Cerebro-spinal fluid, CSF, is produced constantly inside each of the four spaces or ‘ventricles’ inside the brain: between 400 and 600ml is produced each day. The CSF normally flows through narrow pathways from one ventricle to the next, then out over the outside of the brain and down the spinal cord, and is absorbed into the bloodstream.
From around the middle of pregnancy, CSF begins to flow through holes to the outer surface of the brain and spinal cord, between the membranes which cover the brain, called meninges.
If the drainage of CSF is prevented at any point, the fluid accumulates in the ventricles, causing them to swell, which then compresses the surrounding tissue.
In babies and infants, this will cause the head to enlarge, as the bones which form their skull are not yet fully fused.
Once the bones of the skull begin to join together, the head can no longer enlarge, so the pressure inside the head rises. This pressure begins to stretch brain tissue and reduce the blood flow to the brain. If the increase is sudden, damage to the brain may occur, and the brain may be pressed against or even down the foramen magnum.
This can crush important cranial nerves and can be life threatening. Fortunately, hydrocephalus is treatable for most people.
This is still being studied, but CSF may support the brain and allow it to ‘float’ inside the head to prevent the blood vessels being squashed. CSF helps supply the brain with vitamins, and removes toxic waste chemicals, like beta-amyloid (associated with normal pressure hydrocephalus and Alzheimer’s).
The CSF has an important role in brain development in the womb: it carries chemical messages to guide brain cells to their correct positions. Without these chemicals, the development of the baby’s brain may differ from the norm, and some learning or behavioural effects may arise during childhood.
