sections include: diagnosis and treatment
Hydrocephalus, from the Greek words meaning “water” and “head,” is caused by excess cerebrospinal fluid (CSF) in the spaces within and surrounding the brain.
Most cases of hydrocephalus occur in infants and children, at a rate of 3 in every 1,000 live births. However, people can also suffer hydrocephalus later in life in association with brain tumors intracranial hemorrhage, head injury, or meningitis (infection of the meninges covering the brain). We do not know exactly how common hydrocephalus is in adults, but adult cases account for approximately 40 percent of the total.
In the healthy brain, the choroid plexus produces CSF at a rate of approximately 1 pint per day. The fluid is secreted into the ventricles of the brain and subsequently flows into the spaces surrounding the brain and spinal cord. The average volume of CSF within the skull at any given time is about 5 fluid ounces.
CSF acts as a cushion to protect the brain and spinal cord. It also supplies the brain with such nutrients as minerals and proteins, and carries away the waste products of metabolism. Normally the body reabsorbs CSF through specialized channels that connect the ventricles with the superior sagittal sinus, a large vein that returns blood from the brain to the heart. This removal balances the rate of fluid production, producing a healthy equilibrium.
For hydrocephalus to develop, one of several factors must upset the normal flow of CSF:
- The brain produces too much CSF.
- Outflow from the ventricles is blocked, a condition called obstructive hydrocephalus.
- The bloodstream is unable to reabsorb CSF, leading to a relative excess of fluid, referred to as communicating hydrocephalus.
Each of these factors results in a buildup of fluid within the skull. In infants whose cranial sutures (the fusion joints between skull bones) have not yet closed, the extra fluid causes the head to expand. For older children and adults, whose skulls are already hardened, hydrocephalus produces increased pressure within the skull, and this increased pressure on the brain creates neurological symptoms. Some adults may exhibit swollen ventricles with no increase in pressure (referred to as normal-pressure hydrocephalus).
Because the skull of an infant can expand until the cranial sutures close, the most frequent sign of hydrocephalus in infancy is rapid head growth, associated with a bulging anterior fontanel (“soft spot”) when the infant is held upright and not crying. The cranial sutures may be separated and the skin overlying the skull may appear thin and transparent, with scalp veins clearly visible. In more advanced cases, the infant’s eyes may be directed downward, with the white of the eye visible above the iris—an appearance known as the setting sun sign. In babies with hydrocephalus, this sign is often accompanied by crossed eyes or abnormal involuntary eye movements. Parents should be aware, however, that both an enlarged head and the setting sun sign may appear in infants without hydrocephalus, so a pediatrician must consider various possibilities. If an infant with hydrocephalus is left untreated, over time he or she will lose developmental progress, including verbal and motor skills.
In children, hydrocephalic symptoms result from the effects of increased intracranial pressure. The most common acute symptoms are headache, vomiting, and lethargy (changes in consciousness). Chronic increases in pressure within the head will show up as intermittent, progressive headaches with nausea and vomiting, abnormal eye movements, and poor appetite. Eventually, continued brain damage will lead to behavioral changes and deteriorating performance in school.
Hydrocephalus in childhood has many possible causes. Prenatal hydrocephalus most commonly arises from genetic or sporadic developmental abnormalities that block the outflow of CSF from the ventricles. It can also result from maternal infections and disorders of the blood vessels. Problems appearing after birth include tumors or other masses (cysts, abscesses, and blood clots) that obstruct CSF flow; meningitis; hemorrhage; or blockage of the drainage channels into the bloodstream. In many cases, however, the cause is unknown.
Treated hydrocephalus has a very good prognosis: most children attain normal intelligence with few or no physical limitations. In some cases, a degree of neurological impairment may remain, such as a learning disability. But if the condition is untreated, it is debilitating and eventually lethal in 50 percent to 60 percent of cases. Prolonged delay in treatment, particularly in children, will cause irreversible brain damage.
In adults, the symptoms depend on the type of hydrocephalus. High-pressure symptoms include headache, nausea, abnormal gait, and visual disturbances. Symptoms of normal pressure hydrocephalus include dementia, abnormal gait, and urinary incontinence; the result may resemble Alzheimer’s disease.
Diagnosis and Treatment
Many cases of hydrocephalus are first diagnosed by pediatricians. A sudden increase in head growth can alert an infant’s doctor to possible hydrocephalus even before the head becomes very enlarged. Confirmed cases are referred to neurosurgeons for evaluation. Prompt diagnosis and treatment are extremely important, especially in children. Early relief of the increased pressure prevents the permanent developmental and neurological consequences that will otherwise occur.
Confirmed diagnosis is based on the history of the illness in combination with the doctor’s physical examination of the person and X rays. In infants, transfontanellar ultrasound—scanning the soft spot where bones have not yet fused—provides a simple and noninvasive diagnostic technique but is often not enough to make a definitive diagnosis. A computed tomography (CT) or magnetic resonance imaging (MRI) scan of the head is the best diagnostic test.
While the nature of hydrocephalus has been recognized for several centuries, successful surgical treatment was not possible until the twentieth century. Neurosurgeons knew that draining the fluid from the skull would be a useful treatment but were frustrated by technical impediments. Metal, plastic, and rubber tubes to divert the fluid, called shunts, caused severe tissue inflammation. A major boost was provided during World War II with the development of silicones, originally used as insulation in bomber spark plugs. Silicone elastomer (Silastic™) proved to be an excellent material for shunts because it did not inflame the tissues it touched. Another problem was overshunting, or removing too much fluid. In the 1950s, John Holter, an engineer with a hydrocephalic child, designed a pressure-sensitive valve that made it possible to control CSF drainage as needed.
Currently, the most widely performed treatment for hydrocephalus is to drain the excess fluid from the brain through a shunt into the abdomen’s peritoneal cavity, where the body can reabsorb it more easily. This operation is called a ventriculoperitoneal shunt, meaning a diversion from the ventricle to the peritoneum. One end of a flexible Silastic tube is inserted into a lateral ventricle of the brain. The other end is attached to a valve on the surface of the skull, which is connected to a second tube tunneled under the skin into the abdominal region, where its free end is tucked into the peritoneal cavity. Some shunts are fitted with on-off valves or other devices to regulate the drainage of CSF.
The ventriculoperitoneal shunt operation itself is generally straightforward. However, shunts can, and often do, become infected, blocked, or otherwise nonfunctional, especially in growing children. While some individuals need only a single shunt placement, others have to have multiple operations. The average number of replacements is about two per child. People with hydrocephalus and their caregivers should be aware of symptoms of increased intracranial pressure that could indicate that a shunt is malfunctioning, in which case they should notify a physician promptly. Children and adults with shunts for hydrocephalus should also avoid rough contact sports.
Surgeons can also alleviate some cases of obstructive hydrocephalus with endoscopic procedures that avoid shunt placement. The doctor inserts a small fiber-optic instrument (endoscope) into the ventricular system of the brain and relieves obstructions that impede CSF flow.
Medical treatment of hydrocephalus with drugs to retard the production of CSF is generally only a temporary measure, being ineffective in the long term.
While some researchers aim to perfect CSF shunts, the common malfunction of these devices suggests that other cures will ultimately be better. At present, approximately 25 percent of cases can be cured without shunt placement. This number should increase with more widespread use of endoscopic procedures and the development of specific drugs. In cases of hydrocephalus without a known cause, further research using animals that develop similar conditions should lead us toward a more satisfactory cure.
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