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

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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.

ABBREVIATIONS AC = alternating current; AVM = arteriovenous malformation; cMEP, tMEP, UE-tMEP = cortical motor evoked potential, transcranial MEP, upper-extremity tMEP; DC = direct current; FE = finite element; LSO = lateral suboccipital; pEF, tEF = perpendicular electric field, tangential EF; TES = transcranial electrical stimulation.

Article Information

Correspondence Ryosuke Tomio, Department of Neurosurgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan. email: tomy0807@hotmail.com.

INCLUDE WHEN CITING Published online October 7, 2016; DOI: 10.3171/2016.7.JNS152759.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    The craniotomy models (upper row) and CSF-decreased models (lower row) in 1 × 1 × 1 mm3–resolution images. Starting from the left, the frontotemporal craniotomy model, parietal craniotomy model, temporal craniotomy model, and occipital craniotomy model are presented. Figure is available in color online only.

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    The electric field of the normal head models is shown (A). The electric field in the brain radially diffuses from the brain surface at a maximum just below the electrodes in the axial and coronal sections (B and C). The electric field of the brain surface (D) and the pEF component (E) and tEF component (F) of the normal head model are also shown. Figure is available in color online only.

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    The electric field in each craniotomy model is shown (from the top: normal head, frontotemporal craniotomy, parietal craniotomy, temporal craniotomy, and occipital craniotomy). Starting from the left, the 3D model view, axial section, coronal section, surface view of the electric field, pEF component, and tEF component are shown for each model. The color scale ranges from 0 V/m (blue) to 60 V/m (red). Figure is available in color online only.

  • View in gallery

    The electric field of all CSF-decreased models is shown (from the top: normal head, frontotemporal craniotomy, parietal craniotomy, temporal craniotomy, and occipital craniotomy). Starting from the left, the 3D model view, axial section, coronal section, surface view of the electric field, pEF component, and tEF component are shown for each model. The color scale ranges from 0 V/m (blue) to 60 V/m (red). Figure is available in color online only.

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    Preoperative MR images and intraoperative photographs showing lesions and approaches in 3 frontotemporal craniotomy cases. A: Case 8. The patient had a tuberculum sellae meningioma removed through a right-side frontotemporal craniotomy. Cisternal CSF was drained, but the frontal lobe was lifted by the retractor after dural incision. B: Case 10. The patient had a left convexity meningioma removed. The craniotomy window was in close proximity to the motor cortex. The CSF was minimally drained after dural incision. C: Case 11. The patient had clipping of a right internal carotid artery (IC) aneurysm. Cisternal CSF was drained considerably, but the frontal lobe was also lifted by the retractor. Figure is available in color online only.

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    Preoperative MR images and intraoperative photographs showing parietal and bifrontal craniotomy findings. A: Case 1 (parietal). The patient had multiple meningiomas removed via parietooccipital craniotomy in the prone position. The skin flap was widely inverted, and the electrodes were also detached from the skull. B: Case 2 (parietal). The patient underwent parietooccipital AVM removal in the prone position. The craniotomy window was located posterior-medial to the motor cortex and the frontal lobe sank, seeming to be pressed into the skull after dura incision. C: Case 3 (i.e., Case 1 for bifrontal). The patient had an olfactory groove meningioma removed via bifrontal craniotomy, and the craniotomy window was more anterior than the motor cortex. Figure is available in color online only.

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    Preoperative MR images and intraoperative photographs showing temporal craniotomy findings. A: Case 2. The patient underwent right occipitotemporal glioblastoma removal. It was obvious that the brain sank after dural incision. B: Case 3. The patient had a right petroclival meningioma removed. The brain was lifted using the retractor epidurally away from the subcentral space. C: Case 5. The patient had a right trigeminal schwannoma removed also via temporal craniotomy. The brain sank after dural incision and was supported only by the retractor. Figure is available in color online only.

References

  • 1

    Holdefer RNSadleir RRussell MJ: Predicted current densities in the brain during transcranial electrical stimulation. Clin Neurophysiol 117:138813972006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Lee JJKim YIHong JTSung JHLee SWYang SH: Intraoperative monitoring of motor-evoked potentials for supratentorial tumor surgery. J Korean Neurosurg Soc 56:981022014

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Miranda PCMekonnen ASalvador RRuffini G: The electric field in the cortex during transcranial current stimulation. Neuroimage 70:48582013

  • 4

    Motoyama YKawaguchi MYamada SNakagawa INishimura FHironaka Y: Evaluation of combined use of transcranial and direct cortical motor evoked potential monitoring during unruptured aneurysm surgery. Neurol Med Chir (Tokyo) 51:15222011

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Rampersad SMStegeman DFOostendorp TF: Single-layer skull approximations perform well in transcranial direct current stimulation modeling. IEEE Trans Neural Syst Rehabil Eng 21:3463532013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Szelényi ABueno de Camargo AFlamm EDeletis V: Neurophysiological criteria for intraoperative prediction of pure motor hemiplegia during aneurysm surgery. Case report. J Neurosurg 99:5755782003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Szelényi AHattingen EWeidauer SSeifert VZiemann U: Intraoperative motor evoked potential alteration in intra-cranial tumor surgery and its relation to signal alteration in postoperative magnetic resonance imaging. Neurosurgery 67:3023132010

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8

    Szelényi ALanger DKothbauer KDe Camargo ABFlamm ESDeletis V: Monitoring of muscle motor evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome. J Neurosurg 105:6756812006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Tanaka STashiro TGomi ATakanashi JUjiie H: Sensitivity and specificity in transcranial motor-evoked potential monitoring during neurosurgical operations. Surg Neurol Int 2:1112011

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10

    Tomio RAkiyama THorikoshi TOhira TYoshida K: Visualization of the electric field evoked by transcranial electric stimulation during a craniotomy using the finite element method. J Neurosci Methods 256:1571672015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11

    Zhou HHKelly PJ: Transcranial electrical motor evoked potential monitoring for brain tumor resection. Neurosurgery 48:107510812001

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