Hydrocephalus is a condition where cerebrospinal fluid (CSF) builds up inside the brain’s cavities, called ventricles, causing them to enlarge and press on surrounding brain tissue. It can occur at any age, from before birth through late adulthood, and affects roughly 1 in 1,000 infants. Treatment almost always involves surgery, and outcomes have improved dramatically over the past several decades.
How Fluid Builds Up in the Brain
Your brain constantly produces cerebrospinal fluid, a clear liquid made by a structure called the choroid plexus deep inside the ventricles. Under normal conditions, this fluid circulates through a series of connected chambers in the brain, exits through small openings into the space surrounding the brain and spinal cord, and gets reabsorbed into the bloodstream. The whole system stays in balance: the brain produces about the same amount of fluid that gets absorbed each day.
Hydrocephalus develops when something disrupts that balance. Either the fluid can’t drain properly, or it can’t be reabsorbed fast enough. The result is the same: fluid accumulates, the ventricles swell, and pressure builds inside the skull. That pressure compresses and stretches brain tissue, which can cause damage if left untreated.
Two Main Types
Hydrocephalus is classified based on where the blockage occurs:
- Non-communicating (obstructive) hydrocephalus happens when fluid flow is physically blocked within the narrow passages connecting the ventricles. A tumor, a cyst, or a structural abnormality can create this obstruction. Fluid backs up behind the blockage like water behind a dam.
- Communicating hydrocephalus occurs when fluid flows freely between the ventricles but gets blocked or poorly absorbed after it exits into the surrounding space. The ventricles themselves stay open and connected to each other, but the drainage system downstream isn’t working properly.
There’s also a special form called normal pressure hydrocephalus (NPH), which primarily affects adults over 70. In NPH, the ventricles enlarge even though the fluid pressure inside them may measure close to normal on a single test. It produces a distinctive combination of three symptoms: a shuffling gait where the feet barely lift off the floor, gradual cognitive slowing, and urinary problems ranging from frequency to incontinence. NPH is important to recognize because, unlike many causes of cognitive decline in older adults, it can sometimes be reversed with treatment.
What Causes It
In infants, hydrocephalus is often present at birth or develops shortly after. Some cases are linked to structural brain malformations that form during fetal development. Others result from premature birth, which carries a higher risk of bleeding inside the brain’s ventricles.
In older children and adults, hydrocephalus is typically acquired. The most common causes include brain or spinal cord tumors that physically obstruct fluid flow, infections like meningitis that scar the drainage pathways, bleeding in the brain from a stroke or head injury, and other forms of brain injury that disrupt the normal circulation or absorption of cerebrospinal fluid.
Symptoms by Age Group
The signs of hydrocephalus look very different depending on the person’s age, largely because an infant’s skull can expand while an adult’s cannot.
In babies, the most visible sign is a rapidly growing head. Because the skull bones haven’t yet fused, rising pressure causes the head to enlarge beyond normal growth curves. The soft spot (fontanelle) on top of the head may feel tense or bulge outward. Babies may also be unusually irritable, feed poorly, vomit, or seem excessively sleepy.
In older children and adults, the skull is rigid, so pressure builds without outward expansion. Symptoms include headaches (often worse in the morning), nausea and vomiting, blurred or double vision, balance problems, and difficulty concentrating. In severe or rapidly worsening cases, people may become confused or lose consciousness.
How It’s Diagnosed
Brain imaging is the cornerstone of diagnosis. MRI or CT scans show whether the ventricles are enlarged, and they can often reveal the cause of the blockage. Doctors use a measurement called the Evans index to quantify how swollen the ventricles are. It compares the width of the front part of the ventricles to the maximum width of the skull. A ratio above 0.3 is the standard threshold for definite ventricular enlargement. Normal values fall between 0.20 and 0.25.
For normal pressure hydrocephalus, diagnosis can be trickier because the symptoms overlap with other conditions like Alzheimer’s or Parkinson’s disease. When NPH is suspected, doctors may perform a large-volume spinal tap to remove some fluid and then watch whether symptoms temporarily improve. A noticeable improvement in walking or thinking after the tap is a strong indicator that surgical treatment could help.
Surgical Treatment Options
Hydrocephalus doesn’t resolve on its own. The standard treatment is a ventriculoperitoneal (VP) shunt: a thin tube system implanted under the skin that drains excess fluid from the brain’s ventricles into the abdominal cavity, where the body reabsorbs it. The shunt has four components: a catheter placed in the ventricle, a one-way valve that controls flow, a small reservoir, and a second catheter that runs under the skin down to the abdomen.
VP shunts work well, with success rates around 91% in studies of obstructive hydrocephalus. The trade-off is that shunts are lifelong devices that can malfunction. Mechanical failure is the most common problem, particularly blockage of the catheter inside the ventricle by tissue that grows into the tip. Shunts can also fracture (most often near the collarbone or lower ribs), disconnect at junction points, or become infected. The yearly infection rate runs between 5 and 12%, with skin bacteria being the usual culprit. In growing children, the catheter can migrate out of position as the child gets taller, sometimes requiring surgical revision.
Functional problems are also possible. A shunt that drains too much fluid can cause headaches when standing, while one that drains too little fails to relieve symptoms.
Endoscopic Third Ventriculostomy
For some types of obstructive hydrocephalus, surgeons can avoid a shunt altogether using a procedure called endoscopic third ventriculostomy (ETV). A tiny camera is guided into the brain, and a small hole is made in the floor of the third ventricle, creating a new pathway for fluid to bypass the blockage. ETV has a success rate of about 77%, lower than shunting, but it eliminates the need for an implanted device and the long-term maintenance that comes with it. It’s most commonly used for non-communicating hydrocephalus where a clear obstruction exists.
Long-Term Outlook
The prognosis for hydrocephalus depends heavily on its cause, how early it’s caught, and how well treatment works. But the overall picture is more encouraging than many people expect.
A long-term follow-up study of adults who were treated for hydrocephalus as infants found that their median IQ was 101, squarely in the normal range. These adults had preserved cognitive function despite many having experienced multiple shunt malfunctions over the years. Some specific areas of thinking, particularly working memory and processing speed, showed mild deficits compared to the general population, but overall intellectual ability remained stable from childhood into adulthood.
People living with treated hydrocephalus do need ongoing monitoring. Shunts can fail at any point, sometimes years or decades after placement, and the symptoms of a failing shunt (headache, nausea, vision changes, cognitive decline) require prompt medical evaluation. Many people with shunts learn to recognize the early warning signs of malfunction and act quickly when something feels off. With appropriate surveillance and timely intervention, most people with hydrocephalus lead full, active lives.