Hydrocephalus

The term hydrocephalus is derived from two words (Hydro = water, Cephalus = head). Hydrocephalus is a condition in which too much cerebrospinal fluid accumulates within the ventricles of the brain and may increase pressure within the cranium. The condition may occur at any age. The human brain is encased within the skull of the cranium, which provides it with significant protection. Inside the cranium, the brain floats in a sea of liquid, which is called cerebrospinal fluid (CSF). This fluid is constantly being produced in the brain and circulated around the brain and spinal cord in a regular pattern. The CSF is subsequently absorbed by mushroom-like structures over the brain called arachnoid villae, and is then returned to the bloodstream. The amount of CSF within the brain remains fairly constant. As a consequence the water pressure, which contributes to the overall pressure inside the skull [known as the intracranial pressure (ICP)] also remains fairly constant.

Hydrocephalus occurs when CSF circulation is altered in some way. For instance, the flow of CSF may be obstructed and the CSF may not be adequately reabsorbed into the bloodstream, or less often, too much CSF is produced. Obstruction of CSF flow can be the result of a birth defect, brain tumour, infection, haemorrhage, or brain injury. In some infants, particularly those born with spina bifida, the condition may accompany other malformations of the brain or spinal cord. The ability of the brain to absorb CSF may be reduced by a previous infection (meningitis) or brain injury. The production of too much CSF is usually caused by a rare brain tumour called a choroid plexus papilloma. The neurological examination will also help determine how severe the condition is. Further tests such as an ultrasound (if the patient is an infant), computed tomography (CT) scan, or magnetic resonance imaging (MRI) may be ordered if they have not already been performed.

Hydrocephalus can be treated in many ways. The problem can be treated directly (by removing the cause of CSF obstruction or overproduction if one can be found) or indirectly (by diverting the fluid build-up to somewhere else, typically into another body cavity by implanting a device known as a shunt that can divert the excess CSF away from the brain). The place into which the CSF is diverted is usually the peritoneal cavity (the area surrounding the abdominal organs).

Hydrocephalus is generally the end result of some other neurological condition so there is no uniform profile that fits every patient with hydrocephalus. However, some symptoms are common to many patients. Headaches, drowsiness, poor appetite, trouble walking, difficulty focusing the eyes, extreme irritability, urinary incontinence, increasing head size (in infants), weakness, or paralysis are examples. Medical intervention is necessary to determine and, if possible, treat whatever is causing the hydrocephalus and to relieve pressure on the brain from the excess fluid. Without treatment the patient may suffer irreparable damage from increased pressure within the brain and compression of vital brain tissues.

The brain is somewhat hollow in that there are cavities within it known as ventricles which are also filled with CSF. Actually, the CSF is produced within these cavities by a specialised tissue known as the choroid plexus. About 70 percent of the fluid produced by the central nervous system is secreted by the choroid plexus, a collection of blood vessels in the walls of the lateral ventricles. The fluid drains via interventricular foramina, or openings, into a slit-like third ventricle, which, situated along the midline of the brain, separates the symmetrical halves of the thalamus and hypothalamus. From there it passes through the cerebral aqueduct in the midbrain and into the fourth ventricle in the hindbrain. Openings in the fourth ventricle permit cerebrospinal fluid to enter so-called subarachnoid spaces surrounding both brain and spinal cord.

Typically, one or more ventricles become enlarged as CSF accumulates. There may be profound enlargement of the skull in very young children because the immature skull is not yet fused (joined together) and can therefore expand to accommodate the excess fluid. In an adult, the skull has fused and is quite rigid so the fluid cannot enlarge the skull and the water pressure may increase significantly. The increased pressure may be insidious and cause no symptoms until very late in the progression of the condition or it may cause symptoms such as headache, drowsiness, vomiting, mental disturbances, or difficulty with walking (especially in the elderly). These tests will provide useful information as to the type of hydrocephalus and its likely cause. The neurosurgeon may also request that you see other specialists such as a paediatrician (if your child is the patient) or an ophthalmologist (to accurately assess your vision).

