Hydrocephalus & Shunts
- Hydrocephalus is too much cerebrospinal fluid (CSF) in the ventricles, with enough pressure to puff them up — it's a plumbing problem, not just "big spaces."
- Split it into two buckets: obstructive (a blockage somewhere in the pipes) and communicating (the pipes are open, but CSF isn't getting reabsorbed or made appropriately).
- The classic tells are ventricles that look too round and tense, the temporal horns ballooning, and the edges of the ventricles looking blurry from fluid pushing into the brain.
- A shunt is a tube that drains CSF somewhere it can be reabsorbed; the two things that break are obstruction (it clogs) and disconnection/migration (it comes apart or wanders).
- The fastest read on a kid with a shunt and a headache: compare today's ventricles to their old scan. Bigger than baseline is the alarm bell.
Your brain floats in a private, constantly refreshed bath of cerebrospinal fluid. The body makes it, circulates it through four connected chambers called ventricles, and then reabsorbs it — a slow, tidy river that's supposed to come in and go out at the same rate. Hydrocephalus is what happens when that river dams up or the drain clogs: fluid keeps arriving, has nowhere to go, and the pressure inflates the ventricles like water balloons inside the skull.
In a baby, the skull can stretch (the sutures aren't fused yet), so the head just gets bigger. In an older kid, the skull is sealed shut, so the pressure has nowhere to go but in — onto the brain. That difference is the whole reason this disease feels so urgent in pediatrics.
Obstructive vs. communicating: where's the clog?
Here's the one distinction worth burning into memory, because it tells you where to look and what to do.
Obstructive (non-communicating) hydrocephalus is a physical blockage within the ventricular system. CSF backs up upstream of the dam, exactly like a kinked garden hose — everything before the kink swells, everything after it stays normal. The classic chokepoint is the cerebral aqueduct, the narrow channel between the third and fourth ventricles. Block that, and the lateral and third ventricles balloon while the fourth stays small.
Communicating hydrocephalus means the ventricles all "communicate" fine — fluid flows through the whole system — but it isn't being reabsorbed (or, rarely, it's being overproduced). The dam is downstream, out where CSF is supposed to leave. Here the whole system enlarges, fourth ventricle included.
The naming is genuinely confusing because "communicating" sounds like the good outcome. It isn't a value judgment — it just describes whether CSF can still travel between the ventricles. Read it as "the blockage is outside the ventricles" and you'll never mix it up again.
What you're actually hunting on the scan
The trap is that big ventricles aren't automatically hydrocephalus. A brain that has lost tissue (atrophy) also has roomy ventricles — but that's empty space passively filling in, not pressurized fluid shoving outward. You're looking for signs of pressure, not just size.
The tells of pressure:
| Finding | What it means |
|---|---|
| Temporal horns of the lateral ventricles dilated | Early, sensitive sign — these balloon before you'd guess. |
| Ventricles look rounded and tense, frontal horns ballooned | Fluid under pressure pushes outward like an inflating balloon, not a slack one. |
| Periventricular blurring (transependymal flow) | CSF is being forced through the ventricle wall into the brain — a pressure giveaway. |
| Effacement of the brain surface sulci | The swollen brain is squashed against the skull. |
Big ventricles + crisp sharp edges + widened sulci everywhere = probably atrophy, not active hydrocephalus. Big ventricles + rounded tense shape + blurry periventricular edges + squashed sulci = pressure. When in doubt, the single best move is to pull the patient's prior imaging and ask: bigger than their own baseline?
The same logic applies to adults, and the size-vs-pressure question is the heart of the adult hydrocephalus page too — worth a look once this clicks.
Shunts: the plumber's bypass
When the brain can't drain itself, we install a bypass: a ventriculoperitoneal (VP) shunt. A catheter sits in a ventricle, runs under the skin down the neck and chest, and dumps CSF into the belly (the peritoneum), where the body reabsorbs it. A pressure-sensitive valve in the middle keeps flow from running too fast. It's a literal drainpipe with a one-way valve — beautifully simple, which is exactly why it's a magnet for problems.
Two things break, and your job is to spot them:
- Obstruction — the tube clogs (debris, tissue, the tip getting walled off). CSF backs up again and the ventricles re-enlarge. This is the big one.
- Disconnection or migration — the tubing comes apart at a joint or the tip wanders out of position.
The "shunt series" is a set of plain radiographs covering the entire shunt from skull to abdomen, used to trace the hardware end to end looking for a break, kink, or disconnection. Pair it with a CT or fast MRI of the head to check whether the ventricles have grown. Radiographs show the tube; the head scan shows whether it's working.
And the most important sentence on this whole page: in a child with a shunt who suddenly has headaches, vomiting, or sleepiness, compare today's ventricles to their baseline scan. A shunt patient's "normal" ventricles can be small, slit-like, or just their own particular shape. Bigger than baseline = the shunt may be failing, and that's a neurosurgical conversation, not a wait-and-see.
Shunt malfunction can be a genuine emergency — rising pressure in a sealed skull is dangerous. Don't anchor on "the ventricles aren't that big." If they're bigger than this child's prior scan and the kid looks sick, that's enough.
Where it comes from in kids
Pediatric hydrocephalus has its own usual suspects: aqueductal narrowing, bleeding in the ventricles of premature babies, infection, and congenital malformations of the brain. Masses matter too — a posterior fossa tumor pressing on the fourth ventricle is a classic cause, which is one reason pediatric brain tumors and hydrocephalus keep showing up in the same sentence.
The single thing to carry out of here: hydrocephalus is a pressure-and-plumbing story. Find the clog, judge whether the fluid is under pressure (not just spacious), and — if there's a shunt — always, always compare to baseline.