Hydrocephalus is a condition where there is excessive accumulation of fluid in the brain. Although hydrocephalus was once known as "water on the brain," the "water" is actually cerebrospinal fluid (CSF) — a clear fluid that surrounds the brain and spinal cord. This accumulation of CSF creates potentially harmful pressure on the brain.
The brain has spaces called ventricles. This ventricular system is made up of four ventricles connected by narrow passages. Normally, CSF flows through the ventricles, exits at the base of the brain, bathes the surfaces of the brain and spinal cord, and then reabsorbs into the bloodstream.
The balance between production and absorption of CSF is critically important. Because CSF is made continuously (about 500ml is produced each day), medical conditions that block its normal flow or absorption will result in an over-accumulation of CSF. The resulting pressure of the fluid against brain tissue is what causes hydrocephalus.
What are the different types of hydrocephalus?
Hydrocephalus may be congenital or acquired. Congenital hydrocephalus is present at birth and may be caused by either events or influences that occur during fetal development, or genetic abnormalities. Acquired hydrocephalus develops at the time of birth or at some point afterward. This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease.
Hydrocephalus may also be communicating or non-communicating. Communicating hydrocephalus occurs when the flow of CSF is blocked after it exits the ventricles. This form is called communicating because the CSF can still flow between the ventricles, which remain open. Non-communicating hydrocephalus - also called "obstructive" hydrocephalus - occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles.
Normal pressure hydrocephalus can happen to people at any age, but it is most common among the elderly. It may result from a subarachnoid hemorrhage, head trauma, infection, tumor, or complications of surgery.
What causes hydrocephalus?
Hydrocephalus may result from inherited genetic abnormalities (such as aqueductal stenosis) or developmental disorders (such as those associated with neural tube defects including spina bifida and encephalocele). Other possible causes include complications of premature birth such as intraventricular hemorrhage, diseases such as meningitis, tumors, traumatic head injury, or subarachnoid hemorrhage, which block the exit of CSF from the ventricles to the cisterns or eliminate the passageway for CSF into the cisterns.
Congenital causes in infants and children:
- Brainstem malformation causing stenosis of the aqueduct of Sylvius: This is responsible for 10% of all cases of hydrocephalus in newborns.
- Dandy-Walker malformation: This affects 2-4% of newborns with hydrocephalus.
- Arnold-Chiari malformation type 1 and type 2
- Agenesis of the foramen of Monro
Acquired causes in infants and children:
- Mass lesions: Mass lesions account for 20% of all cases of hydrocephalus in children. These are usually tumors (eg, medulloblastoma or astrocytomas), but cysts, abscesses, or hematoma also can be the cause.
- Hemorrhage: Intraventricular hemorrhage can be related to prematurity, head injury, or rupture of a vascular malformation.
- Infections: Meningitis (especially bacterial) and, in some geographic areas, cysticercosis can cause hydrocephalus.
- Increased venous sinus pressure: This can be related to achondroplasia, some craniostenoses, or venous thrombosis.
Causes of hydrocephalus in adults:
- Subarachnoid hemorrhage (SAH) causes one third of these cases by blocking the arachnoid villi and limiting resorption of CSF. However, communication between ventricles and subarachnoid space is preserved.
- Idiopathic hydrocephalus represents one third of cases of adult hydrocephalus.
- Head injury, through the same mechanism as SAH, can result in hydrocephalus.
- Tumors can cause blockage anywhere along the CSF pathways. The most frequent tumors associated with hydrocephalus are ependymoma, subependymal giant cell astrocytoma, choroid plexus papilloma, craniopharyngioma, pituitary adenoma, hypothalamic or optic nerve glioma, hamartoma, and metastatic tumors.
- Prior posterior fossa surgery may cause hydrocephalus by blocking normal pathways of CSF flow.
- Congenital aqueductal stenosis causes hydrocephalus but may not be symptomatic until adulthood. Special care should be taken when attributing new neurological deficits to congenital hydrocephalus, as its treatment by shunting may not correct these deficits.
- Meningitis, especially bacterial, may cause hydrocephalus in adults.
- All causes of hydrocephalus described in infants and children are present in adults who have had congenital or childhood-acquired hydrocephalus.
Causes of NPH(Normal Pressure Hydrocephalus):
- Most cases are idiopathic and are probably related to a deficiency of arachnoid granulations.
- Head trauma
What are the symptoms?
Symptoms of hydrocephalus vary with age, disease progression, and individual differences in tolerance to the condition. For example, an infant's ability to compensate for increased CSF pressure and enlargement of the ventricles differs from an adult's. The infant skull can expand to accommodate the accumulation of CSF because the sutures of the skull have not yet closed. This results in a gradual ballooning of the infant’s skull.
In infancy, the most obvious indication of hydrocephalus is often a rapid increase in head circumference or an unusually large head size. Other symptoms may include vomiting, sleepiness, irritability, downward deviation of the eyes and seizures.
Older children and adults may experience different symptoms because their skulls cannot expand to accommodate the accumulation of CSF. Symptoms may include headache followed by vomiting, nausea, papilloedema, blurred or double vision, difficulty with looking upwards, problems with balance, poor coordination, gait disturbance, urinary incontinence, slowing or loss of developmental progress, lethargy, drowsiness, irritability, or other changes in personality or cognition including memory loss.
Symptoms of normal pressure hydrocephalus include, problems with walking, impaired bladder control leading to urinary frequency and/or incontinence, and progressive mental impairment and dementia. An individual with this type of hydrocephalus may have a general slowing of movements or may complain that his or her feet feel "stuck".
Because some of these symptoms may also be experienced in other disorders such as Alzheimer's disease and Parkinson's disease, normal pressure hydrocephalus is often incorrectly diagnosed and never treated.
There are a variety of tests, including brain scans (CT and/or MRI), a spinal tap or lumbar catheter, intracranial pressure monitoring, and neuropsychological tests, to help them accurately diagnose normal pressure hydrocephalus and rule out any other conditions.
The symptoms described in this section account for the most typical ways in which progressive hydrocephalus manifests itself, but it is important to remember that symptoms vary significantly from one person to the next.
What is the current treatment?
Hydrocephalus is most often treated by surgically inserting a shunt system. This system diverts the flow of CSF from the CNS to another area of the body where it can be absorbed as part of the normal circulatory process.
A shunt is a flexible but sturdy plastic tube. A shunt system consists of the shunt, a catheter, and a valve. One end of the catheter is placed within a ventricle inside the brain or in the CSF outside the spinal cord. The other end of the catheter is commonly placed within the abdominal cavity, but may also be placed at other sites in the body such as a chamber of the heart or areas around the lung where the CSF can drain and be absorbed. A valve located along the catheter maintains one-way flow and regulates the rate of CSF flow.
A limited number of individuals can be treated with an alternative procedure called third ventriculostomy. In this procedure, a neuro-endoscope — a small camera that uses fiber optic technology to visualize small and difficult to reach surgical areas — allows a view of the ventricular surface. Once the scope is guided into position, a small tool makes a tiny hole in the floor of the third ventricle, which allows the CSF to bypass the obstruction and flow toward the site of resorption around the surface of the brain.