Treatment

Hydrocephalus can be treated in many ways. The problem can be treated directly (by removing the cause of CSF obstruction or overproduction if one can be found) or indirectly (by diverting the fluid build-up to somewhere else, typically into another body cavity by implanting a device known as a shunt that can divert the excess CSF away from the brain). The place into which the CSF is diverted is usually the peritoneal cavity (the area surrounding the abdominal organs). This is known as a ventriculo-peritoneal shunt. Sometimes two procedures are performed, one to divert the CSF and another at a later stage to remove the cause of obstruction (e.g., a brain tumour). Once inserted, the shunt system usually remains in place for life (periodic adjustments may be necessary) and continuously performs its function of diverting the CSF away from the brain thereby keeping the intracranial pressure within normal limits. The shunt is basically a tube which is inserted inside one of the brain's ventricles . It is then inserted beneath the skin of the head, neck, and chest, and threaded into another body cavity or organ (peritoneal cavity, heart, gall bladder, chest, etc.) into which the CSF is drained and subsequently safely absorbed.

In order to properly regulate the amount of CSF being drained, an in-line valve is attached to the shunt. This valve allows CSF flow in a single direction only (away from the brain). One of several different valve systems will be selected by the surgeon depending on the patients particular needs. Each valve works in essentially the same way. It opens automatically when the pressure exceeds a certain limit and allows CSF to drain. The valve closes again when the pressure returns to the permitted level. Most shunt systems also contain a fluid-collecting reservoir and a cylinder through which a surgeon can access the system if needed. There are many types of shunts to choose from and the surgeon will select one that best suits the situation.

The surgical procedure to implant a shunt is relatively simple. A general anaesthetic is usually administered for the procedure. All or part of the hair over the scalp is shaved and the exposed area is then swabbed with an antiseptic solution to reduce bacterial contamination. The surgeon makes a small hole through the skull bone, usually in the back or front of the right side of the head . The shunt tubing is placed through this hole into the ventricle. Some CSF is collected for laboratory testing. To place a catheter in the peritoneal cavity, a small incision is made in the abdomen. Next, the ventricular and peritoneal catheters are attached along with a valve or reservoir. Antibiotics are often prescribed for a short period of time to reduce the risk of infection. There is minimal pain involved with this surgery, and the hospital stay is typically short. After surgery the shunt system is completely inside the body and often cannot be felt, even by experienced hands. Certain risks must be considered with any surgery. Although your surgeon will take every precaution to avoid complications, among the most common risks possible with shunt surgery are infection, malfunction, disconnection, or obstruction.

The sudden release of CSF during or after surgery can cause a subdural haematoma (blood clot) to form. Other possible risks include haemorrhage (excessive bleeding) within the brain. Although complications are rare, you should discuss these with your surgeon prior to surgery.

Recovery after surgery: the patient will be carefully observed in a neurological care unit, or elsewhere by specially trained nurses. Some symptoms such as headaches may disappear immediately because of the release of excess pressure build-up. Generally, the patient may be allowed to be up and about, and a gradual return to normal activity will be encouraged. The length of the patient's hospital stay will be determined by his or her rate of recovery and availability of support at home. By the time of your post-operative visit to the surgeon you may have noticed some further improvement and the incisions may be less sore. The skin sutures (stitches) are removed - that are not absorbable - and the incision will be examined. May also evaluate neurological function. If a neurological problem remains, rehabilitation may be necessary to maximize the patient's improvement. However, recovery may be limited by the extent of damage already caused by the hydrocephalus or associated condition and by the brain's limited ability to heal.

If further surgery is needed to remove a brain tumour or correct a birth defect, this may be scheduled for a subsequent operation. Follow-up tests may be required, including ultrasound, CT scanning, magnetic resonance imaging (MRI), or plain x-rays to ensure the shunt is working correctly.

Hydrocephalus - questions and answers

What is hydrocephalus? Hydrocephalus is a build-up of cerebrospinal fluid within and around the brain.

