Hydrocephalus literally means 'water in brain', but the term is used to denote an abnormal increase in the water content within the cavities of the brain. This clear fluid, called as 'cerebropinal fluid or CSF', is produced within cavities of the brain called 'ventricles', circulates within various channels, escapes the ventricles through small holes, bathes the brain surface from outside and gets absorbed in the large veins outside the brain by a special system. CSF is essential for brain functioning and production and absorption are matched. If, either the circulation or absorption of CSF gets hampered due to some reason, it leads to accumulation of the fluid inside the brain cavities, leading to enlargement of the cavities and pressure on the brain tissue, damaging brain cells, leading to potentially harmful effects - ranging from just headaches to head enlargement, physical incapacity, mental retardation, blindness and death.
Hydrocephalus is known from ancient times and it is supposed to occur in one in 200 live births. Hydrocephalus has many causes dependent on age of patient
- Causes in the pediatric population
- congenital (due to malformations like aqueductal stenosis or due to intrauterine bleeding in the brain
- acquired (complication of trauma, infection or tumour).
- In adults the causes are
- late onset aqueductal stenosis
- consequences of trauma
- bleed, infection and normal pressure hydrocephalus.
As far as management is concerned, hydrocephalus is classified according to the mechanism which leads to accumulation of the fluid in the brain cavities –
- Obstructive hydrocephalus – a structural lesion causes hindrance to the flow of CSF, blocking it within the ventricular system, e.g. aqueductal stenosis or a tumour tentorial notch preventing the CSF flow from IIIrd to IVth ventricle.
- Communicating hydrocephalus
- Sometimes, a third, Mixed type is proposed, when the mechanism is poorly or incompletely understood.
Surgeries for relief from this condition are obviously aimed at the drainage of the fluid, have been performed since more than 100 years. They can be grossly divided into external diversion procedures, called shunts (where the fluid is taken out of head with help of a tube and released into abdominal cavity or blood) or internal diversion procedures like ventriculostomy, where 'stoma' or opening is created for draining the trapped fluid inside the ventricle to the exterior of brain, to be absorbed by the natural mechanism. This opening could be done with a major open surgery (as was done long ago) or with help of an endoscope, called as endoscopic third ventriculostomy, or ETV. This ETV surgery is ideal for most of the cases of obstructive hydrocephalus and will be discussed in detail. ETV aims at forming a new pathway for 'internal' (intracranial) drainage of CSF, thus bypassing the 'obstruction', and hence, is more physiological as against 'external' drainage, shunt surgery.
The idea of ventriculostomy itself for the management of hydrocephalus was conceived long ago by one of the great pioneers of neurosurgery, Dr. Walter Dandy in 1920s. It had fallen out of favor due to high complications mainly because the instrumentation was underdeveloped.