What Is Hydrocephalus?

Start by following the fluid. Deep inside the brain are open spaces called ventricles, and they are constantly filled with a clear liquid — cerebrospinal fluid — that cushions the brain, carries nutrients, and washes waste away. The fluid is made inside the ventricles, flows through narrow connecting channels, spreads over the brain's surface, and is absorbed back into the bloodstream. Hydrocephalus is what happens when that circulation breaks down: the fluid keeps being made, but it cannot drain or be absorbed properly, so it builds up inside the ventricles and presses on the brain around them.

The video at the top of this page shows one of the operations used to fix that build-up. "Endoscopic Third Ventriculostomy" runs about 8 minutes, and its description states its subject plainly: an endoscopic third ventriculostomy in a patient with obstructive hydrocephalus — the form of the condition where something is physically blocking the fluid's route. Watching it after the steps below will make much more sense, because the operation only does one thing, and it does it elegantly: it opens a new doorway for the fluid.

Step one: the flow gets interrupted

Hydrocephalus is usually grouped by where the circulation fails. In the obstructive form, a channel between the ventricles is narrowed or blocked — sometimes from birth, sometimes because a growth, bleeding, or scarring is in the way — so fluid collects behind the blockage like water behind a dam. In the communicating form, the fluid can still travel through the ventricles, but it is not absorbed back into the blood as it should be, so the whole system slowly fills.

It can appear at very different ages. Some babies are born with it, and it is sometimes noticed before birth on a pregnancy scan or soon afterwards because the head grows faster than expected — a baby's skull bones can still expand, so extra fluid shows up as growth. In older children and adults, whose skulls cannot expand, the same build-up raises pressure inside the head instead, and that pressure is what produces symptoms.

Step two: the pressure makes itself known

Because a baby's head can grow, the earliest sign in infancy is often measurement rather than misery: a head circumference that climbs faster than the growth charts expect, sometimes with a bulging soft spot. In older children and adults, raised pressure tends to announce itself with headaches, nausea, blurred or double vision, unsteadiness, and a general slowing down — feeling drowsy, less sharp, less yourself.

None of those signs belongs to hydrocephalus alone, which is why they are a prompt for assessment rather than a diagnosis. Pressure inside the skull is a serious thing, though, so new or worsening symptoms of that kind should never be watched and waited on at home. If the picture fits a plumbing problem, the next step is to look at the plumbing.

Step three: pictures of the ventricles

Diagnosis rests on imaging. A scan of the head — CT or MRI — shows the ventricles directly, and in hydrocephalus they appear enlarged, stretched by the fluid they are holding. The pattern matters as much as the size: which ventricles are enlarged can point to where the blockage sits, and that distinction decides which operation makes sense. In a baby whose soft spot is still open, an ultrasound through it can sometimes give the first look without any radiation at all.

This is also where related conditions are separated out. An enlarged space inside the head is not always hydrocephalus, and hydrocephalus is not the only cause of pressure symptoms — a scan finding is interpreted alongside the examination, not on its own. For another condition where head imaging and pressure inside the skull are central, see our article on what an aneurysm is.

Step four: give the fluid another way out

Treatment is mechanical, because the problem is mechanical: the fluid needs a working route out of the ventricles. There are two established ways to give it one, and the anchor video shows the first.

An endoscopic third ventriculostomy — ETV — is the operation in the video. Through a small opening, the surgeon passes a thin endoscope into the ventricles and makes a tiny opening in the floor of the third ventricle. Fluid can then bypass the blockage downstream and reach the surface of the brain, where it can be absorbed as normal. Nothing is implanted, which is one reason the approach is attractive when the anatomy suits it — it works best for the obstructive form, where there is a definite blockage to bypass.

The second route is a shunt, and it is the longer-established of the two. A shunt is a soft tube placed into a ventricle, tunnelled under the skin, and led down to another space in the body — usually the abdomen — where the fluid can be absorbed. A small valve in the system regulates the flow. Our second video, "Insertion of a CSF shunt" (just over a minute long), follows a shunt operation, and its description makes a point worth knowing: careful closure of the abdominal wall is a basic but important part of these operations, not least because some patients need abdominal surgery more than once over a lifetime of shunt care.

Living with the fix

Whichever route is used, hydrocephalus becomes a condition that is managed rather than finished. Shunts are dependable but they are devices, and devices can block, break, or become infected months or years later — so anyone with a shunt is taught the warning signs of it failing, which are the same pressure symptoms returning, and follow-up is lifelong. An ETV opening can also narrow again over time, so its patients are followed too, even though there is no hardware to maintain.

What stays constant is the underlying logic from step one: keep the fluid moving, and the brain is protected. If you or your child is being assessed for hydrocephalus, the questions worth asking your team are the step-by-step ones — where is the blockage, which route out are you planning, and what follow-up will we have? A good neurosurgical team will walk you through exactly that sequence.

Frequently Asked Questions

What does hydrocephalus mean, literally?

The name comes from Greek words for "water" and "head". The "water" is cerebrospinal fluid — the clear liquid that normally cushions the brain — building up inside the ventricles, the brain's fluid-filled spaces.

Is hydrocephalus the same at every age?

The fluid problem is the same, but it shows differently. In babies, the skull can still expand, so a fast-growing head is often the first sign. In older children and adults the skull cannot expand, so pressure symptoms such as headache, nausea, and vision changes come first.

What is the difference between a shunt and an ETV?

A shunt is an implanted tube that drains fluid from the ventricles to another part of the body, usually the abdomen, where it is absorbed. An endoscopic third ventriculostomy (ETV) implants nothing — the surgeon makes a small opening inside the brain so fluid can bypass a blockage and be absorbed naturally. ETV suits obstructive hydrocephalus in particular.

Can hydrocephalus go away on its own?

Established hydrocephalus does not reliably resolve by itself, because the blockage or absorption problem causing it remains. It is a condition that is treated and then followed over time, which is why keeping follow-up appointments matters even when you feel well.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about hydrocephalus, not medical advice and not a diagnosis. Headaches with vomiting, vision changes, unusual drowsiness, or a baby's head growing unusually fast need prompt in-person medical assessment.