Hydrocephalus is a condition in which the flow of cerebrospinal fluid (CSF) in the central nervous system is interrupted or blocked. CSF is the liquid that circulates between the layers of tissue that cover the brain, within the ventricles (hollow cavities) of the brain, and around the spinal cord. It serves to cushion the structures of the central nervous system, deliver nutrients to the brain, and regulate the amount of blood within the brain. In normal circumstances, the CSF moves within the ventricles in the brain, exits through closed spaces at the base of the brain, flows over the surface of the brain and spinal cord, and is then reabsorbed into the bloodstream.
Hydrocephalus develops when there is an imbalance between the production of CSF and its reabsorption or when its flow is blocked. The cerebrospinal fluid builds up inside the brain, putting pressure on the tissues of the central nervous system and causing symptoms ranging from visual disturbances and headache to mental disturbances and difficulty walking.
Doctors classify hydrocephalus into several different categories:
- Congenital. This type of hydrocephalus is present at birth and may be caused by genetic disorders or problems that occur during the baby's development before birth.
- Acquired. Acquired hydrocephalus develops later in life as the result of brain tumors, head injuries, infections of the brain, or other brain disorders.
- Communicating. This type of hydrocephalus is one in which the CSF can flow between the ventricles of the brain but is blocked from leaving the brain.
- Noncommunicating or obstructive. In this type of hydrocephalus, the CSF cannot flow freely among the ventricles inside the brain.
- Normal pressure hydrocephalus (NPH). This is a form of communicating hydrocephalus most commonly found in the elderly. It is a condition in which CSF builds up within the ventricles of the brain.
The symptoms and course of hydrocephalus vary widely depending on the person's age, the cause of the condition, and its severity. In infants, the bony plates that form the skull have not yet completed their joining together. This incomplete development of the skull allows the infant's head to expand from the pressure of the CSF, sometimes very rapidly. The baby may vomit, sleep a lot, be irritable, or have seizures. In older children and adults, the skull has already completed its development and the buildup of CSF results in increased pressure on the tissues of the brain and spinal cord. Hydrocephalus in these age groups is more likely to produce such symptoms as headaches, double vision, vomiting, problems with balance or coordination, drowsiness, personality changes, or other signs of damage to the central nervous system.
Elderly adults with normal-pressure hydro-cephalus often have difficulties with bladder control and movement as well as dementia. Because these symptoms are also found in such disorders as Parkinson disease or Alzheimer disease, many older adults with NPH are never properly diagnosed or treated.
The exact number of people with hydrocephalus in the United States is not known because the disorder has so many possible causes—particularly acquired hydrocephalus—and because the diagnosis is often missed in elderly patients. The National Institutes of Health (NIH) estimates that there are 700,000 children and adults living with hydrocephalus in the United States. It is the leading cause of brain surgery for American children and costs the nation about $1 billion every year in health care expenses. The disorder is most common in the very young and the very old. About three babies in every 1,000 are diagnosed with congenital hydrocephalus. About 60 percent of cases of acquired hydrocephalus occur in children, with the remaining 40 percent in adults.
As far as is known, hydrocephalus is equally common in both sexes and in all races and ethnic groups.
Risk factors for hydrocephalus in infants and young children include:
- Premature birth. Prematurity increases the risk of bleeding into the brain.
- Spina bifida. This is a condition in which the spinal column fails to close completely over the spinal cord.
- An infection within the mother's uterus.
An Unusual Case of Hydrocephalus
In July 2007, the British medical journal The Lancet published a report by three French surgeons who had treated a forty-four-year-old man in a Marseille hospital for weakness in his left leg. When the doctors performed some imaging studies of the man's brain, they were amazed to find that the ventricles in his brain had filled with cerebrospinal fluid (CSF) to the point that his brain had been crushed against the sides of his skull. There was very little brain tissue left. The chief surgeon was quoted as saying, “The images [from the scans] were most unusual…the brain was virtually absent.”
The surgeons thought that the man's condition was the result of an operation he had had at the age of six months to treat hydrocephalus. Although the man had an IQ of 75, somewhat below normal, he had led a normal life without any unusual medical symptoms until his leg disorder. He was married and the father of two children and was employed as a civil servant. The surgeons treated the man by inserting a new shunt to drain the excess CSF, which relieved his leg symptoms and allowed him to return to work.
The causes of hydrocephalus range from genetic disorders and incomplete development before birth to brain tumors, head injuries, infectious diseases that affect the brain, and bleeding in the brain.
The symptoms of hydrocephalus depend partly on the patient's age:
- Infants: Enlargement of the skull; bulging of the soft spot at the top of the skull; veins in the scalp are enlarged; baby feeds poorly, vomits, has seizures, sleeps a great deal, or has eyes that look downward much of the time (“sunsetting”).
- Children: Headache; nausea; vomiting; fever; blurred or double vision; unstable balance; irritability; sleepiness; delayed progress in walking or talking; poor coordination; change in personality; difficulty staying awake or waking from sleep.
- Adults: Headache; constant drowsiness; loss of ability to think clearly or concentrate; difficulty walking; personality changes and loss of social skills. Job performance is often affected.
- Elderly adults: Loss of coordination or balance; shuffling gait, memory loss; headache; or bladder control problems.
