Hydrocephalus

Definition

The word hydrocephalus derives from the Greek words hydro, meaning water, and cephalus, meaning head. Hydrocephalus is the result of the excessive accumulation of fluid in the brain. Traditionally, hydrocephalus has been described as a disease characterized by increased intracranial pressure (ICP), increased cerebrospinal fluid (CSF) volume, and dilatation of the CSF spaces known as cerebral ventricles.

Description

Hydrocephalus is the result of an imbalance between the formation and drainage of cerebrospinal fluid. This imbalance appears when an injury or illness alters the circulation of CSF; one or more of the ventricles of the brain become enlarged as CSF accumulates. However, hydrocephalus is not a single disease entity, as a wide number of underlying diseases are responsible for causing retention of CSF, resulting in ventricular dilatation and increased intracranial pressure (ICP). In infants and children, for example, hydrocephalus usually results from a birth defect, viral infection, head injury, hemorrhage, meningitis, or tumor.

In adults, the causes of hydrocephalus include brain damage due to stroke or injury, Alzheimer's disease, or obstruction of the ventricles. Often, the cause is unknown. Conditions responsible for hydrocephalus in a fetus include infantile congenital (present at birth) hydrocephalus, hydrocephalus associated with encephalocele or myelomeningocele, posthemorrhagic hydrocephalus in newborns, and postmeningitic hydrocephalus. Conditions responsible for hydrocephalus in adults include hydrocephalus following subarachnoid hemorrhage, idiopathic adult hydrocephalus, and posttraumatic hydrocephalus. Tumors can also result in hydrocephalus in both children and adults. Based on the different kind of CSF circulation in the brain, hydrocephalus can be divided into two types: communicating and non-communicating. In communicating hydrocephalus, the CSF circulation pathways are competent from the ventricles inside of the brain to the fluid spaces just below the third ventricle. Non-communicating (obstructive) hydrocephalus refers to hydrocephalus that

develops from a blockage of the normal circulation of CSF within the brain. In most cases, it refers to a blockage between the third and fourth ventricles.

Demographics

Overall incidence of infantile hydrocephalus is approximately one to two per 1,000 live births. The overall prevalence of hydrocephalus in the United States is about 0.5%. When cases of spina bifida are included, congenital hydrocephalus occurs in two to five births per 1,000 births. The incidence of acquired hydrocephalus in adults is not known because it occurs as a result of injury, illness, or environmental factors. Normal pressure hydrocephalus was found to be significantly more prevalent in males, and can occur in adults of any age group. The age distribution in children and teenagers is disputed.

Causes and symptoms

Approximately 16 oz (500 ml) of CSF are formed within the brain each day, by cells located on the wall of the four ventricles in the brain. Once formed, CSF circulates among all the ventricles before it is absorbed. The normal adult volume of circulating CSF is about 2 oz (150 ml). The CSF turnover rate is more than three times per day. Because production is independent of absorption, reduced absorption causes CSF to accumulate within the ventricles.

Hydrocephalus can be subdivided into three forms, involving the following:

• Disorders of cerebrospinal fluid circulation. Tumors, hemorrhages, congenital malformations, and infections can cause such obstructions in the circulation of cerebrospinal fluid.
• Disorders of cerebrospinal fluid absorption, resulting from diseases such as the superior vena cava syndrome and sinus thrombosis.
• Disorders of cerebrospinal fluid production: This is the less common form of hydrocephalus resulting from tumors that secrete cerebrospinal fluid in excess of its absorption.

Congenital hydrocephalus is thought to be caused by a complex interaction of genetic and environmental factors. The origin of hydrocephalus in congenital cases is unknown. Very few cases (less than 2%) are inherited (X-linked hydrocephalus). The most common causes of hydrocephalus in acquired cases are tumor obstruction, trauma, intracranial hemorrhage, and infection.

