[The use of intraoperative auditory evoked brainstem responses in the treatment of congenital ossicular anomalies].

Intraoperative auditory brainstem responses (ABRs) were monitored in 3 patients undergoing middle ear surgery for congenital ossicular anomalies. It was investigated whether this technique was capable of providing useful information to the operating surgeon. After the induction of anaesthesia and intubation, standard disc electrodes were attached to the vertex (active), ipsilateral mastoid (reference), and forehead (ground). These electrodes were draped out of the surgical field. The general anaesthesia was maintained by inhalation of enflurane. Stimulus intensity was decreased from 80 dBnHL in 10 dB steps until no response was obtained. Thus latency-intensity functions for wave V of ABR were obtained. First (A) recording was performed before the incision. The tympanomeatal flap was then elevated and the bony annulus overloading the oval window was drilled out. This enabled to visualize and confirm the anomalies of the ossicles. Before reconstructing the ossicles, the tympanomeatal flap was returned to its normal position and second (B) recording was obtained. During the reconstruction, recordings (C1, C2,...) were repeated as indicated. Then it was confirmed whether the effective reconstruction was obtained for auditory function. The results suggest that latency of wave V was significantly decreased when the effective reconstruction of the ossicular chain was done. Latency-intensity function is shifted to the left of A and B functions. Intraoperative auditory assessment using ABR in the reconstructive surgery for the ossicular channel is promising in providing useful information for auditory function and in predicting postoperative hearing improvement.