In this condition the volume of cerebrospinal fluid(CSF) is abnormally high and is usually accompanied by increased intracranial pressure(ICP). An obstruction to CSF flow is the most common cause. It is described as communicating when there is free flow of CSF from the ventricular system to the subarachnoid space and non-communicating when there is not,ie,there is obstruction in the system of ventricles,foramina or ducts.
Enlargement of the head occurs in children when ossification of the cranial bones is incomplete but ,in spite of this,the ventricles dilate and cause stretching and thinning of the brain. After ossification is complete,hydrocephalus leads to a marked increase in ICP and destruction of a nervous tissue.
PRIMARY HYDROCEPHALUS.
In this condition there is accumulation of CSF accompanied by dilation of the ventricles. It is usually caused by obstruction to the flow of CSF but is occasionally due to malabsorption of CSF by the arachnoid villi. It may be communicating or non-communicating. Without treatment,permanent brain damage occurs.
Congenital primary hydrocephalus is due to malformation of the ventricles,foramina or ducts,usually at a narrow point.
Acquired primary hydrocephalus is caused by lesions that obstruct the circulation of the CSF,usually expanding lesions,eg.tumours,haematomas or adhesions between arachnoid and pia maters,following meningitis.
SECONDARY HYDROCEPHALUS.
Compensatory increases in the amount of CSF and ventricle capacity occur when there is atrophy of brain tissue,eg in dementia and following cerebral infarcts. There may not be a rise in ICP.
