HYDROCEPHALUS

DEFINITION

Hydrocephalus (hi-dro-sef-a-lus), commonly known as ‘water on the brain”, is a problem presenting most commonly in infancy. The incidence of hydrocephalus is 4 per 1,000 births. Hydrocephalus is termed “congenital” when it exists at birth, or “acquired” when it occurs as the result of injury to the brain after birth (examples are infection, bleeding or tumor).

INTRODUCTION

The head contains three main components: brain tissue, blood vessels, and clear liquid similar to salt water. This clear cerebrospinal fluid (CSF) makes up about 10% of the volume within the skull and has two main purposes. First, it cushions delicate brain and spinal cord tissues from injury. Secondly, it maintains the proper balance of protein, sugar and salts to nourish these central nervous system tissues. Cerebrospinal fluid is continuously made (approximately .3 cc per minute) in the ventricles. The ventricles are four connecting cavities deep within the brain which provide a pathway through which CSF circulates. At the back of the head, the CSF passes out of the brain and then over the surface of the brain and spinal cord and finally returns to the blood system through absorbing structures in the lining surrounding the brain. Under normal conditions, almost all this fluid is absorbed into the bloodstream, thus maintaining the delicate balance between production and absorption of CSF. When this system becomes unbalanced, almost always due to obstruction in the circulation pathways or malfunction of the CSF absorbers, production of CSF continues, excess fluid builds up in the brain and the condition known as hydrocephalus occurs.

TYPES OF HYDROCEPHALUS

The two major types of hydrocephalus are obstructive (or non-communicating) and communicating. Anything that interferes with the circulation of CSF acts much like a dam in a river. Just as a river above a dam expands into a lake, the CSF expands into a lake of fluid in the ventricles. In communicating hydrocephalus, there is a malfunction of the absorption mechanism that returns CSF to the bloodstream (usually due to birth defect or the result of a hemorrhage or meningitis) whereas obstructive hydrocephalus is usually due to blockage of the CSF pathways inside the brain (usually caused by tumors). In either type of hydrocephalus, the fluid accumulates in the ventricles. In order to accommodate the increased CSF volume, the ventricular system enlarges and pushes on the brain tissue and blood vessels. This increased pressure in the head (intracranial pressure or lCP) produces various symptoms, depending on the age of the patient.

DIAGNOSING HYDROCEPHALUS

In infancy and early childhood, the skull is not completely closed. The bones of the head are still pliable, and a “soft spot” or fontanels on the top of the head can be felt where the bones have not yet joined together. If the baby’s hydrocephalus is untreated, the head will grow too rapidly because the pressure inside it is high, and the fontanel will be larger than normal and bulge because of the increased tension. The doctor or nurse measures your child’s head with a tape and plots it on a chart. This allows detection of hydrocephalus by comparing rate of head growth to that expected for babies of similar age and weight. Fortunately, since the head has the ability to expand to accommodate the high volume of CSF, little damage to the brain results. The baby may feel poorly and be more irritable than usual when the head pressure increases.

As we get older, the points of union of bones (sutures) start to close and increased pressure will more easily damage brain tissue. Headaches, vomiting, drowsiness, blurred vision, decreased mental function and incoordination often are the warning signals.

The doctor may order a study to be performed. These are a highly sophisticated types of studies with which the neurosurgeon can note the size of the ventricles. During the scan, the subject has to lie still and if the patient is too young to cooperate, some medicine for sedation or anesthesia may be given that will make the youngster sleepy enough to lie still for the scan.

METHODS TO STUDY VENTRICULAR SIZE AND HYDROCEPHALUS

There are various techniques to “look inside” the head in a non-invasive method to see how much fluid is building up in the brain.

CRANIAL ULTRASOUND: This method uses ultrasound waves to map the ventricle size. The ultrasound device (transducer) is placed over the openings of the bony skull (fontanels). The ultrasound waves bounce off the ventricle walls and map out the anatomy through a computer system. Ultrasonography has the advantage of being a rapidly performed test, reliable, and some movement from the infant does not alter the technique. However, it can only be performed when the cranial bones have not united, so that when the fontanel is closed, another technique needs to be used, such as CT or MRI.

CRANIAL COMPUTERIZED TOMOGRAPHY: (CT scan) This is a technique that uses x-rays to show the anatomy. For this study, the patient needs to be completely still for 10-20 minutes. If not, the images come out blurred and cannot be used. For that purpose, in the smaller child, sedation or anesthesia is performed.

MAGNETIC RESONANCE IMAGING: (Cranial MRI) This technique employs a magnet to create a magnetic field that temporarily changes the position of some of the structures that make up the atoms of the brain. The signal sent out by them is then used by the computer to reconstruct the anatomy. This study may take a longer time to do than CT scans. Sedation and/or general anesthesia is mandatory for immobilization in the un-cooperative patient.

