Otoacoustic Emissions II. EOAE after Otological Operations. Effect of the Middle Ear Condition and Postoperative Changes on Otoacoustic Emissions

Overview

The clinical application of otoacoustic emissions as an indicator of cochlear function is limited to a considerable extent by the state of the middle ear. Adequate transduction function of the middle ear is an essential prerequisite for detection of otoacoustic emissions in the external auditory meatus. The authors decided to evaluate otoacustic emissions in 60 ears (52 subjects) after various types of ear surgery. The condition for inclusion in the investigation was a threshold of air conduction at frequencies of 0.5 - 4.0 kHz < 25 dB and aie-bone gap Ł 10 dB. TEOAE were produced in 17 of 20 ears after tympanostomy. The detectability of TEOAE did not depend on the time interval after insertion of the grommet. Contrary to TEOAE, DPOAE as a rule were negative or unmeasured or had a very low amplitude. TE and DPOAE could be elicited in three of 134 ears after fascial retromyringal myringoplasty, in one case only DPOAE could be detected. In the remaining nine ears EOAE could not be evoked. TE and DPOAE were absent in ears after insertion of hydroxylapatite TORP, PORP as well as after reconstruction of incudostapedial articulation by means of ionomeric cement. Evoked otoacoustic emissions were detectable only in one of 19 ears operated on account of otosclerosis (stapedoplastiy according to Schuknecht). Conversely, clearly positive emissions were obtained in two ears after antromastoidectomy on account of acute mastoiditis and in two ears after surgicals removal of exostoses of the external auditory meatus. The described obervations lead to the conclusion that the absence of EOAE after middle ear microsurgery is probably due to minor changes in the middle ear and not damage of the inner ear. EOAE are not suitable for examination of cochlear function after tympanoplastic operations. They can be recommended only in conditions after tympanostomy. A more suitable test in ears with grommets is TEOAE. In mild deafness otoacoustic emissions may contribute in a substantial way to differentiation of conductive and perception types of the disorder.

Key words:
otoacoustic emissions, influence of middle ear, tympanoplasty, conductive deafness.