Degree of Conductive Hearing Loss from Canal Stenosis
Canal stenosis can cause conductive hearing loss exceeding 33 dB, with severe cases producing significant hearing impairment that warrants surgical intervention. 1
Magnitude of Hearing Loss
Acquired medial external auditory canal stenosis consistently produces conductive hearing loss greater than 33 dB across all three related pathologies (medial EAC stenosis, anterior tympanomeatal angle blunting, and lateralized tympanic membrane). 1
The severity of conductive hearing loss from canal stenosis is independent of the underlying air conduction hearing thresholds, meaning stenosis adds a consistent conductive component regardless of baseline hearing status. 2
In documented surgical series, the average air-bone gap reduction achieved after treating inflammatory canal stenosis was 13.40 dB (SD = 9.0 dB), indicating that the preoperative conductive component was at least this magnitude and likely substantially higher. 3
Clinical Context and Mechanism
Canal stenosis causes conductive hearing loss by physically obstructing sound transmission through the external auditory canal to the tympanic membrane, similar to other external canal pathologies like cerumen impaction or foreign bodies. 4
Inflammatory external auditory canal stenosis arises from infiltration of inflammatory cells, edema, and eventual sclerosing of the medial EAC, leading to complete obstruction and significant conductive hearing loss. 3
The American Academy of Otolaryngology-Head and Neck Surgery identifies structural abnormalities such as stenosis, atresia, or large exostoses as disorders affecting the ear canal that contribute to conductive hearing loss requiring medical or surgical intervention. 4
Diagnostic Considerations
CT temporal bone without contrast is the first-line imaging modality for evaluating conductive hearing loss when canal stenosis is suspected, as it provides excellent delineation of the external auditory canal and can identify structural abnormalities. 4
Pure-tone audiometry with air and bone conduction testing definitively establishes the air-bone gap that quantifies the conductive component, with an air-bone gap ≥15-20 dB at frequencies 0.5,1,2, and 4 kHz confirming conductive hearing loss. 5
Otoscopic examination easily establishes the diagnosis of canal stenosis in most cases, though the physical findings may be subtle in mild stenosis with normal pinna appearance. 6, 1
Surgical Outcomes and Prognosis
Surgical treatment of medial canal stenosis has disappointing results with 62.5% recurrence rates and mean functional gain of only 9 dB, though auditory results are good when fibrosis does not recur. 1
Endoscopic transcanal treatment with split-thickness skin grafting shows more favorable outcomes, with no recurrence observed over mean follow-up of 90 months and statistically significant improvement in air-bone gap. 3
The high recurrence rate of fibrous stenosis makes surgical indication questionable unless patients are significantly bothered by their hearing loss, as the risk-benefit ratio is less favorable than for other conductive pathologies. 1
Common Pitfalls
Do not assume mild hearing loss from partial stenosis—even incomplete stenosis can produce conductive hearing loss exceeding 33 dB. 1
Underlying external auditory canal cholesteatoma was found in 3 of 8 cases of medial stenosis, making thorough evaluation essential before any intervention. 1
Chronic inflammatory processes must be addressed, as they drive the fibrotic replacement of normal epithelium that leads to progressive stenosis and obliteration. 7
Patients with canal stenosis are excellent candidates for cartilage conduction hearing aids regardless of hearing threshold severity, with over 70% purchase rates after trial periods. 2