**6.1 Microsurgery**

Craniotomy and surgical resection of cAVMs were first introduced in the 1920s, where the outcomes were inferior. The development of angiography played an essential role in understanding vascular anatomy and hemodynamics of AVM lesions. The introduction of microsurgery and bipolar diathermy has resulted in significant improvement of morbidity and mortality in comparison to the early known surgical resections. Microsurgical excision of cAVMs is considered as the most efficient approach as it offers the best chance of immediate cure and eliminates morbidity and mortality associated with its potential rupture. Before taking patients to the operating theater for surgical resection, preoperative angiogram and MRI should be done for intraoperative stereotactic localization of the lesion. Moreover, endovascular embolisation has frequently been considered to improve surgical safety and to possibly magnify the pool of cAVMs amenable to safe surgical resection. The main goals of endovascular embolisation are elimination of arterial feeders (particularly those that would be challenging to access in early stages of surgical intervention), decrease of nidus volume that would warrant safer surgical resection, and management of high-risk angiographic characters such as feeding artery and intranidal aneurysms.

Essential steps in the resection process of AVM are wide dural opening, identification of AVM lesion, elimination of superficial feeding arteries, circumferential resection of the nidus with control of deep arterial pedicle, and transection of draining veins. When all arterial feeders to the nidus have been determined and coagulated, the direct venous drainage can be blocked and the nidus resected. Intraoperative vascular imaging, such as DSA, is beneficial to confirm complete nidus resection at the time of surgery. Furthermore, indocyanine green videoangiography with either fluorescein or indocyanine can be very useful to intraoperatively map the angioarchitecture of the lesions, including distinguishing arterial feeders from arterialized draining veins.

The surgeons should vigilantly inspect the resection bed microscopically to make sure that hemostasis has been achieved, during which the blood pressure is maintained at 15–20 mm Hg above the baseline. Oxidized cellulose (Surgicel) can be used to line the nidus bed, and the patient's goal blood pressure should be maintained within the normal range for the first 24 hours after surgical resection.

Although the microscopic complete nidus resection has long-term durability and leads to abrupt elimination of hemorrhage risks, it is an invasive intervention and associated with neurological risks [23, 25].

## **6.2 Stereotactic radiosurgery (SRS)**

Radiosurgery is typically reserved for the obliteration of compact cAVMs (less than 3 cm) in patients who are poor surgical candidates either radiographically (Spetzler-Martin grades >III) or due to existing medical comorbidities. SRS promotes endothelia cell proliferation, gradual, concentric vessel wall thickening, and ultimately luminal closure. Numerous studies about efficiency and safety of radiosurgery indicated that radiosurgery seems to be suitable for small-tomoderate volume lesions (less than 12 cm3 in volume or less than 3 cm in maximum diameter). Furthermore, radiosurgery is best suited for injuries situated in deep or eloquent regions of the brain. The primary goal of SRS is the obliteration of cAVMs. With obliteration, the risk of hemorrhage from cAVM nidus is eliminated. Complete obliteration of cAVM nidus after SRS is associated with fading of cAVMassociated epilepsy as well as improvement of nidus-associated neurological signs and symptoms.


**Table 3.**

*Radio-surgical outcomes for unruptured cAVMs [23].*

Most series with long-term follow-up show obliteration in 70–80% of cAVMs and it is achieved within 2–3 years after starting stereotactic radiosurgery (**Table 3**) [17, 20]. The time between starting radiosurgery and complete obliteration is named the latency period; it varies from 1 to 3 years. During this latency period, the risk of hemorrhage ranges between 1 and 3% per year. The outcome of radiosurgery has been affected by many factors such as age, nidus volume, preceding embolisation, and previous hemorrhage. Therefore, all these factors should be considered before deciding to proceed with radiosurgery.

Though preceding endovascular embolisation may shrink large nidus to a suitable target volume for SRS as well as eradicate high-risk characters associated with cAVM such as perinidal or intranidal aneurysms, it may lead to difficulties in precisely targeting residual nidus and reducing successful obliteration rates after SRS.

Radiosurgery is not entirely safe; during latency period, symptomatic changes secondary to radiation occur in 10 percent of the patients. However, permanent neurological changes are reported only in 2–3% of patients.

The main risk factors for symptomatic changes secondary to radiations are the location of AVM, target volume, and dose to surrounding healthy tissue (margin dose). The symptomatic changes secondary to radiation effect can be reduced with corticosteroids and bevacizumab.

Delayed cyst formation and radiation-induced neoplasia are uncommon although may occur after 10 years from radiosurgery [23, 26, 27].

#### **6.3 Embolisation**

Endovascular embolisation plays a crucial role in multidisciplinary approach to treat cAVMs. Embolisation may be considered in the following scenarios:

#### *6.3.1 Preoperative embolization*

The primary goal of preoperative embolisation is to facilitate surgical resection of cAVMs and reduce complication rates of microsurgery. It is instrumental in the reduction of intraoperative bleeding and postoperative complications such as healthy perfusion pressure breakthrough. The healthy brain tissue surrounding cAVMs exposes to chronic low perfusion pressure. When the lesion is wholly or partially resected, these areas are suddenly subject to normal perfusion pressure, and their autoregulation ability may be impaired. Therefore, a sudden increase in perfusion pressure may lead to brain edema, delayed hemorrhage, and seizures. Large cAVMs should go through staged embolisation to gradually

reduce flow to the AVM before resection. Moreover, preoperative embolisation may be useful in the elimination of feeding artery pedicles that may be deep and not accessible [23, 28, 29].
