Hydrocephalus occurs when there is a build-up of cerebrospinal fluid (CSF) within the head usually because of inadequate absorption of the CSF. Hydrocephalus can be likened to a bathroom tub with the faucet always on and a partially clogged drain. CSF is normally produced continuously by specialized brain cells within the ventricles (fluid filled pockets) of the brain. This CSF circulates first within the ventricles and later finds its way outside the brain where it bathes the brain and spinal cord; eventually, CSF is reabsorbed back into the blood stream. A blockage to the flow or drainage of CSF (analogous to a clogged drain) results in a build-up of CSF, enlargement of the ventricles, and increased pressure within the head. Most people with hydrocephalus have a partial blockage to the circulation or absorption of CSF and both the size and rate of growth of the ventricles is variable. Although most cases are straight-forward and obvious, for some people with only moderately enlarged ventricles and few or no symptoms, deciding when to treat can be difficult; in these cases, some neurosurgeons might treat the hydrocephalus whereas others might not. Unfortunately, there is no established minimum ventricular size that requires treatment, so there is disagreement on this issue.

The most common treatment for hydrocephalus is to insert a tube, called a shunt, between the ventricles and another part of the body to divert the excess CSF to another site where it can then be reabsorbed back into the blood stream. Shunts have valves that regulate both the direction and amount of CSF that is drained. All shunts have three essential parts – a ventricular catheter that is inserted into the ventricles of the brain, a valve of some sort (there are many different types), and tubing that carries the CSF from the valve to the area of the body that will accept the excess CSF. The most common types of shunts are ventriculo-peritoneal – or VP – shunts which drain the CSF from the ventricle to the abdominal cavity. Less commonly, ventriculo-atrial shunts (VA shunts, which direct the CSF into a vein, usually in the neck or under the collarbone), ventriculo-pleural shunts (which direct the CSF to the chest cavity around the lungs) or the ventriculo-gall bladder shunt (which directs the CSF to the gall bladder) are used.

There are several types of shunt valves, but all of them function similarly to control the amount of CSF that is drained. Most are made in several different pressure ranges that drain CSF when the pressure in the head exceeds the shunt valve pressure. Some valves may also have a siphon-control device that limits over-drainage of CSF. It is important to know that studies have not convincingly demonstrated a clear-cut advantage of one shunt system over another, and the choice of shunt system is generally left up to the neurosurgeon. Shunts may be inserted in one of three places on the head – at the edge of the soft spot (a frontal shunt), above and behind the ear (a parietal shunt), or in the back of the head (an occipital shunt). Studies have not consistently demonstrated any advantage of one over the other, and this too is generally left up to the surgeon's preference.

About 80% of people with Spina Bifida have hydrocephalus that requires treatment. Almost all shunts are inserted during the first days or weeks after the child's birth; occasionally the shunt will be inserted at the time of the initial back closure. A child who has not required a shunt by 5 months of age will likely never need one. In infancy, the signs of hydrocephalus (or of shunt malfunction) may include a rapid head growth; a full or tense soft spot (fontanelle) unusual irritability; repeated vomiting; crossed eyes or an inability to look up; periods in which the baby stops breathing (called apnea), difficulty swallowing; a hoarse or weak cry, difficulty in keeping the infant awake, or any worsening brain function. A head ultrasound, Computed Tomography (CT) scan, or a Magnetic Resonance Imaging (MRI) scan will show an increase in the size of the ventricles as the CSF builds up.

Shunt malfunction may be present even if it doesn't show on a CT or MRI scan. Newer treatments using small endoscopes may provide an alternative, long-term treatment and eliminate the need for a shunt. All patients with hydrocephalus should be evaluated by a neurosurgeon at least every 1-2 years.

Although there are exceptions, most people with Spina Bifida and shunted hydrocephalus will need the shunt for life. The most common problem with shunts is that they can plug or obstruct, break, or come apart, resulting in a shunt malfunction. About 40% of shunts will malfunction and need to be changed (or revised) within 1 year of insertion, 60% will require a revision within 5 years, and 80-85% within 10 years. About 20% will require multiple revisions in their lifetime.