What is the cause of hydrocephalus? Cerebrospinal fluid (CSF) is a liquid (that is clear and looks like water) which is produced within the brain and which protects and nourishes the brain. The CSF is formed within pockets (called ventricles) within the brain. The brain contains four such ventricles - two lateral ventricles (located within each of the cerebral hemispheres), the third ventricle (in the middle of the brain), and the fourth ventricle (in the back, or posterior, part of the brain). The CSF is formed at a fairly constant rate from birth to adulthood: about 400-450 millilitres (ml) of CSF are produced each day. The CSF travels within the brain in a well-defined pathway, from the lateral ventricles to the third ventricle, and then from the third to the fourth ventricle. The spinal fluid passes between the third and fourth ventricles through a narrow passageway called the cerebral aqueduct. Once in the fourth ventricle, the CSF passes to the outside of the brain through three tiny holes near the base of the brain, and circulates around the outside of the brain and spinal cord before being absorbed back into the blood stream. Normally, the production and absorption of CSF are balanced so that the amount of CSF within the brain remains fairly constant.

Hydrocephalus occurs when there is an imbalance between CSF production and absorption. This can best be explained by making an analogy between hydrocephalus and a shower. The showerhead produces water, which flows into the shower stall and empties through the drain at the bottom of the shower. If the showerhead produces too much water, or the shower drain gets plugged, there is an imbalance between production and drainage and the water accumulates in the shower stall. Similarly, if CSF production is too fast (a very rare occurrence) or drainage is blocked in some way, then the CSF accumulates within the head and produces hydrocephalus. The ventricles become abnormally enlarged because they are filled with CSF; this enlargement can be seen on ultrasound, computed axial tomographic (CT or CAT) scans, or Magnetic Resonance Imaging (MRI) scans. As you can imagine, blockage of CSF can occur from a variety of conditions, including spina bifida and other birth defects of the brain, certain brain infections (like meningitis), haemorrhage within or around the brain (due to pre-maturity or a ruptured aneurysm), brain trauma, or tumours (just to name a few). In most cases, the underlying cause of the blockage is apparent. In a few, the cause may not be readily apparent. The blockage can be within the ventricles themselves (a condition that has been referred to as obstructive hydrocephalus) or outside the brain in the areas where the spinal fluid is reabsorbed back into the blood stream (a condition referred to as communicating hydrocephalus).

Why is hydrocephalus a problem? Once CSF begins to accumulate within the head, one of two things can happen. If the head is able to expand (which occurs in infants before the skull bones fuse), the head grows too quickly (this is one of the reasons a paediatrician should measure a child's head size at each visit up until about 3 years of age). If the head is unable to expand, then the accumulation of CSF causes the pressure inside of the head (the intracranial pressure) to increase. The rise in pressure can injure the brain and cause a variety of problems.

What are the signs and symptoms of hydrocephalus? In infancy (usually before 3 years of age) the head size grows too rapidly and the head becomes too large. The baby's soft spot at the top of the head may be full or tense. The baby may be irritable or unusually fussy. The appetite may be poor and repeated vomiting may occur. The eyes may be deviated downward (a condition referred to as sun-setting eyes or there may be limited ability to look upward. The eyes may cross. The infant or young child may have delays in development. In the older child in whom the skull bones have fused, the head size usually doesn’t grow abnormally. The increased intracranial pressure can cause headaches, irritability, nausea or vomiting, seizures (rarely), or a change in behaviour or school performance. Again, the child may have difficulty looking upward, have crossed eyes, or have sun-setting eyes.

How is hydrocephalus diagnosed? The diagnosis of hydrocephalus is usually made after obtaining some sort of radiographic study of the head. Unfortunately, plain X-rays of the head are not sufficient to diagnose hydrocephalus because they can only 'see' the bones; instead a test is used that will be able to 'see' inside of the head and visualise the brain itself. There are three possibilities. In the infant before the soft spot closes, an ultrasound of the head may show the enlarged ventricles. Once the soft spot closes, however, an ultrasound cannot 'see' inside the head any longer and either a CT or MRI scan must be used to visualise the brain and the ventricles. The CT scan is a quick, easy, and inexpensive way to diagnose hydrocephalus. It is sufficient in many cases of hydrocephalus, particularly when the cause of the hydrocephalus is already known. However, a CT scan involves a small amount of radiation, and it may not adequately detect some of the causes of hydrocephalus.

