Hydrocephalus
Overview
The word hydrocephalus is derived from two Greek words, hydro, meaning water, and cephalus, meaning head, and once was called "water on the brain." Hydrocephalus is the condition caused by the accumulation of an abnormally large amount of cerebrospinal fluid (CSF) in the skull, or cranium. Normally, CSF flows continually from the interior cavities in the brain (ventricles) to the thin subarachnoid space that surrounds the brain and spinal cord.
About a pint of this clear fluid is produced a day and is absorbed by the blood stream.
CSF performs the following functions:
- Balances the amount of blood in the head.
- Bathes and protects the brain and spinal cord.
- Carries nutrients between the brain and spinal cord while removing waste.
Normal flow and absorption through the subarachnoid space is dependent on proper CSF pressure in the head (called intracranial pressure). A build up of CSF often causes a dangerous increase in pressure. The combination of CSF buildup and the subsequent increase in intracranial pressure can stress brain tissue and can cause the characteristic symptoms of hydrocephalus, though they also may occur with normal pressure.
Incidence and Prevalence
Congenital hydrocephalus affects about one in every 1000 births. The overall prevalence in the United States is about 0.5%. Most cases are detected early, either at or soon after birth. The incidence of acquired hydrocephalus in adults is not known because it occurs as a result of injury, illness, or environmental factors.
Types
The two main types of hydrocephalus are congenital (developed before birth) and acquired (developed during or after birth). Hydrocephalus is further classified as communicating and noncommunicating.
In communicating hydrocephalus, the obstruction occurs in the subarachnoid space. Noncommunicating hydrocephalus means the obstruction is located within the ventricles. Intracranial pressure is usually increased and significant neurological abnormalities may develop, including damage to brain tissue. This type is most commonly caused by stroke or traumatic brain injury.
Normal pressure hydrocephalus (NPH) is more common in patients over the age of 60. In NPH, obstruction develops over time, slowly enlarging the ventricles and increasing pressure in the brain. NPH usually affects areas of the brain that control the bladder, movement in the legs, and cognitive abilities (e.g., memory, reasoning, problem solving).
Causes
Obstruction causes CSF to build up in the brain. If the cause is congenital, symptoms such as an enlarged head may be present at birth. Acquired hydrocephalus can develop at any age as a result of head trauma or illness.
Congenital hydrocephalus
Congenital hydrocephalus occurs during fetal development and is present at birth. Causes include infections (e.g., cytomegalovirus [CMV], toxoplasmosis, rubella) and hemorrhaging or internal bleeding in the brain.
The following congenital malformations are commonly associated with CSF obstruction:
- Aqueductal stenosis-narrowing of the pathway to the fourth ventricle
- Arnold-Chiari malformations-small part of the cerebellum protrudes into the spinal canal
- Dandy-Walker syndrome-enlarged fourth ventricle due to obstruction in pathway
- Spina bifida-portion of the spinal cord is pushed through an abnormal opening between two vertebrae
Acquired hydrocephalus
Acquired hydrocephalus can occur at any age. The following conditions may cause CSF obstruction and subsequently acquired hydrocephalus:
- Bleeding (hemorrhage)
- Brain trauma (i.e., result of injury)
- Brain tumor
- Cyst (i.e., a fluid-filled sac)
- Infection (e.g., cerebral abscess, bacterial meningitis)
Hemorrhaging, traumatic brain injury, and infection are seen in some premature births; premature births may be a risk factor for hydrocephalus.
Signs and Symptoms
Symptoms of hydrocephalus are determined by the following factors:
- Age
- Degree of ventricular enlargement
- Rate of hydrocephalus development
- Type
- Underlying condition
Infants
The characteristic symptom seen in infants is enlargement of the head. An infant's skull expands to accommodate excess CSF because the bones of the skull have not closed yet.
Very young children commonly experience irritability, poor feeding, and lethargy.
Children and Adults
Children and adults may experience the following symptoms:
- Blurred or double vision
- Cognitive difficulties
- Downward gaze or "sun-setting eyes"
- Headache
- Imbalance and dizziness
- Incontinence
- Irregular gait
- Lethargy
- Nausea
- Poor coordination
- Visual disturbances
- Vomiting
- Weakness
Normal pressure hydrocephalus (NPH), which is more common in patients over the age of 60, often causes memory loss, trouble speaking, emotional changes, incontinence, irregular gait, and dementia.
