An Arteriovenous Malformation Model for Stereotactic Radiosurgery Research

Arteriovenous Malformations-Current Understanding of the Pathogenesis with Implications for Treatment

Arteriovenous malformations are a vascular anomaly typically present at birth, characterized by an abnormal connection between an artery and a vein (bypassing the capillaries). These high flow lesions can vary in size and location. Therapeutic approaches are limited, and AVMs can cause significant morbidity and mortality. Here, we describe our current understanding of the pathogenesis of arteriovenous malformations based on preclinical and clinical findings. We discuss past and present accomplishments and challenges in the field and identify research gaps that need to be filled for the successful development of therapeutic strategies in the future.

Focused Ultrasound Ablation of an Arteriovenous Malformation Model

Brain AVMs are rare but serious vascular lesions that often pose a management dilemma between the risk of various treatment modalities and uncertain natural history during observation. We describe preliminary data on the use of focused ultrasound as a novel therapeutic strategy. In an AVM model, one session of ultrasound gradually reduced flow through the lesion without inducing rupture. Due to its non-invasive yet immediate ablative effects, focused ultrasound may allow safer treatment of AVMs. However, further studies are needed to clarify its efficacy and side effect profile.

Lacunar Stroke, Cavernous Angioma, and Fusiform Aneurysm Due to Irradiation for Pilocytic Astrocytoma-A Case Report

Radiotherapy is a useful modality for the treatment of brain tumors, but may induce brain degeneration, tumor formation, and vasculopathy in the irradiated field. We describe a rare case of a pediatric patient who presented multiple different types of vascular events consecutively in the irradiated field including lacunar stroke because of occlusion of perforating artery, intraventricular hemorrhage from cavernoma, and subarachnoid hemorrhage because of the rupture of fusiform aneurysm, 6 years after radiotherapy against pilocytic astrocytoma. The life-threatening aneurysm was resected, and its histologic findings revealed the radiation-induced vasculopathy. We should avoid irradiation, and repeat surgical resection for the pediatric cases with pilocytic astrocytoma. Once irradiation was indicated for them, however, we should carefully follow-up not only tumor recurrence but also angiograms to predict any cerebrovascular events.

Novalis Stereotactic Radiosurgery for Spinal Dural Arteriovenous Fistula

The spinal dural arteriovenous fistula (SDAVF) is rare, presenting with progressive, insidious symptoms, and inducing spinal cord ischemia and myelopathy, resulting in severe neurological deficits. If physicians have accurate and enough information about vascular anatomy and hemodynamics, they achieve the good results though the surgery or endovascular embolization. However, when selective spinal angiography is unsuccessful due to neurological deficits, surgery and endovascular embolization might be failed because of inadequate information. We describe a patient with a history of vasospasm during spinal angiography, who was successfully treated by spinal stereotactic radiosurgery using Novalis system.

Animal Models in Studying Cerebral Arteriovenous Malformation

Brain arteriovenous malformation (AVM) is an important cause of hemorrhagic stroke. The etiology is largely unknown and the therapeutics are controversial. A review of AVM-associated animal models may be helpful in order to understand the up-to-date knowledge and promote further research about the disease. We searched PubMed till December 31, 2014, with the term “arteriovenous malformation,” limiting results to animals and English language. Publications that described creations of AVM animal models or investigated AVM-related mechanisms and treatments using these models were reviewed. More than 100 articles fulfilling our inclusion criteria were identified, and from them eight different types of the original models were summarized. The backgrounds and procedures of these models, their applications, and research findings were demonstrated. Animal models are useful in studying the pathogenesis of AVM formation, growth, and rupture, as well as in developing and testing new treatments. Creations of preferable models are expected.

Focused post mortem dissection technique for harvest of rete mirabile in domestic swine (Sus scrofa)

BACKGROUND

Rete mirabile (RM) of the domestic pig is a popular animal model of arteriovenous malformations. The RM (Latin for 'wonderful net)' comprises the arterioarterial portal connecting ascending pharyngeal arteries and the internal carotid arteries, which exists in the skull base of even-toed ungulates. Although angiographic access of the RM is relatively easy, its post mortem procurement is complicated and its detailed technique has not been well described.

OBJECTIVE

To present our focused post mortem dissection technique for undamaged and complete harvest of the RM.

MATERIALS AND METHODS

Fourteen domestic (40-70 lb (18-32 kg)) swine were used in this study. Angiographies were performed under general anesthesia in all animals. A 5F Berenstein catheter was used for angiography and a 014 microcatheter was used to obtain superselective angiography. A stepwise surgical dissection technique has been developed to efficiently harvest RM. Angiographic and surgical anatomy were also compared.