An MRI scan takes a lot longer to perform (and therefore may require sedation or even general anaesthesia for some infants and children), may be difficult for people who are claustrophobic, is more involved and expensive to perform. It often is not necessary to make the diagnosis of hydrocephalus, but may be very helpful in cases where the cause of the hydrocephalus is in doubt or if there are other abnormalities of the brain. In addition, the MRI scan can give information about whether the cerebral aqueduct (the passageway between the third and fourth ventricles) is blocked, and may suggest a newer form of treatment for hydrocephalus, called endoscopy.

How is hydrocephalus treated? The treatment of hydrocephalus since the 1950s has been a shunt. This is a device that allows the excess fluid to drain from the head to another part of the body, allowing it to be reabsorbed. One end is inserted into the ventricles of the brain, and the other end is passed under the skin to another part of the body. The most common site to divert fluid is to the peritoneal cavity (the cavity in the abdomen in which all of the intestines and abdominal organs are located) - this is called a ventriculo-peritoneal shunt. If the peritoneal cavity is not appropriate, the surgeon may choose to place the shunt into the pleural space (the cavity within the chest which surrounds the lungs - this is called a ventriculo-pleural shunt. A third common site to insert the shunt is into the jugular vein in the neck, called a ventriculo-jugular (sometimes also called a ventriculo-cardiac or ventriculo-atrial) shunt. The catheter is threaded into the jugular vein and down into the heart. Rarely, other sites such as the gall bladder are selected when no other site is available.

What is a shunt and what does it do? A variety of shunt systems are available, and all function similarly. The exact type of shunt chosen by the neurosurgeon is a matter of personal choice and the circumstances of the patient. The shunt has three basic components: a catheter (or tube) which is inserted into the brain ventricles, a valve which regulates the flow of spinal fluid and a long catheter which carries the CSF from the head to wherever the CSF is being diverted (the peritoneal or chest cavity, the jugular vein, etc.). Usually there is also a reservoir of some type, through which the shunt can be accessed through the skin if necessary. The shunt valve performs two functions. First, it allows fluid to go only in one direction - from the brain to the receptacle at the other end of the shunt. Second, the valve allows fluid to flow only when the pressure in the head exceeds some value (usually called the 'opening pressure' of the shunt). This prevents all of the CSF from being drained from the head.

What are the complications of a shunt operation? The most common problem encountered in patients with shunts is that the shunts can malfunction. Usually the problem is that the shunt catheter (either in the brain or the abdomen) becomes blocked with debris or tissue and the shunt can't properly drain. Rarely, the shunt valve becomes blocked or stops functioning. Shunt malfunctions occur in approximately 30-40% of children in the year after the shunt is inserted. By five years, approximately 60% of children will have had their shunts changed, and by 10 years, nearly 85% will have had at least one shunt revision.

What are the signs and symptoms of shunt malfunction? The signs and symptoms of shunt malfunction are the same as for hydrocephalus itself - headache, nausea, vomiting, irritability, change in behaviour or intellectual performance, etc.

How is a shunt malfunction diagnosed? A shunt malfunction is usually diagnosed with an ultrasound (in infants) or a CT scan (in older children and adults). The size of the ventricles is commonly compared with the 'baseline' ventricular size as seen on a scan done previously (usually while the patient was not having troubles). The ventricles are usually larger during a shunt malfunction. However, if a previous scan is not available to compare the ventricular size, it can be very difficult to be assured that the shunt is working correctly. Moreover, the ventricles may, in rare instances, change little or not at all, even when the shunt has malfunctioned. Therefore, if the signs of a shunt malfunction are unmistakable yet the CT or ultrasound shows no change in ventricular size, further diagnostic steps must be taken. Some doctors suggest pumping the shunt (by pressing on the skin overlying the shunt valve) to see if the shunt is functioning properly. However, others have demonstrated that there is little information to be gained from pumping the shunt and do not recommend this. Shunt function can also be assessed by performing a shunt tap. This is performed by washing the skin over the shunt with a sterile antibacterial solution and placing a small needle (similar to those which are used to draw blood) through the skin into the shunt (this procedure is about as uncomfortable as drawing blood). The spinal fluid pressure can be measured from the shunt and fluid withdrawn to test for infection. Fluid can also be withdrawn to see if symptoms improve temporarily.

