrodes were performed within normal carotid retia mirabilia, the faster-flowing nidus (bilateral retia) of a carotid-jugular fistula-type model of an arteriovenous malformation, and a small-caliber H-type direct arteriovenous fistula. Controllable atraumatic placement of the electrodes was possible deep within each rete and in the middle of the fistula. The devices were soft and flexible, allowing them to conform to the tight turns and branches of rete vessels. Marked diminution of flow was achieved by release of multiple devices within each rete. Migration of the electrode occurred when detached within the larger-caliber arteriovenous fistula. The main advantages of this technique appear to be the controlled delivery and assured release of an occlusive radiopaque embolic agent within the nidus.     

Laboratory simulations and training in endovascular embolotherapy with a swine arteriovenous malformation model.

We assessed the suitability of a swine experimental arteriovenous malformation model for laboratory simulations and training in endovascular embolotherapy. Embolizations with liquid glue or particles were performed in 10 animals. The parameters of injection (microcatheter position, concentration and volume of embolic agent, injection rate) were deliberately varied to simulate results that may be observed in clinical practice. A range of successful and less desirable therapeutic outcomes or complications was simulated. In one model, intravascular mean blood pressure in the "terminal feeder" rose after "nidus" embolization, consistent with observations in feeders of cerebral arteriovenous malformations. Experience in the technical aspects of embolotherapy was gained by repeated performances using this model. Simplicity of creation, clear angiographic visibility of feeders, a nidus and a draining vein, and hemodynamic similarities with cerebral arteriovenous malformations make this an attractive in vivo experimental model for learning the principles of embolotherapy, testing new embolic agents, and training/gaining experience in embolization techniques.     

Use of a new mixture for embolization of intracranial vascular malformations

Summary The internal carotid artery system in swine has a special anatomic configuration similar to a brain arterial-arterial malformation. The internal carotid artery breaks up into a multitude of fine channels (rete mirabile) situated at the base of the skull on the side of the hypophysis. This anatomic arterial model was used to analyze acute and chronic angiographic and histological changes after occlusion of the rete mirabile with I) avitene, II) avitene, and 50% ethanol, III) avitene, 30% ethanol and Polyvinyl alcohol, IV) avitene 50% ethanol and Polyvinyl alcohol, V) IBCA and VI) silk. Histopathological changes observed in the rete mirabile six weeks following occlusion demonstrated that a mixture of avitene, 30% ethanol and Polyvinyl alcohol and IBCA produced the best anatomic results. Embolization with avitene, PVA and ethanol induced a more bland histological reaction than the one observed with IBCA. Preliminary clinical experience with this mixture is reassuring in those cases in which the AVM was surgically resected. The partially thrombosed AVM was easily depressed and compressed by the neurosurgeon allowing for satisfactory hemostasis in and around the nidus of the AVM.This paper was presented in part at the International Symposium on Cerebral Stroke, Sendai, Japan, 1987     

Site-specific thromboembolism: a novel animal model for stroke

BACKGROUND AND PURPOSE: To develop a technique for site-specific placement of a thrombus of predetermined volume in an animal model for the purpose of evaluating methods of intravascular thrombolysis and clot retrieval. METHODS: Six swine were subjected to thrombus injection bilaterally in the ascending pharyngeal artery (APA). Each animal underwent transfemoral angiography while under general anesthesia. A nondetachable balloon catheter and a 3-French microcatheter were then advanced into the common carotid artery through a 7-French guide catheter. With the microcatheter in the proximal APA and the balloon inflated proximally, a bolus of preformed thrombus composed of 0.9 mL of autologous blood and 0.1 mL of bovine thrombin (200 IU/mL) was injected through the microcatheter while local flow arrest was maintained for 15 min. The balloon was deflated and removed. The occluded arteries were observed by serial angiography for 3 hr and then resected for gross examination and hematoxylin and eosin staining. RESULTS: Each APA was occluded angiographically and did not recanalize during the 3-hr observation period. Persistent, proximal progression of thrombus to the superior thyroid artery origin occurred in three animals. Gross inspection revealed that the resected arteries contained thrombus in the proximal APA but not in the common carotid artery. Histologic examination revealed organized thrombus, without evidence of intimal injury. CONCLUSION: Our model provides a simple, reliable method for site-specific injection of a thrombus of predetermined volume. Site-specific placement is important for evaluation of the efficacy of thrombolytic agents and techniques. Angiographic evidence of brain revascularization can be used to grade revascularization and clot volume. The ability to specifically localize and estimate clot volume makes our model well suited for the evaluation and comparison of thrombolytic agents and endovascular techniques.     

