Causes of hydrocephalus
The causes of hydrocephalus may be classified according to whether they are -:
Prenatal
This means the cause occurred before the onset of labour. The most common causes are malformations. These include -:
Chiari malformations (formerly called Arnold – Chiari malformations) which are problems with the base of the skull and the hole in the base of the skull (foramen magnum) that the spinal cord exits through into the neck. There are two types, which occur when the cerebellum (or hind brain which is responsible for coordination and balance) and brain stem are forced through the foramen magnum. Type 2 is associated with spina bifida. Chiari malformations are associated with hydrocephalus because there may be obstruction to the flow of cerebrospinal fluid (CSF) by the malformation. Symptoms from the malformation can present in childhood but most often present in adult life.
Depending upon the age of the child these may include characteristic headaches (worse on coughing, straining etc), sensory disturbance, visual disturbance with double vision or nystagmus (uncontrollable jerking movements of the eyes), swallowing problems, alteration in speech, poor coordination on walking, choking, breath holding attacks, brief recurrent respiratory arrests (apnoeic episodes), and opisthotonos (holding the head forced backwards).
Dandy Walker syndrome is a rare condition in which there is an abnormality of the fourth ventricle and the CSF spaces around the cerebellum and under-development of the cerebellum. About 90% of affected children have hydrocephalus. About 70% of affected children have associated abnormalities of the central nervous system (CNS). For example, 25% have underdevelopment of the corpus callosum (nerve tracts that connect the two sides of the brain). About one third of children have non – CNS malformations, for example, cardiac abnormalities. Children with Dandy Walker syndrome usually present with developmental delay and signs of hydrocephalus. Difficulty with balance, increased muscular tone and poor motor control are common. Associated problems may include respiratory failure due to poor respiratory control, swallowing problems, epilepsy, hearing or visual problems (nystagmus and tracking problems), and learning disability in a significant proportion of children.
Aqueduct stenosis
Narrowing of the cerebral aqueduct.
Chromosome abnormalities
Examples are Down’s syndrome and achondroplasia - like (restricted growth) syndromes.
Perinatal
This means the cause occurred between the onset of labour and the 28th day of life. The most common cause is intraventricular haemorrhage which is bleeding into or around the ventricles of the brain. Infection is also a common cause.
Intraventricular haemorrhage is more common in low birth weight, preterm and very preterm infants.
Postneonatal
This means the cause occurred after the 28th day of life. The most common causes are -:
- Idiopathic (i.e. there is no obvious cause)
- Infection - most commonly as a result of meningitis
- Haemorrhage - bleeding
- Tumours - especially those affecting the back of the brain, are a rare cause