The two most common adult forms of hydrocephalus are hydrocephalus ex-vacuo and normal pressure hydrocephalus. Hydrocephalus ex-vacuo occurs when a stroke or injury damages the brain, yielding a brain substance. Although there is more CSF than usual, the CSF pressure may or may not be elevated. Normal pressure hydrocephalus is an abnormal increase of CSF in the brain's ventricles due to the gradual blockage of the CSF-draining pathways. This may result from a subarachnoid hemorrhage, head trauma, infection, tumor, or complications of surgery. The ventricles enlarge to handle the increased volume of the CSF, and the compression of the brain from within by the fluid-filled ventricles destroys or damages brain tissue. Fluctuation of CSF pressure from high to normal to low can also be present.

For congenital-onset hydrocephalus, early symptoms include enlargement of the head (increased head circumference), bulging fontanelles (soft spots) with or without enlargement of the head size, separation of sutures (the flexible and fibrous joints between the skull bones of an infant), and vomiting. Symptoms of continued hydrocephalus include irritability and muscle spasticity . Late symptoms of congenital-onset hydrocephalus seen in children up to five years of age include decreased mental function, delayed development, slow or restricted movement, difficulty feeding, lethargy, and delayed growth.

In children, symptoms depend on the amount of damage caused by ICP. Symptoms may be similar to many of those in infants or may include headache , vomiting, vision changes such as crossed eyes, uncontrolled eye movements, loss of coordination, poor gait (walking pattern), mental confusion, or psychosis. For adult-onset hydrocephalus, headaches and nausea are the most common symptoms. Other signs of the condition include difficulty focusing the eyes, unsteady gait, weakness of the legs, sudden falls, and a distinctive inability to walk forward. As hydrocephalus progresses, decreased mental activity appears, including lethargy, apathy, impaired memory, and speech problems. Urinary and bowel incontinence can also occur. During the final stage, dementia involving loss of movement, sensory functions, and cognitive abilities may result.

Diagnosis

Ultrasound can be used to diagnose prenatal hydrocephalus. Although fetal hydrocephalus may be an isolated finding, it is more frequently found along with other cerebral anomalies, including neural tube defects. Diagnosis after birth may be suggested by symptoms; however, imaging studies of the brain are the mainstay of diagnosis. Computed tomography (CT ) and magnetic resonance imaging (MRI) reveal enlarged ventricles and may indicate a specific cause of hydrocephalus, such as a tumor or hemorrhage. The presence of papilledema (elevation or swelling of the optic disc) also indicates that hydrocephalus that is well developed. In rare cases, long-standing hydrocephalus causes blindness.

Small abnormalities that may not be seen with CT scanning, such as cysts and abscesses, are often seen with MRI . These studies can also help the neurosurgeon differentiate between communicating and non-communicating hydrocephalus. In cases of suspected normal pressure hydrocephalus, a lumbar puncture (spinal tap) may help determine CSF pressure. Also, a cisternagram can be useful to evaluate the dynamics of CSF flow in the brain and spinal chord. Cisternography can reveal CSF concentration, obstruction, leakage, and pressure. Also, certain biochemical markers in the blood have been described in the disease. They include increased neurofilament light protein (NFL) and tau protein, both markers of neuronal degeneration; increased myeline basic protein (a marker of demyelination; and albumin); and a marker of the blood-brain barrier function.

Treatment team

Treatment of hydrocephalus for children or adults will likely involve a neurologist , neurosurgeon, obstetrician, pediatrician, and specialty nurses and physical therapists.

Treatment

Medical treatment is first aimed at reducing intracranial pressure, while the need for a more permanent solution is determined. Reduction of fluid intake and administration of drugs such as mannitol, glycerol, urea (drugs with an osmotic effect), or furosemide (a diuretic) are able to reduce ICP and CSF production.

