**5.1 Spetzler-Martin (S-M) grading**

In 1986, Spetzler and Martin introduced the most commonly used grading scale for cAVMs; it uses three anatomical features of AVM (nidus size, nidus location relative to the eloquent brain (**Figure 10**), and pattern of venous drainage) to generate five cAVM grades (**Table 1**).

To determine S-M grade of cAVMs, size of the nidus, venous drainage, and eloquence of adjacent brain tissue are determined in angiography, brain CT scan, and/ or MRI of the brain. A numerical value is assigned for each category, as described in **Table 1**. The grade is derived from adding the points awarded for each category; for example, for grade I, the lesion would be small (less than 3 cm/1 point), in noneloquent region (0 point), and have only superficial drainage (0 point) (**Figure 11**); therefore, excision of such lesion would be complete, minimally invasive, and associated with low surgical complications. Whereas for grade V, the lesion would be large (more than 6 cm/3 points), sited within or immediately close to eloquent brain

#### **Figure 10.**

*The anatomic areas considered neurologically eloquent. (A) Deep eloquent area (hypothalamus, thalamus, brain stem, and cerebellar peduncle). (B) Eloquent area in cerebral cortex (sensory-motor, primary visual, and language area) [19].*


#### **Table 1.**

*Spetzler-Martin (S-M) grading scale is used to make decisions about treatment risks.*

#### **Figure 11.**

*Grade I AVM; (A) Vertebral angiograms. (B) Anteroposterior view cerebellar AVM less than 3 cm (1 point), superficial on cerebellar cortex (0 point), superficial drainage (through superficial cerebellar hemisphere veins–arrows: 0 point) [19].*

(1 point), and venous drainage would drain into deep venous system (**Figure 12**), so excision of such lesion is extremely difficult and associated with significant risk of bleeding and surgical morbidity and mortality. Moreover, obliteration of large cAVMs leads to sudden increase in perfusion, which leads to vasogenic edema or hemorrhage (normal perfusion pressure break through phenomenon). There are certain lesions that should not be considered for surgery such as large AVM that invades eloquent critical area or diffuse nidus that involves crucial structure such as hypothalamus or brain stem (**Figure 13**), so the surgical resection of such lesions would necessarily be associated with significant neurological deficit or death. These AVMs are graded under separate category (grade VI) and considered as inoperable AVM [22, 23].

The S-M grading scale was introduced to predict the outcome of surgical resection but can also be used to predict the radiosurgical outcome. Lower grades (grades I and II) are associated with a good result and less postoperative neurological deficit in comparison with grades IV and V [21–23].

Multiple retrospective studies showed that rates of poor outcome were highly correlated with S-M grade. Precisely, rates of poor outcome were calculated as follows: S-M grade I = 4% (95% CI, 2–7), S-M grade II = 10% (95% CI, 7–13), S-M

#### *Cerebral Arteriovenous Malformations (cAVMs): What Is New? DOI: http://dx.doi.org/10.5772/intechopen.90096*

grade III = 18% (95% CI, 15–22), S-M grade IV = 31% (95% CI, 25–37), and S-M grade V = 37% (95% CI, 26–49). These results prove that microsurgical resection is suitable for low-grade cAVMs (S-M grades I and II), whereas surgical resection of high-grade cAVMs (S-M grades IV and V) is associated with a high risk of poor patient outcome. Lawton and Davies et al. subcategorized grade III into three groups based on a specific combination of the same anatomical features (size, location, and venous drainage) to improve prediction of treatment outcome:

Group 1: Patients with S-M grade III cAVMs (a combination of small size, eloquent location, and deep venous drainage) have surgical outcomes similar to those of S-M grades I and II.

#### **Figure 12.**

*Grade VAVM; (A) Carotid angiogram, arterial phase. (B) Venous phase, AVM greater than 6 cm (3 points), situated in corpus callosum with a deep thalamic component (eloquent: 1 point), draining into a hugely dilated internal cerebral vein (deep drainage–arrow 1 point) [19].*

#### **Figure 13.**

*Grade IV AVM (inoperable AVM), (A) Vertebral angiogram, anteroposterior view. (B) Lateral view, arterial phase this lesion fed by multiple vessels from rostral basilar artery, surrounding and invading the mesencephalon [19].*


#### **Table 2.**

*Supplementary Spetzler-Martin or Lawton-Young cAVM grading scale.*

Group 2: Patients with S-M grade III cAVMs (a combination of medium size, noneloquent location, and deep venous drainage) have a poor surgical outcome similar to that of S-M grades IV and V.

Group 3: Patients with S-M grade III cAVMs (a combination of medium size, eloquent location, and superficial venous drainage) have a poor surgical outcome similar to that of S-M grades IV and V [23].

Supplementary grading scale to traditional S-M grading scale was proposed in 2010 to enhance its predictive power for predicted outcomes after surgical resection of cAVMs. This supplemental scoring system added three factors that affect patient's outcome (age, hemorrhagic presentation, and nidus configuration) (**Table 2**). The supplementary grading scale named Lawton-Young supplementary grading scale has been authorized in a separate cohort of 1009 patients [21, 23].

#### **6. Treatment of cAVMs**

Complete resection or obliteration of the nidus and AV shunt is considered as the treatment of choice of cAVMs. Incomplete nidal resection does not decrease hemorrhage risk. However, There are few reports of partial resection may improve neurological symptoms in patients who have neurological symptoms related to hemodynamic. There are three complementary therapeutic techniques that have been developed to achieve these goals (microsurgery ± embolization, stereotactic radiosurgery, and embolisation). The treatment plans of cAVMs should be carefully taken by a multidisciplinary team of knowledgeable and skilled physicians. They should take the size, location, and vascular features of the AVM in consideration. Moreover, risks of significant complications such as short- and long-term hemorrhage risk, feasibility, associated aneurysm, patient's age, risks of intervention, availability of interventional radiologist, and size and compactness of the nidus should be assessed. The short- and long-term hemorrhage risk is associated with a history of raptured cAVM, patient age, AVM location, size, and vascular morphological features [23–25].

Children and young adults have a long life expectancy, and the risk of intracerebral hemorrhage (ICH) is gradually increasing over the years. Therefore, curative therapy and complete obliteration are recommended whenever possible, while conservative treatment may be considered for elderly patients. The cumulative risk of hemorrhage can be calculated by the formula: lifetime risk of hemorrhage = 1 – (1 − P) × N (N is the expected years of life remaining, and P is the annual probability of hemorrhage). Another more straightforward formula is as follows: lifetime risk of hemorrhage = 105-patient's age in years.
