Hydrocephalus: the fluid pressure on the brain, the shunt that drains it, and the NPH that hides as dementia
Last updated September 3, 2026.
Hydrocephalus is a build-up of cerebrospinal fluid inside the brain, raising pressure where there should be free flow. It has two famous faces: the baby whose head grows too fast because the fluid cannot drain, and the older adult whose walking, bladder, and memory slip together in a pattern easily misread as dementia or Parkinson's. Both deserve to be known, because both are treatable. The treatment is drainage: a shunt, a thin tube that carries the fluid from the brain to the abdomen, where the body absorbs it, or in some babies a camera procedure that opens a new channel inside the brain. Shunts are lifelong companions for many: they work, they need watching, and they occasionally block or infect, which is why every family and every patient learns the blocked-shunt symptoms by heart. The older-adult form, normal pressure hydrocephalus, is the great missed diagnosis of its age group: the triad of a slowed walk, urinary urgency, and memory trouble, when recognized, can be substantially reversed by a shunt, which makes it one of the few treatable causes of a dementia-like picture. The worth-knowing part: outcome depends on timing, and timing depends on recognition, so the pattern is worth more than the word.
What does it look like?
In babies: a head growing too fast across the centile lines, a bulging soft spot, downward-turned eyes, vomiting, sleepiness, and irritability. In the older adult: the triad, a walk that has become slow, wide, and glued to the floor, a bladder that has become urgent, and a memory and thinking that have dulled, usually over months. The walking change typically arrives first and is the most reversible when treated early.
Why does it happen?
The cerebrospinal fluid is made continuously and must drain and absorb continuously; hydrocephalus is any break in that balance. In babies: a channel too narrow from development, bleeding after premature birth, or spina bifida. In adults: bleeding, infection, tumors, or head injury, and in the older-adult form, an absorption that fails with age for reasons not fully understood. It is nobody's fault in any of its forms.
How is it treated?
- The shunt is the standard treatment. A thin tube with a valve drains the fluid from the brain to the abdomen under the skin, and it starts working immediately; most people keep theirs for life, with the surgical team checking it along the way.
- A camera procedure suits some babies and adults. For certain blockage patterns, a tiny opening made inside the brain restores flow without a shunt, and the neurosurgeon weighs who fits it.
- Everyone learns the blocked-shunt symptoms. Headache, vomiting, sleepiness, and a return of the original symptoms mean the shunt may have blocked or infected, and that is always a same-day emergency, because a blocked shunt lets the pressure climb.
- The older-adult form gets a trial before a verdict. A test that drains fluid through a lumbar puncture, with walking measured before and after, predicts who a shunt will help, and the improvement in walking is often the first thing families notice.
When is it urgent?
A blocked or infected shunt is the emergency: headache with vomiting, unusual sleepiness or confusion, fever in someone with a shunt, or the original symptoms returning are each a same-day trip to the emergency department. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
How can this look like dementia but be treatable?
Because normal pressure hydrocephalus is a near-perfect mimic, and that is its known danger. The slowly building fluid produces exactly the three changes families file under aging or dementia: the shuffling walk, glued to the floor,, the bladder urgency, and the dulled memory. The differences live in the pattern: the walking usually changes first and most, the memory problem is more slowed than lost, and the three arriving together over months is the classic shape. It is one of the few dementia-like conditions a treatment can reverse, which is why the neurologist tests rather than guesses: the lumbar puncture drain, with walking measured before and after, is the instrument that separates the mimic from the real thing.
Why did nobody spot it a year ago?
Because it is rare next to dementia, because its signs overlap almost completely, and because its scan changes are easy to read as ordinary age-related shrinkage until someone assembles the walking, the bladder, and the memory into one picture. The miss is common enough that the condition has a reputation in the medical literature for being found late, sometimes years late, and the people who miss it include good doctors. It is not negligence, and it is not the family's miss either: you brought him to the office that assembled the picture, and the year was the route there, not time wasted. The question that matters now is the test result, not the calendar.
Should I let myself hope about the shunt?
Yes, with the calibration the test gives you, and that is precisely what the test is for. The lumbar puncture drain, with his walking measured before and after, predicts the shunt response: a clear improvement after the drain is the strongest sign a shunt will help, and the walking, the first thing that went, is often the first thing back. Families of responders sometimes describe the weeks after a successful shunt as getting their person back. The honesty on the other side: not everyone responds, the memory improves less reliably than the walking, and the test exists to find out which side he is on before anyone operates. Hope in proportion to the test, and let the test speak.
What does the lumbar puncture test actually involve?
A needle into the fluid space in the lower back, under local anesthetic, draining a measured amount of the cerebrospinal fluid, with his walking and sometimes his thinking timed before the drain and again after, over the following hours to days. The team is looking for a visible change, usually in the walking first. It is a day procedure, the headache afterward is the commonest side effect and passes, and the fluid refills itself within hours. Some centers use a longer version, a small drain left in for a few days, when the single drain leaves the answer unclear. It is the least invasive way of asking the shunt question before anyone commits to surgery.
What is life with a shunt actually like?
For most people, surprisingly ordinary, with one discipline. The shunt sits under the skin, a thin tube from the brain to the abdomen with a valve, and once healed it is mostly invisible to daily life: no activity restrictions for most, occasional checks with the surgical team, and a long working life for the device. The one discipline is knowing the blocked-shunt symptoms by heart, headache with vomiting, unusual sleepiness, fever, or the old symptoms returning, and treating them as a same-day emergency every time, because a blocked shunt lets the pressure climb. Families make it second nature within months, and then the shunt fades into the background where it belongs.
If the test does not show improvement, what then?
Then the test has done its job: it has saved him an operation that would not have helped, and the diagnosis returns to the dementia pathway with one important difference, it has been properly checked for the treatable mimic, which most dementia diagnoses never are. The care from that point is real care, not a consolation: the memory services, the walking and bladder support, and the planning that families do better early than late. Some centers repeat or extend the test when the answer is borderline and the scan pattern is persuasive, so an unclear first result is a conversation, not a door closing. Either way, he leaves the process with a firmer diagnosis than he had.