What needs to be done if the shunt is malfunctioning? If a shunt obstruction is found, the shunt or certain parts will need to be replaced. Of course, the exact components that need to be changed depends upon which part of the shunt is occluded.

What other complications can follow a shunt operation? Shunt infections may arise after any shunt operation (insertion or revision), and occur in about 5-10% of cases. Most commonly the bacteria responsible are those that reside normally in the skin of the patient - Staphylococcus species. About 70% of infections occur within 8 weeks of the operation. Rarely, however, a shunt infection can occur in a delayed fashion. The signs of shunt infection may include fever, neck stiffness, light sensitivity (also called photophobia), headaches, or signs of shunt malfunction. The shunt may be reddened along its course under the skin, or the wounds may be reddened and/or draining pus.

Are there any other treatments for hydrocephalus? Although shunts have been a wonderful treatment of hydrocephalus, there have had their problems. Over a 10 year period, 85% of shunts will have had to be replaced at least once, and 20% of these patients will have had multiple operations to revise or replace malfunctioning shunts. Additionally, once shunts are placed, they usually are there with the patient for life - they control, but do not cure, hydrocephalus.

A new and very exciting operation for hydrocephalus has become popular in the last 10 years. Called endoscopy, these operations involve inserting a small endoscope (similar to, but much smaller than, the 'scopes used for gall bladder surgery or arthroscopy) into the ventricle through a tiny incision and a single small hole in the skull. The endoscope is connected, via a micro-camera, to a television monitor, on which the surgeon can see inside the ventricles. Using these endoscopes, neurosurgeons can now create a bypass, allowing CSF to flow around certain blockages and restoring normal CSF flow. Only certain patients are eligible for endoscopic surgery, and the patients must be selected carefully. In particular, patients with blockages within the ventricles themselves (those with obstructive hydrocephalus) are potentially candidates for endoscopic surgery.

What is endoscopic third ventriculostomy? Steering the endoscope down through the ventricles, the surgeon can make a hole in a very thin membrane in the bottom of the third ventricle to bypass the obstruction and directly communicate the ventricular fluid with the fluid around the outside of the brain (this is called an endoscopic third ventriculostomy). Going back to the bathroom shower stall analogy, if the drain is plugged and the water is building up, we can make another hole in the bottom of the shower to drain the excess fluid. Similarly, when the 'drain' is plugged, neurosurgeons can make an additional hole to drain the excess CSF.

Can the endoscope be used to do other procedures? Other endoscopic procedures can reduce the number of shunts that are required in specific cases. For example, a hole can be made (called fenestration) in the sheet of tissue that separates the two lateral ventricles to communicate them in instances where shunts have been (or would otherwise have to be) placed, eliminating the need for one of the two shunts and reducing the complications (especially from shunt malfunction). Certain cysts within the brain and/or ventricles can cause problems and can require the insertion of a shunt to control the fluid build-up in the cyst. Some of these cysts can similarly be fenestrated by making holes in their walls using the endoscope and communicating them with the rest of the ventricles. This may eliminate the need for a shunt into the cyst. Finally, although not directly related to hydrocephalus, endoscopes can be used to biopsy or remove small tumours within the ventricles of the brain. The advantage of the endoscopes is that, like other branches of medicine, the endoscopes are extremely small and operations can be performed through small incisions and very small openings in the skull, making the operation less painful for the patient and reducing the need for long hospital stays.

Contents