What Is Hydrocephalus and How Many Types Are There?
CSF produced in the brain each day circulates in the ventricles, passes to the brain surface and is absorbed into the blood by arachnoid villi. When the balance between production and absorption is disturbed, the ventricles swell and press on the brain. There are three main types: in obstructive hydrocephalus there is a blockage in CSF flow (aqueductal stenosis, tumor, haemorrhage); in the communicating type flow is free but absorption is impaired; normal-pressure hydrocephalus (NPH) is a treatable condition seen in the elderly that runs with the triad of gait disturbance, urinary incontinence and dementia (Hakim's triad). Distinguishing the type (with a CSF-flow MRI when needed) is the basis of the treatment plan, because the treatment method changes completely with the type. Saying 'there is hydrocephalus' alone does not define the plan; the question of whether it is obstructive, communicating or NPH must be answered.
Symptoms: From Infant to Elderly
Symptoms differ by age. In infants whose fontanelle has not yet closed, a rapidly enlarging head circumference, a bulging fontanelle, vomiting, irritability and downward deviation of the eyes (the 'sunsetting' sign) may be seen. In older children and adults, a severe headache that is especially marked in the morning and accompanied by vomiting, blurred or double vision, balance disturbance and confusion come to the fore. In the elderly the earliest sign of NPH is a 'magnetic gait' in which the feet feel stuck to the floor; urinary incontinence and weakening attention-memory are added. The importance of NPH is that it is a treatable cause of dementia; as the elderly population grows, making this diagnosis correctly becomes increasingly critical, because some patients thought to have Alzheimer's actually have NPH that can improve with a shunt.
Ventriculo-Peritoneal (VP) Shunt
A VP shunt is a permanent drainage system that diverts excess CSF from the ventricles via a valve and tubing to the abdominal cavity, where it is absorbed naturally. The system consists of a ventricular catheter, a valve that regulates flow and a peritoneal catheter, and works passively; it contains no battery. It is preferred in communicating hydrocephalus, in NPH and in many infant/child cases, or where ETV is not suitable. Its advantage is that it can be applied across a wide range of patients and quickly returns pressure to normal; in NPH significant improvement in gait and cognitive function is reported in a substantial proportion of patients. Its drawback is lifelong dependence on the system and the cumulative increase over time of complications such as infection, blockage or disconnection; in these situations shunt revision may be needed. The great majority of shunted patients return to school, work and daily life; swimming, walking and cycling are suitable, and only high-impact contact sports and deep diving are not recommended.
Endoscopic Third Ventriculostomy (ETV)
ETV is a method that, by endoscopically opening a small hole (stoma) in the floor of the third ventricle, allows CSF to bypass the blockage and drain into the natural subarachnoid space, engaging the body's own absorption mechanism. For it to succeed, the blockage must be below the third ventricle (at the level of the aqueduct) and the absorption mechanism must be intact; its main indication is therefore obstructive hydrocephalus such as aqueductal stenosis. Its greatest advantage is that it leaves no foreign body in the body, so the risk of shunt infection is almost zero, and when successful it offers a permanent solution. In uncomplicated cases the procedure takes 30–60 minutes and a 1–2 day stay is usually sufficient. Its drawback is that it is not suitable for every type of hydrocephalus (it is not preferred especially in the communicating type and in NPH), the chance of success is low in infants under one year, and it requires surgical experience because of the proximity of the basilar artery and the hypothalamus. Suitability is estimated before surgery with the ETV Success Score (ETVSS).
Which Method for Which Patient, and Programmable Valves
The decision is always made according to the type of hydrocephalus and the patient. In communicating hydrocephalus and NPH a shunt is usually used; in obstructive hydrocephalus ETV comes to the fore first if suitable. In infants under one year ETV success is low, so a shunt is mostly preferred; the ETVSS score gives objective guidance in this decision (age, aetiology and shunt history are scored). When a shunt is chosen the valve type also matters: fixed-pressure valves are suitable for simple and standard cases, while programmable valves that can be adjusted externally with a magnet without surgery are valuable especially in NPH, in those with a history of overdrainage or in complex patients requiring multiple revisions. A programmable valve is more costly but markedly increases shunt success in the right indication. In NPH a 'tap test' (CSF removal test) that helps predict the outcome may be done before the shunt decision. In selected cases such as idiopathic intracranial hypertension (pseudotumour cerebri), a lumboperitoneal (LP) shunt offers an alternative. No method gives a 100% guarantee of success in every patient; our aim is to choose the right method for the right patient.