External drainage of the CSF is useful for urgent reduction of intracranial pressure, as well as of ventricular or subarachnoid hemorrhage. Complications include overdrainage, blocked tube, or bacterial contamination. The placement of a permanent ventricular shunt (internal shunting) is a common procedure. Around 33,000 shunts are placed in the United States each year; almost half of them to replace previous shunt devices. CSF from the ventricles in the brain is usually shunted to the peritoneum, pleura, ureter, bladder, or vascular spaces such as the jugular or subclavian veins. Most shunts are connected to the peritoneum. Some shunts operate according to intracranial pressure by using a valve system able to regulate the flow at a pressure close to the normal values of ICP. Others are programmable and can be adjusted to open at a given ICP. Complications include overdrainage that may cause intracranial hypotension, subdural hematoma , shunt occlusion, and infection. The risk of shunt failure is greater within the first year (between 25–40% of shunts must be replaced). The subsequent failure rate is around 5% for each year.

Other surgical procedures include, in some cases, choroid plexectomy, third ventriculostomy, and ventricular reservoir. Ventricular reservoir is basically a catheter inserted into a ventricle of the brain to draw CSF. This procedure is much simpler than placing a full shunt system and is used to provide temporary control of ICP until a full shunt can be placed.

Recovery and rehabilitation

Hydrocephalus is a chronic condition, and clinical symptoms are based on the time of insurgence of the disease. With appropriate, early treatment, a normal lifespan with few limitations can be reached. After surgery, specially trained medical professionals carefully monitor the patient. Some symptoms such as headaches may disappear immediately due to the release of excess pressure. The symptoms associated with normal pressure hydrocephalus (walking difficulties, mild dementia, poor bladder control) may improve quickly, or may take weeks to months to improve. In some patients, little or no improvement is also possible.

The length of the patient's hospital stay will be determined by the rate of recovery. If neurological problems persist, rehabilitation may be required to further the patient's improvement. However, recovery may be limited by the extent of the damage already caused by the hydrocephalus. Because hydrocephalus is an ongoing condition, patients do require long-term follow up. Follow-up diagnostic tests, including CT scans, MRI, and x rays, may be performed to determine if the shunt is working correctly.

Clinical trials

Ventricular shunts are the most common surgical treatment for hydrocephalus and appear to be the safest. It is possible that choroid plexectomy and third ventriculostomy may become more feasible in the future if better procedures and equipment are developed.

As of mid-2004, several clinical trials to study hydrocephalus were underway, including a trial to evaluate the efficacy and safety of endoscopic choroid plexus coagulation with third ventriculostomy in the treatment of idiopathic normal pressure hydrocephalus, sponsored by the Frenchay Hydrocephalus Research Fund. The National Institute of Neurological Disorders and Stroke is sponsoring a study to establish the physiology of syringomyelia . Updated information on these and other ongoing clinical trials may be found at the National Institutes of Health website for clinical trials at <http://www.clinicaltrials.gov>.

Prognosis

Untreated hydrocephalus has a survival rate of 40–50%, with the survivors having varying degrees of intellectual, physical, and neurological disabilities. Prognosis for treated hydrocephalus varies, depending on the cause. If the child survives for one year, more than 80% will have a fairly normal lifespan. Approximately one-third will have normal intellectual function, but neurological difficulties may persist. Hydrocephalus not associated with infection has the best prognosis, and hydrocephalus caused by tumors has a very poor prognosis. About 50% of all children who receive appropriate treatment and follow up will develop IQs in the near-normal or normal range.

Resources

BOOKS

Matsumoto, Satoshi. Hydrocephalus: Pathogenesis and Treatment. New York: Springer-Verlag, 1991.

The Official Parent's Sourcebook on Hydrocephalus: A Revised and Updated Directory for the Internet Age. San Diego: Icon Group International, 2002.

Toporek, Chuck, and Kellie Robinson. Hydrocephalus: A Guide for Patients, Families and Friends. Sebastopol, CA: Patient-Centered Guides, 1999.

PERIODICALS

Arriada, N., and J. Sotelo. "Review: Treatment of Hydrocephalus in Adults." Surg Neurol. (2002) Dec 58 (6): 377–84.

Davis, G. H. "Fetal Hydrocephalus." Clin Perinatol. (2003) Sep 30 (3): 531–9.

Meier, U., and C. Miethke. "Predictors of Outcome in Patients with Normal-Pressure Hydrocephalus." J Clin Neurosci. (2003) Jul 10 (4): 453–9.

