**6.2 Standard microsurgery protocol**

We briefly (and humbly) review key steps involved with AVM microsurgery [23, 37]. Once a patient is designated for microsurgery, **treatment planning and evaluation** begins. Often, additional imaging is performed to provide maximal data for a solid operating plan. Here, 3D reconstruction can prove very helpful and emphasis should be given to study the AVM main feeders. **Pre-operative steps** include patient positioning (one that provides a good venous return and preferably has the AVM surface aspect horizontal at the top of the approach and the longest axis of the nidus vertical) and craniotomy (removal of part of the skull to expose the brain), which provides exposure to the lesion area. Here, caution must be exerted to ensure the craniotomy is larger than the AVM surface while safeguarding the delicate dilated and exposed draining veins during dura opening (against adhesion). Only then can **AVM resection** be performed. The procedure in general is directed from the arterial towards the venous side of the nidus. All vessels must be coagulated or clipped. It is customary to leave true feeders to the end since their earlier occlusion can lead to the recruitment of blood flow from deep feeders and may cause their rupture [23]. It is important to ensure that draining veins present no evident flow. Eventually, the nidus is gently rolled out of the resection cavity**. Post-operative management** includes admitting the patient (while completely sedated) to the Intensive Care Unit for close observation for evidence of postoperative bleeding or swelling. A post-operative CT is typically performed shortly after the procedure to rule out any such complication followed by a mandatory angiography performed on day 2–3 after surgery.

### **6.3 Results and complications**

The main advantage of AVM microsurgery is its "straightforward" approach, which allows relatively definite lesion resection and rapid clear follow-up. Microsurgery is considered the gold standard in AVM obliteration. It presents a high success (cure) rate reaching 99% in small SM 1–2 grades [91–93]. Treatment challenges include limitations regarding accessibility (deep locations) and a high risk of severe complications that contribute to the mortality and permanent morbidity rates of 3.3 and 8.6%, respectively, as seen in a meta-analysis performed in 2425 patients between 1990 and 2000 [8]. A more recent study found permanent mortality and morbidity rates of 1.7 and 4.8% (2.2% permanent significant morbidity) [91], and yet, another study found the permanent mortality and morbidity rates of 7.9 and 14.8% (though obliteration rate was 87.2%) [92]. Additional studies present early and permanent disabling deficits in 12.3 and 4.5%, respectively, permanent neurological deficit in 16.1% [93], perioperative neurological deficits of 17%, annual hemorrhage rate of 0.3%, and a recurrence rate of 0.9% in children [94]. These findings and others clearly demonstrate the pronounced variations in the modality outcomes depending on surgeons' expertise, patients' AVM grading distribution (e.g., 7% neurological deficits at SM Grade 1 compared with 50% at SM 5 in [90]), prior bleeding presentations, multi-modality protocol (e.g., surgery following embolization or radiosurgery as in [95]), and so forth. A review of the literature indicates that the leading risks of surgical resection are intraoperative rupture, post-operative hemorrhage, and post-operative edema. These hemodynamic events can become life threatening and disabling. Additional

complications of reduced risk are neurologic deficits from over-dissection or ischemia, seizures, hydrocephalus, and infections [23, 37]. The subject of lesion recurrence following microsurgery has been controversial. Different centers report highly varied outcomes. Recently, Aboukaïs et al. analyzed the subject and reported the recurrence as a fairly rare case (7/138 cases) affecting mostly pediatric patients. They recommend particularly long-term angiographic follow-up in children to detect AVM recurrence or remnants [96].

#### **6.4 Emerging trends**

Brain microsurgery is a proliferating field presenting many interesting developments in imaging, treatment management, surgical approach, and so forth. We very briefly mention a few promising directions. **Molecular imaging** employs specific antibodies combined with detectable agents such as gadolinium [55]. This technique was used to image particular receptors on tumors and could non-invasively detect biological markers in AVM vessels. If an appropriate biomarker imaging probe for AVM is discovered, it will facilitate highly selective lesion diagnosis and analysis. Specific conditional biomarkers (activated by physiological occupancy of enzymes, ions, and metabolites) can possibly even support super-selective procedures. Rad et al. demonstrated that vessels within the mature rat AVM exhibit elevated phosphatidylserine (PS) externalization compared with normal vessels [97]. Ionizing radiation increased PS externalization in a time-dependent manner. They concluded that the AVM localization of PS externalization may function as a tool in future SRS treatment. **Image guidance** provides a promising technique, particularly when incorporated into patient intraoperative 3D viewing and simulating systems [98]. It facilitates improved AVM localization, clearer venous anatomy, better definition of craniotomy, and so forth for the surgeons, and may reduce intraoperative risks. Spetzler and Sanai used **dynamic retraction** (retractorless surgery) and a variety of advanced handheld instruments with considerable success and suggest that fixed retraction can be supplanted by this approach, thus limiting the risk of retractor-induced tissue edema and injury [99]. There are additional promising directions outside the scope of this chapter. However, most of those mentioned (as well as those not discussed here) still lack a large enough database for establishing clinical superiority.

#### **6.5 Summary**

The neurosurgical aspect of AVM treatment presents a versatile picture. While SM Grade 1–2 lesions are treated with good efficacy and low risks (as well as a few Grade 3 cases), successful outcome rapidly declines in medium-to-large lesions, demonstrating high risk for adverse outcomes (transient and permanent neurological deficits as well as mortality). These high risks do not markedly decline when addressing large AVMs using a multi-modality approach. Perhaps because such procedures are not yet sufficiently established, we cannot currently provide this statement with distinct supporting evidence. Small AVMs constitute a large portion (~40% or so based on our literature observations) of all lesions. This leaves many cases without direct surgical solutions and greatly limits the use of this approach as a single modality. Future developments include further advancements in imaging methods, augmented reality and simulation systems, and innovative tools and approach methods. These will certainly facilitate continuous improvement in efficacy and safety with regard to small lesions and an increased ability to effectively treat medium lesions. However, we fear that treating the majority of medium-to-large lesions will continue to necessitate multi-modal, fractionated, or novel approaches.

*Advocating Intraluminal Radiation Therapy in Cerebral Arteriovenous Malformation Treatment DOI: http://dx.doi.org/10.5772/intechopen.89662*
