Cholesteatoma

Cholesteatoma is a destructive cyst-like growth that develops within the middle ear or mastoid — the air cell system within the temporal bone behind the ear. Despite the name suggesting a fatty tumour (the “chol-” and “steat-” prefixes), cholesteatoma contains neither cholesterol nor fat: it is a collection of desquamating stratified squamous epithelium (skin cells) trapped in an enclosed space, progressively accumulating and expanding in a manner that erodes the surrounding bone. Left untreated, a cholesteatoma will continue to expand indefinitely, destroying the structures it encounters along the way — the hearing ossicles, the walls of the mastoid, and potentially the inner ear, the facial nerve canal, the tegmen (the thin bone separating the ear from the brain), and even the brain itself.

Cholesteatoma is not cancer — it is a benign process — but its progressive, destructive nature means it requires surgical removal. There is no medical treatment that stops or reverses its growth.

What Is Cholesteatoma Made Of?

Normal skin — including the skin of the ear canal — has a remarkable property: epithelial migration. The skin cells of the ear canal migrate continuously outward from the eardrum toward the ear canal opening, carrying wax, debris, and dead cells with them. This migration — at approximately the same rate as fingernail growth — is the ear’s self-cleaning mechanism and explains why healthy ears do not fill up with wax accumulation.

A cholesteatoma forms when this skin gets into the wrong place — specifically, into the middle ear space behind the eardrum or into the mastoid. Once skin cells are in the middle ear, they continue their normal behaviour: shedding (desquamating) keratin and accumulated skin cells. But because there is no pathway out, the shed cells accumulate, packing the available space and generating expanding pressure. The growing mass releases proteolytic enzymes and inflammatory mediators that dissolve bone (osteolysis), allowing further expansion through the path of least resistance.

Types of Cholesteatoma

Acquired Cholesteatoma (most common)

The vast majority of cholesteatomas are acquired — they develop in the context of chronic middle ear or Eustachian tube disease. There are two principal mechanisms:

Retraction pocket cholesteatoma (attic / pars flaccida)

The most common type. The pars flaccida — the upper, lax portion of the eardrum — is the part most vulnerable to retraction under chronic negative middle ear pressure from Eustachian tube dysfunction. The chronically negative pressure gradually draws the eardrum inward, creating a pocket or sac in the attic (the space above the ossicular chain). This retraction pocket progressively deepens and accumulates keratin from its lining. Once it can no longer clean itself, it begins to expand — first laterally into the mastoid, then medially toward the ossicular chain, and eventually wherever bone offers least resistance.

Perforation-related (pars tensa) cholesteatoma

When a perforation exists in the lower portion of the eardrum (pars tensa), skin from the ear canal can migrate through the perforation into the middle ear. This is less common than attic retraction cholesteatoma but represents an important reason why persistent perforations — particularly those with squamous epithelium invading the middle ear space — require surveillance and potentially surgical repair.

Congenital Cholesteatoma

Congenital cholesteatoma arises from a rest of embryonic squamous epithelium trapped within the middle ear during development — before the eardrum has formed its definitive structure. It presents classically as a white pearl visible through an intact, normal-appearing eardrum, typically found incidentally on examination of a child with no history of ear disease or infection. Because it arises from embryonic tissue rather than through the eardrum, the eardrum is intact and there is no preceding history of Eustachian tube disease. Congenital cholesteatomas are detected earlier (because the appearance is more striking on examination) and tend to have a better prognosis than acquired cholesteatomas.

What Structures Does Cholesteatoma Destroy?

The expanding cholesteatoma erodes bone by a combination of direct mechanical pressure and enzyme-mediated osteolysis. The structures at risk reflect the anatomy of the middle ear and mastoid:

Symptoms

Cholesteatoma is often insidious in its early course — it may be present for years before producing symptoms. When symptoms do develop, they reflect the structures being destroyed:

• Otorrhoea (ear discharge): Persistent or recurrent foul-smelling discharge from the ear is the most consistent presenting symptom. The discharge from a cholesteatoma has a characteristic musty or offensive odour that distinguishes it from the odourless discharge of simple otitis media. It persists despite antibiotic treatment because its source — the expanding keratinous mass — is not bacteriological.
• Hearing loss: Conductive hearing loss from ossicular chain erosion is common. The onset is typically gradual. A patient with a long history of ear problems who reports worsening hearing should be assessed for ossicular destruction.
• Ear fullness or pressure
• Tinnitus
• Vertigo or dizziness: Suggests labyrinthine involvement — a lateral semicircular canal fistula is the most common cause. Vertigo in the context of cholesteatoma requires urgent assessment.
• Facial weakness: Any facial palsy associated with ear disease requires urgent assessment to exclude cholesteatoma with facial nerve involvement.
• Severe headache, fever, neck stiffness: These suggest an intracranial complication and require emergency assessment.

