Definition of Hydrocephalus
CSF is produced primarily in the brain, by tissue known as the choroid plexus. Normally we make about four to five teaspoons of CSF an hour, regardless of age. The fluid then flows through the pathways as described above and ultimately gets resorbed back in the bloodstream. We should be absorbing the same four to five teaspoons an hour, such that the volume of CSF really doesn’t change much over time. Hydrocephalus is defined by excessive CSF, as a consequence of imbalance between the production and absorption of CSF. Most commonly it is absorption of CSF that is the problem. When this imbalance occurs, the ventricles and perhaps the SAS become enlarged as the fluid builds up. An analogous situation is like a sink with a faucet that is always on at a constant rate. As long as the drain at the bottom of the sink is open, there is no build-up of fluid. If the drain starts to get plugged then fluid will start to well up within the sink.
Signs and Symptoms
The way in which children with hydrocephalus are affected is dependent upon their age at the time of diagnosis. In children less than two years, the most common way it is detected is an abnormally rapid head growth. Rather than following a normal growth curve on a head circumference chart, these children start to cross curves and often ultimately exceed the curve for the 95th percentile. This occurs since the young child’s skull bones are not yet fused. Thus as the fluid builds up, it separates the bones and causes the skull to expand too quickly. Less frequently, children in this age group develop vomiting, excessive sleepiness, unexplained irritability, loss of development milestones or even developmental delay, downward deviation of their eyes and seizures. When examined, the soft spot tends to be full and the gaps between the skull bones are often split wider than normal. Children older than five years have skull bones that are less likely to expand as fluid builds up thus they tend to show signs of raised pressures within the brain itself. This typically causes them to complain of headaches, nausea with or without vomiting, listlessness or lethargy, unexplained irritability, loss of developmental milestones, change in behavior, change in school performance and rarely seizures. Medical examination of these children can range from normal to showing pressure induced changes in the eye nerves (papilledema), problems with eye movements, gait disorders and/or problems with cognition. Children between two to five may have a mixture of clinical findings that fall somewhere between the older and young age groups.
Several studies can be helpful in establishing the diagnosis of hydrocephalus, including ultrasound, computed tomography (CT) scan and magnetic resonance imaging (MRI). Ultrasounds are only useful in the very young children that still have open soft spots. This study is very good at looking at the size of the ventricles but doesn’t provide as much detail as a CT or MRI does about the structure of the brain tissue itself. A CT is sort of the middle-tiered study that gives both good views of the ventricles and brain tissue and can potentially identify sites of blockage within the brain. Sometimes the addition of intravenous contrast (dye) can add further information. The advantage of CT is that the study itself is quick so that sedation is not needed and thus can be scheduled in relatively short order. The most elaborate way of imaging the brain is MRI and this is certainly the best study to look at specific sites of blockage within the brain. A MRI, however, does require sedation or anesthesia if the child cannot hold still for at least 30 to 45 minutes. As a consequence it cannot be as easily scheduled as a CT scan. Thus, patients may have at least two of these studies done during the course of their evaluation.
Unfortunately, there is not a reliable, long-term non-surgical treatment for hydrocephalus. There are some medications available that might reduce production of CSF but they often cause significant side effects and are not effective over the long-term. There are two forms of surgical treatments that can be employed; the first is a ventricular shunt and the second is an endoscopic third ventriculostomy. The former can be used on all patients with hydrocephalus, whereas the latter is reserved for only those with non-communicating hydrocephalus.
A shunt is a device made of silastic that is placed under the skin and runs from the head to the belly (peritoneum), chest (pleura) or heart (atrial). Every shunt has three parts; the catheter that goes into the brain, the valve, and the tubing that goes to one of the three above mentioned distal sites. The shunt serves as a separate pathway to drain CSF in the brain that will ultimately be absorbed by the lining of the belly cavity, chest cavity or directly into the heart. The valve serves as a regulator of CSF flow through the shunt system. Surgery for placement of a shunt requires an incision in the head and over the site for the distal catheter (belly, chest or around the neck or collarbone). The surgery takes about one hour and children are usually discharged the next day. It is important to note these shunts are self-sufficient and do not require that you do anything to keep them working. You will see parts or all of the shunt as it bulges underneath the skin, particularly evident in the neck. This should not be of concern.
Shunts are mechanical devices and as such, are prone to malfunctioning. About 30 to 40% of all shunt failures occurs within one year of placement, 50% by five to six years; however, some can last a lifetime. If the shunt malfunction occurs the shunt will need to be “revised” to get it working again. There is no way of predicting how long any particular individual can go before the shunt needs to be revised. The signs and symptoms of shunt failure are similar to those that can be present at the time of the original diagnosis of hydrocephalus. If shunt malfunction is a concern then a evaluation will likely include some or all of the following: careful review of the symptoms, medical examination, a CT scan of the head, a series of x-rays to follow the course of the shunt to make sure it’s not broken (shunt series), abdominal ultrasound and maybe a shunt tap (where a small needle is inserted into part of the shunt to measure pressure within the brain and assess shunt flow). The most important feature in evaluation is review of the problems that the patient is experiencing followed by the results of the CT scan and shunt tap. Of note, in the presence of shunt malfunction, the CT scan does not necessarily have to show enlarged ventricles.
Once a functioning shunt is in place, we will see your child back in one month with a CT scan, which we will use as a baseline study to which further studies can be compared. Routine CT scans are not helpful unless the child has significant developmental delay and cannot communicate well. If stable, patients are usually followed on a once a year basis.
Endoscopic Third Ventriculostomy (ETV)
An alternative treatment for non-communicating hydrocephalus is a surgery known as endoscopic third ventriculostomy (ETV). In these cases the blockage of CSF flow occurs beyond the third ventricle and presumes that the ability to absorb CSF back into the bloodstream is normal. Thus, if a communication between the ventricle upstream from the site of the blockage and the subarachnoid space can be made, the hydrocephalus could be effectively treated. This is done by placing an endoscope into the lateral ventricle, and then under direct vision the tip of the device is guided into the third ventricle. The fluid within the ventricle can escape through the hole into the subarachnoid space and ultimately get absorbed back into the bloodstream through the normal pathways. In properly selected patients, about 80% can be effectively “cured” of the hydrocephalus by an ETV. The remaining 20% will need to be treated with a shunt.