Different forms of hydrocephalus may be distinguished:

congenital, if it develops before or at birth.

acquired, if it develops after birth, for example after a head injury, meningitis, cerebral haemorrhage, or either neoplastic or cystic disease.

Hydrocephalus is commonly classified into two types:

Non-communicating or obstructive hydrocephalus

Communicating or non-obstructive hydrocephalus

Non-communicating hydrocephalus is caused by blockage of the circulation of CSF in the ventricular cavities. This blockage usually occurs at the level of the aqueduct of Sylvius and may also be seen in the foramina of Monro and other foramina. This type of hydrocephalus is commonly associated with clinical signs of raised intracranial pressure.

The major causes of non-communicating hydrocephalus are:

Congenital stenosis of the aqueduct of Sylvius
Arnold Chiari Syndrome (Spina Bifida)
Tumours of the posterior fossa.

Communicating hydrocephalus occurs when the circulation of CSF around the brain is disturbed or if the absorption sites are non-functioning.

The major causes of communicating hydrocephalus may be grouped into two categories:

Hydrocephalus due to excessive production of CSF:

• Choroid plexus papilloma (a very rare tumour)

Hydrocephalus due to impaired re-absorption of CSF:

• Idiopathic hydrocephalus, i.e. for which no cause can be found. This is commonly known as Chronic Adult Hydrocephalus (CAH) or, alternatively, Normal Pressure Hydrocephalus (NPH), as in this instance the hydrocephalus is usually associated with near normal intraventricular pressure.
• Post-meningitis hydrocephalus
• Post-haemorrhagic hydrocephalus (head injury, rupture of an aneurysm, or arterio-venous malformation, etc.).
• Hydrocephalus of the premature infant (following intraventricular haemorrhage, etc.).

The clinical manifestations of hydrocephalus occur as a result of ventricular dilatation and, in part, due to the increase in pressure within the cranium.

These manifestations may differ between patients and as a function of age; the clinical signs for instance in infants and young children, whose cranial bones have not yet completely fused together, are different from those seen in adults.

The usual symptoms of hydrocephalus in infants include:

downward shift in gaze (sunset eyes), behavioural difficulties (irritability, drowsiness etc) or even seizures.

Depending on the cause, raised intracranial pressure may produce signs in older children and adults. The major ones of these are:

consciousness disorders: drowsiness, progressive lethargy or even coma.

Other signs may be found and are examined for systematically by doctors. These include bradycardia or seizures.

The characteristic Hakim's Triad may be seen in normal pressure hydrocephalus, which is found mostly in adults:

psychiatric disorders, mimicking the appearances of dementia

This involves mostly slow and poor quality ideation and activity, with apathy and indifference, serious memory and orientation disturbance, particularly in time, loss of attention and unawareness of reality.

gait disorders, with instability

This is due to static abnormalities, which may develop into titubation. The person moves around slowly and with care and may, occasionally, walk on the spot. Turning around, or either starting or stopping suddenly leads to imbalance.

sphincter disturbance (incontinence++)

On occasions, the person is incontinent of urine and occasionally faeces. It is not clear whether this is due to inattention, reduced awareness or urgency of micturition. The patient may pass urine anywhere and soil his clothing.