What is hydrocephalus?
Sometimes referred to as “water on the brain,” hydrocephalus is a disorder that can be congenital or acquired. The fluid is actually a relatively small amount (about 10 cubic centimeters for every kilogram of body weight) of cerebrospinal fluid (CSF), which surrounds and cushions the brain and spinal cord on both the inside and the outside. Within the brain are four CSF-filled spaces called ventricles. The CSF is continuously formed here and then moves down through the central canal, a tube that runs the length of the spinal cord. From the base of the spine, the fluid moves upward on the outside of the spinal cord and returns to the skull where it covers the outer surfaces of the brain. Here it is absorbed by the brain’s outer lining. If interference occurs in any part of this process, CSF continues to accumulate in the brain. This usually causes increased pressure to develop within the skull, and abnormally high pressure can lead to permanent brain damage and even coma or death. In infants, this accumulation also causes the skull to enlarge, including frontal bossing or bulging fontanelle, since the growth regions of the skull have not yet become firm.
Excessive CSF may develop due to overproduction of fluid in the brain, a blockage of the fluid’s circulation, or a blockage of fluid reabsorption on the brain’s surface. Hydrocephalus can be congenital or may develop as a result of a head injury, infections such as meningitis and ventriculitis, intracranial hemorrhage, brain tumors, multiple sclerosis plaques, or colloid cysts. Congenital hydrocephalus and most cases of hydrocephalus that begin in infancy are characterized by an enlarged head, which continues to grow at an abnormally rapid pace.
Symptoms and signs that accompany congenital hydrocephalus include lethargy, vomiting, irritability, epilepsy, rigidity of the legs, and the loss of normal reflexes. If left untreated, the condition causes drowsiness, seizures, and severe brain damage and can lead to death possibly within days or weeks. Hydrocephalus is also often associated with other anomalies of the brain and nervous system, such as spina bifida.
When hydrocephalus develops in older children and adults, the head size will not increase because the growth lines in the bones of the skull have hardened. If the CSF pressure increases, resulting symptoms include headaches, nausea and vomiting, loss of appetite, vision problems, problems with muscle coordination (ataxia), tremors, gait disturbance, difficulty swallowing, and a progressive decrease in mental activity and memory.
Diagnosis of hydrocephalus and related nervous system defects sometimes can be made before birth, either by fetal ultrasound or by testing for the presence of an abnormal amount of a brain-associated protein, alpha-fetoprotein, in the pregnant woman’s blood. However, even with early diagnosis and surgical intervention promptly after birth, the prognosis is guarded.
Older children and adults suspected of having hydrocephalus should be examined by a neurologist. A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the brain can visualize the structure of the brain and the extent of the hydrocephalus.
Surgical correction is the primary treatment for hydrocephalus. The excess pressure must be drained from within the brain, or a balance between the production and elimination of CSF must be established. In some cases, a combination of surgery and medication is successful. For example, diuretics such as drugs furosemide (Lasix), osmotic agents such as mannitol, and carbonic anhydrase inhibitors such as acetazolamide (Diamox), when used for increased CSF pressure from brain hemorrhage, may reduce the amount of CSF fluid produced and thereby decrease the amount of swelling.
Relieving the CSF pressure within the brain is commonly achieved by the surgical insertion of a tube, called a shunt, through brain tissue into one of the cerebral ventricles. A one-way valve is attached to the tube; this allows CSF to escape from the skull cavity when the pressure exceeds a certain level. The tubing is then passed beneath the skin into either the right side of the heart or the abdominal cavity where the excessive CSF can be absorbed safely. Complications of this procedure are fairly common and include headaches, subdural hematomas, peritonitis, and infections such as septicemia or meningitis.
A second procedure that is becoming increasingly common in treating hydrocephalus is called an endoscopic third ventriculostomy and involves a surgeon creating a small hold in the bottom of the third ventricle of the brain. There, a thin membrane separates the inside from the outside of the brain, and the tiny hole allows excess CSF to drain normally into the spaces outside the brain in order to be absorbed into the bloodstream. It has become the procedure of choice for children older than six months, but it is also showing promise in younger children. Another surgical treatment is endoscopic choroid plexus cauterization, in which a neurosurgeon inserts a flexible endoscope into the lateral ventricles and sends an electric current to this area, burning the tissue so that CSF production is lowered.
The outcome of treated patients with hydrocephalus has improved over the years, but the condition is still associated with long-term problems. A modest percentage of newborns with congenital hydrocephalus will survive and achieve normal intelligence.
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