About hydrocephalus

What is hydrocephalus?

Hydrocephalus (pronounced HIGH-droh-SEF-uh-lus) is a build-up of fluid inside the brain. The fluid is called cerebrospinal fluid, or CSF. It is the clear, watery fluid that cushions the brain and spinal cord.

The brain has hollow spaces inside it called ventricles. CSF is made in the ventricles, flows through them, then moves out around the brain and spinal cord before being absorbed back into the bloodstream. When something disrupts this flow or absorption — or, as recent research suggests, when other things in the fluid pull extra water in — CSF builds up. The ventricles enlarge. Pressure can rise.

Hydrocephalus is not one disease. It is a condition with many causes, and it looks different in babies, children, and adults.

Cerebrospinal fluid and the ventricles

An adult brain holds about 150 milliliters of CSF at any one time — roughly half a cup. The body makes and absorbs about 500 milliliters of CSF every day, which means the entire volume turns over three to four times daily.

CSF does several jobs at once. It cushions the brain inside the skull. It carries nutrients in and waste products out. It helps maintain the right chemical balance around brain cells. When too much CSF accumulates, the surrounding brain tissue is pressed and stretched, which can affect how the brain works.

Who hydrocephalus affects

An estimated 70,000 people in the United States are living with hydrocephalus. Anyone can develop it, but it is most common at two stages of life:

• Babies and children. Hydrocephalus that is present at birth is called congenital hydrocephalus. It affects roughly 1 in 1,000 newborns. Children can also develop hydrocephalus later after an infection, a brain bleed, or an injury — this is called acquired hydrocephalus.
• Adults over 60. Normal pressure hydrocephalus (NPH) most often appears in older adults. It is estimated to affect around 700,000 adults in the United States. NPH is frequently mistaken for Alzheimer's disease or general aging because its main signs — trouble walking, urinary changes, and memory difficulties — overlap with those conditions.
• People of any age can develop hydrocephalus after a head injury, a brain hemorrhage, meningitis, or a tumor that blocks CSF flow.

Hydrocephalus is the most frequent reason children undergo brain surgery in the United States. Care for hydrocephalus is estimated to cost about $2 billion in the U.S. each year.

Why hydrocephalus happens

For decades, hydrocephalus has been understood as a problem with how CSF moves — either a blockage along the fluid's path, or a problem with how it is absorbed back into the bloodstream. This is sometimes called the circulation model.

The circulation model explains many cases. But it does not explain all of them. There are patients with hydrocephalus whose CSF pathways look open. There are patients whose absorption seems to work. Something else is also at play.

How hydrocephalus is diagnosed

Diagnosis combines a clinical examination with imaging of the brain. Doctors look at the size of the ventricles, the appearance of surrounding brain tissue, and the symptoms the patient is having.

• In babies, the most visible sign is often a rapidly growing head, because the skull bones have not yet fused. Doctors measure head circumference at every well-child visit for this reason. Ultrasound can be used through the soft spot on a baby's head (the fontanelle) to look at the ventricles.
• In older children and adults, doctors use MRI or CT scans to see the ventricles directly. MRI gives a more detailed picture and avoids radiation.
• In suspected NPH, the workup may include a lumbar puncture (spinal tap) to measure CSF pressure and to see whether removing some fluid temporarily improves symptoms.

A diagnosis of hydrocephalus is made by a clinician based on the full picture — not from imaging alone, and not from a single test. If you or someone you care for has symptoms that concern you, talk to a doctor.

How hydrocephalus is treated today

Today, the standard treatment for hydrocephalus is surgical. There is no approved medication that treats hydrocephalus directly. Two procedures are used most often:

• A shunt is a thin, soft tube that is implanted to drain excess CSF from a ventricle to another part of the body — usually the abdomen — where the fluid can be safely absorbed. The most common type is called a ventriculoperitoneal shunt, or VP shunt. A small valve in the shunt controls how much fluid drains.
• Endoscopic third ventriculostomy (ETV) is a procedure in which a surgeon uses a small camera to create a new opening in the floor of one of the ventricles. This gives CSF a new path to flow when its normal route is blocked. ETV avoids implanting a device, but it is only appropriate for certain kinds of hydrocephalus.

Both surgeries work, and both have limitations. Shunts can fail, become blocked, or become infected, and many patients — especially children — need revision surgeries over their lifetime. ETV is not effective for every type of hydrocephalus and can fail over time. Choosing between them, and managing follow-up care, is a decision made with a neurosurgeon.

Improving today's care matters too. Dr. Krishnamurthy's lab has published on better ways to place shunts, detect shunt failure earlier, reduce infections, and minimize radiation exposure from follow-up imaging. See the shunt technology research →

Living with hydrocephalus

With treatment, many people with hydrocephalus live full lives — they go to school, work, raise families, and pursue careers. Outcomes vary widely depending on the cause of the hydrocephalus, the age at which it began, whether complications arise, and how it is managed over time.

Long-term care often includes regular check-ins with a neurosurgery team, routine imaging, and attention to signs that a shunt may not be working well. Families learn what is normal for their child or family member and what is worth a call to the doctor. National patient organizations and pediatric hospital programs offer detailed resources for day-to-day life with hydrocephalus — see the list below.

Where the science is heading

The standard of care for hydrocephalus has not fundamentally changed in decades. Most of the research effort in the field has focused on improving shunts and shunt outcomes — important work that this lab also contributes to.

Our research initiative is pursuing a different question: can we treat hydrocephalus with medication? If the macromolecular transport model is correct, then drugs that help the brain clear large molecules — or drugs that work on the osmotic forces that pull water into the ventricles — could one day reduce the need for surgery for some patients.

This is early-stage science. There is no medication for hydrocephalus today, and we are not running clinical trials. We are doing the underlying research and building the scientific case. Read more about our research approach →

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Deeper pages on specific topics:

Other trusted resources

We are one voice in this space, and not the only one worth listening to. These organizations and academic programs publish in-depth, clinician-reviewed information on hydrocephalus and run patient communities and support services.