Hydrocephalus in adults is a buildup of cerebrospinal fluid (CSF) inside the brain’s cavities, called ventricles. When fluid accumulates faster than the body can drain it, the ventricles expand and press against surrounding brain tissue, causing problems with walking, thinking, and bladder control. It can develop at any age, though the most common adult form, normal pressure hydrocephalus, primarily affects people over 60.
How CSF Builds Up in the Brain
Your brain continuously produces cerebrospinal fluid at a rate of about 0.20 to 0.35 milliliters per minute, mostly from tissue inside the ventricles called the choroid plexus. This fluid cushions the brain, delivers nutrients, and carries waste. Normally, CSF circulates through the ventricles, flows around the brain and spinal cord, and is reabsorbed into the bloodstream at roughly the same rate it’s made.
Hydrocephalus develops when something disrupts that balance. There are two broad ways this happens. In obstructive hydrocephalus, a physical blockage (a tumor, cyst, or narrowed passage) prevents CSF from flowing out of the ventricles. In communicating hydrocephalus, the fluid flows freely but the body fails to reabsorb it properly. Both types lead to the same result: fluid backs up, the ventricles swell, and pressure builds against brain tissue.
What Causes It in Adults
Unlike childhood hydrocephalus, which is often present at birth, the adult form usually develops after an injury or illness. The most common triggers include bleeding in the brain from a stroke or head injury, brain infections like meningitis, and tumors that block CSF pathways. Surgery on the brain or spine can also disrupt normal fluid absorption. In some cases, the body simply becomes less efficient at reabsorbing CSF, particularly after swelling or inflammation from illness or injury.
In many older adults, no clear cause is ever found. This form is called idiopathic normal pressure hydrocephalus (iNPH), and it develops gradually over months or years. Because its symptoms overlap with Alzheimer’s disease, Parkinson’s disease, and age-related decline, it often goes undiagnosed or misdiagnosed.
The Three Hallmark Symptoms
Normal pressure hydrocephalus produces a recognizable pattern of three symptoms that tend to appear in a specific order. Gait problems typically come first, followed by cognitive changes, then bladder issues. Not everyone develops all three, and severity varies widely.
Walking Difficulty
The gait changes are distinctive. People with NPH tend to walk with their feet wider apart than normal, creating a shuffling, side-to-side stepping pattern sometimes described as penguin-like. Turns become hesitant and clumsy, especially wide turns. The feet may rotate outward, and steps become short and magnetic, as if the feet are sticking to the floor. This is different from the forward lean and festinating gait seen in Parkinson’s disease, though the two can look similar at first glance.
Cognitive Decline
The mental changes involve a general slowing down rather than the memory loss typical of Alzheimer’s. People think more slowly, respond more slowly, and may appear apathetic or disengaged. Processing speed drops, decision-making takes longer, and attention wanders. These changes can be subtle at first and are easy to dismiss as normal aging.
Urinary Problems
Bladder symptoms start as increased urgency, the feeling that you need to go right now, and more frequent urination. Over time this can progress to full incontinence. Some people seem unaware of or unbothered by their loss of bladder control, which itself can be a sign of the cognitive changes the condition causes.
How It’s Diagnosed
Diagnosis relies on brain imaging combined with clinical symptoms. An MRI or CT scan shows whether the ventricles are enlarged. Radiologists use a measurement called the Evans Index, which compares the width of the front portion of the ventricles to the widest diameter of the skull. A ratio of 0.30 or greater has traditionally indicated abnormal enlargement, though newer research suggests the threshold should be slightly higher in older adults (around 0.34 to 0.37 depending on age and sex) because ventricles naturally grow somewhat with age.
Enlarged ventricles alone don’t confirm hydrocephalus. Brain atrophy from Alzheimer’s and other conditions also causes the ventricles to expand. The key distinction is whether the enlargement is “disproportionate,” meaning the ventricles are bigger than you’d expect given the overall amount of brain shrinkage.