Diagnosis

Otoscopy and Microscopy

The diagnosis is clinical — made by examining the eardrum and ear canal under direct vision with an otoscope or, more usefully, under the operating microscope. The characteristic finding is a retraction pocket in the pars flaccida containing white keratinous debris, or a perforation with squamous epithelium migrating into the middle ear space. The white debris of a cholesteatoma — sometimes described as resembling “wet tissue paper” — is pathognomonic. Early retraction pockets may appear as simple eardrum retraction without visible debris; surveillance and monitoring is required to determine whether the pocket is self-cleaning or accumulating.

High-Resolution CT of the Temporal Bone

CT imaging provides essential information about the extent of the cholesteatoma, the structures it has involved, and the degree of bony destruction. It guides surgical planning by showing the anatomy of the facial nerve canal, the tegmen, the semicircular canals, and the ossicular chain. It also identifies any intracranial or intraorbital extension. CT does not reliably distinguish residual or recurrent cholesteatoma from post-surgical changes, which is why surveillance strategies increasingly use MRI.

Non-Echo-Planar Diffusion-Weighted MRI (DWI-MRI)

Cholesteatoma has a characteristic appearance on non-echo-planar diffusion-weighted MRI sequences — a high-signal focus reflecting the restricted diffusion of the densely packed keratin matrix. This imaging technique is increasingly used both for pre-operative characterisation and for post-operative surveillance: a DWI-MRI at approximately one year after surgery can identify residual or recurrent cholesteatoma (as small as 3–4mm) without requiring a second-look surgical exploration. This non-invasive surveillance strategy is now standard practice in many centres.

Surgical Treatment

Surgery — tympanomastoid surgery — is the only effective treatment for cholesteatoma. There is no medical therapy that arrests its progression. The goals of surgery are disease eradication (removing all cholesteatoma matrix), prevention of recurrence (eliminating the conditions that allowed the cholesteatoma to develop), and reconstruction of hearing where possible.

Canal Wall Up (CWU) Mastoidectomy

The posterior wall of the ear canal (the bony bridge between the ear canal and the mastoid) is preserved, maintaining the normal ear canal anatomy and allowing normal hearing aid use and water entry into the ear. The mastoid air cells and middle ear are opened through an incision behind the ear and the cholesteatoma systematically removed. The advantage of canal wall up surgery is that the ear retains a more normal anatomy with a normal ear canal. The disadvantage is that the preserved canal wall creates a “hidden” space in the mastoid that is more difficult to fully inspect, increasing the risk of residual or recurrent cholesteatoma — typically requiring a planned second-look operation at twelve months to confirm complete clearance, or DWI-MRI surveillance.

Canal Wall Down (CWD) Mastoidectomy (Modified Radical)

The posterior canal wall is removed, creating a widely open mastoid cavity that communicates with the ear canal. This “modified radical” cavity is easier to inspect and clean at follow-up, has a lower rate of residual disease, and eliminates the “hidden” space problem of the CWU approach. The trade-off is a larger cavity that must be regularly cleaned at ENT appointments, restrictions on water entering the ear, and a mastoid bowl that can accumulate wax and debris requiring lifelong surveillance. Canal wall down surgery is more often employed for extensive cholesteatoma, revision cases, or where the anatomy makes CWU surgery higher-risk.

Ossicular Chain Reconstruction

Where the ossicular chain has been partially or completely destroyed by cholesteatoma, reconstruction of the hearing mechanism is performed at the time of cholesteatoma removal or at a planned second-stage procedure. Titanium ossicular prostheses — total or partial ossicular replacement prostheses (TORP or PORP) — are used to bridge the gap in the ossicular chain. Hearing improvement following ossicular reconstruction varies depending on the extent of the damage; most patients achieve meaningful improvement in conductive hearing.

Recurrence and Long-Term Surveillance

Cholesteatoma has a significant recurrence rate — estimates range from 10–40% depending on the surgical technique, the extent of disease at surgery, and the length of follow-up. Recurrence can arise from residual disease (microscopic remnants left at the original surgery) or true recurrent disease (reformation of a retraction pocket or re-invasion of squamous epithelium). This recurrence risk mandates long-term surveillance after cholesteatoma surgery, regardless of how thorough the initial procedure appeared.

Surveillance protocols typically include annual ENT reviews with microscopic examination of the ear canal and eardrum, and non-echo-planar DWI-MRI at twelve months post-operatively (and subsequently where there is any clinical concern). A second-look operation under general anaesthesia may be recommended in selected cases — particularly for extensive disease, CWU surgery where residual disease could not be excluded, or in children where the recurrence risk is higher.

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