Cholesteatoma — What It Is and Why It Matters

The name is misleading. Cholesteatoma is not a tumour, contains no cholesterol (in most cases), and the “-oma” suffix implies a benign growth that this lesion emphatically is not — it is a locally aggressive, bone-destroying expansion of keratinizing squamous epithelium that has no business being in the middle ear. A more accurate historical term, keratoma, never caught on. Understanding cholesteatoma requires understanding what squamous epithelium normally does, why its presence in the middle ear is so destructive, and why surgical removal is the only effective treatment.

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What Cholesteatoma Is

Normal skin has a remarkable property: the stratified squamous epithelium of skin migrates outward, carrying desquamated keratin debris toward the surface where it sloughs off harmlessly. In the ear canal, this self-cleaning migratory process (skin migration from the eardrum radially outward) keeps the canal clear. The tympanic membrane, ear canal, and auricle are among the only places in the body where this epithelial self-cleaning is essential — and where disruption is consequential.

Cholesteatoma is squamous epithelium that has gained access to the middle ear and mastoid — either congenitally, or through a defect in the tympanic membrane. Once inside the middle ear, the epithelium continues doing exactly what it always does: proliferating and migrating, desquamating keratin. But now it is in a closed, irregular cavity with ossicles, the facial nerve canal, the labyrinthine capsule, and the dural plate as its boundaries. As keratin accumulates and the epithelium expands, it does not stop. Instead, it erodes everything in its path.

The expansion is driven by:

• Enzymatic bone resorption: The epithelium and the inflammatory tissue at the advancing edge produce matrix metalloproteinases (MMPs) and collagenases that directly degrade bone matrix
• Osteoclast activation: Cytokines from the inflammatory process (IL-1, TNF-α, RANKL) recruit osteoclasts that accelerate bone resorption
• Mechanical pressure: The expanding keratin mass physically compresses surrounding structures

The result is progressive destruction of the ossicular chain, the bony labyrinthine capsule, the facial nerve canal, the tegmen (bone separating the middle ear from the dural plate above), and the sigmoid sinus plate below.

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Classification — Congenital vs Acquired

Congenital Cholesteatoma

Congenital cholesteatoma arises from a congenital rest of squamous epithelium in the middle ear, without any history of ear infections, perforation, or previous ear surgery. It is found behind an intact tympanic membrane — the classic presentation is a white pearly mass visible in the anterosuperior quadrant of the drum (the most common site) in a child with no ear disease history.

The proposed mechanism involves failure of programmed regression of an epidermal cell rest (the “epidermoid formation”) that normally involutes by 33 weeks of gestation. It is uncommon but important because it is found in children who appear to have entirely normal ears, and audiometric or otoscopic abnormalities may be the only clue.

Staging (Potsic classification): Grade I (limited to one quadrant), Grade II (multiple quadrants), Grade III (ossicular involvement or mastoid extension), Grade IV (extensive mastoid or extramedial disease).

Acquired Cholesteatoma

The vast majority of cholesteatomas are acquired. There are two mechanisms:

Primary acquired (pars flaccida retraction pocket): The pars flaccida of the tympanic membrane (Shrapnell’s membrane — the small, loosely supported region above the short process of the malleus, where the membrane lacks a fibrous layer) is less mechanically stable than the pars tensa. Eustachian tube dysfunction causes persistent negative middle ear pressure, which retracts the pars flaccida progressively. The retraction pocket deepens, becomes self-retaining, accumulates keratin in its depths, and begins eroding into the epitympanum (attic). This is the most common type of cholesteatoma in the developed world.

Secondary acquired (marginal perforation ingrowth): A perforation at the margins of the pars tensa (a marginal perforation — unlike safe central perforations, which do not touch the drum annulus) allows skin from the ear canal to migrate directly into the middle ear. Squamous epithelium grows through the defect and establishes itself in the mesotympanum.

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Clinical Presentation

The Warning Symptoms

Cholesteatoma characteristically produces a specific combination of symptoms that, when recognised, should trigger prompt referral:

Foul-smelling, non-resolving otorrhoea. The keratin debris in a cholesteatoma rapidly becomes infected with gram-negative organisms (Pseudomonas aeruginosa and Proteus most commonly). The result is a persistent, often offensive-smelling discharge that does not resolve with standard antibiotic eardrops — the biofilm-covered keratin mass is not accessible to topical antibiotics. This contrasts with the mucopurulent discharge of tubotympanic (safe) CSOM, which tends to be less offensive and is more responsive to treatment.

Conductive hearing loss. Present in most cases due to erosion of the ossicular chain. The long process of the incus is the most commonly eroded ossicle — its tenuous blood supply makes it the most vulnerable. Conductive loss in the context of a chronic discharging ear should always raise the question of cholesteatoma.

Attic crust or retraction. The classic otoscopic finding: a scaly, crusted, or retracted area in the posterosuperior quadrant of the drum, or a keratin-filled retraction pocket in the pars flaccida (attic). This is the physical manifestation of the expanding epithelium and keratin accumulation.

When Cholesteatoma Becomes Dangerous

Untreated, cholesteatoma destroys whatever is adjacent to it. Complications follow directly from the structures eroded:

Structure Eroded	Complication
Ossicular chain	Conductive hearing loss (most common)
Labyrinthine capsule (lateral SCC)	Labyrinthine fistula → sensorineural hearing loss, vertigo
Facial nerve canal (tympanic segment)	Facial nerve palsy
Tegmen tympani / tegmen mastoidei	Extradural abscess, meningitis, brain abscess
Sigmoid sinus plate	Sigmoid sinus thrombophlebitis
Mastoid tip	Bezold’s abscess

A patient presenting with facial nerve palsy, vertigo, or any sign of intracranial extension in the context of chronic ear disease has a complication of cholesteatoma until proven otherwise.