OTHER

"NINDS Hydrocephalus Information Page." National Institute of Neurological Disorders and Stroke. May 15, 2004 (May 22, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/hydrocephalus.htm>.

"What is Hydrocephalus?" Hydrocephalus Foundation, Inc. May 15, 2004 (May 22, 2004). <http://www.hydrocephalus.org/>.

ORGANIZATIONS

Hydrocephalus Association. 870 Market Street, Suite 705, San Francisco, CA 94102. (415) 732-7040 or (888) 598-3789; Fax: (415) 732-7044. [email protected]. <http://www.hydroassoc.org>.

National Hydrocephalus Foundation. 12413 Centralia Road, Lakewood, CA 90715-1623. (562) 402-3523 or (888) 857-3434; Fax: (562) 924-6666. [email protected]. <http://nhfonline.org>.

Antonio Farina, MD, PhD

Hydrocephalus

Definition

Hydrocephalus is an abnormal expansion of cavities (ventricles) within the brain that is caused by the accumulation of cerebrospinal fluid. Hydrocephalus comes from two Greek words: hydros means water and cephalus means head.

There are two main varieties of hydrocephalus: congenital and acquired. An obstruction of the cerebral aqueduct (aqueductal stenosis) is the most frequent cause of congenital hydrocephalus. Acquired hydrocephalus may result from spina bifida, intraventricular hemorrhage, meningitis, head trauma, tumors, and cysts.

Description

Hydrocephalus is the result of an imbalance between the formation and drainage of cerebrospinal fluid (CSF). Approximately 500 milliliters (about a pint) of CSF is formed within the brain each day, by epidermal cells in structures collectively called the choroid plexus. These cells line chambers called ventricles that are located within the brain. There are four ventricles in a human brain. Once formed, CSF usually circulates among all the ventricles before it is absorbed and returned to the circulatory system. The normal adult volume of circulating CSF is 150 ml. The CSF turn-over rate is more than three times per day. Because production is independent of absorption, reduced absorption causes CSF to accumulate within the ventricles.

There are three different types of hydrocephalus. In the most common variety, reduced absorption occurs when one or more passages connecting the ventricles become blocked. This prevents the movement of CSF to its drainage sites in the subarachnoid space just inside the skull. This type of hydrocephalus is called "noncommunicating." In a second type, a reduction in the absorption rate is caused by damage to the absorptive tissue. This variety is called "communicating hydrocephalus."

Both of these types lead to an elevation of the CSF pressure within the brain. This increased pressure pushes aside the soft tissues of the brain. This squeezes and distorts them. This process also results in damage to these tissues. In infants whose skull bones have not yet fused, the intracranial pressure is partly relieved by expansion of the skull, so that symptoms may not be as dramatic. Both types of elevated-pressure hydrocephalus may occur from infancy to adulthood.

A third type of hydrocephalus, called "normal pressure hydrocephalus," is marked by ventricle enlargement without an apparent increase in CSF pressure. This type affects mainly the elderly.

Hydrocephalus has a variety of causes including:

• congenital brain defects
• hemorrhage, either into the ventricles or the subarachnoid space
• infection of the central nervous system (syphilis, herpes, meningitis, encephalitis, or mumps)
• tumor

Hydrocephalus is believed to occur in approximately one to two of every 1,000 live births. The incidence of adult onset hydrocephalus is not known. There is no known way to prevent hydrocephalus.

Causes and symptoms

Hydrocephalus that is congenital (present at birth) is thought to be caused by a complex interaction of genetic and environmental factors. Aqueductal stenosis, an obstruction of the cerebral aqueduct, is the most frequent cause of congenital hydrocephalus. As of 2001, the genetic factors are not well understood. According to the British Association for Spina Bifida and Hydrocephalus, in very rare circumstances, hydrocephalus is due to hereditary factors, which might affect future generations.