WHAT IS A SHUNT?

The primary treatment for hydrocephalus is to place a system which diverts or “shunts” CSF out of the brain to reduce pressure in the head. This is an acceptable method of drainage and indeed mimics the normal process by which CSF is absorbed back into the bloodstream. A better method would be to reduce the production of CSF to match the ability of the patient to absorb it but we have no such method.

A silicone rubber inflow tube, designed to be compatible with the body tissue, is inserted into the brain ventricle and is connected to a reservoir which is connected to an outflow silicone tube which is threaded under the skin down onto the peritoneal cavity (the abdominal cavity) where the CSF is gradually absorbed back into the bloodstream. This is called a ventriculoperitoneal (VP) shunt.

In some rare instances, the outflow tube is threaded into the atrial chamber of the heart instead of the abdomen, and this is called a ventriculojugular (VJ) shunt. The CSF is thus deposited directly into the bloodstream.

A third kind of shunt, called the lumboperitoneal (LP) shunt is inserted into the spinal canal at the bottom of a patient’s back (lumbar region) and is threaded around the waist just under the skin to again empty into the peritoneal cavity of the abdomen. This type of shunt does not involve entry into the brain but has the disadvantage of being difficult to regulate.

Successful treatment for hydrocephalus has been achieved only within the last fifty years using this relatively simple and safe shunt procedure. A baby’s head will continue to grow, even after the shunt has been placed, but at more normal rate. Within a period averaging two years, the child’s body and head should be in proportion to each other. As the child becomes taller, it is sometimes necessary to replace the original tube leading to the heart or abdominal cavity with a longer one, For many children, this lengthening operation will only be needed once, though some may need it done twice. Adults will not require a lengthening operation.

THE CHILD WITH A SHUNT AND SUBSEQUENT GROWTH

If effective treatment of hydrocephalus is begun early, the baby’s head may be relatively normal in size and development unimpaired. Ultimate outcome also depends on good follow-up care and the child’s innate intellectual and motor abilities. Most conditions that require ventricular shunting continue for the remainder of a person’s life. For this reason, it is extremely important to help the child lead a life as normal as possible. This is mainly accomplished by treating the child as any other child, both emotionally and physically.

ACTIVITY: There are generally no restrictions on daily living. The child should be allowed to perform those activities which he is capable of doing according to motor and developmental skills. The shunt is very tough and tolerates all activities including vigorous sports.

DIET: A balanced diet is very important because expansion of the bowels when the child is constipated may limit the entry of CSF into the peritoneal cavity. Increasing the amount of liquid and fruit consumed will usually relieve the problem. Consult your pediatrician if your child seems constipated.

SHUNT PUMP: If the shunt is the type that has the inflow end inserted into the ventricles, a lump will be felt under the scalp and is called the reservoir or pump. Normally, this chamber is soft and full of fluid. If it is compressed with the finger, it will empty and on release can be felt to refill. It is positioned here so that the doctor can easily test it and can also obtain CSF by puncturing the skin and pulling out the fluid with a needle. This is only done if one suspects an infection or if malfunctioning outflow tubing necessitates rapid reduction in the intracranial pressure by reducing fluid build-up in the head.

SHUNT MALFUNCTION

There are two main problems that may be encountered: shunt infection and shunt obstruction.

Shunt infection: This may manifest itself by fevers that keep recurring and treatment of other possible infections does not resolve the fevers. If this occurs, your neurosurgeon should be consulted for the possibility of a shunt infection. A “shunt tap”, wherein a fine needle is introduced into the reservoir and CSF is obtained, can be performed and the fluid sent to the lab and studied. If the shunt is infected, the usual treatment is antibiotic therapy and most often removal and replacement of the infected shunt with a clean one.

Signs of shunt infection:

1. Fever above 101 degrees rectally or 100 degrees orally or by axillary measurement
2. Persistent decreased appetite, abdominal swelling or pain
3. Redness, tenderness, and warmth along the shunt tract
4. Persistent decreased activity level or listlessness

Shunt obstruction: This is a common problem with shunt tubing. Tissues in the ventricles or in the peritoneal cavity can grow around the shunt tubing and plug up the inflow holes in the ventricles or the outflow slits in abdomen. This leads to a progressive rise in ICP and symptoms are then seen. Headache, vomiting, irritability, and progressive lethargy are the usual findings. The pediatrician first sees the young patient to see if there is an obvious cause such as a viral infection. He/she will examine the child and then order a CT scan. Unfortunately, the symptoms of shunt malfunction and infection are also the symptoms that all children get when they have the usual childhood illnesses. This means that it is especially difficult for parents to distinguish between other illness symptoms and those associated specifically with the shunt. It will take time to get comfortable with the situation and develop that sixth “shunt sense”.

