Also known as “water on the brain,” hydrocephalus is one of the most frequently seen problems in a busy pediatric neurosurgical practice. The term “water on the brain” is actually more of a misnomer. In reality most cases of hydrocephalus represent a build up of spinal fluid inside the brain. Everyone produces spinal fluid inside their brains every minute of their lives. This fluid is very similar to the liquid portion of blood and contains various salts and products such as sodium and glucose. The fluid is primarily produced in connected chambers within the brain known as ventricles. The fluid volume produced in an adult is about equal to one pint per day. This fluid then circulates through the ventricles and around the brain and spinal cord. Eventually it is reabsorbed over the surface of the brain into large veins which carry the fluid back to the heart. This orderly cycle of spinal fluid production, flow and absorption maintains a protective environment to the nervous system. In addition, there is no loss of fluids or the salts contained in the spinal fluid.
Hydrocephalus is that state in which something has occurred to prevent this orderly procession of events. If this occurs, there is a relative build up of spinal fluid in the brain which can lead to injury or even death if not treated. It is very important to realize that hydrocephalus is the result of some event on the nervous system and that a child’s prognosis is not so much based on the hydrocephalus as the cause of the hydrocephalus. While many cases have no clear cause, the following have been associated with the development of hydrocephalus; bleeding, infection, trauma, tumors, vascular problems, and structural problems. Some occur during pregnancy and others after birth. In addition, a small number can be transmitted genetically.
In early infancy hydrocephalus is usually detected by the family or pediatrician as a rapidly enlarging head. This may or may not be associated with symptoms such as vomiting, failure to thrive, irritability, delay or loss of developmental milestones. Later in infancy and into childhood, there are rarely rapid changes in head size, but rather symptoms as already described. Depending on the child’s age at the time of discovery various radiographic techniques are available to confirm the diagnosis. In the first six to twelve months of life, the diagnosis can often be made with an ultrasound of the brain. After the skull fuses the diagnosis is best made with MRI or CT. Each of these tests have their plusses and minuses, but overall most neurosurgeons would favor an MRI scan. While this test takes longer than a CT scan and usually requires sedation, it gives a much better picture of the brain and the possible cause of the hydrocephalus. This information may effect the treatment options for the child.
It is important to realize that while hydrocephalus is very treatable, the underlying cause may not be or may have caused irreversible damage to the brain. It is important for the doctors taking care of a child with hydrocephalus to determine if the problem is ongoing or if it has resolved but left enlarged but stable ventricles. This can sometimes be difficult to tell and often the decision will be based on many factors including symptoms, eye exams, changes in level of activity or school performance. In addition to this often the child will have repeated (serial) radiographic exams to look for changes in the ventricles.
If the diagnosis of hydrocephalus has been made there are rarely options other than surgery for treatment. If a definable mass is causing the obstruction of flow it may be possible if not essential to remove the mass and allow for normal flow and resolution of the hydrocephalus. More often then not the blockage cannot be removed and the fluid needs to bypass the normal circulation. Most surgeons use various types of systems called shunts to channel the fluid from the ventricles to other sites in the body such as the abdominal cavity, chest cavity or the heart. Each of these sites have various pros and cons, but by far and away the most popular for pediatrics is the abdominal cavity. Here the spinal fluid is absorbed onto the surface of the bowels to be returned to the blood stream along with the vital salts and other products it contains.
There are many different shunt systems on the market and there is no such thing as a luxury model versus an economy model. Most neurosurgeons are comfortable with one or more systems and utilize these almost exclusively. What is most important is that your surgeon be well trained in all shunt systems, and shunting methods. In its most simplistic form, a shunt is an inert plastic tube less than an eighth of an inch thick that allows for fluid to flow through it in one direction. There is usually a valve system that regulates the flow as well as a reservoir or “bubble” which can be felt through the skin. This reservoir allows for sampling of the spinal fluid with the use of a tiny needle if indicated to test for function or infection. Like all foreign bodies, the shunts can malfunction or become infected which will lead to the replacement of the shunt system.
In addition to these operations, certain types of hydrocephalus can be treated by making a tiny hole internally in the ventricle to reestablish normal flow. This procedure called a ventriculostomy is becoming very popular due to better surgical instruments and imaging techniques. As with shunts, the third ventriculostomy can fail over time, requiring further surgery. The risk of infection with a ventriculostomy is certainly lower than in shunting and this is one of the main reasons it has become an attractive alternative to shunting in the appropriate patient.
As mentioned earlier, the prognosis for successful management of hydrocephalus is excellent. It is however the underlying cause that will ultimately determine a child’s outcome.