Signs and symptoms of elevated-pressure hydrocephalus include:

• headache
• nausea and vomiting, especially in the morning
• lethargy
• disturbances in walking (gait)
• double vision
• subtle difficulties in learning and memory
• delay in children achieving 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. This leads to abnormal expansion of the skull.

Symptoms of normal pressure hydrocephalus include dementia, gait abnormalities, and incontinence (involuntary urination or bowel movements).

Diagnosis

Imaging studies—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.

Treatment

The primary method of treatment for both elevated and normal pressure 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 include glycerol, digoxin, and isosorbide.

Some cases of elevated pressure hydrocephalus may be avoided by preventing or treating the infectious diseases which precede them. Prenatal diagnosis of congenital brain malformation is often possible, offering the option of family planning.

Prognosis

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.

Resources

BOOKS

Toporek, Chuck, and Kellie Robinson. Hydrocephalus: A Guide for Patients, Families & Friends. Cambridge, Mass.: O'Reilly & Associates, 1999.

PERIODICALS

"Hydrocephalus." Review of Optometry 137, no. 8 (August 15, 2000): 56A.

ORGANIZATIONS

Association for Spina Bifida and Hydrocephalus. 42 Park Rd., Peterborough, PE1 2UQ. UK 0173 355 5988. Fax: 017 3355 5985. [email protected]. 〈http://www.asbah.demon.co.uk〉.

Hydrocephalus Foundation, Inc., (HyFI). 910 Rear Broadway, Saugus, MA 01906. (781) 942-1161. [email protected]. 〈http://www.hydrocephalus.org〉.

OTHER

"Hydrocephalus." American Association of Neurological Surgeons/Congress of Neurological Surgeons. 〈http://www.neurosurgery.org/pubpages/patres/hydrobroch.html〉.

"Hydrocephalus." Institute for Neurology and Neurosurgery. Beth Israel Medical Center, New York, NY. 〈http://nyneurosurgery.org/child/hydrocephalus/hydrocephalus.htm〉.

"Hydrocephalus." National Library of Medicine. MEDLINEplus. 〈http://www.nlm.nih.gov/medlineplus/hydrocephalus.html〉.

KEY TERMS

Cerebral ventricles— Spaces in the brain that are located between portions of the brain and filled with cerebrospinal fluid.

Cerebrospinal fluid— Fluid that circulates throughout the cerebral ventricles and around the spinal cord within the spinal canal.

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 small tube placed in a ventricle of the brain to direct cerebrospinal fluid away from the blockage into another part of the body.

Stenosis— The constricting or narrowing of an opening or passageway.

Subarachnoid space— The space between two membranes surrounding the brain, the arachnoid and pia mater.

Hydrocephalus

Two types of hydrocephalus

Resources

Hydrocephalus, which means literally water on the brain, is a condition in which excessive fluid collects inside the skull. The fluid is a naturally produced liquid that normally is found in the brain. Accumulation of excessive amounts of the fluid may build pressure to levels that cause brain damage and subsequent disability. According to the Hydrocephalus Foundation, just over one in 1,000 live births are affected by hydrocephalus in the United States, with the disorder being one of the more common birth defects, afflicting over 10,000 babies in the United States annually. In the U.S., over the past 30 years, the death rate from hydrocephalus has decreased from 54 to 5%. As of 2006, the World Health Organization states that one in every 2,000 live births involve hydrocephalus on a worldwide basis.

The brain rests within the natural bony vault of the cranium. There it is protected by the skull and by layers of fibrous material that help to stabilize it and to contain the fluid that surrounds it. The brain itself is a very soft, gelatinous material that requires substantial protection. Three layers of connective tissue line the skull and surround the brain. The pia mater (which means literally tender mother) lies directly on the brain, following its contours and continuing along the spinal cord as it descends through the spine. The second layer is the arachnoid (like a spider’s web), a very thin, fibrous membrane without blood vessels. It, too, lies close to the brain but does not follow its every bump and wrinkle. The space between the pia mater and the arachnoid, called the subarachnoid space, contains the arteries and veins that circulate blood to the brain and the cerebrospinal fluid that bathes the nervous tissues. The outermost layer, the dura mater (hard mother) is a two-layered, leathery, tough membrane that adheres closely to the inside of the skull. The inner layer is contoured to the brain to support it. The outer layer lies against the cranium and continues into the spinal canal.

