Risk management of asymmetrical hearing impairment in an armed forces population.

The prevalence of asymmetrical hearing impairment in the entire service population (1490 individuals) of a Royal Air Force flying station was estimated from routine audiometric testing recorded in individuals' medical records. Criteria for magnetic resonance imaging (MRI) scanning to exclude the possibility of vestibular schwannoma were determined in accordance with the risk management principle that the cost of the screening should not exceed the value of the likely benefit. MRI scanning should be carried out in the presence of an asymmetrical sensorineural hearing impairment of (a) 15 dB or more at two adjacent frequencies, or (b) 15 dB or more averaged over 0.5, 1, 2, 3, 4, 6 and 8 kHz.