Effect of perilymphatic fistulas on evoked otoacoustic emissions in the guinea pig.

Round window perilymphatic fistulas were surgically created in 20 guinea pigs. Distortion product otoacoustic emissions (DPOAEs) at 2fl - f2 were recorded prior to and immediately following laceration of the round window. The stimuli were equal level sinusoids (f1 < f2) with f2 ranging from 2 to 10 kHz, a fixed f2:f1 ratio of 1.25, and stimulus levels (L2 = L1) ranging from 20 to 80 dB SPL. After an 18-day survival period, emission measurements were repeated, and fluorescein was infused into the cerebrospinal fluid to verify patency or closure of the fistula. Nine animals demonstrated patent fistulas, whereas 11 had closed fistulas. There was a statistically significant reduction in DPOAE amplitude after an acute fistula across all stimulus levels (p < .001). At 18 days the DPOAE amplitudes in animals with healed fistulas could not be differentiated from controls, whereas DPOAE amplitudes in animals with patent fistulas were statistically different from controls (p < .05). The results suggest that evoked otoacoustic emissions may be useful in detecting perilymphatic fistulas.