Hydrocephalus is a condition in which too much cerebrospinal fluid, often called CSF, builds up inside spaces in the brain known as ventricles. CSF normally cushions the brain and spinal cord, helps remove waste, and supports normal brain function. In hydrocephalus, that fluid does not circulate or drain the way it should, so the ventricles enlarge and pressure or stretching can damage brain tissue.

Hydrocephalus is sometimes described in simple terms as “water on the brain,” but that phrase is not medically accurate because the fluid involved is cerebrospinal fluid, not ordinary water. The condition can happen in babies, children, adults, and older adults. It may be present at birth, develop after an injury or illness, or appear later in life as a form called normal pressure hydrocephalus.

How the fluid system normally works

The brain constantly produces cerebrospinal fluid. That fluid flows through the ventricles, around the brain and spinal cord, and is then absorbed into the bloodstream. Hydrocephalus develops when there is an imbalance in this system. The fluid may be blocked, absorbed poorly, or, more rarely, produced in excessive amounts. When that happens, the ventricles can expand and the brain can be compressed or stretched.

Main types of hydrocephalus

Doctors often group hydrocephalus into a few broad categories. Congenital hydrocephalus is present before birth or recognized soon after birth. Acquired hydrocephalus develops later because of bleeding, infection, tumors, head injury, stroke, or other medical problems. Another important form is normal pressure hydrocephalus, usually seen in older adults, where the ventricles enlarge and the person may develop walking difficulty, bladder problems, and thinking changes even though pressure readings may not always be dramatically high.

Hydrocephalus may also be described by how the fluid is disrupted. In obstructive, also called non-communicating hydrocephalus, the flow of CSF is blocked somewhere along its pathway. In communicating hydrocephalus, the fluid can still flow through the ventricles, but absorption is impaired. This distinction helps guide treatment decisions.

What causes hydrocephalus?

The causes depend on age and situation. In infants, hydrocephalus may result from developmental abnormalities, bleeding around the time of birth, infection, or certain genetic conditions. In children and adults, causes can include brain tumors, head trauma, bleeding in or around the brain, meningitis, stroke, or complications after surgery. In some older adults with normal pressure hydrocephalus, no clear cause is found.

Symptoms of hydrocephalus

Symptoms vary with age, how quickly the fluid builds up, and the cause. In babies, signs can include a rapidly enlarging head, a bulging soft spot, vomiting, sleepiness, irritability, poor feeding, and downward deviation of the eyes.

In older children and adults, symptoms may include headache, nausea, vomiting, blurred or double vision, balance problems, drowsiness, trouble concentrating, personality or memory changes, and difficulty walking. When hydrocephalus appears as normal pressure hydrocephalus, the classic pattern is gait difficulty, cognitive decline, and urinary urgency or incontinence.

Because the condition can worsen brain function, hydrocephalus is not something to ignore. Untreated pressure can lead to lasting neurological damage and can become life-threatening.

How it is diagnosed

Diagnosis usually combines a medical history, neurological examination, and brain imaging. Doctors often use ultrasound in infants, or CT and MRI scans in children and adults, to see whether the ventricles are enlarged and to look for a blockage or other cause. In suspected normal pressure hydrocephalus, additional testing may include gait assessment and removal of some spinal fluid to see whether symptoms improve.

How hydrocephalus is treated

Treatment usually aims to lower pressure and restore safer movement of cerebrospinal fluid. The most common treatment is a shunt, which is a thin tube with a valve that drains excess fluid from the brain to another part of the body, often the abdomen, where it can be absorbed.

Some patients may instead have an endoscopic third ventriculostomy, often shortened to ETV. In that procedure, a surgeon makes a small opening in the floor of the third ventricle so fluid can bypass the blockage and flow more normally. This is not right for everyone, but it can be an alternative to shunt placement in selected cases.

Long-term outlook

The outlook depends on the cause, how quickly it is found, the person’s age, and whether treatment works well. Many people improve significantly after treatment, especially when the condition is recognized early. At the same time, treatment devices such as shunts can sometimes fail, become blocked, or get infected, so long-term follow-up is important.

Why hydrocephalus matters

Hydrocephalus is more than a buildup of fluid. It is a disorder of brain fluid circulation that can affect movement, memory, development, vision, and daily independence. The good news is that it is often treatable, and in some cases, especially certain forms of normal pressure hydrocephalus, some symptoms may improve after proper treatment.

A simple definition

In the clearest terms, hydrocephalus is a condition where cerebrospinal fluid builds up inside the brain’s ventricles because it is blocked, not absorbed properly, or otherwise out of balance. That buildup enlarges the ventricles and can injure the brain if it is not treated.