Delayed recanalization of a cerebral arteriovenous malformation following angiographic obliteration with polyvinyl alcohol embolization

Hemodynamic Study of Cerebral Arteriovenous Malformation: Newtonian and Non-Newtonian Blood Flow

OBJECTIVE

Arteriovenous malformation is a disease of the vascular system that occurs mainly in the cerebral arteries and spine. Numerical simulation as a powerful method is used to investigate the Cerebral Arteriovenous Malformation hemodynamic after occlusion of the abnormality step by step by embolization.

METHODS

The computed tomography (CT) Angiographic imaging data of 2 patients are used and a geometric model is extracted by the Mimics software. Numerical simulation of blood flow is performed in both Newtonian and non-Newtonian models. The Navier-Stokes and continuity governing equations are solved by a finite element method using the COMSOL Multiphysics software (the commercial computational fluid dynamics (CFD) simulation software). To validate the numerical results, the real data on blood flow rate in the feeding artery and draining veins are used, as well as angiographic images at different times.

RESULTS

Regarding the comparison of pressure contours for different occlusions of 0, 30, 50, and 90%, by increasing the amount of occlusion in the nidus, there is an increase in the blood pressure. Regarding the comparison of the blood flow velocity in the feeding artery, draining veins, and inside the AVM nidus for Newtonian and non-Newtonian models, there is a significant difference between these 2 simulations in vessels with smaller dimensions (such as vessels inside the nidus).

CONCLUSIONS

By increasing the amount of nidus occlusion, the blood pressure is increased, so the blood supply process is better. According to a significant difference between the Newtonian and non-Newtonian simulations in vessels with smaller dimensions (such as vessels inside the nidus), therefore, non-Newtonian simulation should be done for different occlusions of 30, 50, and 90%.

Endovascular treatment of arteriovenous malformations

Cerebral arteriovenous malformations (AVM) are tangles of blood vessels that permit shunting of blood from the arterial to venous phase without intervening capillaries. The malformation's arterialization of a low-pressure system creates a risk of rupture that is substantially higher when associated with an aneurysm. The annual hemorrhage rate is 2.2% per year as reported in the randomized trial of unruptured brain AVMs (ARUBA; rupture risk is increased after the first event. Ruptured AVMs have a 10% mortality rate and 20%-30% morbidity rate. The treatment of choice for AVMs is microvascular resection with or without preoperative embolization. Surgical risk can be stratified based on the Spetzler-Martin grading system. Liquid embolic material and coils may be used for the treatment of AVM associated aneurysms, especially in the setting of acute rupture as a bridge to delayed surgical resection. There is some limited reported success in total endovascular treatment of AVMs, but this is not considered standard therapy at this time. Stereotactic radiosurgery (SRS) has been recently described but mainly limited to AMVs deemed too risky to approach in an open fashion and limited to 2.5cm-3cm in size. The delayed protection from hemorrhage (approximately 2-3 years) and high marginal failure/recurrence rate are the greatest concerns.

Direct continuous measurement of draining vein pressure during Onyx embolization in a swine arteriovenous malformation model

OBJECTIVE

Periprocedural intracranial hemorrhage secondary to intranidal flow redirection may develop after arteriovenous malformation (AVM) embolization. We hypothesized that continuous draining vein pressure monitoring may identify clinically relevant hemodynamic changes during devascularization. Our goal was to characterize the draining vein pressures in a swine rete mirabile AVM model during embolization with Onyx.

METHODS

An acute swine AVM model was constructed in six animals. Baseline, transoperative and final AVM area measurements were used to determine the degree of AVM embolization. Continuous video recordings were captured at 10 s intervals of active embolization. Draining vein pressure, arterial feeder pressure and heart rate were continuously monitored.

RESULTS

The baseline and post-embolization mean draining vein pressures were 49.8±17.2 and 33.0±11.7 mm Hg (p=0.01), mean arterial pressures were 79.8±19.4 and 79.6±25.2 mm Hg (p=0.94), mean transnidal pressures were 35.8±19.7 and 45.4±33.7 mm Hg (p=0.37) and mean heart rates were 81.1±11.9 and 83.1±12.8 bpm (p=0.38), respectively. The draining vein pressure was averaged according to the degree of AVM embolization and represented as a relative change compared with the baseline draining vein pressure, and the slopes were found to decrease in all cases (p=0.02). In half of the animals the draining vein pressure decreased progressively as the AVM was embolized. In the remaining animals the venous pressure only started to decline after the AVM had been devascularized by > 50%.

