Choroid Plexus Tumors
- The choroid plexus is the brain's plumbing department — it makes cerebrospinal fluid (CSF). When it grows a tumor, that tumor lives inside the ventricles and tends to crank out even more fluid.
- The classic look: a lobulated, avidly enhancing mass sitting in a ventricle, often with hydrocephalus. People describe the surface as "cauliflower-like" for a reason.
- Age picks the location. In little kids it favors the lateral ventricle; in adults it favors the fourth ventricle.
- The spectrum runs from papilloma (benign, WHO grade 1) through atypical papilloma up to carcinoma (aggressive, grade 3) — and the carcinoma is the one that invades brain and seeds the CSF.
- They love to bleed a little and to drop calcium, so don't be surprised by spots of hemorrhage or calcification.
Every ventricle in your brain has a frilly little structure tacked to its wall whose entire job is to brew cerebrospinal fluid — the cushioning bathwater your brain floats in. That structure is the choroid plexus, and on a normal scan it's the unremarkable enhancing tissue you learned to ignore. Choroid plexus tumors are what happen when that quiet little fluid factory decides to become a small business and expand. The punchline writes itself: a tumor made of CSF-producing cells often makes too much CSF.
What it actually is
Think of the choroid plexus as a sponge dangling in a bathtub, constantly wringing fluid out into the room. A choroid plexus papilloma is that sponge growing into a shaggy, cauliflower-shaped lump — still well-behaved, still doing its job, just bigger and noisier about it. A choroid plexus carcinoma is the same sponge gone rogue: it stops respecting the tub walls, chews into the surrounding brain, and sheds cells into the fluid to float downstream. In between sits the atypical papilloma, the awkward middle child the pathologists grade by counting how busy the cells look under the microscope.
These are predominantly tumors of the very young — papillomas especially show up in infants and small children — but they can appear at any age. They're uncommon overall, so they're more of a "don't forget this exists" entity than a daily read.
Where to look: age tells you the room
Here's the one fact that makes you look smart on rounds. Choroid plexus tumors live wherever choroid plexus normally lives — inside the ventricular system — but which ventricle depends on the patient's age.
| Patient | Favorite location |
|---|---|
| Children | Lateral ventricle (often the atrium/trigone) |
| Adults | Fourth ventricle |
The third ventricle and the cerebellopontine angle can play host too, but if you remember "kid = lateral, grown-up = fourth," you've captured the bulk of them. Because these masses are intraventricular, they belong to the family of intraventricular masses and sit on the differential alongside ependymoma, meningioma, and others.
The imaging fingerprint
On CT the mass is usually well-defined and a touch denser than brain, often speckled with calcification, and it lights up brightly with contrast. On MRI it tends to be mixed-to-isointense on T1, variable on T2, and — the headline feature — it enhances avidly and somewhat heterogeneously, frequently with a lobulated, frond-like surface. That bumpy "cauliflower" texture is the histology showing through: it's literally a heaped-up overgrowth of the normal frilly plexus.
Vivid enhancement plus a lobulated surface plus an intraventricular location plus a young patient is the combination that should make you say "choroid plexus tumor" out loud.
Why these kids show up: too much water in the tub
Most of these patients present with signs of raised intracranial pressure — in an infant, that's a bulging fontanelle and a head growing off its curve. The reason is hydrocephalus, and it happens by two mechanisms that often gang up. First, the tumor is a fluid factory, so it overproduces CSF — the sponge wringing out faster than the drains can keep up. Second, the bulky mass can physically plug the ventricular outflow, like a beach ball wedged in the bathtub drain. Either way, fluid backs up and the ventricles balloon.
Telling benign from nasty
The big fork in the road is papilloma versus carcinoma, and imaging gives you clues even before the pathologist weighs in.
A papilloma is typically smooth-bordered and stays politely inside the ventricle. Features that should make you worry about carcinoma instead: frank invasion of the adjacent brain, surrounding edema, necrosis, and — the giveaway — CSF seeding, where enhancing tumor deposits show up along the ventricular lining or down the spine. When carcinoma is on the table, the whole neuraxis gets imaged.
A caution about that distinction: imaging tilts the odds but doesn't clinch it. Some papillomas misbehave at the margins and some carcinomas look deceptively tidy, so the final grade is a tissue diagnosis, not a radiology diagnosis.
There's a recognized association between choroid plexus carcinoma and germline TP53 alterations (Li–Fraumeni syndrome), so a carcinoma in a young child is a flag to think about an underlying cancer-predisposition syndrome and family history.
The one thing to carry out the door
When you see a lobulated, brightly enhancing mass sitting inside a ventricle in a child with a big head and big ventricles, the choroid plexus tumor should be at the very top of your list — and your next question is always whether it merely looks like an overgrown sponge (papilloma) or whether it's clawing into brain and seeding fluid (carcinoma). Location tells you to consider it; behavior at the edges tells you how scared to be.