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Keratosis obturans

Keratosis obturans is imaged in younger patients (typically <40 years old) presenting with acute severe ear canal pain and conductive hearing loss, with bilateral involvement in 50% of cases. It is associated with bronchiectasis and chronic paranasal sinus disease, particularly in the pediatric population.

Key Images

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Look For First
  • Well-defined soft tissue mass completely filling and dilating the bony external auditory canal without bony erosion on CT
  • Preserved tympanic membrane or only slight thickening without involvement of the tympanic canal
  • Bilateral presentation in 50% of cases with symmetric canal expansion
Key Image Findings
  • CT shows a well-defined soft tissue density plug within the bony external auditory canal that may diffusely enlarge the canal lumen without evidence of bone erosion or remodeling of the canal walls.
  • The keratin plug demonstrates diffuse remodeling and expansion of the bony canal, reflecting the chronic accumulation of desquamated keratin debris with underlying epithelial hyperplasia.
  • The tympanic canal is usually spared or only shows slight thickening, which helps distinguish keratosis obturans from cholesteatoma which more aggressively involves the middle ear.
  • No evidence of osseous erosion or necrosis is present, in contradistinction to external auditory canal cholesteatoma which demonstrates focal bony erosion.
  • The soft tissue mass is typically homogeneous and does not show air foci, whereas simple external auditory canal debris may contain small air pockets within partially filling material.
Differential Diagnosis
  • External auditory canal debris: partially fills the canal with preserved air foci interspersed within the material, whereas keratosis obturans is a dense homogeneous plug without air
  • External auditory canal cholesteatoma: presents as soft tissue density with associated bony erosion and may show aggressive middle ear involvement, while keratosis obturans has no bone erosion
  • External auditory canal carcinoma: irregular mass with or without bony erosion and typically in older patients, versus the well-defined margins and younger age group of keratosis obturans
  • Otitis externa: demonstrates surrounding inflammatory fat stranding and edema in the surrounding soft tissues, whereas keratosis obturans shows no surrounding inflammation
  • Epidermal inclusion cyst of the external auditory canal: typically smaller, more localized lesion without diffuse canal expansion and remodeling
Discussion

Keratosis obturans is characterized by abnormal accumulation of desquamated keratin within the deep meatus leading to progressive expansion and remodeling of the bony external auditory canal without erosion, distinguishing it from erosive pathology like cholesteatoma.

The condition is bilateral in 50% of cases and strongly associated with bronchiectasis and chronic paranasal sinus disease in up to 80% of pediatric patients but only 20% of adult patients, suggesting underlying airway pathology may be contributory.

The dense keratin plug causes conductive hearing loss and acute severe pain due to occlusion of the canal, requiring treatment by EAC toilet rather than major surgery.

High recurrence rate necessitates multiple excisions of keratin plugs, making imaging follow-up important to assess for recurrent accumulation and canal expansion.

Unlike cholesteatoma, keratosis obturans does not erode bone and typically does not require surgical intervention, making accurate diagnosis essential to avoid unnecessary ear canal surgery.

Reporting Pearls

Describe keratosis obturans as a well-defined soft tissue mass densely filling and expanding the bony external auditory canal without erosion, with preserved tympanic membrane, and specify presence or absence of bilateral involvement and associated paranasal sinus or lung findings to guide clinical management toward conservative EAC toilet rather than surgery.

Pitfalls
  • Misdiagnosis as external auditory canal cholesteatoma due to similar presentation as canal-filling soft tissue; key distinguishing feature is absence of bony erosion in keratosis obturans versus characteristic erosion in cholesteatoma
  • Overlooking bilateral involvement in 50% of cases which may be subtle on unilateral focused imaging and requires careful assessment of both ear canals
  • Failure to assess for associated bronchiectasis and chronic sinusitis, which are present in the majority of pediatric cases and may guide further workup or underlying etiology evaluation
  • Confusing keratosis obturans with simple cerumen impaction or EAC debris; keratosis obturans shows dense homogeneous soft tissue without air foci and causes canal remodeling/expansion
Source: Reference source

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