PMC9357452_01
Preoperative magnetic resonance imaging 4 weeks after the onset of symptoms. a T2-weighted image presenting a lesion with hyperintensity located within the internal auditory canal. b T1-weighted image presenting an isointense mass. c Gadolinium-enhanced T1-weighted image presenting a heterogeneously enhanced mass extending into the geniculate ganglion (arrow).
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Magnetic resonance imaging (MRI) revealed a lesion localized within the patient's left IAC with hyperintensity on T2-weighted image (WI) and isointensity on T1WI (Fig. 1a, b). Gadolinium-enhanced T1WI revealed a heterogeneously enhanced mass extending into the geniculate ganglion (Fig. 1c).
Intraoperative findings of continuous monitoring of evoked facial nerve electromyograms (CFN-EMGs) for the orbicularis oris (Oris) and mentalis (Mentalis) muscles. a No response was observed after applying 1.0-mA stimulation at 1-Hz frequency, whereas stable CFN-EMGs were obtained when stimulation was increased to 2.7 mA (single arrowhead). b After incising the dura of the IAC, the surgical field suddenly vibrated every second with 2.7 mA of stimulations (single arrowheads). The vibration stopped when the stimulation was interrupted (suspension). The vibrations were caused by contractions of the facial muscles. Stable CFN-EMGs were observed even at 1.0 mA (double arrowheads) after opening the dura mater of the IAC. The threshold was decreased, suggesting that the responsiveness of the facial nerve improved.
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Stable CFN-EMGs were obtained when the stimulus was increased to 2.7 mA (Fig. 2a). Stable CFM-EMGs were subsequently observed even after applying a stimulus of 1.0 mA (Fig. 2b).
Intraoperative view after bone removal of the posterior wall of the internal auditory canal and incision of the dura mater. The normal vestibular nerve appeared to be compressed by the tumor from its ventral side.
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A normal vestibular nerve without a tumor was confirmed after a dural incision (Fig. 3), which supported the diagnosis of FNS.
Comparison of preoperative and postoperative constructive interference in steady-state MRI. a Preoperative image at the level of the left IAC. b Postoperative image presenting the removal of the posterior wall of the IAC.
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Postoperative constructive interference in steady-state MRI showed the removal of the posterior wall of the IAC (Fig. 4).