The fluid that bathes the brain and spinal cord—cerebrospinal fluid or CSF—is manufactured and secreted in the brain by a structure called the choroid plexus. Cerebrospinal fluid is a colorless, clear fluid that contains oxygen, some proteins, and glucose (a form of sugar). Normally the fluid will circulate through the cranium and down the spinal column. It will be absorbed by special structures called villi in the arachnoid tissue or it will drain from one of several outlets. Excessive fluid accumulates because the brain is manufacturing too much CSF or the drainage routes are blocked and the fluid cannot drain properly.

The capacity of the ventricles in the brain and the space around the spinal cord is approximately 0.5 c (125 ml). The choroid plexus manufactures from 2 to 3 c (500 to 750 ml) of fluid each day. The pressure of the CSF within the nervous system, therefore, is related to the rate of manufacture versus the rate of drainage of the fluid. Fluid pressure can be measured by inserting a needle between two of the lumbar vertebrae into the spinal canal. The needle is connected to a meter that indicates the fluid pressure.

The choroid plexus is composed of specialized cells that line the ventricles of the brain. The ventricles are four small, naturally formed cavities in the brain that act as reservoirs for CSF. Overproduction of fluid or its failure to drain can enlarge the ventricles and press the brain against the bony vault of the skull.

Newborn babies who have hydrocephalus often will develop grossly swollen heads. The bones of the skull have not fused and the pressure of the fluid inside the skull can expand the disconnected bony plates.

Two types of hydrocephalus

The two types of hydrocephalus are called communicating and noncommunicating. Communicating hydrocephalus is caused by overproduction of fluid by the choroid plexus. The fluid, which overwhelms the absorption capacity of the arachnoid, collects inside the ventricles as well as outside the brain. This is the most common form of hydrocephalus occurring in adults and is the result of injury or infection such as encephalitis. At the onset of the condition, the patient will become clumsy in walking and appear tired. Other signs will develop indicating a brain injury. To diagnose communicating hydrocephalus the physician will review the patient’s recent history to determine whether an infection or head injury has occurred. In addition, such diagnostic measures as a magnetic resonance image (MRI) of the skull can reveal the presence of excess fluid. This condition is readily treatable.

Noncommunicating hydrocephalus is the most common form of the condition in childhood. Usually it will be diagnosed immediately after birth, when signs such as a swollen cranium are seen. Here the problem lies in a narrowing of a drainage aqueduct that inhibits passage of the CSF out of the cranium. The ventricles enlarge greatly and the fluid pressure begins to push the brain against the skull. In this case a drain can be implanted in the skull to drain the fluid into a vein to relieve the pressure.

This form of hydrocephalus also is associated with a congenital condition called meningomyelocele. A newborn with this condition is born with the spinal cord and its superficial coverings exposed. The spinal canal, the opening through which the spinal cord passes, has not fused, so the cord can protrude through the open side. Almost always, the surgical repair of the meningomyelocele will result in hydrocephalus, which will in turn require surgical correction.

This form of hydrocephalus also can occur in an adult and generally is the result of the formation of a tumor that blocks the drainage area.

All forms of hydrocephalus can be treated surgically, so it is important that diagnosis be made as soon

KEY TERMS

Congenital —A condition or disability present at birth.

Hydro —Reference to water.

Lumbar —Reference to the lower back; the vertebrae below the ribs or thorax.

Meninges —Collectively, the three membranes that cover the brain and line the skull; the pia mater, arachnoid, and dura mater.

Tumor —An uncontrolled growth of tissue, either benign (noncancerous) or malignant (cancerous).

Ventricle —An opening in the brain that forms a reservoir for the cerebrospinal fluid.

as possible after the condition develops. With excessive fluid pressure inside the skull brain damage can occur, leading to various forms of disability. That can be avoided if treatment is timely.

