"inadequate drainage of cerebral fluid resulting in an enlargement of the cerebral ventricles as a result of increased pressure in the brain"

1. Introduction

Hydrocephalus, the accumulation of "water on the brain", is due to an impairment in the circulation of the cerebrospinal fluid (liquor). To understand how this works, it is necessary to have some notions of skull and brain anatomy and of the formation and drainage of the liquor.

The brain is the largest organ within the skull. It has numerous blood vessels, and it is surrounded by cushioning liquor, you could almost say that the brain floats in it. Liquor is the cerebral fluid, which usually looks like water. Liquor is produced in cavities present in the brain, the ventricles. There are two side, or lateral, ventricles, a third ventricle (which is positioned in the centre) and a fourth ventricle, located in or under the cerebellum.

schematic representation of the liquor circulation.

Illustration: This longitudinal section of the brain shows a schematic representation of the liquor circulation.
bv = brain ventricles
4 = 4th ventricle
a = aqueduct

The liquor is produced by tufted tissue bands (the choroid plexus) in the ventricles. Daily production is between 400 and 500 ml. This also works if the pressure is increased. The total volume of liquor in and around the brain is approximately 150 ml. This means that the liquor is entirely renewed three times every day. The liquor's primary function is that of a shock absorbing cushion for the brain and also to ensure a good biochemical environment for the nerve cells. The normal liquor pressure in adults is approximately 15 cm water pressure (when lying down).

From the lateral ventricles, the liquor flows through two openings to the third ventricle. From there it flows via a narrow canal, the aqueduct, into the fourth ventricle. Through a three-part outlet in the fourth ventricle the liquor can finally flow out into the space around the brain. On the brain surface the liquor is again taken up into the bloodstream (we say that it is resorbed) through small folds and recesses (the arachnoid granulations) which are primarily located in the middle and on top of the brain. The production, circulation and resorption of liquor is an ongoing process. In normal circumstances there is an equilibrium, or balance, between production and removal from the system through resorption. When the liquor cannot leave the ventricles or be resorbed into the bloodstream, it accumulates in the ventricles, which causes them to expand, and this is the condition called hydrocephalus. Hydrocephalus due to excess production of liquor occurs only rarely and will not be discussed here. We will only take a further look at drainage anomalies as a cause of hydrocephalus.

2. Hydrocephalus can be subdivided into:

2.1. Obstructive hydrocephalus:

This condition occurs when the flow within the ventricle system is closed off. Because there is no connection between the innermost liquor spaces (the ventricles) and the spaces around the brain, this condition is also often called "non-communicating hydrocephalus". The causes of this type of hydrocephalus can include: congenital narrowing of the aqueduct, adhesions following infections, tumours in the brain cavities.

2.2. Communicating hydrocephalus:

This condition occurs when the flow is unimpeded, but the uptake into the bloodstream is impaired. This therefore involves a resorption disorder, which is why this form is also called "non-resorptive" hydrocephalus. This sometimes occurs due to adhesions after certain brain haemorrhages, after infections or with changes due to age. In addition, hydrocephalus can be congenital (present at birth) or be acquired later in life. A special form is called Normal Pressure Hydrocephalus.

1. Diagnosis

A diagnosis of hydrocephalus should always be considered whenever the patient presents with signs or symptoms indicating increased brain pressure. These signs and symptoms will depend on the patient's age. In infants, the cranial sutures and the fontanel are not yet closed. Therefore, the head will swell along with the enlargement of the ventricles. A frequent sign is rapid growth of the head, a stretched fontanel, distended veins, irritability, big eyes (the so-called "sunset eyes") and sometimes convulsions. In older children and adults, the skull is already closed and can therefore not expand. The increase in pressure as a result of the expansion of the ventricles of the brain often leads to headache, nausea and/or vomiting, blurred or double vision, listlessness and even drowsiness. A different clinical picture involves signs and symptoms sometimes occurring in older patients, such as confusion, forgetfulness, urinary incontinence and problems walking. These symptoms sometimes resemble those seen with dementia.

2. Examination

There are a number of examinations that can confirm a suspected case of hydrocephalus:

  • An ultrasound examination of the skull. This examination can faithfully reproduce the size of the ventricles, but can only be performed on children, when the fontanel has not yet fused.
  • Computer tomography (CT scan). In this examination, a rotating X-ray tube connected to a computer takes images that represent a section through the skull. Aside from (low) exposure to radiation, this is a routine examination that can be repeated multiple times if necessary. Other possible causes for the hydrocephalus, besides the enlarged ventricles, can also be shown.
  • Magnetic Resonance Imaging (MRI). This examination, which is entirely harmless, as the images are created by means of a magnetic field, resembles a CT scan, but is much more detailed. Certain techniques even make it possible to visualise the liquor flows. Currently, MRI equipment is still somewhat less available than that used for CT scans, both the equipment and therefore also the examination are much more expensive. However, MRIs are steadily encroaching on the role of CT scans.
  • Cisternography. In this examination, a small amount of radioactive material is introduced into the liquor by means of an injection in the back. Snapshots are taken on a number of different occasions over two consecutive days. This examination provides information on the flow and resorption of the liquor in the brain. It is still relatively rarely performed, but some doctors believe that it is useful when formulating a diagnosis of "Normal Pressure Hydrocephalus".

3. Treatment

Actually, the only treatment for hydrocephalus is surgery. It consists in bypassing the obstruction by creating a direct connection (a shunt) from the ventricles to the outside world (on a temporary basis, by means of an external drain) or on a permanent basis to another body cavity. Currently, the fluid is usually diverted towards the abdominal cavity or into the heart via a vein in the neck.

Shunt surgery (placing a drainage system from the brain to the heart or the abdominal cavity)