Can Induction of Systemic Hypotension Help Prevent Nidus Rupture Complicating Arteriovenous Malformation Embolization?: Analysis of Underlying Mechanisms Achieved Using a Theoretical Model

BACKGROUND AND PURPOSE: Nidus rupture is a serious complication of intracranial arteriovenous malformation (AVM) embolotherapy, but its pathogenetic mechanisms are not well described. An AVM model based on electrical network analysis was used to investigate theoretically the potential role of hemodynamic perturbations for elevating the risk of nidus vessel rupture (Rrupt) after simulated AVM embolotherapy, and to assess the potential benefit of systemic hypotension for preventing rupture. METHODS: Five separate hypothetical mechanisms for nidus hemorrhage were studied: 1) intranidal rerouting of blood pressure; 2) extranidal rerouting of blood pressure; 3) occlusion of draining veins with glue; 4) delayed thrombosis of draining veins; and 5) excessively high injection pressures proximal to the nidus. Simulated occlusion of vessels or elevated injection pressures were implemented into the AVM model, and electrical circuit analysis revealed the consequent changes in intranidal flow, pressure, and Rrupt for the nidus vessels. An expression for Rrupt was derived based on the functional distribution of the critical radii of component vessels. If AVM rupture was observed (Rrupt > or = 100%) at systemic normotension (mean pressure [P] = 74 mm Hg), the theoretical embolization was repeated under systemic hypotension (minor P = 70 mm Hg, moderate P = 50 mm Hg, or profound P = 25 mm Hg) to assess the potential benefit of this maneuver in reducing hemorrhage rates. RESULTS: All five pathogenetic mechanisms under investigation were able to produce rupture of AVMs during or after embolotherapy. These different mechanisms had in common the capability of generating surges in intranidal hemodynamic parameters resulting in nidus vessel rupture. The theoretical induction of systemic hypotension during and after treatment was shown to be of significant benefit in attenuating these surges and reducing Rrupt to safer levels below 100%. CONCLUSION: The induction of systemic hypotension during and after AVM embolization would appear theoretically to be of potential use in preventing iatrogenic nidus hemorrhage. The described AVM model should serve as a useful research tool for further theoretical investigations of AVM embolotherapy and its hemodynamic sequelae.     

Inter- and intraobserver variability in the assessment of brain arteriovenous malformation angioarchitecture and endovascular treatment results

BACKGROUND AND PURPOSE: Several angiographic features of brain arteriovenous malformations (BAVMs) have been associated with an increased risk of hemorrhage. However, interpretation of these features may not be consistent between observers. We conducted a study to determine inter- and intraobserver agreement of various angioarchitectural characteristics of BAVM. MATERIALS AND METHODS: Two experienced interventional neuroradiologists independently reviewed pre- and post-endovascular treatment angiograms from 50 consecutive patients. Axial CT and/or MR images before treatment were included. We collected the following data: Spetzler-Martin grades, number of involved arterial territories, associated aneurysms by location (circle of Willis, feeding artery, intranidal, and venous), and nidus reduction after endovascular treatment (<33%, 33%-66%, and >66%). The reviewers were compared with each other, and 1 was compared with himself after a 3-month interval. Measures of agreement were performed by using the kappa statistic (kappa) for nominal data and the weighted kappa for ordinal data. RESULTS: Inter- and intraobserver agreement were higher for assessment of the Spetzler-Martin grade (weighted kappa = 0.70/0.75) and nidus size reduction after endovascular treatment (kappa = 0.74/0.77). Inter- and intraobserver agreement were inferior for findings concerning feeding artery aneurysms (kappa = 0.19/0.36), intranidal aneurysms (kappa = 0.34/0.35), and venous aneurysms (kappa = 0.50/0.67). CONCLUSION: Angiographic characteristics of BAVMs considered as risk factors for hemorrhage, such as aneurysms, are not reliably detected on global angiograms between different observers. In contrast, the Spetzler-Martin grading system and angiographic results of endovascular treatment can be used with high observer agreement.     

Successful radiosurgical treatment of arteriovenous malformation accompanied by venous malformation

We present a patient with a rare cerebrovascular malformation consisting of a typical arteriovenous malformation (AVM) with a nidus and a venous malformation (VM) in a single lesion. The AVM component was successfully obliterated by radiosurgery, whereas the VM was completely preserved. Radiosurgery can be an effective treatment technique for treating this type of malformation because it allows targeted obliteration of the AVM yet carries a low risk of damaging the venous drainage toward and away from the VM.     

An experimental arteriovenous malformation model in swine: anatomic basis and construction technique.