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Otoscopic Examination

The most important clinical skill for diagnosing cholesteatoma is systematic, complete otoscopic examination of the entire drum — particularly the posterosuperior quadrant and the pars flaccida (attic area above the short process of the malleus). The classic findings:

White pearly mass — keratin debris, often glistening, visible through the drum or through a perforation in the posterosuperior quadrant or attic Attic crust or keratin — in the superior portion of the canal, just above the drum margin Marginal perforation (especially posterosuperior) — a perforation extending to the drum annulus Granulation tissue adjacent to a retraction area — indicates active erosion and inflammation

Any crust in the attic should be presumed cholesteatoma until microscopy proves otherwise. Cleaning the ear under a microscope (aural microsuction) is frequently needed to adequately visualise the drum and determine the extent of disease.

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Investigation

CT temporal bones (HRCT): The primary imaging investigation. Shows the extent of cholesteatoma, the degree of ossicular chain erosion, the proximity to the facial nerve canal and labyrinthine capsule, and any extradural extension. CT cannot reliably distinguish cholesteatoma from granulation tissue or mucosa, but it identifies bony erosion and maps surgical anatomy.

MRI (diffusion-weighted imaging, DWI-MRI): Cholesteatoma contains keratin, which restricts diffusion on DWI. Non-echo-planar DWI (HASTE/PROPELLER-DWI) has become the modality of choice for detecting residual or recurrent cholesteatoma after surgery (avoiding reoperation for a second-look procedure in some centres). The sensitivity and specificity of this technique have improved significantly over the past decade.

Audiogram: Conductive hearing loss characterised by an air-bone gap is almost invariably present. Sensorineural component if labyrinthine erosion or toxic inner ear damage has occurred.

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Treatment

Surgery is the only treatment. There is no medical management for cholesteatoma. Antibiotics can reduce associated infection temporarily but do not arrest expansion or erosion.

The goal of surgery is complete removal of the cholesteatoma matrix — the epithelium itself, not just the keratin contents. If any matrix is left behind, the epithelium will continue to desquamate, re-accumulate keratin, and the cholesteatoma will recur (residual cholesteatoma).

Two main surgical approaches:

Canal wall up (CWU) mastoidectomy: The posterior canal wall is preserved, maintaining a near-normal ear canal and allowing a hearing reconstruction in the same procedure. Advantage: better cosmesis and hearing potential. Disadvantage: the preserved canal wall creates an enclosed space where residual disease may hide — a second-look operation (or follow-up MRI) is typically planned 12–18 months later.

Canal wall down (CWD) mastoidectomy (modified radical mastoidectomy): The posterior canal wall is removed, creating a single open cavity (the mastoid bowl) that opens into the ear canal. The cavity can be inspected directly at each follow-up otoscopy. Advantage: more thorough disease clearance and simpler surveillance. Disadvantage: the open cavity requires lifelong water avoidance and regular cleaning, and hearing reconstruction is constrained (typically a Type III tympanoplasty is performed at the same time or later).

The choice between CWU and CWD depends on disease extent, middle ear anatomy, the patient’s contralateral hearing, and the surgeon’s judgement about the likelihood of complete removal.

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Residual vs Recurrent Cholesteatoma

Two terms with different meanings that are often confused:

Residual cholesteatoma: Disease that was left behind at the time of the original operation — incompletely removed. It appears in the first one to two years after surgery.

Recurrent cholesteatoma: New cholesteatoma developing from a new retraction pocket or epithelial ingrowth after surgery — the original cause reasserts itself on the reconstructed ear. It appears after a longer interval and is more common in ears with ongoing Eustachian tube dysfunction.

Both are detected on follow-up otoscopy or imaging and require reoperation.

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Key Numbers

Parameter	Value
Most common ossicle eroded	Long process of incus
Most common site of acquired cholesteatoma	Posterosuperior/pars flaccida (attic)
Most common organism in cholesteatoma discharge	Pseudomonas aeruginosa
Most common bony labyrinth complication	Lateral SCC fistula
Canal wall up: planned second-look timing	12–18 months
Imaging for residual/recurrent disease	Non-EPI DWI-MRI

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Frequently Asked Questions

Why does the long process of the incus erode first in cholesteatoma? The long process of the incus has a particularly tenuous blood supply — the vascular supply to this slender bony projection is end-arterial and minimal. Chronic inflammation and the enzymatic activity at the cholesteatoma margin further compromises this supply, making ischaemic necrosis of the long process the most common ossicular event in both CSOM and cholesteatoma. This is also why the incus is the ossicle most commonly absent or eroded when a surgeon explores a chronically diseased middle ear.

Can cholesteatoma be a coincidental finding? Small, well-controlled retraction pockets can be observed rather than operated on immediately, particularly in elderly patients where the surgical risk-benefit ratio shifts. However, any cholesteatoma with evidence of expansion, ossicular erosion, or proximity to dangerous structures (facial nerve, labyrinth, tegmen) should be operated on without undue delay. The natural history of untreated cholesteatoma is progressive expansion and, eventually, one or more of the complications listed above.

What is the difference between “safe” and “unsafe” CSOM? “Safe” (tubotympanic) CSOM involves a central perforation of the pars tensa, without cholesteatoma, and is associated with mucopurulent discharge that is amenable to treatment. “Unsafe” (atticoantral or epitympanic) CSOM involves disease in the posterosuperior quadrant or attic — typically with retraction, a marginal perforation, or frank cholesteatoma — and is associated with bone-destructive, offensive discharge and potential complications. The terms are somewhat archaic but remain in common use; “unsafe” disease in any form warrants urgent surgical referral.