Hearing Preservation in Acoustic Neuroma Surgery: Value of Monitoring Cochlear Nerve Action Potentials

Abstract

This study reviews the hearing results in 80 consecutive patients who underwent complete removal of histologically proven acoustic neuromas by use of the suboccipital approach. Of these, 56 patients had successful monitoring of cochlear compound action potentials; 20 were not monitored because their surgery predated monitoring; and 4 had unsuccessful monitoring. A significant difference was found in hearing preservation rates between the group in whom compound action potential monitoring was performed and those in whom monitoring was either unavailable or failed (p = 0.02). Overall, 38% (30 of 80) had preserved hearing. There were 51 patients in whom the click threshold for the cochlear compound action potential was measured during surgery. Twenty-one patients had a threshold shift of 20 dB or less, 15 (71%) of these retained serviceable hearing (speech reception threshold < or = 50 dB; speech discrimination score > or = 60%). Of 12 patients in whom the threshold shift was 30 to 60 dB, none had serviceable hearing after surgery. The click threshold shift was predictive of a significant postoperative hearing change (p < 0.001).

Intraoperative neurophysiological monitoring in vestibular schwannoma surgery: advances and clinical implications

“…The main benefit is the ability to predict outcome in those patients who have diminished responses at the end of surgery. 13,20 Both CNAP and ECOG have the advantage of being near-field techniques in which electrodes are placed close to the CN VIII or cochlea. Larger amplitude signals are produced and acquisition takes only 2-3 seconds (in contrast to minutes with BAEP), thus allowing near real-time feedback to the surgeon.…”

“…Several studies have reported that CNAP monitoring and ECOG are more reliable than BAEP monitoring, while others have failed to prove their superiority in terms of hearing preservation (Table 1). 6,18,19,20,22,25,27 Outcome Prediction and Improvement Ambitions to improve vestibular schwannoma surgery were beyond simply prediction of procedural outcome. The introduction of intraoperative monitoring has taken vestibular schwannoma surgery from impressionism to realism.…”

“…The different patterns of BAEP have been identified and correlated with postoperative hearing outcome. 13,20 Direct intraoperative cochlear nerve monitoring is a relatively new tool that has been applied for hearing preservation during the past decade; however, its role is still controversial. 18,22 Recently, identification of certain intraoperative pathognomonic electrophysiological patterns has translated into perioperative vasoactive and neuroprotective pharmacotherapy with calcium channel blockers in an attempt to decrease delayed hearing loss and facial paresis.…”

Cochlear Microphonic Potentials in Patients with Vestibular Schwannomas

“…Among these three responses, SP and AP have generally been used for the diagnosis of endolymphatic hydrops [3,4] and for intraoperative monitoring during hearing preservation surgery [5,6]. CM has been considered to be less suitable than the others for clinical ECochG due to its response reliability and difficulty in recording [1].…”

Advantages of a New, Atraumatic, Self-Retaining Electrode for Direct Cochlear Nerve Monitoring

“…8 Typically, the auditory brain stem response (ABR) or the cochlear nerve compound action potential (CNAP) has been the potential recorded. 13,6,9,10 The ABR represents a far-field recording utilizing surface electrodes, while the near-field recording is used to acquire the CNAP with transtympanic or peritympanic electrodes. Both of these techniques require signal averaging and, therefore, do not provide real-time data pertaining to the immediate status of the VlIIth cranial nerve.…”