Schwannoma of the intermediate nerve

Case report

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The intermediate nerve is seldom identified as the site of tumor origin in cerebellopontine angle schwannomas. A 29-year-old man presented with a 6-month history of slowly progressive hearing loss and dizziness; facial nerve weakness was not observed clinically. Magnetic resonance imaging revealed a tumor in the left cerebellopontine angle region extending up to the geniculate ganglion and along the course of the superficial petrosal nerve. A CT scan showed enlargement of the facial nerve canal. Microsurgery was performed via an extended retrosigmoid approach. Intraoperative and electrophysiological findings identified the intermediate nerve as the site of tumor origin.

Abbreviations used in this paper: CPA = cerebellopontine angle; EMG = electromyography.

Article Information

Address correspondence to: Christian Scheller, M.D., Department of Neurosurgery, Martin-Luther University of Halle-Wittenberg, Ernst-Grube-Strasse 40, 06097 Halle, Germany. email: christian.scheller@medizin.uni-halle.de.

© AANS, except where prohibited by US copyright law.

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Figures

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    Axial (A–C) and sagittal (D) contrast-enhanced T1-weighted MR images showing a lesion in the CPA region extending into the base of the middle cranial fossa. An enlarged facial canal is visible (B). The tumor progressed along the course of the petrosus major nerve (D).

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    Intraoperative photograph demonstrating the area of positive electrical response (dotted line) exclusively in the orbicularis (orb) oris muscle. The facial nerve is seen anteriorly and superiorly. M = muscle; VII = facial nerve.

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    Traces (4 electrodes per branch) of the results of electrical stimulation (0.05 mA) of the intermediate nerve with motor response in the orbicularis (Orb.) oris muscle. Nasal = nasalis.

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    Intraoperative photograph of the dissected superior vestibular nerve (N. vest. sup.) showing the intermediate nerve (N. intermedius) clearly as the site of tumor origin.

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    Traces (4 electrodes per branch) of the results of electrical stimulation (0.05 mA) of the facial nerve with motor response in all 3 branches.

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