title: [Intraoperative monitoring of hearing function in the removal of cerebellopontine angle tumor: auditory brainstem response and cochlear nerve compound action potential].
abstract: Intraoperative hearing monitoring may be the best approach for hearing preservation in the removal of cerebellopontine angle (CPA) tumors. We designed an intracranial electrode for a reliable and consistent recording of the cochlear nerve compound action potential (CNAP), and compared the efficiency of the CNAP and auditory brainstem response (ABR) while monitoring the CPA tumor removal. Simultaneous intraoperative monitoring of CNAP and ABR were performed in 7 patients with CPA tumors (5 acoustic neurinomas and 2 epidermoids) undergoing tumor removal aimed at hearing preservation. We designed an intracranial electrode for CNAP monitoring made of a fine malleable insulated wire with a tiny tuft of oxidized cellulose on the tip. Postoperatively, the hearing of 6 patients was preserved. Useful hearing was preserved in 5 of those. ABR recordings were unsatisfactory because of severe artifacts during the tumor removal. It was discernible only in 2 of the 7 patients. Postoperatively, useful hearing was preserved in the 2 patients with a discernible ABR during the tumor removal. Four of 5 patients with no discernible ABR during the tumor removal preserved hearing. Before the tumor removal, all patients showed a reproducible CNAP of an amplitude 20 times larger than the amplitude of ABR without artifacts. A reliable CNAP was recorded consistently throughout the tumor removal in 5 patients, in whom useful hearing was preserved postoperatively. CNAP disappeared completely during the tumor removal in 1 patient who lost hearing postoperatively. Because of severe artifacts and poor specificity, the intraoperative ABR monitoring can not predict the postoperative hearing condition. Our newly designed intracranial electrode enables consistent CNAP recording during tumor removal. CNAP reflects the effect of surgical manipulations on hearing and predicts the postoperative hearing condition. CNAP is a more efficient form of intraoperative monitoring than ABR during CPA tumor removal.
authors.affiliation: Department of Neurosurgery, Chiba University School of Medicine, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan.
authors.forename: Iwao
authors.initials: I
authors.lastname: Yamakami
authors.forename: Osamu
authors.initials: O
authors.lastname: Ushikubo
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Uchino
authors.forename: Eiichi
authors.initials: E
authors.lastname: Kobayashi
authors.forename: Naokatsu
authors.initials: N
authors.lastname: Saeki
authors.forename: Akira
authors.initials: A
authors.lastname: Yamaura
authors.forename: Nobuo
authors.initials: N
authors.lastname: Oka
mesh_terms: D000200:Action Potentials; D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000601:surgery*; D002528:Cerebellar Neoplasms / Q000601:surgery*; D002530:Cerebellopontine Angle; D003056:Cochlear Nerve / Q000502:physiology*; D003638:Deafness / Q000209:etiology / Q000517:prevention & control; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009464:Neuroma, Acoustic / Q000601:surgery*; D019635:Neurosurgical Procedures / Q000009:adverse effects