Diagnosis
Hydrocephalus may be suggested by symptoms; however, imaging studies of the brain are the mainstay of diagnosis. Computed tomography (CT scan) and magnetic resonance imaging (MRI scan) typically reveal enlarged ventricles and may indicate a specific cause. Abnormalities such as tumors and hemorrhages can also be detected.
Small abnormalities that may not be detected using CT scan, such as cysts and abscesses, are often seen with MRI. These studies can also help the neurosurgeon differentiate between communicating and noncommunicating hydrocephalus. In cases of suspected normal pressure hydrocephalus, a spinal tap may help determine CSF pressure.
A cisternagram evaluates the dynamics of CSF flow in the brain and spinal cord. In this procedure, a diagnostic dye is injected into the subarachnoid space around the brain. A series of pictures is taken once the dye has circulated through the entire CSF path. Cisternography can reveal CSF concentration, obstruction, leakage, and pressure.
In older people, pressure in the head can cause papilledema, swelling of the optic nerve. Papilledema can often be seen while examining the eyes. Unfortunately, it typically indicates hydrocephalus that is well developed. In rare cases, long standing hydrocephalus causes blindness.
Treatment
Treatment usually requires draining the excess fluid from the brain by diverting it to another place in the body.
Shunt
A shunt is a soft, flexible tube usually made of silicone rubber or plastic. Most shunts consist of a valve that promotes drainage and a catheter, a tube that connects the drainage site to the deposit site. If there is high intracranial pressure, a small sensor may be added near the valve. This sensor allows the neurosurgeon to monitor pressure levels.
The shunt used for treating hydrocephalus is usually permanent. The shunt is inserted with one tip in one of the ventricles of the brain and the other tip in the abdominal (peritoneal) cavity. This is known as a ventriculoperitoneal (VP) shunt. Less commonly used drainage sites include the right ventricle of the heart, the gall bladder, and the pleural space around the lungs. Depending on the location of the obstruction, fluid also may be drained from the subarachnoid space that surrounds the brain.
Although insertion and immediate operation of the shunt is usually uncomplicated, problems can arise.
- Abdominal problems:
- Bowel twisting
- Excess fluid collection
- Blockage of the shunt
- Brain injury:
- Clots on brain surface
- Loss of sensation
- Memory loss
- Paralysis
- Seizures
- Speech problems
- Headaches caused by overdraining
- Mechanical failure (e.g., separation of parts, valve failure)
Other complications include bleeding, problems with anesthesia, and infection. The body may react negatively to the shunt because it is made of foreign material.
Approximately 70% of shunts fail within 10 years of placement. To accommodate normal growth and to ensure long term function, shunts in infants and children are replaced frequently until adulthood. A child may require as many as five shunts during this period. A neurosurgeon periodically checks shunt function in adults.
Third Ventriculostomy
Third ventriculostomy involves entering the brain through the bones at the top of the skull. The neurosurgeon passes an endoscope (a thin telescopic instrument) through the lateral ventricle into the third ventricle and uses a laser to make a hole in its floor. Excess fluid drains through the hole into the subarachnoid space.
The overall success rate of third ventriculostomy is about 65%. When used to treat blockage caused by tumor or by aqueductal stenosis, success rates are slightly higher. In hydrocephalus caused by hemorrhaging or infection, they are slightly lower.
There are few risks associated with third ventriculostomy. CSF drains through a hole in the ventricle floor instead of a valve, so there is no risk of overdrainage. The absence of a tube eliminates the risk associated with a shunt.
Rarely, the basal artery near the third ventricle is injured during the procedure, which can cause life threatening hemorrhaging in the brain. However, use of the endoscope has lowered this risk.
Spinal Tap
In patients with normal pressure hydrocephalus, repeated spinal taps are performed to remove excess CSF. If this results in improvement, inserting a permanent shunt may be appropriate.
Prognosis
Hydrocephalus is usually a lifelong disorder. Prognosis depends on a number of factors, including the underlying condition that resulted in hydrocephalus, its duration and degree, as well as response to treatment.