Changes in external ear resonance after 3 types of surgery in the patients with chronic otitis media

This study was designed to identify the external ear resonance characteristics of patients with tympanic membrane perforation and to investigate subsequent changes in external ear resonance, depending on the length of the postoperative period and which of 3 different types of operation was performed: tympanoplasty with canal wall-up mastoidectomy, epitympanoplasty, and canal wall-down mastoidectomy.

A total of 227 ears of 188 patients and 96 control ears comprised the study. We measured the gain and frequency of the first peak of external ear resonance with a real ear analyzer.

Gain and frequency of the first peak recorded in the preoperative group did not differ from those of the control group. However, negative peaks appeared around 1 to 1.5 kHz in half of these ears. The gain increased markedly in all 3 postoperative groups. The canal wall-down mastoidectomy and epitympanoplasty groups showed significantly lower frequencies compared with the tympanoplasty with canal wall-up mastoidectomy and control groups, but there was no difference between them. The increased gain diminished over time, but the peak gain did not equalize with that of the controls, even after 15 months.

Additional gain should be considered of around 1 to 1.5 kHz for hearing aid users with tympanic membrane perforation. Postoperative changes in external ear resonance should be expected in patients with chronic otitis media, suggesting that fine readjustments of the hearing aid may be necessary.