To understand hydrocephalus, it helps to first understand the fluid at the center of it: cerebrospinal fluid (CSF). Knowing what CSF normally does makes it much easier to grasp what goes wrong in hydrocephalus.
What CSF is Cerebrospinal fluid is a clear, water-like fluid that surrounds the brain and spinal cord and also fills the hollow spaces within the brain. It looks a bit like water but is carefully regulated by the body. Despite being mostly water, it plays several vital roles.
What CSF does This remarkable fluid serves the brain in several ways:
- Cushioning and protection. CSF acts like a liquid shock absorber, allowing the brain to "float" within the skull. This buoyancy protects the delicate brain from bumping against bone during everyday movement.
- Support. By floating in CSF, the brain's effective weight is dramatically reduced, which protects it from pressure damage at its base.
- Nourishment and waste removal. CSF helps deliver nutrients and carry away metabolic waste products, contributing to the brain's "housekeeping."
- Chemical stability. It helps maintain a stable environment around the brain and spinal cord.
How CSF is produced and absorbed CSF is produced mostly by a structure called the choroid plexus, located within the ventricles (the brain's fluid chambers). It's produced continuously — the body makes a substantial amount each day, far more than is present at any one moment, because CSF is constantly being renewed. After circulating, it is absorbed back into the bloodstream, primarily through small structures along the surface of the brain (and, as research increasingly shows, through other pathways too).
The balance that matters Here is the key idea: in a healthy person, the production, circulation, and absorption of CSF are in balance. The amount made roughly equals the amount absorbed, and the fluid flows freely along its normal route. This keeps the volume and pressure of CSF within a healthy range.
Where hydrocephalus comes in Hydrocephalus develops when this balance is disrupted — most commonly when CSF can't flow through its normal pathway (a blockage) or can't be absorbed properly. Because the body keeps producing CSF, any obstruction or absorption failure causes fluid to back up and accumulate in the ventricles. (Far more rarely, a tumor of the choroid plexus can cause overproduction.) Understanding CSF as a fluid in constant, balanced motion is the foundation for understanding everything else about hydrocephalus.
In the next article, we follow the actual path CSF takes through the brain — the ventricular system — which is exactly where many blockages occur.