The specific diagnostic techniques that the doctor will use depend on the person's age and recent medical history. The doctor will note the specific symptoms and when they first appeared. If the patient is an infant, his or her head will be measured and compared to the normal range for babies of the same sex and age. A head larger than 97 percent of the heads of normal children usually indicates hydrocephalus.
Older children and adult patients will usually be referred to a neurologist (a doctor who specializes in treating disorders of the central nervous system) for a complete evaluation of his or her vision, memory, coordination, and other functions that may be affected by hydrocephalus.
The neurologist will order one or more imaging studies of the brain in order to determine whether the hydrocephalus is communicating or noncommunicating and whether other abnormalities of the brain are present. Ultrasound is often used to evaluate hydrocephalus in infants, and computed tomography (CT) scans or magnetic resonance imaging (MRI) is used for older children and adults.
Normal-pressure hydrocephalus is diagnosed by lumbar puncture (spinal tap) followed by withdrawal of some of the cerebrospinal fluid. If the patient has NPH, their symptoms will usually improve after the fluid is removed. This test is known as the Fisher test.
The usual treatment of hydrocephalus, whatever its cause, is the surgical insertion of a shunt system. A shunt is a flexible plastic tube that carries extra CSF away from the brain. The shunt system consists of the shunt itself, a valve that keeps the CSF flowing in the correct direction, and a long thin tube called a catheter. The shunt is inserted into one of the brain's ventricles. The catheter and valve are attached to it, and the catheter tubing is threaded underneath the skin to another part of the body (usually the heart or the abdomen) where the excess CSF can be absorbed. The shunt system needs periodic replacement in children as they grow or in adults if the tubing becomes blocked or infected.
A few people with noncommunicating hydrocephalus can be treated by surgery on the third of the brain's four ventricles. In this procedure, the surgeon uses a miniature camera and instrument to locate the third ventricle and cut a small hole in its floor. This hole allows the CSF to bypass the blockage between the ventricles and flow toward its normal outlet from the brain.
Hydrocephalus cannot be cured. The outcome for a given patient is difficult to predict, as the condition has so many different possible causes. The insertion of a shunt system carries some risk of further brain damage. An estimated 50 percent of all shunts fail within two years, requiring further surgery to replace them. Since 1980, however, death rates associated with hydrocephalus have decreased from 54 percent to 5 percent; and intellectual disability in children with hydrocephalus has decreased from 62 percent to 30 percent.
The best way to prevent hydrocephalus in newborns is to take steps to reduce the risk of premature birth and to protect infants and small children against head injuries. In addition, vaccinating children against meningitis—a type of infection that can cause hydrocephalus—offers further protection.
Some possible new treatments for hydrocephalus as well as various improvements in shunt systems are currently being studied in clinical
trials. As of 2008 the NIH was sponsoring thirty-two separate trials for these treatments.
SEE ALSO Alzheimer disease; Brain tumors; Meningitis; Prematurity; Spina bifida; Stroke
WORDS TO KNOW
Dementia: Loss of memory and other mental functions related to thinking or problem-solving.
Shunt: A flexible plastic tube inserted by a surgeon to drain cerebrospinal fluid from the brain and redirect it to another part of the body.
Sunsetting: A term used to describe a downward focusing of the eyes.
Ventricle: One of four hollow spaces or cavities in the brain that hold cerebrospinal fluid.
Judd, Sandra J., ed. Brain Disorders Sourcebook, 2nd ed. Detroit, MI: Omnigraphics, 2005.
Judd, Sandra J., ed. Congenital Disorders Sourcebook, 2nd ed. Detroit, MI: Omnigraphics, 2007.
Jablons, Beverly. “Cases: A Mind Emerges after Years Lost in a Cloud.” New York Times, February 10, 2004. Available online at http://query.nytimes.com/gst/fullpage.html?res=9907E7DC173AF933A25751-C0A9629C8B63&sec=&spon=&pagewanted=all (accessed July 19, 2008). This is an article about the effects of undiagnosed hydrocephalus on a writer and her recovery following surgical treatment.
“Report: Man with Almost No Brain Has Led Normal Life.” Fox News, July 25, 2007. Available online at http://www.foxnews.com/story/0,2933,290610,00.html (accessed July 21, 2008). This is a news item about the patient in the Lancet article described in the sidebar. It includes a photo of the patient's brain scan.
American Association of Neurological Surgeons. Hydrocephalus. Available online at http://www.neurosurgerytoday.org/what/patient_e/hydrocephalus.asp (updated September 2005; accessed November 5, 2008).
Hydrocephalus Association. FAQs: What Is Hydrocephalus? Available online at http://www.hydroassoc.org/education_support/faq#22 (updated December 2007; accessed July 20, 2008).
National Institute of Neurological Disorders and Stroke (NINDS). Hydrocephalus Fact Sheet. Available online at http://www.ninds.nih.gov/disorders/hydrocephalus/detail_hydrocephalus.htm (updated June 23, 2008; accessed July 20, 2008).
National Institute of Neurological Disorders and Stroke (NINDS). Normal Pressure Hydrocephalus Information Page. Available online at http://www.ninds.nih.gov/disorders/normal_pressure_hydrocephalus/normal_pressure_hydrocephalus.htm (updated June 23, 2008; accessed July 20, 2008).
Neuroanimations. What Is Hydrocephalus? Available online at http://www.neuroanimations.com/Defn_Obst_Com/Definition.html (accessed July 20, 2008). There are other animations and text explanations of hydrocephalus on this website listed on the home page.