**1. Definition and etiology**

The modern definition of cerebral artery aneurysms began in 1874 with Duret's description of the middle cerebral artery (MCA). It is known that 20% of all aneurysms are composed of MCA aneurysms and 90% of aneurysms originate from anterior circulation. It is more common in women aged 35–60 years [1]. Subarachnoid hemorrhage (SAH) is a major health problem worldwide with a high mortality rate. Despite a 17% decrease in case fatality in the last three decades associated with improved management strategies, 30-day mortality and sudden death rate unfortunately are still high, around 35 and 15%, respectively [2].

Cerebral arteriovenous malformations (AVM) are composed of a complexity of abnormal arteries and veins and are a major source of brain hemorrhage, resulting in morbidity and mortality, representing a diagnostic and therapeutic challenge in young adults. Cerebral AVM generally represents 1 and 3% of the total annual risk for epilepsy and bleeding in patients with AVM. The rate risk of bleeding in undamaged AVMs is 2.2% per year, and the rate of torn lesions is 4.5% per year. Important risk factors for the development of bleeding due to AVM include deep localization, deep venous drainage, associated aneurysms, pregnancy, age, and gender. Disconnection of arteriovenous malformations from circulation and prevention


#### **Table 1.**

*Risk factors for the formation of intracranial aneurysms.*


**Table 2.**

*Risk factors for the rupture of intracranial aneurysms.*

of epileptic seizures remain the mainstay of treatment. The size, location, and presence of deep venous drainage (using the Spetzler-Martin score) determine the mortality and management of the arteriovenous malformations.

The most common causes of aneurysm remain hemodynamic instability, degenerative changes, vascular injury, atherosclerosis, vasculopathy, high flow, arteriovenous malformation, and fistula. In addition, the important risk factors for the development of cerebral aneurysms are hypertension, smoking, chronic alcohol use, family history of intracranial aneurysms in first-degree relatives, and female sex. Autosomal dominant polycystic kidney disease is an inherited systemic disorder that is strongly associated with intracranial aneurysms. Autosomal dominant polycystic kidney disease has a prevalence rate 2–4 times higher than the general population. Other conditions such as Marfan syndrome, Ehler-Danlos syndrome type IV, neurofibromatosis type I, hereditary hemorrhagic telangiectasia, Moyamoya disease, pseudoxanthoma elastum, and fibromuscular dysplasia are weakly associated with intracranial aneurysms. Multiple aneurysms are detected in 10–30% of cases. Both localization and type of aneurysm are important considerations in describing the risk for rupture. Aneurysm rupture is directly proportional to size, and ruptured aneurysm causes subdural, subarachnoid, or intracranial hematoma. 25% of the cases with ruptured aneurysm are lost and 50% of them have partial or complete recovery. Overall incidence of mortality and complications in ruptured aneurysm is 80%. Risk factors for the formation of and rupture of intracranial aneurysms are shown in **Tables 1** and **2** [1, 3, 4].

Aneurysms are classified according to their shape or size. According to the shape:


*Intensive Care Management in Cerebral Aneurysm and Arteriovenous Malformations DOI: http://dx.doi.org/10.5772/intechopen.89714*

3.Dissecting.

According to the size:

1.Small (<15 mm).

2.Large (15–25 mm).

3.Giant (25–50 mm).

4.Super giant (>50 mm).

Saccular berry aneurysms account for 90% of the total aneurysm morphology, and their rupture is the most common cause of SAH. Fusiform aneurysms account for the remaining 10%, and their most common location is posteriorly. Atherosclerosis and dissection are found to be responsible as possible mechanisms for formation of fusiform aneurysms.
