Multimodality Management Strategies and Treatment Selection

19 Multimodality Management Strategies and Treatment Selection

Despite the surgical focus of this book, current management of brain arteriovenous malformations (AVMs) involves other treatment modalities, namely endovascular embolization and stereotactic radiosurgery, as surgical adjuncts or as competitive alternatives. In some cases, conservative observation is the best option. Therefore, designing an individualized, multimodality management strategy that maximizes safety and efficacy remains a major challenge. In light of their significant hemorrhage risks, brain AVMs are treated with the goal of completely resecting or obliterating the AVM with acceptably low therapeutic risk, thereby avoiding neurologic deficits or deaths that come with hemorrhage. Other clinical symptoms such as seizures or progressive neurologic deficits, while not life-threatening, also warrant consideration for treatment.

Individually, the disciplines of neurosurgery, endovascular surgery, and radiosurgery have made technical advances, and, together, multidisciplinary approaches have improved AVM patient outcomes. Unlike other pathologies for which therapies from different disciplines may be competitive and management recommendations may be controversial, AVMs offer a unique opportunity for specialists to join together with integrated treatment strategies. Arteriovenous malformations foster collaboration between the neurosurgical subspecialties such as vascular and skull base surgery in exposing AVMs; among neurosurgeons, neurologists, and epidemiologists in examining hemorrhage risk and selecting patients for treatment; and between neurosurgeons and basic scientists in investigating the biology of AVMs. This chapter summarizes the multidisciplinary approach at my center for managing patients with brain AVMs (Table 19.1).

Single Modality Treatment

Single modality management of AVMs (surgical resection, embolization, or radiosurgery alone) is becoming less common with recognition of multimodality management’s advantages, namely increased therapeutic efficacy, decreased risks, and improved patient outcomes. Concurrently, novel embolization agents, sophisticated radiosurgical devices, and more accurate radiosurgical target planning have not dramatically raised single modality cure rates. Therefore, multimodality management is the standard for the majority of AVMs, but single modality management is indicated in special circumstances.

Microsurgical Resection

Microsurgical resection alone without any adjunctive therapy is utilized in only 8% of all AVM patients and only 14% of my operated AVM patients. The most common indication is neurologic deterioration due to intracerebral hematoma that produces mass effect and increased intracranial pressure (ICP). In these patients, the immediate need to evacuate the hematoma and relieve ICP prevents preoperative embolization, which might delay surgery and compromise outcome. Microsurgery alone is also indicated with AVMs located distally in a vascular territory with poor endovascular access, and with AVMs fed by small arteries arising perpendicularly from parent arteries, such as lenticulostriate arteries, thalamoperforators, or brainstem perforators. Catheterization of perforating arteries is technically difficult, and their embolization is associated with the risk of retrograde escape of the embolic agent. In some cases, superficial feeding arteries, like those from cortical middle cerebral artery (MCA) branches, are accessible endovascularly, but easy surgical accessibility makes embolization unnecessary.

Older series where AVMs were not embolized preoperatively report rates of complete obliteration (80–83%), permanent neurologic morbidity (5–17%), and operative mortality (1–12%) that are inferior to contemporary series where AVMs were routinely embolized preoperatively. The beneficial effects of preoperative embolization, combined with low procedural morbidity rates, have made it a routine surgical adjunct except in these special situations.

Embolization

Embolization alone was utilized in just 5% of our patients. Embolization with complete, curative AVM occlusion is rare, typically between 10 and 15%. However, cure rates are drifting upward (15–50%) with increasing use of aggressive Onyx embolization and prolonged intranidal injection techniques. However, embolization with the intent to cure is associated with high rates of morbidity (4–38%) and mortality (0–7%) due to arterial perforation, nidus perforation, dissection, hemorrhage, thromboembolism, and infarction, all of which can increase further with deep or large AVMs treated in multiple sessions. Curative obliteration is typically observed with small AVMs with a single feeding artery, often distally located away from other critical branch arteries. Pial arteriovenous fistulas can also be cured with endovascular embolization, but these lesions are rare.

Table 19.1 Summary of Multimodality AVM Management During the Author’s 16-Year Experience

Management	N	%
Single modality therapy
Embolization	50	5
Microsurgery	86	8
Radiosurgery	148	14
Multimodality therapy
Embolization–microsurgery	445	41
Radiosurgery–microsurgery	45	4
Embolization–radiosurgery	67	6
Embolization–microsurgery–radiosurgery	24	2
Conservative observation	208	19
Total	1073

Therefore, endovascular AVM obliteration is uncommon, and single modality therapy is often intended for other indications, like palliation of symptoms related to large, high-flow AVMs and cerebral steal (fluctuating neurologic deficit, seizures, and intractable headaches). In selected cases where surgical therapy is too risky, palliative embolization can reduce nidus flow or venous hypertension to improve symptoms, despite significant persistent arteriovenous shunting. It is worth emphasizing, however, that palliative embolization confers no protection against AVM hemorrhage, with some studies documenting no significant difference in hemorrhage rate or clinical outcomes in treated patients compared to natural history, and other studies documenting increased hemorrhage rates. Therefore, palliative embolization should be considered only with AVMs that have no other good treatment options and whose symptoms have become disabling.

The treatment of feeding artery or flow-related aneurysms is another indication for single modality endovascular therapy. These aneurysms are often remote from the circle of Willis and difficult to access surgically. In addition, the proximity of the AVM or its draining veins to the aneurysm can complicate an otherwise straightforward aneurysm clipping. In these cases, treatment consists of coiling the aneurysm and observing the AVM, particularly when the AVM is high-grade. In cases where the patient presents with subarachnoid hemorrhage rather than intracerebral hemorrhage, the aneurysm is usually the lesion responsible for the hemorrhage and aneurysm coiling alone may be appropriate.

With some ruptured AVMs that have intranidal aneurysms, endovascular occlusion of the intranidal aneurysm may be beneficial when a decision has been made not to resect the AVM. In these cases, which again are typically the high-grade AVMs with elevated surgical risks, embolization may reduce the risk of rehemorrhage.