**2. Epidemiology**

The incidence of hydrocephalus (HCP) after aSAH is reported from 6 to 67%, and this wide range is due to various backgrounds and clinical situations of reporting. More recently, the incidence of hydrocephalus has been reported to be around 20–30% of subarachnoid haemorrhage [2].

One of the tertiary cares centre from the Indian subcontinent reported that 18.6% of their aSAH had hydrocephalus. Posterior circulation aneurysms were found to cause more frequent hydrocephalus than anterior circulation aneurysms [3].

### **3. Classification and types of hydrocephalus in aSAH**

Hydrocephalus (HCP) in aSAH is divided into acute, subacute and chronic. In most of these patients, HCP is acute and occurs within 3 days of the bleeding. Subacute HCP occurs within 4 to 14 days of bleeding, and hydrocephalus after 2 weeks of aSAH is called chronic HCP, and it occurs in up to 20% of aSAH patients.

Further to it, HCP can be communicating or non-communicating. In the initial days of aSAH, it is non-communicating due to blockage and obstruction to the free flow of CSF due to narrowing and obstruction of the cerebral aqueduct. However, when it becomes chronic, it becomes communicating due to fibrosis of subarachnoid granulation. In this type, the flow of CSF is obstructed or blocked after the cerebral ventricles and usually results from a thickened arachnoid layer. Details are described in the etiopathology section.

#### **4. Risk factors**

Various reports suggest that the following are the risk factors for the development of acute hydrocephalus (obstructive or non-communicating) following aSAH are mentioned as follows: [4]


*Aneurysmal Subarachnoid Haemorrhage (aSAH) and Hydrocephalus: Fact and Figures DOI: http://dx.doi.org/10.5772/intechopen.110250*

6.Known hypertension

According to Chen S et al., following are risk factors for communicating, nonobstructive chronic hydrocephalus [5]


Other factors, like economy, medical development and techniques for aneurysms obliteration also detect the requirement of temporary or permanent shunts [7].
