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Intraoperative continuous monitoring of evoked facial nerve electromyograms in acoustic neuroma surgery

  • Clinical Article
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Abstract

Background

Preservation of facial nerve function is one of the most important goals in acoustic neuroma surgery. We have been using intraoperative continuous monitoring of evoked facial nerve electromyograms (EMGs) since 1997 in acoustic neuroma surgery. We therefore investigated surgically treated patients to clarify the usefulness of this monitoring, and to determine safety criteria for preserving facial nerve function.

Methods

This intraoperative continuous monitoring of evoked facial nerve EMG is a method for checking the EMG evoked by continuous direct electrical stimulation of the facial nerve during tumor excision. The greatest advantage of this method is the ability to identify changes in EMG in real time. We retrospectively investigated 216 patients with surgically treated acoustic neuroma to identify correlations between parameters in this monitoring and postoperative facial nerve function immediately and 1 year after surgery.

Results

In these patients, the functional preservation rate of the facial nerve (House and Brackmann grade 1 or 2 at 1 year after surgery) was 98.6% with a 98.2% mean tumor resection rate. Amplitude preservation ratio correlated significantly with facial nerve function both immediately and 1 year after surgery. To avoid severe facial nerve palsy, a warning criterion of amplitude preservation ratio >50% appears useful.

Conclusions

Postoperative course of facial nerve function appears predictable using intraoperative continuous monitoring of evoked facial nerve EMGs. This monitoring is useful to increase the tumor excision rate while avoiding severe postoperative facial nerve palsy in acoustic neuroma surgery.

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Acknowledgments

The authors thank Toshinaga Kazama (ME), Ayaka Oguchi (MT), and Chizuko Abe (MT) for their assistance with intraoperative monitoring, as well as the many neurosurgeons who managed the patients in the Department of Neurosurgery and Stroke Center at Tokyo Metropolitan Police Hospital.

Conflicts of interest

None.

Disclosure

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

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Authors and Affiliations

  1. Department of Neurosurgery and Stroke Center, Tokyo Metropolitan Police Hospital, 4-22-1, Nakano, Nakano-Ku, Tokyo, 164-0001, Japan

    Midori Amano, Michihiro Kohno, Shigeo Sora & Hiroaki Sato

  2. Department of Anesthesiology, Saitama Medical Center of Jichi University, Saitama, Japan

    Osamu Nagata

  3. Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Tokyo, Japan

    Makoto Taniguchi

Authors
  1. Midori Amano
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  2. Michihiro Kohno
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  3. Osamu Nagata
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  4. Makoto Taniguchi
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  5. Shigeo Sora
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  6. Hiroaki Sato
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Corresponding author

Correspondence to Michihiro Kohno.

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Comment

The authors should be congratulated for such remarkable results in the resection of vestibular schwannomas and preservation of facial nerve function. In the article, they state that resection of tumors should be carried up to the point of preserving at least 50% of amplitude preservation. However, they also state that in some cases because they wanted to avoid tumor recurrence (an ever present desire) this effort was pushed to a 30/40% amplitude preservation. It is then a personal call whether to stop or to continue the resection in cases where the amplitudes have fallen below 50% with a remaining tumor still in place. I think that for such cases and in the present era a word regarding contemplating the use of radiosurgery would be welcomed. The same issue is present for M-Max. What is the threshold to be followed? 1,000 or 800 μv? The bottom line is: Exactly why and when, based on the neurophysiologic experience acquired in the series and the currently available alternative methods of treatment for these tumors do the authors think that there is a reason to pursue extra resection if amplitude falls below 50% and M-Max below 1000uv?

Manuel Cunha e Sa

Almada, Portugal

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Amano, M., Kohno, M., Nagata, O. et al. Intraoperative continuous monitoring of evoked facial nerve electromyograms in acoustic neuroma surgery. Acta Neurochir 153, 1059–1067 (2011). https://doi.org/10.1007/s00701-010-0937-6

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  • DOI: https://doi.org/10.1007/s00701-010-0937-6

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