Cholesteatoma
- A cholesteatoma is trapped skin in the middle ear — a ball of shed skin cells in a place that has no drain.
- It's not a tumor and not cancer, but it behaves like a bully: it slowly grows and erodes the tiny bones and walls around it.
- Classic CT clue: a soft-tissue mass in the Prussak space (a recess in the attic, just medial to the upper eardrum) with bone erosion, often blunting the scutum.
- The trick CT can't do, MRI can: cholesteatoma lights up bright on diffusion-weighted imaging (DWI), which is how we tell it apart from boring fluid or scar.
- It matters because, left alone, it can eat into the ossicles, the facial nerve canal, the inner ear, and even the roof of the temporal bone.
Here's a sentence I never thought I'd write about the human body: sometimes skin ends up growing on the inside, in a sealed pocket, with nowhere to go — and then it just... keeps shedding. Cholesteatoma is that. It is one of the great misnomers of medicine, because it contains no cholesterol and it is not a -oma in the tumor sense. It's a wad of keratin debris — dead skin flakes — packed into the middle ear like a snowball that never melts.
What it actually is
Your ear canal and eardrum are lined with skin, and skin does what skin does: it constantly sheds its outer layer. Normally those flakes ride out of the ear canal on a little conveyor belt and you never think about them. A cholesteatoma is what happens when that skin gets walled off in the middle ear — the air-filled room behind the eardrum that houses the three hearing bones — where there's no conveyor belt to carry the debris away.
So the debris piles up. The pile grows. And here's the nasty part: that ball of skin releases enzymes that dissolve bone. It's slow, it's painless, and it's relentless — like a tree root that lifts a sidewalk one millimeter a year. Most are acquired, usually downstream of a chronically dysfunctional eustachian tube and a retracted eardrum; a smaller number are congenital, sitting behind an intact drum in a kid with no history of ear infections.
The name is a historical accident. "Cholesteatoma" sounds like a fatty tumor, but pathologically it's just keratinizing squamous epithelium and its shed debris — skin in the wrong room. Don't let the word fool you.
Where it lives and what it wrecks
The classic acquired cholesteatoma starts in the attic — the upper part of the middle ear, also called the epitympanum. The specific pocket radiologists love to name is Prussak space, the little recess just medial to the upper eardrum. From there it expands and starts knocking down the furniture.
The "furniture" is a list worth knowing, because each item is a hearing or balance disaster waiting to happen:
| Structure eroded | Why you care |
|---|---|
| Scutum | The bony spur at the top of the ear canal; blunting/erosion is an early, classic CT sign. |
| Ossicles | The hearing bones (especially the long process of the incus) get eroded → conductive hearing loss. |
| Lateral semicircular canal | Erosion creates a fistula → vertigo, and a surgical hazard. |
| Facial nerve canal | Dehiscence puts the nerve at risk → facial weakness. |
| Tegmen tympani | The thin roof over the middle ear; erosion opens a path to the brain. |
How we image it
The workhorse is high-resolution CT of the temporal bone, which is exquisite at showing the one thing that matters most here: bone, and where it's missing. (If you want the nuts and bolts of that scan, see Temporal Bone CT.)
The problem is that on CT, a cholesteatoma and a blob of plain fluid or granulation tissue can look identical — both are just "soft-tissue density filling the middle ear." CT tells you there's something there and whether bone is being eaten, but it can't always tell you what the something is.
That's where MRI earns its keep. Cholesteatoma is packed with dense, gummy keratin, and that restricts the random jiggling of water molecules — so it glows bright on non-echoplanar diffusion-weighted imaging (DWI). Fluid and scar don't do this. That bright DWI signal is the single most useful trick we have for confirming a cholesteatoma you can't see directly, and for hunting recurrence after surgery without re-opening the ear.
Modern protocols favor non-echoplanar DWI for the temporal bone. Standard echoplanar DWI is wrecked by the air–bone interfaces of the skull base (lots of distortion and false signal), which can hide or mimic small cholesteatomas. The non-EPI version gives cleaner images right where you need them.
The traps
Cholesteatoma vs. simple effusion/granulation tissue. On CT they can be twins. The tiebreakers are bone erosion (favors cholesteatoma) and bright signal on DWI (strongly favors cholesteatoma). Plain mucosal disease and post-inflammatory debris don't restrict diffusion the way packed keratin does.
Don't confuse it with otomastoiditis either — although the two are old friends and often coexist, since the chronically inflamed, poorly ventilated ear is exactly the soil a cholesteatoma grows in.
The bottom line
If you remember one thing: cholesteatoma is trapped, bone-eroding skin in the middle ear. CT shows you a soft-tissue mass with erosion (look at that scutum), and DWI confirms it by lighting up bright. It's benign by the textbook, but it's a slow-motion wrecking ball — which is exactly why we go looking for it.