**1. Introduction**

Arteriovenous malformations (AVMs) are rare congenital anomalies of cerebral blood vessels with critical clinical implications. These anomalies may occur anywhere in the central nervous system (brain and spinal cord). It is a neurosurgical emergency that is characterized by abnormal vascular web, consisting of a tangle of dysplastic vessels (nidus) fed by arteries and drained by veins without intervening capillaries, generating a high flow, low resistance shunt between cerebral arteries and veins (**Figure 1**). They are a significant form of vascular malformation, with dilated arteries congregating from different directions and distended veins twisting from turbulence of shunted blood flow. This gives the pathology its radiological characteristic (early venous drainage) on formal catheter-based cerebral angiography. Although cAVMs are considered as a congenital cerebrovascular disease, patients may present with intracerebral hemorrhage, convulsions, chronic headache, and

#### **Figure 1.**

*(A) Normal vasculature, arteries, and veins communicate at capillary bed. (B) cAVM direct communication between high-flow arterial vessels and low-resistance venous capacitance vessels. And an arteriovenous malformation. Steal phenomenon (blood flow through low resistance shunt (low resistance) and stealing blood flow from adjacent brain) [1].*

progressive neurological deficit. Some of them remain asymptomatic and are noticed only incidentally on cerebral imaging for other indications. AVMs are associated with a lifelong risk of intracerebral hemorrhage (ICH); therefore, these lesions necessitate appropriate assessment, workup, and considerations for treatment based upon many factors such as age, size, and location of the lesions [2–5].

## **2. Epidemiology**

The prevalence of cAVMs is very low, and a collection of population-based studies from the literature estimates the incidence of cerebral AVMs at 0.69–1.32 per 100,000. However, they are considered as an important cause of intracerebral hemorrhage in a young age group. Bleeding rate is almost 1% per year in previously unruptured arteriovenous malformations. cAVMs cause approximately 2–4% of all hemorrhagic strokes [2, 4, 6, 7].

They are a congenital disease that is developed from indistinguishable causes in developing a fetus. While numerous mechanisms of cAVM formation have been suggested, the heterogeneity and lack of inheritance of these pathologies make their exact cause to remain idiopathic. They are associated with a few syndromes, such as hereditary hemorrhagic telangiectasia, Wyburn-Mason syndrome, von Hippel-Lindau disease, and Sturge-Weber syndrome [2].

Cerebral AVMs generally occur as a single lesion, and multiple lesions are observed only in 9% of the patients. cAVMs are equally distributed between sexes [8, 9].

Patients may present at any age, although they most commonly present in the second through fourth decades of life [6, 7].

### **3. Clinical manifestation**

cAVM patients may present with a variety of clinical symptoms such as hemorrhage, seizure, headaches, or focal neurologic deficits. The clinical presentations of cAVMs depend on the patient's age, size, location, and vascular features of the cAVMs. Some patients are asymptomatic at presentation and cAVMs are accidently discovered when imagines are performed for potentially unrelated reasons.

#### **3.1 Hemorrhage**

Hemorrhage is the most common initial presentation of cAVMs. Studies reported that hemorrhage is the initial presentation in 50% of patients with cAVMs. The risk of hemorrhagic stroke in cAVM patients is about 2–5% per year. It is fatal

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

in 5–25% of all cAVM patients. Children more frequently present with intracerebral hemorrhage than do adults. Hypertension, previous intracerebral hemorrhage (ICH), AVMs with feeding artery aneurysm, AVMs with multiple arterial feeders, deep-seated cAVMs, and cAVMs with limited venous drainage are associated with increased risk of hemorrhagic stroke. Hemorrhage begins in the lesion itself and then accumulates, increases in size, and produces a mass effect. Therefore, hemispherical lesions generate less severe syndromes in comparison with primary hemorrhage that originates from functioning parts of the brain. Hemorrhages in polar regions such as frontal, temporal, and occipital regions may cause only minor headache, while those in deeper structures affect vital regions packed into tiny spaces and produce severe neurological manifestations. Hence, patients with ICH may present with a wide span of presentations such as sudden severe headache, drop in the level of consciousness, progressive neurological deficits, hemiparesis, aphasia, cranial nerve palsy, visual field deficits, and coma [2, 9–11].

The type of the hemorrhage and clinical presentations depend on the location of cAVMs. Superficial lesions cause subarachnoid hemorrhage with low risk of cerebral vasospasm and the bleeding confined in local sulci, whereas lesions with deep drainage may vent blood in the ventricular system, causing hemohydrocephalus. Lesions embedded in the brain parenchyma cause parenchymatous hemorrhage. **Figure 2** [11, 13].

## **3.2 Seizure**

Seizures are the second most common presentation of cAVMs; it occurs in 20–29% of patients with cAVMs at initial diagnosis. One study showed that the 5-year risk of first seizure was 8% (95% CI 0–20). The risk of the seizures rose to 23% in the presence of ICH and focal neurological deficit. The seizures are frequently observed in male patients with cortical lesions, especially in the frontal and temporal lobe. Large lesions (nidus greater than 3 cm in diameter) and superficial venous drainage are associated with increase in seizure frequency. Posterior fossa, coexisting aneurysms, and deep locations were associated with the absence of seizures. AVM may cause focal or generalized seizures or both. The exact pathophysiology of the seizures is not completely understood. However, increased venous back pressure secondary to venous outflow obstruction may be involved. cAVM-related seizures may occur secondary to ICH, from the hemosiderin deposition, or secondary to venous hypertension, and ischemia following steal. Seizure control rate ranges between 49 and 85% according to approach (surgery, radiosurgery, or embolisation), and the highest seizure freedom has been achieved in patients with approved complete angiographic obliteration after radiosurgery [2, 9, 14].

#### **Figure 2.**

*(A) Axial and (B) sagittal plain CT brain of 13-year-old patient presented with sever headache; the scan demonstrates right parieto-occipital intra-axial hemorrhage with intra-ventricular extension. Urgent craniotomy was done due to deterioration of the neurological status confirming underlying AVM [12].*

## **3.3 Headache**

Approximately 0.2% of cAVM patients present with headache and normal neurologic examination. The headache associated with cAVMs is incidental, without any specifications. Headache is the presenting symptom in nearly 15% of cAVM patients without evidence of rupture. Headache can be characterized as similar to migraines with lateralization to one side [11, 13]. The attack occurrence, aurae, duration, and pulsatile quality are all shared. Treatment of headache in AVM patients has not been studied so far. No specific medication has been exclusively useful in headache management. Expert opinions do not recommend using any vasoconstrictors in these patients as it may lead to rupture and ICH. However, there are limited data to support this recommendation [9].
