The impact of several craniotomies on transcranial motor evoked potential monitoring during neurosurgery

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3 Citations (Scopus)

Abstract

OBJECTIVE: Transcranial motor evoked potential (tMEP) monitoring is popular in neurosurgery; however, the accuracy of tMEP can be impaired by craniotomy. Each craniotomy procedure and changes in the CSF levels affects the current spread. The aim of this study was to investigate the influence of several craniotomies on tMEP monitoring by using C3-4 transcranial electrical stimulation (TES). METHODS: The authors used the finite element method to visualize the electric field in the brain, which was generated by TES, using realistic 3D head models developed from T1-weighted MR images. Surfaces of 5 layers of the head (brain, CSF, skull, subcutaneous fat, and skin layer) were separated as accurately as possible. The authors created 5 models of the head, as follows: normal head; frontotemporal craniotomy; parietal craniotomy; temporal craniotomy; and occipital craniotomy. The computer simulation was investigated by finite element methods, and clinical recordings of the stimulation threshold level of upper-extremity tMEP (UE-tMEP) during neurosurgery were also studied in 30 patients to validate the simulation study. RESULTS: Bone removal during the craniotomy positively affected the generation of the electric field in the motor cortex if the motor cortex was just under the bone at the margin of the craniotomy window. This finding from the authors' simulation study was consistent with clinical reports of frontotemporal craniotomy cases. A major decrease in CSF levels during an operation had a significantly negative impact on the electric field when the motor cortex was exposed to air. The CSF surface level during neurosurgery depends on the body position and location of the craniotomy. The parietal craniotomy and temporal craniotomy were susceptible to the effect of the changing CSF level, based on the simulation study. A marked increase in the threshold following a decrease in CSF was actually recorded in clinical reports of the UE-tMEP threshold from a temporal craniotomy. However, most frontotemporal craniotomy cases were minimally affected by a small decrease in CSF. CONCLUSIONS: Bone removal during a craniotomy positively affects the generation of the electric field in the motor cortex if the motor cortex is just under the bone at the margin of the craniotomy window. The CSF decrease and the shifting brain can negatively affect tMEP ignition. These changes should be minimized to maintain the original conductivity between the motor cortex and the skull, and the operation team must remember the fluctuation of the tMEP threshold.

Original languageEnglish
Pages (from-to)543-552
Number of pages10
JournalJournal of Neurosurgery
Volume127
Issue number3
DOIs
Publication statusPublished - 2017 Sep 1

Fingerprint

Motor Evoked Potentials
Craniotomy
Neurosurgery
Motor Cortex
Head
Bone and Bones
Skull
Upper Extremity
Brain
Subcutaneous Fat

Keywords

  • Craniotomy
  • Diagnostic technique
  • Finite element method
  • Neurosurgery
  • Transcranial electrical stimulation
  • Transcranial motor evoked potential

ASJC Scopus subject areas

  • Surgery
  • Medicine(all)
  • Clinical Neurology

Cite this

@article{e9a9b0951d40437c93cfc41484d103f0,
title = "The impact of several craniotomies on transcranial motor evoked potential monitoring during neurosurgery",
abstract = "OBJECTIVE: Transcranial motor evoked potential (tMEP) monitoring is popular in neurosurgery; however, the accuracy of tMEP can be impaired by craniotomy. Each craniotomy procedure and changes in the CSF levels affects the current spread. The aim of this study was to investigate the influence of several craniotomies on tMEP monitoring by using C3-4 transcranial electrical stimulation (TES). METHODS: The authors used the finite element method to visualize the electric field in the brain, which was generated by TES, using realistic 3D head models developed from T1-weighted MR images. Surfaces of 5 layers of the head (brain, CSF, skull, subcutaneous fat, and skin layer) were separated as accurately as possible. The authors created 5 models of the head, as follows: normal head; frontotemporal craniotomy; parietal craniotomy; temporal craniotomy; and occipital craniotomy. The computer simulation was investigated by finite element methods, and clinical recordings of the stimulation threshold level of upper-extremity tMEP (UE-tMEP) during neurosurgery were also studied in 30 patients to validate the simulation study. RESULTS: Bone removal during the craniotomy positively affected the generation of the electric field in the motor cortex if the motor cortex was just under the bone at the margin of the craniotomy window. This finding from the authors' simulation study was consistent with clinical reports of frontotemporal craniotomy cases. A major decrease in CSF levels during an operation had a significantly negative impact on the electric field when the motor cortex was exposed to air. The CSF surface level during neurosurgery depends on the body position and location of the craniotomy. The parietal craniotomy and temporal craniotomy were susceptible to the effect of the changing CSF level, based on the simulation study. A marked increase in the threshold following a decrease in CSF was actually recorded in clinical reports of the UE-tMEP threshold from a temporal craniotomy. However, most frontotemporal craniotomy cases were minimally affected by a small decrease in CSF. CONCLUSIONS: Bone removal during a craniotomy positively affects the generation of the electric field in the motor cortex if the motor cortex is just under the bone at the margin of the craniotomy window. The CSF decrease and the shifting brain can negatively affect tMEP ignition. These changes should be minimized to maintain the original conductivity between the motor cortex and the skull, and the operation team must remember the fluctuation of the tMEP threshold.",
keywords = "Craniotomy, Diagnostic technique, Finite element method, Neurosurgery, Transcranial electrical stimulation, Transcranial motor evoked potential",
author = "Ryosuke Tomio and Takenori Akiyama and Masahiro Toda and Takayuki Oohira and Kazunari Yoshida",
year = "2017",
month = "9",
day = "1",
doi = "10.3171/2016.7.JNS152759",
language = "English",
volume = "127",
pages = "543--552",
journal = "Journal of Neurosurgery",
issn = "0022-3085",
publisher = "American Association of Neurological Surgeons",
number = "3",