RESULTS

The RM was supplied by bilateral ascending pharyngeal arteries. Bilateral anterior cerebral arteries, middle cerebral arteries, and the basilar system were identified rostral to the RM. Our surgical dissection technique was developed during a project to streamline harvesting of the RM and a stepwise description is as follows: (1) decapitate the swine by removing the head through the plane of the occiput and C1 vertebral body; (2) remove the tongue and oropharynx via a ventral approach; (3) dissect through the posterior pharyngeal wall identifying bilateral tympanic bullae and the basisphenoid bone; and (4) remove the basisphenoid bone about one and half inches above the rostral end of the tympanic bullae to fully expose the rete.

CONCLUSIONS

The RM can be procured efficiently and effectively with our technique, without requiring any sophisticated surgical devices.

Experimental Animal Models of Arteriovenous Malformation: A Review

Arteriovenous malformations (AVMs) are congenital lesions that cause brain haemorrhage in children and young adults. Current treatment modalities include surgery, radiosurgery and embolization. These treatments are generally effective only for small AVMs. Over one third of AVMs cannot be treated safely and effectively with existing options. Several animal models have been developed with the aims of understanding AVM pathophysiology and improving treatment. No animal model perfectly mimics a human AVM. Each model has limitations and advantages. Models contribute to the understanding of AVMs and hopefully to the development of improved therapies. This paper reviews animal models of AVMs and their advantages and disadvantages.

De Novo Aneurysm Formation Following Gamma Knife Surgery for Arteriovenous Malformation: A Case Report

Background Stereotactic radiosurgery plays a critical role in the treatment of central nervous system neoplasm and cerebrovascular malformations. This procedure is purportedly less invasive, but problems occurring later including tumor formation, necrosis, and vasculopathy-related diseases have been reported. Clinical Presentation We report on a 65-year-old man who had experienced a de novo aneurysm in an irradiated field and an acute onset of right hemiparesis and aphasia. He had undergone gamma knife radiosurgery to treat an arteriovenous malformation 15 and 12 years prior, with 18 and 22 Gy marginal doses. At current admission, radiologic studies showed a de novo aneurysm in the irradiated field without recurrence of malformation. The aneurysm was resected. Histologic findings showed a disruption of the internal elastic lamina accompanied by fibrous degeneration. Conclusion Stereotactic radiosurgery is a promising treatment tool, but long-term risks have not been fully researched. The treatment procedure for benign lesions should be chosen prudently.

Surgical management of combined intramedullary arteriovenous malformation and perimedullary arteriovenous fistula within the hybrid operating room after five years of performing focus fractionated radiotherapy: case report

Perimedullary arteriovenous fistula (AVF) shunts occur on the spinal cord surface and can be treated surgically or by endovascular embolization. In contrast, the nidus of an intramedullary arteriovenous malformation (AVM) is located in the spinal cord and is difficult to treat surgically or by endovascular techniques. The benefits of radiotherapy for treating intramedullary AVM have been published, but are anecdotal and consist largely of case reports. We present a case of combined cervical intramedullary AVM and perimedullary AVF which received surgical treatment within a hybrid operating room (OR) after 5 years of focus fractionated radiotherapy. A 37-year-old male presented with stepwise worsening myelopathy. Magnetic resonance imaging and spinal angiography revealed intramedullary AVM and perimedullary AVF at the C3 to C5 levels. In order to reduce nidus size and blood flow, we first performed focal fractionated radiotherapy. Five years later, the lesion volume was reduced. Following this, direct surgery was performed by an anterior approach using corpectomy in the hybrid OR. The spinal cord was monitored by motor-evoked potential throughout the surgery. Complete obliteration of the fistulous connection was confirmed by intraoperative indocyanine green video-angiography and intraoperative angiography, preserving the anterior spinal artery. We conclude that surgical treatment following focal fractionated radiotherapy may become one strategy for patients who are initially deemed ineligible for endovascular embolization and surgical treatment. Furthermore, the hybrid OR enables safe and precise treatment for spinal vascular disorders in the fields of endovascular treatment and neurosurgery.

Advances in Radiosurgery for Arteriovenous Malformations of the Brain

Arteriovenous malformations of the brain are a considerable source of morbidity and mortality for patients who harbor them. Although our understanding of this disease has improved, it remains in evolution. Advances in our ability to treat these malformations and the modes by which we address them have also improved substantially. However, the variety of patient clinical and disease scenarios often leads us into challenging and complex management algorithms as we balance the risks of treatment against the natural history of the disease. The goal of this article is to provide a focused review of the natural history of cerebral arteriovenous malformations, to examine the role of stereotactic radiosurgery, to discuss the role of endovascular therapy as it relates to stereotactic radiosurgery, and to look toward future advances.

