1. Aqueductal stenosis Aqueductal stenosis is a condition where the Aqueduct of Sylvius, which connects the 3rd and 4th ventricles, becomes damaged and blocks the flow of CSF. There are several possible cause for stenosis, eg. the aqueduct may develop without having any openings to the ventricles, or have developed with a membrane of cell blocking the aqueduct. Cases of hydrocephalus which are caused by aqueduct stenosis is usually present at birth, or then develope soon there after. Chiari malformations are a possible cause of stenosis as this malformation will squeeze or bend the aqueduct.

2. Intraventricular haemorrhage In premature infants weighing less than 1500g, 50-60% will develop intraventricular haemorrhage (IVH). Shortly after the haemorrhage, nearly 3/4 of infants will develop ventricular enlargement. Signs which are indicative of bleeding include: stupor, respiratory difficulty, seizures, unstable vital signs, and a bulging fontanelle. Several pharmacological agents can be used to prevent intraventricular haemorrhage. When IVH occurs, and is accompanied by hydrocephalus, the initial treatment is to relieve the hydrocephalus without a shunt. This is done because: the blood would occlude (block) the catheter; the infant is usually too small to support a shunt; and the hydrocephalus may resolve itself over time. While the incidence of acute hydrocephalus is up to 60%, the long term incidence of progressive hydrocephalus requiring a shunt has fallen to 10 - 20%.

3. Postmeningitic and postinflammatory hydrocephalus causes Postmeningitic and postinflammatory hydrocephalus are usually a communicating hydrocephalus due to obstruction at the basal cisterns. E. Coli meningitis and Hemophilus influenza meningitis are the usual infectious agents. Moderate ventricular enlargement is very common. This will either resolve itself; progress into hydrocephalus which requires a VP shunt; or evolve into a case of atrophy with hydrocephalus-ex-vacuo. The finding of progressive ventricular enlargement and an enlarging head circumference confirms the need for a shunt..

4. Trauma Trauma to the head or traumatic brain injury may damage the brain’s tissue, nerves and blood vessels. Blood in these vessels may enter the CSF stream, causing inflammation and if there is meningeal scarring, the CSF absorption areas may be blocked.

5. Tumores. Conforme un tumor crece puede llenar o comprimir el cuarto ventrículo, bloqueando el paso (flujo) del líquido espinal (LCR). En otras áreas del cerebro un tumor puede bloquear similarmente o comprimir el sistema ventricular, causando la hidrocefalia.

6. Childhood tumours Obstructive hydrocephalus is caused by many childhood tumours, since these often occur in the mid-line posterior fossa; the suprasellar region; the 3rd ventricle; and the pineal region. Although controversial, it is not common practice to perform a preoperative shunt placement unless the child is very symptomatic from hydrocephalus and cannot be taken right to surgery for tumour removal. In most childhood tumours, the hydrocephalus is treated preoperative, blocking carbonic anhydrase and decreasing CSF production. This relieves elevated intracranial pressure. The surgery to remove the tumour should have as a major goal to open the blocked CSF pathways, frequently avoiding a shunt. Only 20% of children will need a shunt postoperatively. A temporary ventriculostomy is usually needed to control ventricular size in the immediate postoperative period.

7. Cysts Hydrocephalus causes also include various types of cysts. A cyst is a closed area of tissue forming a fluid filled pocket. A cyst will have its own membrane. Porencephalic cysts are located within the brain (adjacent to the ventricle), or arachnoid cysts located inside the ventricles or in the subarachoid space. The arachnoid cyst may require a separate shunt if it goes unnoticed if it goes unnoticed before the original surgical proceedure.