A novel needle electrode for intraoperative fourth cranial nerve neurophysiological mapping
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TECHNICAL NOTE
A novel needle electrode for intraoperative fourth cranial nerve neurophysiological mapping Taku Sato 1 & Takeshi Itakura 1,2 & Mudathir Bakhit 1 & Kensho Iwatate 1 & Hiroto Sasaki 1 & Yugo Kishida 1,3 & Shinya Jinguji 1,4 & Masazumi Fujii 1 & Jun Sakuma 1 & Kiyoshi Saito 1 Received: 14 April 2020 / Revised: 9 August 2020 / Accepted: 28 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Objectives Trochlear nerve (CN-IV) mapping method has not been confirmed to date. The compound muscle action potential (CMAP) of CN-IV cannot be recorded because of the low mapping sensitivity and anatomical characteristics of the superior oblique muscle (SOM). The aim of this study was to evaluate the effectiveness of a novel needle electrode (NNE), for the intraoperative mapping of CN-IV. Materials and methods The NNEs were inserted in the target extraocular muscles in 19 patients. We compared the CMAP amplitude of the NNE with that of the conventional needle electrode (CNE). Furthermore, we investigated the dissimilarity between the CMAP of the CN-IV and other extraocular cranial nerves (ECNs) and the correlation between the readings of the CN-IV mapping and its postoperative functional outcome. Results The CMAP of CN-IV has been measured in nine patients (47.4%). The CMAP of CN-IV was distinguishable from other ECNs. The CMAP of the NNE was found to be three times higher than that of the CNE. Although the NNE has shown the potential to record the CN-IV’s CMAP, 4 cases ended up having a CN-IV postoperative dysfunction. Conclusions For the first time, we confirmed the possibility of intraoperative mapping the CN-IV using an NNE inserted into the SOM. The NNE can also be useful for other neurophysiological monitoring methods. Keywords Needle electrode . Intraoperative neurophysiological mapping . Trochlear nerve
Introduction Preserving the function of the extraocular cranial nerves (ECNs) is necessary to the surgical treatment of skull base and brainstem lesions. Although intraoperative monitoring
* Taku Sato [email protected] 1
Department of Neurosurgery, Fukushima Medical University, 1 Hikarigaoka, Fukushima-shi, Fukushima 960-1295, Japan
2
Department of Orthopedic Surgery, Kansai Medical University, Hirakata-shi, Osaka, Japan
3
Department of Neurosurgery, Japanese Red Cross Nagoya Daini Hospital, Nagoya-shi, Aichi, Japan
4
Department of Neurosurgery, Toyama Prefectural Central Hospital, Toyama-shi, Toyama, Japan
of ECN using various methods has been reported in the literature, an intraoperative monitoring technique of the trochlear nerve (CN-IV) has not been well established until now. The standard method to record compound muscle action potential (CMAP) of the ECN is to insert a needle electrode through the orbital cavity into the extraocular muscles [2, 4, 6, 9]. The standard method failed to get a reading of the CMAP of the CN-IV due to the unique anatomical orientation of the superior oblique muscle (SOM). Additionally, the low action potential amplitude attributable to
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