Article
The Nervus intermedius in vestiblar schwannoma surgery
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Authors
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Christian Strauss
- Universitätsklinikum Halle/Saale, Klinik und Poliklinik für Neurochirurgie, Halle/Saale, Deutschland
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Julian Prell
- Halle, Deutschland
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Christian Scheller
- Halle, Deutschland
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Jörg Illert
- Halle, Deutschland
| Published: | June 9, 2017 |
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Outline
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Objective: The Nervus intermedius is the parasympathetic portion of the facial nerve, exiting the brainstem with the fibers of the VIIth and VIIIth nerve, crossing the CPA adjacent to the superior vestibular nerve and rejoining the facial nerve at the level of the porus of the internal auditory canal. This area is considered most difficult for complete tumor resection and facial nerve preservation. From electrophysiological and anatomical studies the nerve is known to carry motor fibers to facial muscles. The nerve is seldom addressed in vestibular schwannoma surgery and its impact to surgery and outcome has not been evaluated.
Methods: A consecutive series of 203 patients undergoing vestibular schwannoma surgery has been evaluated with respect to presence or absence of a Nervus intermedius, based on operative records and EMG data. Tumor size, tumor origin, extent of resection, and facial nerve function were evaluated.
Results: A separate nerve was identified in more than 50%. There was no statistical significance for presence of absence of the nerve in various Koos size categories, except for Koos I tumors in which the nerve was identified in only 2 of 19 cases. Presence of the nerve had no impact on extent of tumor resection (p=0.626) and on short (p=0.441) and long term facial nerve function (p=0.749). Tumor origin was irrelevant for presence or absence of a separate nerve (p=0.183). The predictability of postoperative severe facial nerve paresis (House-Brackmann>4) based on intraoperative EMG monitoring was significantly lower (Spearman´s rho 0.43) when a nervus intermedius was identified during surgery as compared to those cases in whom no separate nerve was seen (Spearman´s rho 0.73).
Conclusion: The Nervus intermedius poses a substantial challenge for intraoperative EMG monitoring in vestibular schwannoma surgery since at presence it is difficult to reliably distinguish pathological EMG activity arising from the nervus intermedius, which does not imply functional consequences as compared to trains from the facial nerve.
