Management Approach for Asymmetric Hearing Loss
Patients with asymmetric hearing loss should undergo comprehensive audiometric evaluation followed by MRI of the internal auditory canal to rule out retrocochlear pathology, particularly vestibular schwannoma. 1
Diagnostic Evaluation
Initial Assessment
- Obtain a comprehensive audiogram including pure tone thresholds, speech audiometry, tympanometry, and acoustic reflex testing to differentiate the type and severity of hearing loss 1
- Asymmetric hearing loss is defined as:
- Difference in pure tone average (500,1000, and 2000 Hz) between ears of >15 dB, OR
- Difference in word recognition scores >15% between ears 1
- Alternative definitions include >30 dB asymmetry at one frequency OR >20 dB asymmetry at two contiguous frequencies OR >10 dB asymmetry at three contiguous frequencies 2
Determining Type of Hearing Loss
- Identify whether the hearing loss is conductive, sensorineural, or mixed 1
- Conductive hearing loss (CHL): Pathology in external auditory canal or middle ear (cerumen impaction, tympanic membrane perforation, middle ear effusion, cholesteatoma, ossicular discontinuity) 1
- Sensorineural hearing loss (SNHL): Pathology in inner ear, cochlear nerve, or central auditory centers 1
- Mixed hearing loss: Combination of both CHL and SNHL 1
Imaging Studies
MRI Indications
- MRI of the internal auditory canal and posterior fossa should be performed in patients with asymmetric sensorineural hearing loss to rule out retrocochlear pathology 1
- MRI is superior to CT for detecting vestibular schwannomas and other retrocochlear lesions 3
- Non-contrast MRI has been proposed as a cost-effective means to evaluate for vestibular schwannoma 1
Special Considerations
- Poor word recognition scores (≤60%) that are disproportionate to pure tone thresholds warrant evaluation for retrocochlear pathology 1
- Patients with sudden asymmetric hearing loss have a 2.7% to 10.2% prevalence of cerebellopontine angle tumors 1
- The prevalence of acoustic neuroma in patients with asymmetric hearing loss has been reported as approximately 2.1% 4
Management Based on Etiology
Conductive Hearing Loss
- Refer to otolaryngologist for evaluation and potential surgical intervention 1
- Treatable causes include cerumen impaction, foreign body, tympanic membrane perforation, middle ear effusion, and otosclerosis 1
Sensorineural Hearing Loss
- For sudden SNHL (occurring within 72 hours):
Idiopathic Asymmetric SNHL
- If no specific etiology is identified after comprehensive evaluation, monitor with serial audiograms 2
- Consider hearing rehabilitation options based on degree of residual hearing 1
Rehabilitation Options
Hearing Aids
- Appropriate for patients with serviceable hearing (typically word recognition scores >50%) 1
- May benefit from traditional amplification if word recognition scores are useful for understanding speech 1
Special Devices for Profound Unilateral Hearing Loss
- Contralateral routing of sound (CROS) devices may be beneficial for profound unilateral hearing loss 1
- Cochlear implantation may be considered for profound unilateral hearing loss in appropriate candidates 1
Follow-up and Monitoring
- Patients with asymmetric hearing loss should have audiometric follow-up to monitor stability or progression 1
- Assess hearing at least every 3 years in patients with known hearing loss 1
- More frequent monitoring may be warranted in individuals with fluctuating hearing loss 1
Pitfalls to Avoid
- Relying solely on patient self-report of hearing status, as patients cannot accurately differentiate degree or type of hearing loss 1
- Using tuning fork tests alone for clinical screening, as they are not reliable enough for definitive assessment 1
- Delaying evaluation of sudden asymmetric hearing loss, which should be treated as an otologic emergency 1
- Failing to recognize that asymmetric hearing loss may be the first sign of retrocochlear pathology requiring prompt evaluation 3, 5