CONCLUSIONS

The draining vein pressure response during Onyx embolization in the swine AVM model is heterogeneous. Continuous draining vein pressure monitoring is feasible and may potentially identify clinically relevant hemodynamic changes during AVM embolization.

Head and neck arteriovenous malformations: results of ethanol sclerotherapy

BACKGROUND AND PURPOSE

Peripheral AVM is a locally aggressive disease with a high tendency to recur; its treatment is complex, especially in the anatomically delicate head and neck area. Here, we report results of ethanol sclerotherapy for head and neck AVM and discuss its potential use for peripheral AVM.

MATERIALS AND METHODS

We retrospectively assessed degree of AVM eradication, complications, and clinical or imaging signs of recurrence for 19 patients treated with ethanol sclerotherapy for head and neck AVM (1 intraosseous, 18 soft-tissue AVMs).

RESULTS

Of the 19 patients, 11 had complete eradication of arteriovenous shunting at DSA, with 1 recurrence (mean follow-up 15 months), and for 7 patients, treatment is ongoing. During 59 treatment sessions, 12 patients experienced 14 complications, 1 leading to permanent functional damage.

CONCLUSIONS

Ethanol sclerotherapy has potential for complete eradication of head and neck AVM with low recurrence within the first year after completion of treatment. Complete eradication may require several treatment sessions during which complications should be minimized with careful techniques.

Endovascular Treatment Increases but Gamma Knife Radiosurgery Decreases Angiogenic Activity of Arteriovenous Malformations

OBJECTIVE

To compare the angiogenic potentials of embolized, gamma knife–treated or untreated cerebral arteriovenous malformations (AVMs), using a rat cornea angiogenesis model.

METHODS

Tissue samples from cerebral AVM patients who were either untreated or had previously been treated with embolization or gamma knife radiosurgery and who had undergone operations for hemorrhage at the Neurosurgery Department or the Neurological Sciences Institute of Marmara University were used. For the macroscopic evaluation of angiogenesis, tissue samples were inoculated in a micropocket created on the rat eye, and the level of angiogenic activity was graded macroscopically for 15 days, with glioblastoma multiforme and normal brain artery tissues serving as positive and negative controls, respectively. For the other part of the experiment, eyes of another set of rats were inoculated with the study samples only using the same cornea angiogenesis model, in which microvessel count and vascular endothelial growth factor assessment was done at days 3, 7, 11, and 15.

RESULTS

Based on our macroscopic findings in the cornea angiogenesis model, embolized AVMs exhibited the highest angiogenic activity, followed by untreated AVMs and gamma knife–treated AVMs. Evaluations of vascular endothelial growth factor expression and microvessel counts showed a similar relation among the 3 tissue groups with regard to the level of angiogenic activity, supporting the results of macroscopic examinations.

CONCLUSION

This study, for the first time, provides experimental semiquantitative data to compare the angiogenic potentials of embolized and gamma knife–treated AVM tissues. Embolization may increase angiogenic activity, and gamma knife radiosurgery may decrease it when compared with activity in previously untreated AVMs. These data can be useful to understand why recurrence of AVMs after angiographically demonstrated endovascular occlusion is common but after gamma knife occlusion is rare.

Targeting cerebral arteriovenous malformations for minimally invasive therapy

OBJECTIVE

Cerebral arteriovenous malformation (AVM) embolization has been performed for nearly 40 years to reduce the risk of hemorrhage, to reduce symptomatic arteriovenous shunting, and to pretreat patients for surgical excision or radiosurgery. In some cases, embolization alone may be able to angiographically cure an AVM, although this is a small percentage of all AVMs.

METHODS

This report reviews the current limitations of embolic therapy of cerebral AVMs from the standpoint of AVM angioarchitecture and the physical limitations of current embolic materials. In addition, it seeks to identify the areas in which embolization therapy may make advancements both as a pretreatment and as a sole therapy.

