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  • Title: [Intra-operative monitoring with ABR during neurovascular decompression for VIIth and VIIIth cranial nerves: a warning sign for surgeons].
    Author: Sugiyama K, Yokoyama T, Ryu H, Uemura K, Miyamoto T, Shimoyama I.
    Journal: No Shinkei Geka; 1989 Jun; 17(6):545-53. PubMed ID: 2615904.
    Abstract:
    Auditory brain stem responses (ABR) were monitored during 18 cases of neurovascular decompression (12 with hemifacial spasm, and 6 with tinnitus, vertigo and/or hearing disturbance). As criteria for warning the surgeon, we adopted such changes as disappearance or marked decrease in amplitude of wave V. ABR changes were classified into 3 types as follows. Type 1 (7 cases): prolongation of latencies without wave form changes, Type 2 (5 cases): temporary disappearance of the waves after wave II, Type 3 (6 cases): temporary loss of all waves. In all cases except in one of the 2, with technical failure, all the waves reappeared within 5 minutes after releasing the retraction and irrigating the cerebellopontine cistern with warm normal saline solution. No patient had severe post-operative hearing deficit, but type 3 patients showed hearing disturbance of statistically significant magnitude (-8.33 +/- 3.16 dB). In type 1 patients, the mean prolongation of wave V latency during operation reached 1.27 +/- 0.44 msec, but the mean hearing loss after operation was only 3.57 +/- 4.4 dB. We believe that as soon as the waves disappear, one should immediately release the retraction and irrigate cisterns with warm normal saline solution, and wait until the waves reappear. Prolongation of latencies alone does not indicate postoperative hearing disturbances, and even if the waves disappear their prompt recovery suggests that hearing will be preserved after operation.
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