Hydrocephalus (Greek: water [in the] head), or, colloquially, “water on the brain”, can arise due to a number of causes, all of which result in an excess of cerebrospinal fluid (CSF), leading usually to an increase in the diameter of the inner CSF spaces, known as the ventricles, and a consequent increase in pressure inside the skull. An understanding of hydrocephalus requires knowledge of a few physiological facts and relationships:
Most CSF production takes place inside the ventricles through a system of ultrafiltration of blood through the walls of tiny blood vessels. From the lateral ventricles, the CSF flows via two paired openings (the foraminae of Monroe) to the central, third ventricle from where it trickles down a thin tube called the cerebral aqueduct into a final, fourth ventricle (see diagram). From here, the CSF leaves the ventricular system via three openings into the subarachnoid space where the CSF is free to flow around the brain and spinal cord. Most of the CSF is reabsorbed into the bloodstream here.
There are in principle two types of hydrocephalus:
This type of hycrocephalus occurs when cerebrospinal fluid (CSF) resorption is disturbed or, in rare cases, too much is produced. These situations lead to a pressure increase in the whole CSF system and to an increase in size of the ventricle system deep within the brain. Causes of impaired resorption include infection, bleeding or head injury. A special type of communicating hydrocephalus called normal pressure hydrocephalus is seen usually in older people and is due to a disturbance of the CSF flow dynamics resulting in intermittent CSF pressure changes.
This type of hydrocephalus is the result of an obstruction of the natural CSF pathways and results in an increase in size of the components of the ventricle system upstream of the blockage. Obstruction can result from a variety of factors including tumors, cysts or congential abnormalities and also sometimes occurs following bleeding which can block the narrow draining passages of the ventricles.
The symptoms of hydrocephalus result from the associated increase in pressure in the head, which may manifest as:
and in severe cases
In the case of normal pressure hydrocephalus, a classical combination of walking difficulties, bladder incontinence and dementia is described but not every case follows this pattern and the involvement of an interdisciplinary team is important to rule out other problems like Alzheimer’s disease and Parkinson’s syndrome first.
Hydcocephalus is diagnosed after considering symptoms, clinical findings and using neuroimaging in the form of CT and MRI. Particularly in non-communicating hydrocephalus, the cause of the blockage – such as a cyst or tumor – is often seen clearly on MRI. In cases of suspected normal pressure hydrocephalus it is usually necessary to confirm the diagnosis by draining some CSF during a lumbar puncture (spinal tap).
Therapy for hydrocephalusis dependent on the cause of the problem. The implantation of a shunt – a device to divert CSF to another compartment elsewhere in the body – is usually the best option in cases of communicating hydrocephalus. The operation usually takes just under an hour and involves the insertion of a fine tube into the ventricle and (invisible from the outside) tunnelling it under the skin to allow CSF to drain usually into the abdominal cavity (VP shunt). A magnetically-controlled pressure valve permits fine adjustments of flow and pressure parameters non-invasively from outside the body.
If a non-communicating (obstructive) hydrocephalus is diagnosed, it is often possible to use endoscopic techniques to make a small opening in the floor of the third ventricle (see video below), allowing free drainage of CSF into spaces where it can be naturally absorbed. In most cases the implantation of a shunt can be avoided with this approach. If the cause of a non-communicating hydrocephalus is a cyst in the region of the third ventricle (a colloid cyst) it is possible in most cases to remove the cyst and restore CSF flow using purely endoscopic techniques.