A model for perilymphatic fistula induced hearing loss in the guinea pig cochlea

In cases of sudden, reversible hearing loss where perilymphatic fistulas are thought to be the cause, a multitude of causes have been postulated. These include perilymphatic pressure changes, Simmons' double-break theory, perilymphatic hemorrhage, pneumolabyrinth, and others. This study was proposed to explore the role pneumolabyrinth may have in this pathology. Guinea pigs were fitted with cochlear perfusion pumps pumping artificial perilymph into the left scala tympani. One group of animals received a bubble ( approximately 1.5-2 microl) introduced into the scala tympani while the other group of animals received continuous infusion of artificial perilymph. The animals' cochlear function was monitored using distortion product otoacoustic emissions (DPOAEs) while the animals' behavior was assessed to evaluate for vestibular dysfunction. While unaffected by pump surgery, animals that received air into the scala tympani had their DPOAEs eliminated by day 2 after pump placement. On day 6, positional changes in the DPOAEs were observed where the left lateral decubitus position showed a sharp demarcation at 4 kHz, where lower DPOAE frequencies were abolished and higher ones minimally affected, with DPOAEs normal in the prone position. By days 8 and 20, DPOAEs recovered to normal amplitudes. Vestibular dysfunction was never detected in any animal that received a pneumolabyrinth. All control animals receiving a continuous perilymph infusion exhibited no loss of cochlear function throughout the testing period. The reversible nature of pneumolabyrinth induced hearing loss and the pneumolabyrinth's sole presence (without other possible causes of hearing loss, such as pressure differentials or round window membrane perforations) are powerful indicators of the role of air in the pathology of perilymphatic fistulas. In addition, the fluctuation of the hearing loss with positional changes supports the use of positional audiometry when evaluating perilymphatic fistulas.