Asymmetric hearing loss: rule 3,000 for screening vestibular schwannoma

To assess the diagnostic yield of audiograms associated to electronystagmography (ENG) for screening vestibular schwannomas (VSs), to determine what definition of asymmetric sensorineural hearing loss (ASNHL) fits best for the diagnosis of VS, and to determine if cochleovestibular symptoms and atherosclerotic potential risk factors play a role in the VS screening.

Retrospective chart review in a tertiary care center.

One hundred twenty-two patients were included in the study and divided into 2 groups: 1) patients presenting a VS (n = 74) and 2) patients without VS (n = 48). They had received an audiometry assessment, an ENG, and a posterior fossa magnetic resonance imaging (MRI). In addition, a variety of risk factors and clinical data were collected. Mean hearing threshold by frequency, mean asymmetries by frequency, speech discrimination score (SDS), ENG results, and presence or absence of vertigo are studied. Cochleovestibular symptoms and atherosclerotic potential risk factors were collected. Characteristics were studied with analysis of variance, chi2 test, or a paired t test. A receiver operating characteristic curve was obtained. A logistic regression with a step-wise selection based on the likelihood ratio was used to identify the best subgroup of predictors of the VS.

The most revealing data were the mean ASNHL at 3,000 Hz (p < 0.001), the interaural SDS asymmetry (p < 0.001), the vestibular deficit (p < 0.049), and the absence of vertigo (p < 0.001). The ASNHL at 3,000 Hz was the most representative value of all the frequencies and for the SDS asymmetry. Interaural difference of 15 dB or more at 3,000 Hz is sufficient to consider hearing loss as asymmetric. When the cutoff for a positive test was placed at 50% probability, the receiver operating characteristic curve shows a sensitivity of 73%. The grade of the tumor was also related with the degree of ASNHL at 3,000 Hz. Caloric test does not predict the localization or the grade of the VS. Tinnitus and atherosclerotic potential risk factors were not considered significantly linked with VS.

To reduce the number of negative MRI performed in the investigation of an ASNHL, we propose the "rule 3,000," ASNHL of 15 dB or more at the 3,000-Hz frequency. In this case, an investigation with MRI is crucial. If this ASNHL is less than 15 dB, we recommend a biannual audiometric follow-up.