Hydrocephalus is an abnormal expansion of cavities, called ventricles, within the brain, which is caused by an abnormally large accumulation of cerebrospinal fluid ( CSF ).
Hydrocephalus is the result of an imbalance between the formation and drainage of CSF. There are four ventricles in the human brain. CSF is formed by structures within these ventricles. Once formed, CSF circulates among all the ventricles before it is absorbed and returned to the circulatory system. When the ventricles are obstructed, the CSF cannot circulate and be absorbed. An elevated level of CSF in the brain leads to pressure within the ventricles. This pressure pushes against the soft tissues of the brain, resulting in damage to these tissues.
There are three different types of hydrocephalus: communicating hydrocephalus, noncommunicating hydrocephalus, and normal pressure hydrocephalus. Communicating hydrocephalus is the most common type and exists when one or more passages connecting the ventricles become blocked. This blockage prevents the movement of CSF to its drainage sites in the subarachnoid space just inside the skull. In noncommunicating hydrocephalus, the tissue within the brain responsible for absorption of CSF is damaged. Normal pressure hydrocephalus is marked by ventricle enlargement without an apparent increase in CSF pressure. This type affects mainly the elderly and will not be discussed in this entry.
Hydrocephalus may be either congenital (present at birth) or acquired. An obstruction within the brain is the most frequent cause of congenital hydrocephalus. Acquired hydrocephalus may result from other birth defects such as spina bifida , conditions related to prematurity such as intraventricular hemorrhage (bleeding
Hydrocephalus is believed to occur in approximately one to two of every 1,000 live births. It is not more prevalent in males or females, nor in any individual racial group.
Causes and symptoms
Hydrocephalus has a variety of causes including the following:
- congenital brain defects
- hemorrhage, either into the ventricles or the subarachnoid space
- infection of the central nervous system (syphilis, herpes, meningitis, encephalitis , or mumps)
Signs and symptoms of elevated-pressure hydrocephalus include the following:
- nausea and vomiting , especially in the morning
- disturbances in walking (gait)
- double vision
- subtle difficulties in learning and memory
- delay in achieving childhood developmental milestones
Irritability is the most common sign of hydrocephalus in infants. If this is not treated, it may lead to lethargy. Bulging of the fontanelles, or the soft spots between the skull bones, may also be an early sign. When hydrocephalus occurs in infants, fusion of the skull bones is prevented, which leads to abnormal expansion of the skull.
Imaging studies such as x ray, computed tomography scan (CT scan), ultrasound, and especially magnetic resonance imaging (MRI) are used to assess the presence and location of obstructions, as well as changes in brain tissue that have occurred as a result of the hydrocephalus. Lumbar puncture (spinal tap) may be performed to aid in determining the cause when infection is suspected.
The primary method of treatment for hydrocephalus is surgical installation of a shunt. A shunt is a tube connecting the ventricles of the brain to an alternative drainage site, usually the abdominal cavity. A shunt contains a one-way valve to prevent reverse flow of fluid. In some cases of non-communicating hydrocephalus, a direct connection can be made between one of the ventricles and the subarachnoid space, allowing drainage without a shunt.
Installation of a shunt requires lifelong monitoring by the recipient or family members for signs of recurring hydrocephalus due to obstruction or failure of the shunt. Other than monitoring, no other management activity is usually required.
Some drugs may postpone the need for surgery by inhibiting the production of CSF. These include acetazolamide and furosemide. Other drugs that are used to delay surgery are glycerol, digoxin, and isosorbide.
The prognosis for elevated-pressure hydrocephalus depends on a wide variety of factors, including the cause, age of onset, and the timing of surgery. Studies indicate that about half of all children who receive appropriate treatment and follow-up will develop IQs greater than 85. Those with hydrocephalus at birth do better than those with later onset due to meningitis. For individuals with normal pressure hydrocephalus, approximately half will benefit by the installation of a shunt.
There is no known prevention of congenital hydrocephalus. Some cases of elevated pressure hydrocephalus may be avoided by preventing or treating the infectious diseases that precede them. Prenatal diagnosis of congenital brain malformation is often possible, offering the option of family planning.
Parents may be concerned about the intellectual development of a child with hydrocephalus. While nearly 50 percent of all children with hydrocephalus have average intelligence , many do not. Early intervention programs are important to the development of children with special needs and are available in most communities. In addition to developmental issues, many children with hydrocephalus require medical care. It is important for parents to prepare children for medical treatment and surgery. A healthcare team including a pediatrician, surgeon, and social worker is a valuable asset for parents and most children's hospitals can assist parents in finding the support and resources they need.
When to call the doctor
The most common treatment for hydrocephalus is the surgical installation of a shunt. If a child with a shunt has any of the following symptoms, parents should contact the child's doctor because the shunt may not be functioning properly. According to the Spina Bifida Association of America, nearly 40 percent of shunts malfunction and may need to be replaced within one year, 60 percent will require revision within five years, and 80 to 90 percent within ten years.
For this reason, parents need to be aware of the symptoms of shunt malfunction and contact their physician if they notice any of the following symptoms:
- change in intellect or personality
- swallowing problems
- impaired muscle function, balance, or coordination
Cerebrospinal fluid —The clear, normally colorless fluid that fills the brain cavities (ventricles), the subarachnoid space around the brain, and the spinal cord and acts as a shock absorber.
Choroid plexus —Specialized cells located in the ventricles of the brain that produce cerebrospinal fluid.
Fontanelle —One of several "soft spots" on the skull where the developing bones of the skull have yet to fuse.
Shunt —A passageway (or an artificially created passageway) that diverts blood flow from one main route to another. Also refers to a small tube placed in a ventricle of the brain to direct cerebrospinal fluid away from a blockage into another part of the body.
Ventricles —Four cavities within the brain that produce and maintain the cerebrospinal fluid that cushions and protects the brain and spinal cord.
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L. Fleming Fallon, MD, PhD, DrPH Deborah L. Nurmi, MS