The signs of shunt malfunction in the person with Spina Bifida are varied and can be confusing for both families and health care providers. The most common symptoms are headaches, with or without nausea and/or vomiting. It is important to recognize that vomiting is not always present, and projectile vomiting is rare. Less common symptoms of shunt malfunction can include seizures (either the onset of new seizures or an increase in the frequency of existing seizures); a significant change in intellect, school performance, or personality; back pain at the Spina Bifida closure site; worsening arm or leg function (increasing weakness or loss of sensation, worsening coordination or balance, and/or worsening orthopedic deformities); increasing scoliosis; worsening speech or swallowing difficulties; or changes in bowel or bladder functions. Shunt malfunction can mimic any of the symptoms of a Chiari malformation or spinal cord tethering. In fact, any worsening of brain or spinal cord function without another obvious cause should prompt a search for a potential shunt malfunction.

The evaluation of a possible shunt malfunction should include an imaging study of the brain (most commonly a CT scan or, for children under 1 year, a head ultrasound). Although MRI scans can also show a shunt malfunction, they generally are not necessary and are more expensive and may require sedation or anesthesia. An increase in the size of the ventricles is consistent with a shunt malfunction. It is vital to understand, however, that between 5 and 15% of people with Spina Bifida and shunt malfunction may have subtle or even no visible change in the size of the ventricles. At the extreme, some people with shunted hydrocephalus can develop the slit (or stiff) ventricle syndrome. In these people over-drainage of CSF leads to very small (or slit) ventricles; it is thought that the walls of the ventricles temporarily block the ventricular shunt catheter leading to repeated episodes of temporary shunt malfunction without any visible increase in the size of the ventricles. Families and health care providers must therefore pay particular attention to the patient's symptoms, particularly if they are similar to those that were present with previous shunt malfunctions.

Shunt infection is the other major complication of shunt operations. On average, about 5-10% of people will develop a shunt infection following each shunt operation; shunt infection rates are higher in babies than in older children and adults. Seventy percent of shunt infections appear within the first two months after a shunt operation, and 80% develop within 6 months. Skin bacteria (Staphylococcus epidermidis) are the most common types of shunt infection. Half of people with shunt infections present with symptoms of shunt malfunction. Additional problems may include fever or neck stiffness; pain, tenderness, redness, or drainage from the shunt incisions or tract; or abdominal pain. The diagnosis can be confirmed by performing a shunt tap — inserting a small needle into the valve or a tapping chamber of the shunt and withdrawing CSF for study.

Infections are generally treated both with antibiotics and with removal and replacement of the shunt system. There are two approaches to treatment. In the first, the shunt is removed and a temporary external drainage tube placed at the same time as antibiotic treatment is introduced, the temporary tube is then removed and a new shunt is re-inserted at the end of antibiotic treatment. This approach almost always eliminates the infection, but requires two operations. The second approach (assuming that the shunt is working) is to keep the infected shunt in place until the end of the antibiotic treatment, then remove and replace the infected shunt with a new one in a single operation. Although requiring fewer operations, this treatment is unfortunately less successful in treating the infection.

Nowhere in pediatric neurosurgery is clinical judgment so crucial, and misjudgment so treacherous, as in the evaluation of the person with Spina Bifida and shunted hydrocephalus. Advice to clinicians and families is simple:1) pay particular attention to a parent's (and particularly mom's) gut feelings about possible shunt problems – they are usually right; 2) a shunt malfunction can cause any number of symptoms that may not be obviously shunt related; and 3) therefore one should always maintain a high index of suspicion for shunt malfunction, and exclude a shunt malfunction before undertaking other neurosurgical treatments.

This information does not constitute medical advice for any individual. As specific cases may vary from the general information presented here, SBA advises readers to consult a qualified medical or other professional on an individual basis.