For children more than 2 – 3 years, the cranial fontanelles and sutures are closed, and the skull can be considered a rigid container with a fixed volume. Its content includes the brain bulk (80%), the blood volume (10%), and the cerebrospinal fluid (CSF) (10%). According to the Monro-Kellie doctrine, intracranial volume is equal to the sum of the volume of the brain, blood, CSF and other mass lesions. Therefore, an increase in volume of any of these components, such as CSF, can raise intracranial pressure (ICP) and reduce cerebral perfusion pressure and cerebral blood flow. Acute ICP elevation can reduce cerebral perfusion pressure (CPP), which is determined by subtracting ICP from the mean arterial pressure (MAP). A significant change in ICP can lead to changes in brain perfusion which can alter CPP when autoregulation of cerebral blood vessels is impaired (e.g. during stroke), and chronic conditions of elevated ICP can produce papillary oedema, loss of vision and death. Hydrocephalus may also be non-obstructive, in which CSF flow within the ventricular system is not impaired but there is decreased absorption. Additionally, tumours of the choroid plexus may also produce increased CSF secretion in rare cases and if this increased secretion is not compensated for by increased outflow, then hydrocephalus can occur.