When NPH is suspected, a spinal tap test helps predict whether treatment will work. A doctor removes a measured amount of spinal fluid through a lumbar puncture, then checks whether symptoms improve over the next day or two. If walking gets noticeably easier, that’s a strong signal that a permanent drainage procedure will help. The test is good at confirming likely responders (its positive predictive value exceeds 90%), but a negative result doesn’t rule out benefit from treatment, since the negative predictive value is below 20%.
Shunt Surgery: What to Expect
The standard treatment for most adult hydrocephalus is a shunt, a thin tube system implanted under the skin that drains excess CSF from the brain to another part of the body where it can be absorbed. The most common type is a ventriculoperitoneal (VP) shunt, which routes fluid from the brain’s ventricles down to the abdominal cavity.
The system has three parts: a catheter placed into a ventricle through a small hole drilled in the skull (usually behind the ear), a pressure-regulating valve implanted under the skin behind the ear, and a second catheter tunneled under the skin of the neck and chest down into the abdomen. The valve controls how much fluid drains, preventing both over-drainage and under-drainage. A small reservoir built into the valve lets doctors test the system later if needed.
Modern shunts use programmable valves, meaning a doctor can adjust the drainage pressure after surgery using an external magnetic tool placed against the skin. This avoids additional surgery when settings need fine-tuning. One important detail: MRI machines can shift the settings on programmable valves. Patients can safely undergo MRI scans at 3 Tesla or lower, but the valve setting must be checked and reset after every scan.
An Alternative for Obstructive Cases
When hydrocephalus is caused by a blockage, particularly a narrowing of the aqueduct that connects the brain’s third and fourth ventricles, an endoscopic procedure called a third ventriculostomy (ETV) offers an alternative to a permanent shunt. A surgeon threads a tiny camera into the ventricles and creates a small opening in the floor of the third ventricle, giving CSF a new pathway to bypass the blockage and reach the areas where it can be reabsorbed.
In adults with aqueductal stenosis, ETV avoids the need for a shunt in about 72% of cases. The main risk is that the opening can close over time. Roughly 22% of initially successful procedures fail later, with symptoms returning at an average of about 3.75 years, at which point a shunt or repeat procedure becomes necessary.
How Well Treatment Works
For normal pressure hydrocephalus, shunt surgery improves symptoms in the majority of patients. A study of older adults with iNPH who received shunts found that at one year, about 91% showed improvement in their overall symptom scores. Looking at individual symptoms, walking improved in 74% of patients, bladder control in 73%, and cognitive function in 60%. Gait tends to respond the fastest and most dramatically, sometimes improving within days of surgery. Cognitive gains are slower and less predictable.
The overall complication rate for shunt surgery runs around 19%. About 3% of patients develop infections, and roughly 11% experience shunt failure requiring revision. Readmission within six months occurs in about 34% of cases, though not all readmissions involve serious complications. Over-drainage, where too much fluid is pulled from the ventricles, can cause headaches or, less commonly, collections of fluid or blood between the brain and skull. Programmable valves have helped reduce over-drainage by allowing non-surgical pressure adjustments.
Living With a Shunt
A shunt is a lifelong implant. Once placed, you’ll need periodic follow-up to make sure it’s working properly. Signs of shunt malfunction mirror the original symptoms: returning gait problems, worsening cognition, headaches, nausea, or new balance issues. These can appear gradually or suddenly, depending on whether the shunt has slowly clogged or completely failed.
Most daily activities are unaffected. You can fly, swim, and exercise normally once healed from surgery. The valve is usually palpable as a small bump behind the ear but isn’t visible. If you have a programmable valve, you’ll need to carry a card or wear identification noting the device, primarily so medical staff know to recheck the settings after any MRI. Contact sports and activities with significant head-impact risk are generally discouraged, since a blow to the head could damage the catheter or valve.