Multidisciplinary Management of Arteriovenous Malformations

27 Multidisciplinary Management of Arteriovenous Malformations

Federico Cagnazzo, Thomas J. Sorenson, and Giuseppe Lanzino

Abstract

The contemporary management of complex brain arteriovenous malformations (AVMs) often requires a multidisciplinary approach, including embolization, microsurgical resection, and stereotactic radiosurgery (SRS). The current literature regarding the multimodality treatment of AVMs was explored with the aim to report the results of various combinations of these treatment modalities. The combined management usually allows four options. Preoperative embolization can be considered for high-grade AVMs, or as a targeted treatment for portions of the AVM difficult to deal with at surgery. Similarly, presurgical SRS is a feasible option to reduce nidus size, blood flow, and deep/eloquent nidus for easier microsurgical resection. However, surgical approach after radiation should be appropriately timed, considering the fact that during the 3-year latency period necessary to maximize the histological changes incited by SRS, the patient is exposed to a higher risk of hemorrhage. Contrariwise, the real effectiveness of pre-SRS endovascular embolization remains uncertain, and a lower occlusion rate is often reported in the literature. In addition, there is a lack of convincing studies that report the real effectiveness of triplicate treatment, and the sum of procedural risks of each treatment should be carefully considered. Furthermore, target endovascular treatment of brain AVMs associated aneurysms is safe and effective, and can be performed using coils or liquid embolic agents depending on location and size. Several treatment modalities are currently available for the management of complex brain AVMs. However, multidisciplinary approach should be accurately individualized while considering the sum of procedural risks of each treatment.

Keywords: arteriovenous malformations, multidisciplinary management, surgical treatment, stereotactic radiosurgery, endovascular embolization, aneurysms associated with AVMs

Key Points

High-grade arteriovenous malformations are complex lesions that require a multidisciplinary decision-making.
Microsurgical resection, endovascular embolization, and stereotactic radiosurgery can be used in a multimodal strategy.
Patients amenable to treatment with a multidisciplinary approach should be meticulously selected with consideration of the summative procedural risks of each treatment.
Presurgical embolization and radiosurgery are often used to reduce the size of larger AVMs and to allow a safer and effective surgical resection.
Embolization before stereotactic radiosurgery is controversial, but can be used to increase the rate of total obliteration.
Endovascular-targeted treatment of the aneurysms associated with AVMs is safe and effective.

27.1 Introduction and General Principles

Making the decision to treat a patient with a cerebral arteriovenous malformation (AVM) involves an understanding of the complex balance between the risks of rupture and the risks associated with treatment. Because of this fine line, the contemporary management of brain AVMs often requires a multidisciplinary approach and the coordination of several treatment modalities, including embolization, microsurgical resection, and stereotactic radiosurgery (SRS). However, these treatment options alone are not optimal for complex AVMs as microsurgical resection is associated with higher morbidity, but SRS and endovascular treatment are associated with low obliteration rates. To minimalize the disadvantages of each treatment modality, a multidisciplinary approach should be evaluated for certain lesions, including high-grade AVMs with complex angioarchitecture that are large, deep, and located in eloquent brain areas.

27.2 Materials and Methods

The current literature regarding the multimodality treatment of AVMs was explored. In this chapter, we report the results of published series that utilized various combinations of microsurgical resection, endovascular embolization, and SRS.

27.3 Results and Discussion

The combined management of patients with high-grade AVMs usually allows four options:

Endovascular treatment before microsurgical resection.
Endovascular embolization before SRS.
Radiosurgery before microsurgical resection.
Radiosurgery, endovascular embolization, and microsurgical resection.

Because each individual treatment option and each combination therapy carry a specific cure and complication rate, the first decision is whether treatment is indicated.

27.3.1 Multimodal Strategy: Presurgical Endovascular Embolization

In high-grade Spetzler–Martin (SM) AVMs with complex angioarchitecture, complete obliteration is often impractical with endovascular embolization or surgical resection alone, making a combined approach valuable.¹ For this combined approach, embolization is often used as the first modality to allow for an easier, safer, and more thorough subsequent microsurgical resection as preliminary embolization can reduce AVM blood flow, reduce intraoperative blood loss, and facilitate surgical manipulation.² Furthermore, the progressive reduction of blood flow may produce a gradual adaptation of the surrounding parenchyma to the hemodynamic changes, decreasing the risk of normal perfusion pressure breakthrough.