We assessed the feasibility of creating an experimental arteriovenous malformation model in swine by diverting and increasing blood flow through bilateral retia mirabilia. This was achieved by surgical formation of a large right-sided carotid-jugular fistula, in combination with endovascular occlusion of several neck arteries ipsilateral to the fistula. Using this technique, 11 of 13 swine demonstrated an acute-phase angiographic simulation of an arteriovenous malformation. There was rapid circulatory diversion from the left ascending pharyngeal artery ("feeder"), across both retia ("nidus"), and fast retrograde flow into the right ascending pharyngeal and common carotid arteries ("draining vein") toward the fistula. The relevant vascular anatomy of the swine head and neck is outlined, and steps in the construction of this arteriovenous malformation model are detailed.     

髓内血管畸形的血管构筑学及栓塞治疗

目的：探讨髓内动静脉畸形（AVM）的血管构型、血管内栓塞的指征及栓塞治疗的效果。方法：15例患者均有不同程度的肢体瘫痪、感觉障碍、括约肌功能障碍行DSA检查和栓塞治疗。栓塞材料选用PVA颗粒及丝线段。结果：15例中,球型3例,幼稚型12例;球型AVM均为单支动脉供血;幼稚型AVM为多支动脉供血,其中7例为2支供血动脉,5例有3支以上供血动脉,2例伴有动静脉瘘（AVF）;15例患者经27例次栓塞治疗,根据栓塞前后脊髓功能评价,痊愈2例,显效3例,好转6例,4例无变化,无1例加重。经6个月－5年随访,症状较栓塞前改善者4例;栓塞后症状维持者2例;栓塞后症状再次反复者7例,再次行栓塞治疗;失得2例。结论：髓内AVM应栓塞畸形血管团,减轻静脉压力,减少出血机会;血管内栓塞治疗脊髓血管畸形是一种创伤小、安全性高、有效的治疗方法。     

脊髓血管畸形的影像学诊断和血管内栓塞治疗

复杂的脊髓血管解剖，包括脊髓多来源的供养动脉和多去路的引流静脉，导致脊髓血管畸形的影像学诊断变得困难。脊髓血管畸形大致分为三类：髓内动静脉畸形、髓周动静脉瘘和硬脊膜动静脉瘘。髓内动静脉畸形的畸形团位于或大部分位于脊髓实质内。其供血动脉为脊髓前动脉及其分支，脊髓后动脉也经常同时参与供血。其引流静脉常同时向脊髓前、后静脉引流。最典型的临床症状为畸形团破裂出血。其治疗以分次血管内栓塞治疗为主。手术切除弊大于利，一般不采用。治疗的目的是改善症状而非解剖治愈。髓周动静脉瘘是脊髓外的软膜动脉与静脉的直接交通，常常是脊髓前动脉或脊髓后动脉与相应的静脉直接沟通。主要临床症状亦多为出血，亦可源于脊髓缺血或水肿。治疗方法和原则类似髓内动静脉畸形，但流速缓慢的位于圆锥和终丝部位的髓周动静脉瘘多手术切除。硬脊膜动静脉瘘几乎占所有脊髓血管畸形的80%。男女比例7:1,40岁以上多发。其瘘口位于硬脊膜内和硬脊膜内、外层之间，常靠近椎间孔的神经根，是根动脉的硬脊硬支与根髓静脉之间的直接交通。主要临床症状源于脊髓静脉高压引起的脊髓水肿和坏死。应用稀胶栓塞治疗成功率可达90%。胶一定要在瘘口和引流静脉起始端形成良好的铸型方能避免复发。手术夹闭瘘口简单，效果好，但创伤较大。     

Assessment of craniospinal arteriovenous malformations at 3T with highly temporally and highly spatially resolved contrast-enhanced MR angiography

BACKGROUND AND PURPOSE: Patients with arteriovenous malformation (AVM) are known to have an elevated risk of complications with conventional catheter angiography (CCA) but nonetheless require monitoring of hemodynamics. Thus, we aimed to evaluate both anatomy and hemodynamics in patients with AVM noninvasively by using contrast-enhanced MR angiography (CE-MRA) at 3T and to compare the results with CCA.MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained for this Health Insurance Portability and Accountability Act–compliant study. Twenty control subjects without vascular malformation (6 men, 18–70 years of age) and 10 patients with AVMs (6 men, 20–74 years of age) underwent supra-aortic time-resolved and high-spatial-resolution CE-MRA at 3T. Large-field-of-view coronal acquisitions extending from the root of the aorta to the cranial vertex were obtained for both MRA techniques. Image quality was assessed by 2 specialized radiologists by using a 4-point scale. AVM characteristics and nidus size were evaluated by using both CE-MRA and CCA in all patients.RESULTS: In patients, 96.6% (319/330) of arterial segments on high-spatial-resolution MRA and 87.7% (272/310) of arterial segments on time-resolved MRA were graded excellent/good. MRA showed 100% specificity for detecting feeding arteries and venous drainage (n = 8) and complete obliteration of the AVM in 2 cases (concordance with CCA). Nidus diameters measured by both MRA and CCA resulted in a very strong correlation (r = 0.99) with a mild overestimation by MRA (0.10 cm by using the Bland-Altman plot).CONCLUSION: By combining highly temporally resolved and highly spatially resolved MRA at 3T as complementary studies, one can assess vascular anatomy and hemodynamics noninvasively in patients with AVM.

