Postoperative Hearing Changes in Patients Operated via Retrosigmoid Approach with No Unfavorable Intraoperative Changes in BAEP

Introduction: The aim of this paper is to analyze hearing level changes in patients operated via the retrosigmoid approach when no unfavorable changes in intraoperative brainstem auditory evoked potentials (BAEP) were present at the end of surgery.

Material and Methods: Since 1998 in our department during operations in the cerebellopontine angle region we have introduced intraoperative monitoring of many modalities, including BAEP. Until November 2004, monitoring was performed in 172 patients operated via the retrosigmoid approach due to various types of pathology: vestibular schwannoma, other tumors in the cerebellopontine angle, or neurovascular conflict (trigeminalgia, hemifacial spasm, torticollis). One hundred four patients had at least some BAEP waves recordable preoperatively, and in 51 of them BAEP at the end of surgery showed no important unfavorable changes compared to initial recording. We have follow-up BAEP data or pure tone audiometry in 36 patients of this group.

Results: The authors analyze the correlation between postoperative BAEP changes and hearing level assessed by audiometry and influence of type of pathology on these changes. In a group of neurovascular conflict only in one case (11%) did postoperative changes in BAEP occur, while in 48% of patients with tumors (n = 13), BAEP changed from what had been recorded at the end of surgery. In six cases (37% patients with available postoperative audiometry), hearing level assessed according to modified Gardner-Robertson scale changed. In 1 patient with vestibular schwannoma, who had normal BAEP at the end of surgery, later tests revealed complete anacusis, and no BAEP waves could be recorded. One other patient had better hearing level then preoperatively, and four had worse. Although postoperative hearing level in other patients was in most cases slightly worse than preoperative, the difference was not statistically significant.

Conclusions: Our paper demonstrates that even when BAEP at the end of surgery has normal parameters, hearing preservation cannot be guaranteed. Factors other than direct damage during surgical procedures can have a negative influence on the postoperative auditory pathway.