Hydrocephalus is a condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain. CSF surrounds the brain and spinal cord. When the circulatory path of the CSF is blocked, fluid begins to accumulate, causing the ventricles to enlarge and the pressure inside the head to increase, resulting in hydrocephalus.

What are the different types of hydrocephalus?

Communicating hydrocephalus occurs when the flow of CSF is blocked after it exits the ventricles. The word “communicating” refers to the fact that 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. One of the most common causes is aqueductal stenosis, a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain.

Normal pressure hydrocephalus (NPH) is a form of communicating hydrocephalus that can strike 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. However, many people develop normal pressure hydrocephalus even when none of these factors are present for reasons that are unknown. In that case it is called idiopathic normal pressure hydrocephalus.

Hydrocephalus may be also be classified as 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. In rare cases, congenital hydrocephalus may not cause symptoms in childhood but only manifest in adulthood and may be associated with aqueductal stenosis.

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 ex-vacuo is another form of hydrocephalus that does not fit exactly into the categories mentioned above and primarily affects adults. Hydrocephalus ex-vacuo occurs when stroke, degenerative diseases like Alzheimer's disease or other dementias or traumatic injury cause damage to the brain. In these cases, brain tissue may actually shrink.

What are the symptoms of hydrocephalus?

The possible triad of symptoms typically present as follows:

  • gait disturbance and difficulty walking

  • mild dementia

  • impaired bladder control

These symptoms may not occur all at the same time, and sometimes only one or two symptoms are present. The triad of symptoms is often associated with the aging process and a majority of the NPH population is older than 60 years.

How is hydrocephalus diagnosed?

Once a type of hydrocephalus is suspected by a primary physician, one or more of the following tests are usually recommended to confirm the diagnosis and assess the person’s candidacy for shunt treatment. It is important that at this point a neurosurgeon and/or neurologist become part of the medical team. Their involvement is helpful not only in interpreting test results and selecting likely candidates for shunting, but also in discussing the actual surgery and follow-up care as well as expectations and risks of surgery.

  • Clinical Exams – consists of an interview and or a physical/neurologic examination

  • Brain images to detect enlarged ventricles

    • MRI

    • CT or CAT scan
  • CSF tests to predict shunt responsiveness and/or determine shunt pressure

    • Lumbar or spinal tap – large volume

    • External lumbar drainage

    • Measurement of CSF outflow resistance

What treatment options are available?

The only available treatment for hydrocephalus is the surgical implantation of a shunt, a device that channels CSF sway from the brain to another part of the body where it can be absorbed. Most shunt systems consist of three components:

  • A collection catheter situated within the cerebral ventricles

  • A valve mechanism to control how much CFS flows

  • An exit catheter to drain the CSF to another part of the body

After the surgery, all components of the shunt system are entirely under the skin, and nothing is exposed to the outside. A limited number of individuals can be treated with an alternative procedure called endoscopic third ventriculostomy. In this procedure, a neuroendoscope — a small camera that uses fiber optic technology to visualize small and difficult to reach surgical areas — allows a doctor to view 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.

Who is a likely candidate for shunting?

No one single factor is reliable in predicting success from implantation of a shunt. The following findings are generally associated with a better outcome following shunt placement:

  • The onset of gait disturbance as the first and most prominent symptom

  • A known cause for NPH, such as a trauma or hemorrhage

  • The scan shows the ventricle size to be disproportionately larger than the CSF in the subarachnoid space

  • Removal of spinal fluid via lumbar puncture or lumbar catheter gives dramatic, temporary relief of symptoms

  • ICP or spinal fluid pressure monitoring shows an abnormal range or pattern of spinal fluid pressure or an elevated CSF outflow resistance

A complete recovery is possible, but it is not often seen. Many individuals and their families are satisfied when shunt surgery results in reduced disability or dependence than he or she had before surgery, or prevention of further neurological deterioration.