}

TY - JOUR

T1 - The impact of several craniotomies on transcranial motor evoked potential monitoring during neurosurgery

AU - Tomio, Ryosuke

AU - Akiyama, Takenori

AU - Toda, Masahiro

AU - Oohira, Takayuki

AU - Yoshida, Kazunari

PY - 2017/9/1

Y1 - 2017/9/1

N2 - OBJECTIVE: Transcranial motor evoked potential (tMEP) monitoring is popular in neurosurgery; however, the accuracy of tMEP can be impaired by craniotomy. Each craniotomy procedure and changes in the CSF levels affects the current spread. The aim of this study was to investigate the influence of several craniotomies on tMEP monitoring by using C3-4 transcranial electrical stimulation (TES). METHODS: The authors used the finite element method to visualize the electric field in the brain, which was generated by TES, using realistic 3D head models developed from T1-weighted MR images. Surfaces of 5 layers of the head (brain, CSF, skull, subcutaneous fat, and skin layer) were separated as accurately as possible. The authors created 5 models of the head, as follows: normal head; frontotemporal craniotomy; parietal craniotomy; temporal craniotomy; and occipital craniotomy. The computer simulation was investigated by finite element methods, and clinical recordings of the stimulation threshold level of upper-extremity tMEP (UE-tMEP) during neurosurgery were also studied in 30 patients to validate the simulation study. RESULTS: Bone removal during the craniotomy positively affected the generation of the electric field in the motor cortex if the motor cortex was just under the bone at the margin of the craniotomy window. This finding from the authors' simulation study was consistent with clinical reports of frontotemporal craniotomy cases. A major decrease in CSF levels during an operation had a significantly negative impact on the electric field when the motor cortex was exposed to air. The CSF surface level during neurosurgery depends on the body position and location of the craniotomy. The parietal craniotomy and temporal craniotomy were susceptible to the effect of the changing CSF level, based on the simulation study. A marked increase in the threshold following a decrease in CSF was actually recorded in clinical reports of the UE-tMEP threshold from a temporal craniotomy. However, most frontotemporal craniotomy cases were minimally affected by a small decrease in CSF. CONCLUSIONS: Bone removal during a craniotomy positively affects the generation of the electric field in the motor cortex if the motor cortex is just under the bone at the margin of the craniotomy window. The CSF decrease and the shifting brain can negatively affect tMEP ignition. These changes should be minimized to maintain the original conductivity between the motor cortex and the skull, and the operation team must remember the fluctuation of the tMEP threshold.

AB - OBJECTIVE: Transcranial motor evoked potential (tMEP) monitoring is popular in neurosurgery; however, the accuracy of tMEP can be impaired by craniotomy. Each craniotomy procedure and changes in the CSF levels affects the current spread. The aim of this study was to investigate the influence of several craniotomies on tMEP monitoring by using C3-4 transcranial electrical stimulation (TES). METHODS: The authors used the finite element method to visualize the electric field in the brain, which was generated by TES, using realistic 3D head models developed from T1-weighted MR images. Surfaces of 5 layers of the head (brain, CSF, skull, subcutaneous fat, and skin layer) were separated as accurately as possible. The authors created 5 models of the head, as follows: normal head; frontotemporal craniotomy; parietal craniotomy; temporal craniotomy; and occipital craniotomy. The computer simulation was investigated by finite element methods, and clinical recordings of the stimulation threshold level of upper-extremity tMEP (UE-tMEP) during neurosurgery were also studied in 30 patients to validate the simulation study. RESULTS: Bone removal during the craniotomy positively affected the generation of the electric field in the motor cortex if the motor cortex was just under the bone at the margin of the craniotomy window. This finding from the authors' simulation study was consistent with clinical reports of frontotemporal craniotomy cases. A major decrease in CSF levels during an operation had a significantly negative impact on the electric field when the motor cortex was exposed to air. The CSF surface level during neurosurgery depends on the body position and location of the craniotomy. The parietal craniotomy and temporal craniotomy were susceptible to the effect of the changing CSF level, based on the simulation study. A marked increase in the threshold following a decrease in CSF was actually recorded in clinical reports of the UE-tMEP threshold from a temporal craniotomy. However, most frontotemporal craniotomy cases were minimally affected by a small decrease in CSF. CONCLUSIONS: Bone removal during a craniotomy positively affects the generation of the electric field in the motor cortex if the motor cortex is just under the bone at the margin of the craniotomy window. The CSF decrease and the shifting brain can negatively affect tMEP ignition. These changes should be minimized to maintain the original conductivity between the motor cortex and the skull, and the operation team must remember the fluctuation of the tMEP threshold.

KW - Craniotomy

KW - Diagnostic technique

KW - Finite element method

KW - Neurosurgery

KW - Transcranial electrical stimulation

KW - Transcranial motor evoked potential

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