Intraoperative auditory brainstem responses in patients with cerebellopontine angle meningiomas involving the inner auditory canal: analysis of the predictive value of the responses

Object. Meningiomas of the cerebellopontine angle (CPA) can either arise from or secondarily grow into the inner auditory canal (IAC). This location may have a great impact on hearing function following surgery to remove these lesions. The aim of this retrospective study was to investigate the reliability and predictive importance of auditory brainstem responses (ABRs) for the determination of postoperative auditory function in patients with CPA meningiomas in comparison with results obtained in patients who undergo surgery for vestibular schwannomas. Methods. In a consecutive series of 1800 meningiomas Surgically treated between 1978 and 2002, 421 lesions were located in the CPA. In 38 patients with CPA meningiomas involving the IAC, the findings of intraoperative ABR monitoring and the hearing status of each patient before and after surgery were retrospectively analyzed. On analysis, ABR monitoring demonstrated stable findings in 24 patients throughout tumor resection and fluctuating signals in 10 patients. Among the 24 patients with stable ABRs, postoperative hearing function improved in three patients, remained the same in 15, and worsened in six patients, including one patient who displayed postoperative deafness. There was even one patient recovering from preoperative deafness. Among the 10 patients with unstable ABRs, intermittent decreases in amplitude and deformations of variable duration in the ABR wave were noted. The risk of deafness was considerably higher in patients with prolonged phases of intermittent ABR deterioration. Conclusions. The presence and absence of ABRs during surgery for CPA meningiomas reliably predicted the presence and absence of postoperative auditory function. Intermittent deterioration of ABRs may result in postoperative deafness, depending on the duration of these events during surgery. Improvements in hearing are only seen when the ABRs are stable for amplitudes and latencies throughout surgery.