See also Birth defects; Edema.

Resources

BOOKS

Al-Chalabi, Ammar. The Brain: A Beginner’s Guide. Oxford, UK: Oneworld, 2006.

Bear, Mark F. Neuroscience: Exploring the Brain. Philadelphia, PA: Lippincott Williams & Wilkins, 2007.

Larry Blaser

Hydrocephalus

Definition

Hydrocephalus is an abnormal expansion of cavities, called ventricles, within the brain, which is caused by an abnormally large accumulation of cerebrospinal fluid (CSF ).

Description

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 within the brain), infections such as meningitis , or other causes such as head trauma, tumors, and cysts.

Demographics

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)
• tumor

Signs and symptoms of elevated-pressure hydrocephalus include the following:

• headache
• nausea and vomiting , especially in the morning
• lethargy
• 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.

Diagnosis

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.

Treatment

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.

Prognosis

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.

Prevention

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.

Parental concerns

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:

• headaches
• nausea
• vomiting
• seizures
• change in intellect or personality
• swallowing problems
• impaired muscle function, balance, or coordination

KEY TERMS

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.

Resources

BOOKS

Cinalli, G., et al. Hydrocephalus. New York: Springer, 2004.

PERIODICALS

"Hydrocephalus." Review of Optometry 137, no. 8 (August 15, 2000): 56A.

ORGANIZATIONS

Hydrocephalus Foundation Inc. (HyFI). 910 Rear Broadway, Saugus, MA 01906. Web site: <www.hydrocephalus>.

WEB SITES

"Hydrocephalus." American Association of Neurological Surgeons/Congress of Neurological Surgeons. Available online at <www.neurosurgery.org/pubpages/patres/hydrobroch.html> (accessed October 22, 2004).

"Hydrocephalus." Hyman-Newman Institute of Neurology and Neurosurgery. Available online at <http://nyneurosurgery.org> (accessed October 22, 2004).

L. Fleming Fallon, MD, PhD, DrPH Deborah L. Nurmi, MS

Hydrocephalus

Definition

Hydrocephalus is an abnormal expansion of cavities (ventricles) within the brain that is caused by the accumulation of cerebrospinal fluid. Hydrocephalus comes from two Greek words: hydros means water and cephalus means head.

There are two main varieties of hydrocephalus: congenital and acquired. An obstruction of the cerebral aqueduct (aqueductal stenosis) is the most frequent cause of congenital hydrocephalus. Acquired hydrocephalus may result from spina bifida , intraventricular hemorrhage, meningitis, head trauma, tumors, and cysts.

Description

Hydrocephalus is the result of an imbalance between the formation and drainage of cerebrospinal fluid (CSF). Approximately 500 milliliters (about a pint) of CSF is formed within the brain each day, by epidermal cells in structures collectively called the choroid plexus. These cells line chambers called ventricles that are located within the brain. There are four ventricles in a human brain. Once formed, CSF usually circulates among all the ventricles before it is absorbed and returned to the circulatory system. The normal adult volume of circulating CSF is 150 ml. The CSF turn over rate is more than three times per day. Because production is independent of absorption, reduced absorption causes CSF to accumulate within the ventricles.

There are three different types of hydrocephalus. In the most common variety, reduced absorption occurs when one or more passages connecting the ventricles become blocked. This prevents the movement of CSF to its drainage sites in the subarachnoid space just inside the skull. This type of hydrocephalus is called "noncommunicating." In a second type, a reduction in the absorption rate is caused by damage to the absorptive tissue. This variety is called "communicating hydrocephalus."

Both of these types lead to an elevation of the CSF pressure within the brain. This increased pressure pushes aside the soft tissues of the brain. This squeezes and distorts them. This process also results in damage to these tissues. In infants whose skull bones have not yet fused, the intracranial pressure is partly relieved by expansion of the skull, so that symptoms may not be as dramatic. Both types of elevated-pressure hydrocephalus may occur from infancy to adulthood.

