Hydrocephalus and Its Types
The CSF produced daily in the brain circulates through the ventricles, passes to the brain surface, and is reabsorbed into the blood via the arachnoid villi. When the balance between production and absorption is disturbed, the ventricles swell and press on the brain. There are three basic types: in obstructive hydrocephalus there is a physical block in front of the flow (aqueductal stenosis, tumour, haemorrhage); in the communicating type the fluid flows freely but absorption is impaired; and normal-pressure hydrocephalus (NPH) is a treatable condition seen in the elderly, presenting with the triad of gait disturbance, urinary incontinence and dementia (Hakim’s triad). Distinguishing which type is involved (with a CSF-flow MRI when needed) is the basis of the treatment plan, because the method to be chosen depends entirely on this distinction.
Symptoms: From Infant to Elderly
Findings differ markedly by age. In infants whose fontanelle has not yet closed, a rapidly growing head circumference, bulging of the fontanelle, vomiting, restlessness and downward deviation of the eyes (the ‘setting sun’ sign) stand out. In older children and adults, a severe headache that worsens especially towards morning and comes with vomiting, blurred or double vision, balance disturbance and clouded consciousness come to the fore. In the elderly, the earliest sign of NPH is the ‘magnetic gait’, in which the feet feel stuck to the ground; to this are added urinary incontinence and weakening of attention and memory. The importance of NPH is that it is a reversible cause of dementia; that is why correct diagnosis is critical.
The Ventriculo-Peritoneal (VP) Shunt
The VP shunt is a permanent drainage device that carries the excess CSF from the ventricles to the abdominal cavity through a valve and tubes, where it is absorbed naturally. The system consists of a ventricular catheter, a valve that regulates flow, and a peritoneal catheter. It comes into play in communicating hydrocephalus, in NPH, in many infant and child cases, or in situations where ETV is not suitable. Its strength is that it can be applied across a very wide range of patients and quickly returns pressure to normal; in NPH, a significant proportion of patients are reported to have meaningful improvement in walking and cognitive function. Its weakness is lifelong dependence on the system and the accumulation over time of problems such as infection, blockage or fracture; in such situations, shunt revision may be required.
Endoscopic Third Ventriculostomy (ETV)
In ETV, a small hole (stoma) is opened in the floor of the third ventricle with the help of an endoscope, allowing the CSF to bypass the blockage and drain into the natural subarachnoid space; thus the body’s own absorption mechanism is reactivated. For the method to work, the blockage must be below the third ventricle and the absorption apparatus must remain intact; for this reason its main field of use is obstructive hydrocephalus such as aqueductal stenosis. Its greatest advantage is that it leaves no foreign body in the body, thereby reducing the risk of shunt infection to almost zero, and, when successful, offers a permanent solution. In uncomplicated cases the procedure takes 30–60 minutes and a 1–2 day stay is usually enough. By contrast, it is not suitable for every type of hydrocephalus (it is not preferred especially in the communicating type and in NPH), its chance of success is low in small infants, and it requires a certain surgical experience. Suitability is predicted before surgery with tools such as the ETV Success Score (ETVSS).
Which One 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 usually comes to the fore; in suitable obstructive cases ETV is the first choice. In infants under one year, because ETV success is low, a shunt is usually preferred. When a shunt is chosen, the valve type is also decisive: while fixed-pressure valves are suitable for simple and standard cases, programmable valves that can be adjusted from outside with a magnet without surgery gain value especially in NPH, in patients with a history of over-drainage, or in complex patients requiring multiple revisions. A programmable valve is more costly but, in the right indication, markedly raises shunt success. In NPH, before deciding on a shunt, a ‘tap test’ (CSF removal test) that helps predict the outcome can be performed. No method guarantees one-hundred-percent success in every patient; our aim is to choose the right method for the right patient.