Definition of Asymmetric Sensorineural Hearing Loss
Asymmetric sensorineural hearing loss is defined as a difference in pure tone average (at 500,1000, and 2000 Hz) between ears of greater than 15 dB, or a difference in word recognition scores of greater than 15% between ears. 1
Audiometric Criteria
The American Academy of Otolaryngology-Head and Neck Surgery establishes the following specific thresholds for defining asymmetry:
- Pure tone average difference: >15 dB between ears at 500,1000, and 2000 Hz 1
- Word recognition score difference: >15% between ears 1
- Alternative definition: ≥15 dB difference at 2 or more frequencies between ears 2
- Additional criterion: ≥20 dB difference at 2 contiguous frequencies 2
Clinical Context
While age-related hearing loss typically presents as symmetric and gradual bilateral sensorineural hearing loss, asymmetric patterns warrant immediate investigation for underlying pathology. 1 The distinction is critical because symmetric hearing loss is defined as audiometric results within 15 dB for pure tone average between ears with word recognition score differences of 15% or less. 1
Key Clinical Implications
Asymmetric sensorineural hearing loss requires MRI evaluation to rule out retrocochlear pathology, particularly vestibular schwannoma, which is the leading retrocochlear cause. 2, 3 This is not simply age-related hearing loss and demands comprehensive diagnostic workup including:
- Complete audiometry with pure tone thresholds, speech audiometry, tympanometry, and acoustic reflex testing 3
- MRI of the internal auditory canal and posterior fossa 2, 3
Common Pitfall
Do not assume asymmetric hearing loss is simply presbycusis or noise-induced hearing loss without imaging. 4 While these conditions can occasionally present asymmetrically, vestibular schwannoma, meningioma, sudden sensorineural hearing loss, autoimmune inner ear disease, temporal bone fractures, and infections must be excluded. 2 The prevalence of acoustic neuroma in patients with asymmetric sensorineural hearing loss is approximately 2.1% in community-based populations. 5