The cerebro-spinal fluid (CSF) is produced constantly inside each of the four spaces or ventricles inside the brain. It normally

In normal people it flows through narrow pathways from one ventricle to the next, then out over the outside of the brain and down the spinal cord and into the blood. If the drainage pathways are obstructed at any point, the fluid accumulates in the ventricles inside the brain, causing them to swell - resulting in compression of surrounding tissue. In babies and infants, the head will enlarge. In older children and adults, the head size cannot increase as the bones which form the skull are completely joined together.

Lateral ventricles. Normal coronal section

Lateral ventricles. Coronal section enlarged in a case of hydrocephalus

hydrocephalus in 14-month- old infant. Enlargement of the head, associated with the accumulation of CSF within the ventricles of the brain. Source: Correlative Neuroanatomy & Functional Neurology.

Hydrocephalus is commonly known as 'water on the brain', although this is not accurate. It is the condition where the fluid spaces in the brain (ventricles) become enlarged. The ventricular system dilates when CSF flow is obstructed.

Causes

hydrocephalus is caused by the inability of CSF to drain into the bloodstream. There are many reasons why this can happen:

Brain Tumours - Tumours of the brain cause swelling of surrounding tissues and compression, resulting in poor drainage of CSF.

Meningitis - This is an infection of the membranes covering the brain. The inflammation and debris from this infection might block the drainage pathways causing hydrocephalus.

Congenital Hydrocephalus - Hydrocephalus is present at birth but it term does not mean that it is hereditary.

Prematurity - Babies born prematurely are more vulnerable of developing hydrocephalus than one which goes the full term since many parts of the body will not have matured. The activity of the area which lies just beneath the lining of the ventricles in the brain has a plentiful blood supply. Its blood vessels can be easily burst if the baby suffers too large a swing in blood pressure or in the amount of fluid in the system.

Types of hydrocephalus:

Communicating Hydrocephalus - Obstruction to CSF flow in the subarachnoid space after exit from fourth ventricle. Causes include infection such as meningitis (fibrosis obstructs the subarachnoid space and obstructs CSF flow), abnormal aging and absorption failur, subarachnoid hemorrhage, or Blockage with blood from ruptured aneurysms.

Non-Communicating Hydrocephalus - Obstruction to CSF flow within ventricular system or at outlet foramina. Sites of narrowing are commonly obstructed. Examples include Colloid Cysts which obstruct the 3rd ventricle, and tumors of the brainstem with compress the channel between the 3^rd and 4th ventricle (Aqueduct of Sylvius).

Hydrocephalus Ex-Vacuo: Sometimes the brain will shrink in size (as is seen in Alzheimer's Disease), and as a result, the ventricles will enlarge to compensate. Thus though the ventricles are enlarged, they are not under any pressure.

Treatment

Shunts - The most common treatment for hydrocephalus is a shunt - a thin plastic tube inserted entirely under the skin that creates a new path for the CSF, from the brain to another part of the body. Shunting controls the pressure by draining excess CSF, so preventing the condition becoming worse. However, shunts does not cure the hydrocephalus and damage to the brain tissue remains. Shunts are not perfect, they may malfunction, clog, may cause infection or may break.

Ventriculostomy - Ventriculoscopes have been improved to the point that, in some patients, new pathways for CSF can be created within the brain, or the old ones can be re-opened. This is an area of rapid new developments.

See:

Brain Ventricles

Author: Silvia Helena Cardoso, PhD. Psychobiologist, master and doctor in Sciences by the University of São Paulo and post doctoral fellowship by the University of California, Los Angeles. Invited Professor and Associate Researcher of the Center for Biomedical Inofrmatics, State University of Campinas (Unicamp), Brazil. Correspondence