What is hydrocephalus?
The word hydrocephalus comes from two classical Greek words : húdôr (hydro) which means «water» and kephalě (cephalus) which means «head». Nowadays, the term hydrocephalus indicates excess of fluid within the cranium. This is a pathological condition which occurs as a result of imbalance between the production and absorption of CSF. The equilibrium described in the previous part is disrupted. Hydrocephalus only forms if the CSF is unable to leave the ventricular cavities or if its absorption is disturbed. The excess CSF will remain in the ventricles which become much bigger. These hydrocephalic ventricles are called “butterfly ventricles".
As the size of the cranium is fixed (except for children up to around 18 months of age in whom the fontanelles are still open), any increase in the volume of fluid within the ventricles affects the brain and can leads to the development of neurological symptoms due to an increase in the intracranial pressure (ICP), depending on brain compliance for instance.
The clinical manifestations of hydrocephalus occur as a result of ventricular dilatation and of the increased pressure within the cranium.
The usual symptoms of hydrocephalus in infants include:
- abnormal increase in head circumference and bulging fontanelles
- downward shift in gaze (sunset eyes)
- dilatation of the veins on the surface of the cranium
- vomiting and behavioural difficulties (irritability, drowsiness, etc) or even seizures.
Depending on the cause, raised intracranial pressure may produce different signs in older children and adults. The major signs are:
- headaches and vomiting
- visual disturbance (blurred vision, double vision, etc) with papilloedema, which is seen when the fundus of the eye is examined
- consciousness disorders (drowsiness, progressive lethargy or even coma).
Other signs may be found and are systematically looked for 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 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 sometimes 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.
Two different forms of hydrocephalus may be distinguished:
- Congenital, if it develops during pregnancy, at birth or later because of a birth condition that prevents the CSF from circulating and getting drained properly. A congenital hydrocephalus may be caused by a default during fetal development, a pregnancy disease such as toxoplasmosis or cytomegalovirus (type of herpes virus), or genetic inheritance.
- Acquired, if it develops after birth. It can affect any patient of all ages and is diagnosed, for example, after head injury, meningitis, cerebral hemorrhage or neoplasic disease.
Hydrocephalus is commonly classified into two types:
- Non-communicating or obstructive hydrocephalus: it is caused by blockage of CSF circulation 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 are congenital stenosis of the aqueduct of Sylvius, Arnold Chiari Syndrome (Spina Bifida) or tumours of the posterior fossa.
- Communicating or non-obstructive hydrocephalus: it occurs when the CSF circulation 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 caused by a choroid plexus papilloma, a very rare tumour,
- Hydrocephalus due to impaired re-absorption of CSF
In case of impaired re-absorption of CSF, four types of hydrocephalus can be observed:
- 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 case 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, and so on…);
- Hydrocephalus of the premature infant (following intraventricular haemorrhage, etc).