Rule 3,000: a more reliable precursor to perceive vestibular schwannoma on MRI in screened asymmetric sensorineural hearing loss

Nine different definitions of asymmetric sensorineural hearing loss (SNHL) have been reported in literature. The objectives of this study are to: (1) compare all these definitions of asymmetric SNHL; (2) measure the agreement between these definitions in detecting vestibular schwannoma (VS); and (3) determine the strongest association between an asymmetric SNHL definition and positive VS on magnetic resonance imaging (MRI). The study is a retrospective chart review in a tertiary care center. Cases were included if they were evaluated by an audiometric assessment and a posterior fossa MRI. Definitions of asymmetric SNHL reported in literature were applied to request for a further MRI investigation. The likelihood ratio (LR) for a positive test result (LR+) was the highest for the Rule 3,000 (2.91). On comparing all the other definitions with Rule 3,000, seven of the eight existing definitions have a kappa under the clinical usefulness threshold (Kappa < 0.6). When specification tests were applied, the Chi-square test identified Rule 3,000 with a highly significant P value (P < 0.0001). Rule 3,000, defined as asymmetric SNHL of 15 dB or more at the frequency 3,000 Hz, could serve as a universal referral guide for further MRI investigation. Results show that Rule 3,000 is more reliable to detect VS on MRI, a very simple rule that covers all the eight definitions of asymmetric SNHL reported in literature. This would help to reduce the number of negative MRI and to save time and money. If asymmetric SNHL is less than 15 dB, a biannual audiometry testing follow-up could be done.