Brain and Behavior. 2018;8:e00981.
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1 | INTRODUCTION
Vestibular schwannoma, also known as acoustic neuroma, is a be-
nign tumor initiating from the vestibular nerve the so- called cra-
nial nerve (CN) VIII. The tumor grows in the cerebellopontine angle
area, causing stretching and suppression of the surrounding cranial
nerves (trigeminal, cochlear, and facial nerves) and the brainstem.
Postoperative facial nerve palsy can possibly occur if the facial nerve
or CN VII is accidentally damaged.
Preserving CN VII during acoustic neuroma surgery is a criti-
cal concern (George, 2001; Kartush, Graham, Bouchard, & Audet,
1991; Møller, 2011; O’Brien, 2008). Reliable nerve localization
Electrical stimulation- based nerve location prediction for
cranial nerve VII localization in acoustic neuroma surgery
| Sorayouth Chumnanvej
| Yodchanan Wongsawat
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2018 The Authors. Brain and Behavior published by Wiley Periodicals, Inc.
Department of Biomedical
University, Nakhon Pathom, Thailand
Medicine, Ramathibodi Hospital, Mahidol
University, Bangkok, Thailand
Yodchanan Wongsawat, Department
Engineering, Mahidol University, Nakhon
Introduction: Cranial nerve (CN) VII localization is a critical step during acoustic neu-
roma surgery because the nerve is generally hidden due to the tumor mass. The pa-
tient can suffer from Bell’s palsy if the nerve is accidentally damaged during tumor
removal. Surgeons localize CN VII by exploring the target area with a stimulus probe.
Compound muscle action potentials (CMAPs) are elicited when the probe locates the
nerve. However, false positives and false negatives are possible due to unpredictable
tissue impedance in the operative area. Moreover, a single CMAP amplitude is not
correlated with probe- to- nerve distance.
Objectives: This paper presents a new modality for nerve localization. The probe- to-
nerve distance is predicted by the proposed nerve location prediction model.
Methods: Input features are extracted from CMAP responses, tissue impedance, and
stimulus current. The tissue impedance is calculated from the estimated resistance
and capacitance of the tissue equivalent circuit. In this study, experiments were con-
ducted in animals. A frog’s sciatic nerve and gastrocnemius were used to represent
CN VII and facial muscle in humans, respectively. Gelatin (2.8%) was used as a mock
material to mimic an acoustic neuroma. The %NaCl applied to the mock material was
used to emulate uncontrollable impedance of tissue in the operative area.
Results: The 10- fold cross- validation results revealed an average prediction accuracy
of 86.71% and an average predicted error of 0.76 mm compared with the measure-
Conclusion: The proposed nerve location prediction model could predict the probe-
to- nerve distance across various impedances of the mock material.
acoustic neuroma, CMAP, CN VII localization, electrical stimulation