Patterns of hearing loss in non-explosive blast injury of the ear

A prospective study of hearing loss in 120 cases with non-explosive blast injury of the ear, gathered over a six-year period, is presented. Thirty-three (27.5 per cent) patients had normal hearing, 57 (47.5 per cent) conductive hearing loss, 29 (24.2 per cent) mixed loss and one (0.8 per cent) had pure sensorineural loss. The severity of conductive hearing loss correlated with the size of the eardrum perforation; only a marginal difference was found between water and air pressure injuries, with respect to this type of hearing loss. Of all locations, perforations involving the posterior-inferior quadrant of the eardrum were associated with the largest air-bone gap. Audiometric assessment revealed that none of the patients suffered ossicular chain damage. Three patterns of sensorineural hearing loss were identified: a dip at a single frequency, two separate dips, and abnormality of bone conduction in several adjacent high frequencies. Involvement of several frequencies was associated with a more severe hearing loss than a dip in a single frequency. Healing of the perforation was always accompanied by closure of the air-bone gap, while the recovery of the sensorineural hearing loss was less favourable.