The cranial vault contains brain tissue, blood and cerebrospinal fluid (CSF). After closure of a child’s sutures, the cranial vault is similar to a rigid box. As the volume of the three components within the skull (brain matter, blood and CSF) must remain equal, an increase in one component must be accompanied by a decrease in another component. If there is not, an increase in intracranial pressure (ICP) will occur.

ICP can be monitored via a fibre optic monitor (Codman™ microsensor) which is placed on the surface of the brain or in the brain or an external ventricular drain (EVD) system which is a closed sterile system allowing drainage of CSF via a silastic catheter tip which rests in the ventricle.

The ventricular system produces CSF at approximately 20mL/hr (estimated at 0.35mL/min in children) by the choroid plexus in the lateral ventricles. The CSF circulates around the brain and spinal cord and is then reabsorbed via the arachnoid villi.