As another complementary technique to surgical resection, embolization can also be used to target specific components of a complex AVM. Targeted embolization may facilitate the recognition and occlusion of deep feeding arteries that are often encountered in a late phase of AVM resection and can be otherwise difficult to manage during surgery.² Additionally, endovascular therapy is a safe and effective strategy for treating AVM-associated aneurysms, which are often the source of intracranial hemorrhage.³

However, these combined approaches can also be associated with higher rates of complication. Partial occlusion of an AVM by embolization can modify the hemodynamic status of the AVM and the surrounding parenchyma with decreased and increased blood flow areas into the nidus and cerebral vasculature. Similarly, obstruction and/or slowing of venous outflow can increase the risk of rupture. To minimize these risks, timely surgical treatment after embolization is recommended.⁴ The results of presurgical embolization appear inhomogeneous in different clinical series (► Table 27.1).

Table 27.1 Recent series of embolization as adjunctive treatment for microsurgical arteriovenous malformation resection

Theofanis et al reported a higher rate of complications in a group of patients treated with multiple presurgical embolization attempts. Of the 264 AVMs treated with microsurgery, preoperative embolization was used in 38.3%. Complications were seen in 7.2% and were associated with multiple embolization attempts (odds ratio [OR]: 1.6) on multivariate analysis. Seven patients experienced a hemorrhage related to embolization treatment before surgery.³

Comparable results were found by Natarajan et al. Despite a high occlusion rate after combined endovascular and surgical treatment, the authors reported a higher postoperative complication rate (14%) compared to presurgical embolization. Twenty-eight AVMs (average size/volume 3.56 cm/13.03 mL) were embolized preoperatively in 55 sessions with Onyx. The average final percentage of endovascular nidal obliteration was 74.11%. The long-term radiological follow-up showed residual AVM in only one patient who was treated with radiosurgery.²

However, the higher rate of treatment-related complications in combined endovascular and surgical treatment can be potentially related to the more complex angioarchitecture of treated AVMs. Nataraj et al treated 101 patients with presurgical embolization. Of these patients, 100 (99%) had complete occlusion of the AVM at the end of the treatment cycle, and 87 (86%) had a favorable outcome. In all, 37% of SM grade IV–V AVMs were treated with both embolization and surgery, compared to 7% of high-grade AVMs treated with surgery alone. Taking into account the higher SM grade in the combined group, the morbidity rate was slightly higher in the combined group (6% of new severe deficits), compared to the surgical group (0% of new severe deficits).⁴

The aforementioned series show the efficacy of combined treatment, despite the higher rate of complications than surgery alone. When considering treatment options, preoperative embolization should be considered for high-grade SM AVMs or as a targeted treatment for portions of the AVM more difficult to deal with at surgery or to target associated aneurysms.⁹ Preoperative embolization should rarely be indicated for AVMs smaller than 3 cm because of their low rate of surgical morbidity.

27.3.2 Multimodal Strategy: Presurgical Stereotactic Radiosurgery

As stated earlier, the surgical resection of many large, high-grade AVMs is often correlated with a high procedural risk, and many lesions are considered inoperable for their size and angioarchitecture. For these challenging lesions, the use of presurgical SRS can be evaluated to reduce the size and/or to target deeper areas of the AVM, allowing for a safer and more effective subsequent surgical resection.¹⁰

There are two methods of SRS delivery: single session (SS) and volume staged (VS). In SS, a single, high dose of irradiation is applied. This option is best indicated for small AVMs; SS-SRS is not effective for nidal volumes greater than 3 cm in diameter, because the treatment requires reduction of the marginal dose below an acceptable amount. Under this range of radiation dose, the obliteration rate is less than 70%.¹¹

VS SRS is the other strategy that is best indicated for large AVMs. This approach divides a large AVM into smaller portions, and each portion is treated separately with a high-dose radiation and an acceptably low rate of post-SRS complications.^12,13

Recently, Abla et al reported a series of high-grade AVMs that were treated with VS-SRS followed by surgical resection of the residual (after SRS) nidus (► Table 27.2). Sixteen AVMs (mean SM grade: 4; mean diameter: 5.9 cm) underwent treatment, and the average SM grade was reduced to 2.5 and the average maximum AVM size was reduced to 3 cm. The lesions were surgically resected after a mean interval of 5.7 years. Postoperative angiography confirmed curative AVM resection in 15 patients (93.8%).¹¹

Table 27.2 Principal series of combined radiosurgery and surgical treatment