What is the appropriate management for asymmetrical sensorineural hearing loss?

Management of Asymmetrical Sensorineural Hearing Loss

All patients with asymmetric sensorineural hearing loss require MRI of the internal auditory canals with a dedicated IAC protocol to exclude retrocochlear pathology, particularly vestibular schwannoma or meningioma. 1, 2

Defining Asymmetry

Asymmetric sensorineural hearing loss is established when audiometry demonstrates any of the following criteria:

• ≥15 dB difference at 2 or more frequencies between ears 1, 2
• ≥15% difference in speech recognition scores 1, 2
• ≥20 dB difference at 2 contiguous frequencies 1
• ≥15 dB difference at any 2 frequencies between 2000-8000 Hz 1, 2

Notably, ≥15 dB asymmetry specifically at 3 kHz is the strongest audiometric predictor of abnormal MRI findings and should heighten clinical suspicion for retrocochlear pathology. 3

Immediate Triage: Rule Out Otologic Emergency

Before proceeding with standard workup, determine the time course of hearing loss onset:

• If hearing loss developed within 72 hours: This is idiopathic sudden sensorineural hearing loss, an otologic emergency requiring immediate oral corticosteroid therapy 1, 4, 2
• Initiate steroids as soon as possible without waiting for imaging 1, 4
• Still perform MRI, but within 14 days of symptom onset 2
• For treatment failures or patients presenting 2-6 weeks after onset, offer intratympanic steroid therapy 1

Mandatory Imaging Protocol

MRI with dedicated internal auditory canal (IAC) protocol is the imaging modality of choice and should be performed in all cases of asymmetric sensorineural hearing loss. 1, 2

Technical specifications:

• High-resolution 3-D T2-weighted sequences providing submillimeter assessment of the IAC and inner ear structures 1
• Thin sections across the IAC and inner ear 1
• Includes evaluation of brainstem and thalami 1
• Gadolinium contrast administration facilitates visualization of vestibular schwannomas, meningiomas, labyrinthitis, and neuritis 1, 2

Why MRI is mandatory:

• Vestibular schwannoma is found in 4-7.7% of patients with asymmetric sensorineural hearing loss—nearly 4 orders of magnitude higher than the general population incidence 5, 6
• Overall, causative lesions are identified on MRI in 6.9-10.6% of patients with asymmetric hearing loss 5, 6
• Other retrocochlear pathology includes meningiomas, glomus jugulare tumors, ectatic basilar arteries, cholesterol granulomas, and demyelinating disease 4, 6

Critical pitfall to avoid:

Do not use auditory brainstem response (ABR) testing as a screening tool to determine whether MRI is needed. 6

• ABR has only 71% sensitivity and 74% specificity for detecting retrocochlear lesions 6
• ABR misses 29% of causative lesions, including 7 of 24 vestibular schwannomas in one large prospective study 6
• Using ABR as a gatekeeper results in 29 missed or delayed diagnoses per 1,000 patients screened 6
• All patients meeting asymmetry criteria should proceed directly to MRI 2, 6

Alternative Imaging in Specific Scenarios

CT temporal bone should be obtained instead of (or in addition to) MRI when:

• History of head trauma precedes the hearing loss, to evaluate for temporal bone fractures or inner ear anatomic abnormalities 1, 4, 2
• Clinical suspicion exists for superior canal dehiscence or other third window lesions 4

CT head alone is insufficient as it is much less sensitive than MRI for detecting retrocochlear pathology. 1

Serological Testing

Order serological tests only when specific conditions are suspected by history and physical examination. 1, 2

Targeted testing may include:

• Lyme disease serology in endemic areas or with compatible exposure history 1, 4
• Syphilis testing (RPR/VDRL and treponemal-specific tests) when clinical suspicion exists 1, 4, 7
• HIV testing if risk factors present 1, 4
• Testing for autoimmune inner ear disease markers when rapid bilateral progression or steroid-responsive hearing loss is present 1, 4

Avoid routine thyroid function testing, as it has demonstrated little diagnostic value in asymmetric sensorineural hearing loss workup. 7

Specialist Referral

Refer all patients with confirmed asymmetric sensorineural hearing loss to otolaryngology after audiometry establishes the diagnosis. 1, 2

Otolaryngology evaluation is essential because:

• 10% of patients will have causative lesions requiring surgical or medical intervention 5, 6
• Vestibular schwannomas require specialized management decisions (observation, stereotactic radiation, or surgical resection) 4, 2
• Other treatable causes (autoimmune disease, infections, anatomic abnormalities) require subspecialty expertise 1, 4

Audiologic Rehabilitation

Begin audiologic rehabilitation as soon as hearing loss is identified, even while diagnostic workup is ongoing, to prevent auditory deprivation and optimize outcomes. 2

• Refer to audiology for hearing aid evaluation and fitting 1, 2
• Address impacts on communication, sound localization, safety, and quality of life 1, 2
• Counsel patients about associated symptoms including tinnitus and potential dizziness 2

Follow-Up Monitoring

Obtain follow-up audiometry at the conclusion of any treatment and within 6 months, with regular monitoring thereafter to assess for progression and adjust management. 2

This structured approach ensures that the approximately 10% of patients with serious underlying pathology are identified promptly while avoiding unnecessary testing in those without specific clinical indicators. 5, 6