Hydrocephalus describes cerebrospinal fluid (CSF) building up abnormally within the brain and spinal cord. This is a result of either over-production of CSF or a problem with draining or absorbing CSF.


Normal CSF Physiology

There are four ventricles in the brain: two lateral ventricles, the third and the fourth ventricles. The ventricles containing CSF. The CSF provides a cushion for the brain tissue. CSF is created in the four choroid plexuses (one in each ventricle) and by the walls of the ventricles. CSF is absorbed into the venous system by the arachnoid granulations.


Congenital Causes

The most common cause of hydrocephalus is aqueductal stenosis, leading to insufficiency drainage of CSF. The cerebral aqueduct that connects the third and fourth ventricle is stenosed (narrowed). This blocks the normal flow of CSF out of the third ventricle, causing CSF to build up in the lateral and third ventricles.

Other causes:

  • Arachnoid cysts can block the outflow of CSF if they are large enough
  • Arnold-Chiari malformation is where the cerebellum herniates downwards through the foramen magnum, blocking the outflow of CSF
  • Chromosomal abnormalities and congenital malformations can cause obstruction to CSF drainage.



The cranial bones in babies are not fused at the sutures until around 2 years of age. Therefore, the skull is able to expand to fit the cranial contents. When a baby has hydrocephalus it causes outward pressure on the cranial bones. Therefore, babies with hydrocephalus will have an enlarged and rapidly increasing head circumference (occipito-frontal circumference).

Other signs:

  • Bulging anterior fontanelle
  • Poor feeding and vomiting
  • Poor tone
  • Sleepiness


Ventriculoperitoneal Shunt

Placing a VP shunt that drains CSF from the ventricles into another body cavity is the mainstay of treatment for hydrocephalus. Usually the peritoneal cavity is used to drain CSF, as there is plenty of space and it is easily reabsorbed. The surgeon places a small tube (catheter) through a small hole in the skull at the back of the head and into one of the ventricles. A valve on the end of this tube is placed subcutaneously, and a catheter on the other side of the valve runs under the skin into the peritoneal cavity. The valve helps to regulate the amount of CSF that drains from the ventricles.


VP Shunt Complications

  • Infection
  • Blockage
  • Excessive drainage
  • Intraventricular haemorrhage during shunt related surgery
  • Outgrowing them (they typically need replacing around every 2 years as the child grows)


Last updated January 2020