A third type of hydrocephalus, called "normal pressure hydrocephalus," is marked by ventricle enlargement without an apparent increase in CSF pressure. This type affects mainly the elderly.

Hydrocephalus has a variety of causes including:

• congenital brain defects
• hemorrhage, either into the ventricles or the subarachnoid space
• infection of the central nervous system (syphilis, herpes, meningitis, encephalitis, or mumps)
• tumor

Genetic profile

Hydrocephalus that is congenital (present at birth) is thought to be caused by a complex interaction of genetic and environmental factors. Aqueductal stenosis, an obstruction of the cerebral aqueduct, isthe most frequent cause of congenital hydrocephalus. The genetic factors are not well understood. According to the British Association for Spina Bifida and Hydrocephalus, in very rare circumstances, hydrocephalus is due to hereditary factors, which might affect future generations.

Demographics

Hydrocephalus is believed to occur in approximately 1–2 of every 1,000 live births. The incidence of adult onset hydrocephalus is not known. There is no known way to prevent hydrocephalus.

Signs and symptoms

Signs and symptoms of elevated-pressure hydrocephalus include:

• headache
• nausea and vomiting, especially in the morning
• lethargy
• disturbances in walking (gait)
• double vision
• subtle difficulties in learning and memory
• delay in children achieving 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. This leads to abnormal expansion of the skull.

Symptoms of normal pressure hydrocephalus include dementia , gait abnormalities, and incontinence (involuntary urination or bowel movements).

Diagnosis

Imaging studies—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.

Treatment and management

The primary method of treatment for both elevated and normal pressure 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 noncommunicating 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 include glycerol, digoxin, and isosorbide.

Some cases of elevated pressure hydrocephalus may be avoided by preventing or treating the infectious diseases which precede them. Prenatal diagnosis of congenital brain malformation is often possible.

Prognosis

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.

Resources

BOOKS

Drake, James M., and Christian Sainte-Rose. Shunt Book. Boston: Blackwell Science Inc., 1995.

Toporek, Chuck, and Kellie Robinson. Hydrocephalus: A Guide for Patients, Families & Friends. Cambridge, Mass.: O'Reilly & Associates, 1999.

PERIODICALS

Grant, Beth. "Hydrocephalus: diagnosis and treatment."Radiologic Technology 69, no. 2 (Nov–Dec 1997): 17–35.

"Hydrocephalus." Review of Optometry 137, no. 8 (August 15, 2000): 56A.

ORGANIZATIONS

Association for Spina Bifida and Hydrocephalus. 42 Park Rd., Peterborough, PE1 2UQ United Kingdom. 01 73 355 5988. Fax: 017 3355 5985. [email protected]. <http://www.asbah.demon.co.uk>.

Columbia Presbyterian Medical Center. Dept. of Neurological Surgery, 710 West 168 St., New York, NY 10032. (212) 305-0378. Fax: (212) 305-3629. <http://cpmcnet.columbia.edu/dept/nsg/PNS/Hydrocephalus.html>.

Hydrocephalus Association. 870 Market St., Suite 705, San Francisco, CA 94102. (415) 732-7040 or (888) 598-3789. (415) 732-7044. [email protected]. <http://neurosurgery.mgh.harvard.edu/ha>.

Hydrocephalus Foundation, Inc. (HyFI), 910 Rear Broadway, Saugus, MA 01906. (781) 942-1161. [email protected]. <http://www.hydrocephalus.org>.

WEBSITES

"Hydrocephalus." American Association of Neurological Surgeons/Congress of Neurological Surgeons <http://www.neurosurgery.org/pubpages/patres/hydrobroch.html>.

"Hydrocephalus." Beth Israel Medical Center, New York, NY. Institute for Neurology and Neurosurgery. <http://nyneurosurgery.org/child/hydrocephalus/hydrocephalus.htm>.

"Hydrocephalus." National Library of Medicine. MEDLINEplus. <http://www.nlm.nih.gov/medlineplus/hydrocephalus.html>.

L. Fleming Fallon, Jr., MD, PhD, DrPH