Is a swine model of arteriovenous malformation suitable for human extracranial arteriovenous malformation? A preliminary study

OBJECTIVE

A chronic arteriovenous malformation (AVM) model using the swine retia mirabilia (RMB) was developed and compared with the human extracranial AVM (EAVM) both in hemodynamics and pathology, to see if this brain AVM model can be used as an EAVM model.

METHODS

We created an arteriovenous fistula between the common carotid artery and the external jugular vein in eight animals by using end-to-end anastomosis. All animals were sacrificed 1 month after surgery, and the bilateral retia were obtained at autopsy and performed hematoxylin and eosin staining and immunohistochemistry. Pre- and postsurgical hemodynamic evaluations also were conducted. Then, the blood flow and histological changes of the animal model were compared with human EAVM.

RESULTS

The angiography after operation showed that the blood flow, like human EAVM, flowed from the feeding artery, via the nidus, drained to the draining vein. Microscopic examination showed dilated lumina and disrupted internal elastic lamina in both RMB of model and nidus of human EAVM, but the thickness of vessel wall had significant difference. Immunohistochemical reactivity for smooth muscle actin, angiopoietin 1, and angiopoietin 2 were similar in chronic model nidus microvessels and human EAVM, whereas vascular endothelial growth factor was significant difference between human EAVM and RMB of model.

CONCLUSIONS

The AVM model described here is similar to human EAVM in hemodynamics and immunohistochemical features, but there are still some differences in anatomy and pathogenetic mechanism. Further study is needed to evaluate the applicability and efficacy of this model.

Treatment of brain arteriovenous malformations with high-flow arteriovenous fistulas: risk and complications associated with endovascular embolization in multimodality treatment. Clinical article

OBJECT

High-flow fistulas associated with brain arteriovenous malformations (AVMs) pose a significant challenge to both stereotactic radiosurgery (SRS) and surgical treatment. The purpose of this study was to examine the outcomes of multimodality treatment of AVMs in association with a large arteriovenous fistula (AVF), with a special focus on endovascular embolization and its associated complications.

METHODS

One hundred ninety-two patients harboring cerebral AVMs underwent endovascular treatment in the authors' department between 1997 and 2003. Of these, the authors selected 74 patients presenting with an AVM associated with high-flow AVF(s) for a retrospective analysis based on the findings of superselective angiography. After endovascular embolization, 32 patients underwent resection, 33 underwent either SRS or hypofractionated stereotactic radiotherapy (HSRT), and 3 underwent both surgery and SRS. Six patients underwent embolization only. Immediate and midterm treatment outcomes were analyzed.

RESULTS

Fifty-seven (77%) of the 74 patients had AVMs that were Spetzler-Martin Grade III or higher. A complete resection was achieved in all 32 patients. Of patients who underwent SRS/HSRT, 13 patients (39.3%) had either complete or > 90% obliteration of the AVM, and 2 patients (6.1%) had incomplete obliteration. Fourteen patients (42.4%) with residual AVM underwent repeated radiotherapy (and remain under observation). Of the 3 patients who underwent both SRS and resection, resection was complete in 2 and incomplete in one. No follow-up was obtained in 6 patients (8.1%). An endovascular complication was observed in 4 patients (5.4%). Fistula embolization was safely performed in every patient, whereas every endovascular complication was associated with other procedures such as nidus embolization.

CONCLUSIONS

Endovascular occlusion of the fistulous component was successfully achieved in every patient; every endovascular complication in this series was related to other procedures such as nidus embolization. The importance of the fistula treatment should be emphasized to minimize the endovascular complications and to maximize the treatment effect when a multimodality therapy is used to treat brain AVMs with large AVF.

THE APPLICATION OF STEREOTACTIC RADIOSURGERY TO DISORDERS OF THE BRAIN

STEREOTACTIC RADIOSURGERY IS the first widely used “biological surgery.” The opportunity for surgeons working with radiation oncologists and medical physicists to affect cell structures with both direct and indirect vascular effects has transformed neurosurgery. As a minimal access surgical approach, it fits well into the patient goals of functional preservation, risk reduction, and cost-effectiveness. Longer-term results have been published for many indications. For many disorders, it may be better to “leave the tumor in rather than take it out.” Radiosurgery has had an impact on the management of patients with vascular malformations, all forms of cerebral neoplasia, and selected functional disorders such as trigeminal neuralgia and tremor. It can be performed alone when lesion volume is not excessive or as part of a multimodality strategy with resection or endovascular surgery. Epilepsy, behavioral disorders, and other novel indications are the topics of current investigation. The combination of high-resolution imaging, high-speed computer workstations, robotics, patient fixation techniques, and radiobiological research has put radiosurgery into the practice of almost all neurosurgeons.