Characteristics of sensorineural hearing loss secondary to inner ear acoustic trauma

Abstract

Cochlear damage secondary to exposure to acoustic trauma is the consequence of the acoustic energy effects on the hearing cells in Korti's organ. The objective was to assess the correlation between the degree of sensorineural hearing loss and the type of audiogram registered in acoustic trauma exposed patients. We analysed 262 audiograms of patients exposed to acoustic trauma in correlation to 146 audiograms of patients with cochlear damage and hearing loss not related to acoustic trauma. "A" group consisted of acoustic trauma cases, while "B" group incorporated cases with hearing loss secondary to cochlear ischaemia or degeneration. All audiograms were subdivided with regard to the mean hearing loss into three groups: mild (21-40 dB HL), moderate (41-60 dB HL) and severe (over 60 dB HL) hearing loss. Based on audiogram configuration five types of audiogram were defined: type 1 flat; type 2 hearing threshold slope at 2 kHz, type 3 hearing threshold slope at 4 kHz; type 4 hearing threshold notch at 2 kHz; type 5 notch at 4 kHz. Mild hearing loss was recorded in 163 (62.2%) ears in the acoustic trauma group, while in 78 (29.8%) ears we established moderate hearing loss with the maximum threshold shift at frequencies ranging from 4 kHz to 8 kHz. The least frequent was profound hearing loss, obtained in 21 (8%) audiograms in the acoustic trauma group. Characteristic audiogram configurations in the acoustic trauma patient group were: type 1 (N = 66; 25.2%), type 2 (N = 71; 27.1%), and type 3 (N = 68; 25.9%). Audiogram configurations were significanly different in the acoustic trauma group in comparison to the cochlear ischaemia group of patients (p = 0.0005). Cochlear damage concomitant to acoustic trauma could be assessed by the audiogram configuration. Preserved hearing acuity at low and mild frequency range indicates the limited damage to the hearing cells in Korti's organ in the apical cochlear turn.