Signs of malfunction:

1. Fever above 101 degrees rectally or 100 degrees orally or by axillary measurement
2. Persistent decreased appetite, abdominal swelling or pain
3. Redness, tenderness, and warmth along the shunt tract
4. Persistent decreased activity level or listlessness

Please don’t be afraid to be over-cautious in checking with your doctor when the patient exhibits any of these warning signs. Hydrocephalus is a serious illness that requires prompt diagnosis and treatment of problems.

HOW LONG WILL THE SHUNT HAVE TO STAY IN?

Nearly all conditions that cause hydrocephalus requiring shunt placement continue for the remainder of the person’s life. Research is being done on this subject presently, but most neurosurgeons agree that a hydrocephalic patient really depends on the shunt for continued well-being if an adult or continued developmental progress if a child. You may hear the doctor mention one of these terms: arrested hydrocephalus, normal or low-pressure hydrocephalus, or the “slit ventricle syndrome”. Each will be discussed further below, but you should keep in mind that these conditions usually occur in patients who have been doing fine for quite some time after shunt surgery.

ARRESTED HYDROCEPHALUS: This is a very rare occurrence. In certain cases of childhood hydrocephalus, changes in cerebrospinal fluid (CSF) circulation occur so that the ventricles stay at the normal size because pressure is balanced between these fluid-filled cavities and brain tissue. The hydrocephalus is said to be “arrested”. This balance can often be maintained by the body for many, many years. However, should fluid pressure again begin to build up in the head, the shunt is already in place to help maintain stability. If the shunt had been removed previously, another would have to be reinserted quickly to prevent brain damage from taking place. In the follow-up of possible arrested hydrocephalus, close monitoring of the motor and intellectual development is warranted. Any change in these two areas may indicate a pressure imbalance, and the doctor should be called. The CT scan and the MRI have allowed for a simple and safe method of following ventricular size in patients with arrested hydrocephalus, and may be ordered if a problem is suspected.

SLIT-VENTRICLE SYNDROME: Occasionally, children with hydrocephalus and a shunt will develop repeated, transient signs and symptoms of shunt dysfunction. The episodes, characterized as being very severe and coming on without notice, will oftentimes subside just as quickly and without treatment. The process behind this syndrome is felt to be a collapse of the ventricle’s walls around the shunt tubing because of a very good growth of the brain in size. The CT scan will reveal small, slit-like ventricles and one mode of treatment that may need to be performed if these episodes recur is a subtemporal decompression. This involves making another “compartment” by surgically removing part of the skull bone in the area of the temple. This will relieve some of the intracranial pressure that builds up occasionally around the too-small ventricles by permitting the expansion of the brain through the opening in the skull. The area of the surgery can be felt (whether as a depression or bulge) but of course, the brain is protected by muscle and skin.

PRESSURE HYDROCEPHALUS: This Is an interesting syndrome which can occur in the more senior patient and has no known cause but can come on after a minor head injury or for no clear reason at all. There is gradual enlargement of the ventricles causing thinning of the brain and malfunction characterized by dementia, decreasing facility in walking and often incontinence. Headache, a very common symptom of increased pressure hydrocephalus, is absent and a spinal tap will not record an elevated pressure. Even so, these patients can be helped by shunting if an evaluation by a neurologist or neurosurgeon indicates the presence of this disease. It can be very difficult to differentiate between this problem and the dementia associated with aging or with Alzheimer’s disease.

COMPARTMENTALIZED HYDROCEPHALUS: In certain situations, for no currently known reason, the ventricles may no longer remain connected with each other, and then the shunt system drains only part of the total of CSF that is made, since all the CSF can no longer reach it. This will create a local rise in pressure that can “press” on the surrounding brain and cause brain dysfunction. This may manifest itself with difficulty swallowing, difficulty breathing or apneic spells (cessation of breathing for a short time). The CT or MRI scan will clearly demonstrate the build-up of fluid in one of the ventricles. This may be treated by placing another shunt tubing into that particular ventricle. This will control the “local hydrocephalus”.

CONCLUSION

Although no one is ever certain that the shunt will be needed permanently, people should realize that, since characteristics of hydrocephalus may change over time, and since each person responds differently to shunting, a “lifetime” of hydrocephalus is probable.

The support that families of hydrocephalic children receive comes from a team of dedicated professionals. The pediatrician and neurosurgeon follow the child to monitor brain development and assure proper shunt function. Nurses and social workers are available to answer questions on topics ranging from care of the shunt system to meeting financial obligations, and provide parents with emotional support. Other paramedical staff are involved with coordinating services such as physical, occupational, and speech therapy. Finally, a school system which is geared to meet the needs of each individual student will help the hydrocephalic child reach his or her maximum developmental potential.