Letter to the Editor. Awake craniotomy and transcortical MEP monitoring for resection of precentral gliomas

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  • 1 UPUMS, Etawah, Uttar Pradesh, India; and
  • 2 Fujita Health University, Banbuntane Hospital, Nagoya, Japan
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TO THE EDITOR: It was with great interest that we read the article by Saito et al.1 about the combined usage of awake craniotomy and transcortical motor evoked potential (MEP) monitoring for the resection of precentral gliomas (Saito T, Muragaki Y, Tamura M, et al. Awake craniotomy with transcortical motor evoked potential monitoring for resection of gliomas in the precentral gyrus: utility for predicting motor function. J Neurosurg. 2020;132[4]:987–997). We agree, to a great extent, with the usefulness of intraoperative MEP monitoring combined with awake craniotomy when resecting these gliomas. However, we wish to comment on two issues.

1) The combined findings of MEPs (decline > 50%) along with involuntary movements (IVMs) do not always correlate with an intraoperative decline in motor function and vice versa. We strongly believe that it is the point of decline in motor function that is highly correlated with determining the progression of surgery, rather than relying on MEPs, although combined usage is always recommended. How did the authors correlate these two aspects intraoperatively, rather than analyzing the motor deficit 6 months later? A decline in motor function per se for each operation, even with or without any change in MEPs, is a powerful indicator in deciding whether to proceed with resection or not.

2) In financially disadvantaged countries, which lack even basic intraoperative monitoring (IOM) devices, we are still greatly in favor of awake craniotomies in which the operative team evaluates intraoperative motor function, and there are verbal responses in cases of precentral tumors. The simple lack of IOM devices should not deter a surgeon from performing such surgeries.

We await with great enthusiasm further studies on the comparative usage of awake craniotomies with and without IOM devices in such cases of gliomas.

Disclosures

The author reports no conflict of interest.

References

1

Saito T, Muragaki Y, Tamura M, Awake craniotomy with transcortical motor evoked potential monitoring for resection of gliomas in the precentral gyrus: utility for predicting motor function. J Neurosurg. 2020;132(4):987997.

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  • Tokyo Women’s Medical University, Tokyo, Japan
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Response

We thank Dr. Ansari for his interest in our work. We would like to respond to the two issues he raised.

First, he mentioned that the findings of an MEP response do not always correlate with IVMs. Furthermore, monitoring of IVMs is a powerful indicator of motor function and highly sensitive with few false-negative cases in motor function. However, in our experience, monitoring of IVMs may sometimes show false-positive responses in actual motor function, due to removal of a tumor causing physical compression or insufficient awakening. Actually, of 22 patients with a decline in IVMs, 11 patients showed a decline in MEPs ≤ 50%, and only 2 of these 11 patients had mild motor deficits 6 months after surgery, which did not affect daily life. In contrast, 11 of 22 patients with a decline in IVMs showed a decline in MEPs > 50%. Of these 11 patients, 8 (73%) had motor dysfunction 6 months after surgery, including 2 patients with moderate deficits and 1 patient with severe deficits. Therefore, we believe that the combination of these two factors is useful when resecting gliomas in the precentral gyrus and for predicting postoperative motor function. Consequently, we recommend cessation of further tumor removal if a patient shows a decline in both IVMs and MEPs (> 50%).

Second, unfortunately, we have no experience in performing awake craniotomy in patients with a precentral gyrus tumor without an intraoperative monitoring IOM device. The advantage of awake craniotomy with neurophysiological monitoring when resecting gliomas is that the surgeon is able to observe the correlation between the results of MEP monitoring and IVMs.1 As we mentioned above, monitoring of IVMs may sometimes show a false-positive result in actual motor function. Therefore, there is a risk of minimal tumor removal if surgery is performed only by monitoring IVMs. Thus, we believe that the robustness of motor functional monitoring can be improved by combining an awake craniotomy with neurophysiological monitoring during removal of gliomas in the precentral gyrus.

References

1

Saito T, Tamura M, Chernov MF, Neurophysiological monitoring and awake craniotomy for resection of intracranial gliomas. Prog Neurol Surg. 2018;30:117158.

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Contributor Notes

Correspondence Ahmed Ansari: ahmed.ansari2@gmail.com.

INCLUDE WHEN CITING Published online June 12, 2020; DOI: 10.3171/2020.4.JNS201190.

Disclosures The author reports no conflict of interest.

  • 1

    Saito T, Muragaki Y, Tamura M, Awake craniotomy with transcortical motor evoked potential monitoring for resection of gliomas in the precentral gyrus: utility for predicting motor function. J Neurosurg. 2020;132(4):987997.

    • Search Google Scholar
    • Export Citation
  • 1

    Saito T, Tamura M, Chernov MF, Neurophysiological monitoring and awake craniotomy for resection of intracranial gliomas. Prog Neurol Surg. 2018;30:117158.

    • Search Google Scholar
    • Export Citation

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