RESULTS

Currently, liquid embolic agents, ethylene vinyl alcohol, and n-butylcyanoacrylate seem to provide the greatest resistance to recanalization in AVM embolization. These agents, however, elicit only a weak, nonspecific, bioactive inflammatory response by histopathology.

CONCLUSION

The further evaluation and understanding of the vascular biology of AVM vessels and the endothelium cell wall biology will help us devise more bioactive material solutions to AVM nidus obliteration. Targeting specific receptors in AVMs with the embolic material delivered may additionally enhance the effects of radiosurgery in these patients.

Endovascular particulate and alcohol embolization for near-fatal epistaxis from a skull base vascular malformation

A three-year old girl who initially presented at 16 months with epistaxis from an anterior skull base vascular anomaly returned with near-fatal epistaxis despite embolization of the internal maxillary artery at the time of initial presentation. Repeat angiography demonstrated blood supply to the vascular lesion coming from branches of both the external and internal carotid arteries. The patient underwent four sessions of endovascular embolization with polyvinyl alcohol, alcohol, and gelatin microspheres. At the conclusion of treatment, her epistaxis had resolved and the only residual blood supply to the lesions came from bilateral ophthalmic arteries intentionally not sacrificed to prevent loss of vision. Endovascular embolization of both the internal and external carotid arteries is a challenging but important treatment option for life-threatening epistaxis resulting from vascular lesions of the skull base.

Reflections on the management of cerebral arteriovenous malformations

BACKGROUND

The authors report their personal experience in the management of cerebral arteriovenous malformations (AVMs), using the three techniques now available: surgical resection, endovascular embolization, and radiosurgery. They review the recent literature on this topic and present their current management algorithm based on this experience.

METHODS

A series of 90 patients treated for cerebral AVMs is reported (68% Grade I-III and 32% Grade IV-V, Spetzler scale). The three methods of treatment were used, either individually or in combination, based on the size and the location of the malformation. The first intervention was surgical resection in 26% of cases, endovascular embolization in 57%, and radiosurgery in 17%. Surgery and embolization were followed by another technique in some cases and eventually single modality treatment was used in 58% of cases (surgical resection 21%, endovascular embolization 20%, radiosurgery 17%) and multimodality treatment in 42% (embolization + resection, 21%; embolization + radiosurgery, 17%; resection + radiosurgery, 4%). Embolization was used as reductive therapy in 38% of the overall series (65% of all embolized patients), and was followed by surgery in 56% of cases or by radiosurgery in 44%. Angiography was used to assess the cure rates.

RESULTS

The following cure rates were obtained, when each technique was used as a first treatment: surgical resection, 82%; embolization, 6%; and radiosurgery, 83% (2-year angiographic follow-up). After combined treatment, embolization and resection resulted in a 100% cure rate, embolization and radiosurgery produced a 90% cure rate. The clinical outcome was evaluated in terms of deterioration attributable to treatment. Seventy-one percent of patients had no complication, minor complications were observed in 18%, and severe complications in 11%. Treatment mortality was 3%. All deaths were attributable to hemorrhage during the embolization procedure.

CONCLUSIONS

In this management algorithm, AVMs submitted directly to surgery or to radiosurgery were considered "good risk" malformations, and the outcome for these cases was good in terms of clinical result and cure rate. AVMs submitted first to endovascular embolization were considered "poor risk" malformations, including a majority of Spetzler Grade IV-V lesions. Not surprisingly, the majority of severe complications occured in this group during embolization. Thus, the major risk of the treatment of AVMs has now shifted from surgery to endovascular techniques. Endovascular embolization as sole treatment gave a low rate of complete occlusion, but proved to be very useful as a reductive therapy, in preparation for further surgery or radiosurgery. Partial embolization permitted high rates of complete cure in difficult AVMs. Embolization should be used to the maximum extent possible as a reductive technique, despite the risks of the procedure. Because of its risks however, this technique of reductive embolization should be used only if absolutely necessary to allow the complete cure of the malformation. Thus, the use of embolization should be considered very cautiously in small malformations as well as in very large and complex AVMs in which partial embolization will not be sufficient to allow complete cure with either endovascular or surgical techniques.