[Auditory Brainstem Response: ABR].

Intraoperative auditory brainstem response(ABR)monitoring has been established as a reliable method to evaluate cochlear function. Intraoperative ABR is mandatory in microvascular decompression for hemifacial spasm, trigeminal neuralgia, and glossopharyngeal neuralgia. Cerebellopontine tumor with remaining effective hearing function also requires ABR monitoring during surgery to preserve hearing function. Prolonged latency and subsequent amplitude decrease in the ABR wave V predicts postoperative hearing impairment. Therefore, when alerted to an intraoperative ABR during surgery, the surgeon should release the cerebellar retraction stressing the cochlear nerve and wait for the abnormal ABR to recover.