Craniospinal arteriovenous malformation (AVM) typically presents in a young adult with intracranial hemorrhage (30%–82%), headache, seizures, or focal neurologic deficits that are either related to mass effect or to vascular steal phenomena.¹ Hemorrhage occurs with an annual incidence of 2%–4%^2,3 and remains the prime vector for mortality and morbidity (10% and 16%–50%, respectively).^4–6 Several investigators have identified features predictive of hemorrhage, including small nidus size, deep nidus location, single deep venous drainage, associated arterial aneurysm, impaired venous drainage, and high intranidal pressure.^7–10 Safe and accurate diagnostic work-up is essential to provide an architectural map and to define hemodynamic indices and risk predictors. Moreover, follow-up studies may be required for monitoring posttherapy. The current gold standard for assessment of AVM is conventional catheter angiography (CCA), which is associated with ≤1.3% of major complications and death (<0.1%).^11–13 In this context, multiple catheter examinations in patients with AVM are expected to elevate the risk of complications and hemorrhage.Recent advances in the performance of contrast-enhanced MR angiography (CE-MRA) at 3T have underscored its growing potential for detailed evaluation of the supra-aortic arteries and veins.^14–16 Techniques have been established for both highly temporally resolved and highly spatially resolved CE-MRA, by using only modest contrast doses.^17,18 Whereas high-spatial-resolution MRA can quickly provide detailed images of intracranial and extracranial vessels, time-resolved MRA adds hemodynamic information and can capture transient processes, such as early venous filling, which is the hallmark of an arteriovenous fistula (AVF).^17,19 Moreover, cortical venous reflux has a high yearly risk of hemorrhage^20–24 and influences treatment.^24–28 Micro-AVMs as a potential source of fatal intracranial hematoma represent approximately 8%–10% of surgically treated brain AVMs.^29,30 Time-resolved MRA may potentially identify an early filling vein in a micro-AVF because the anatomy of a very small nidus may not be assessable. Furthermore, an early filling vein may be the only evidence of a residual shunt after radiosurgery or endovascular therapy.These 2 approaches can, therefore, provide complementary diagnostic information to each other for evaluation of high-flow AVMs. The purpose of our study was to evaluate the potential of these complementary modes in defining the relevant vascular anatomy and hemodynamics noninvasively in patients with AVM and to compare the findings with those on digital subtraction angiography (DSA).     

Vascular characteristics of intracerebral arteriovenous malformations in patients with clinical steal

In patients with intracerebral arteriovenous malformations (AVMs), symptoms attributed to steal can lead to progressive debilitating deficits. This study was undertaken to determine which morphologic features of the AVM could be correlated with clinical symptoms of steal. Over a 4-year period, 65 patients with intracranial AVMs were evaluated with angiography supplemented by MR (46 cases) and CT (19 cases). Eleven characteristics of AVM vascular architecture were studied; these included size, lobar location, periventricular/intraventricular location, arterial stenosis, arteriovenous fistulae, angiomatous change (the presence of dilated transcortical collateral circulation), venous drainage pattern (central, cortical, mixed), venous stenosis, venous aneurysm or ectasia, venous variation, and delayed drainage. These characteristics were correlated with a history of clinical steal, which was seen in nine (14%) of 65 patients. Three characteristics were found to correlate highly with steal: angiomatous change (p less than .0001), size (p less than .0001), and peripheral venous drainage (p = .045). The mean size of the AVM nidus was 31.3 cm3 for the entire group of patients, 105.0 cm3 for patients with steal, and 19.5 cm3 for those without steal symptoms. Angiomatous change was seen in six (9%) of 65 patients; all six of these had clinical steal. The association of clinical steal with AVM size, angiomatous change, and peripheral venous drainage may contribute to establishing a prognosis and treatment planning. When a patient's symptoms are caused by steal, treatment with subtotal excision or partial embolization may be beneficial.