PMC7749950_01
Preoperative magnetic resonance imaging of the brain axial post contrast-enhanced T1W image (a), coronal T2W image (b), and sagittal T2W image (c) showing a large 30 (AP) x 25 (T) x 30 (CC) mm size hyperintense well-defined mass within the left CPA with intraand extracanalicular extension. The tumor exerts mass effect on the 4th ventricle, with marked dilatation of the third and bilateral lateral ventricles.
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F1
The lesion was consistent with the left side vestibular schwannoma [Figure 1].
Baselines for (a) laryngeal adductor reflex (LAR) left side cR1 (ipsilateral side to the lesion) and (b) LAR right side cR1 and cR2 responses, which are shown at top of both figures, respectively. Schematic illustration of LAR methodology is shown at the bottom. Embedded electromyography tracheal tube electrodes, left (blue) and right (red), are positioned directly with the left and right vocal folds. LAR is evoked through electrodes positioned contralaterally to the surgical field, stimulating independently the right and left side of the laryngeal mucosa. LAR responses (cR1 and cR2) are recorded using endotracheal tube electrodes positioned contralaterally to the stimulating side.
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F2
The monitoring parameter for IONM interpretation of this modality consisted of considerable attenuation (>=60%) in LAR amplitude responses [Figure 2].
Sudden drop of heart rate (HR) ( ) and blood pressure (BP) ( ) values from baseline (a), which correlates with surgical removal of tumor adjacent to the left trigeminal nerve. The anesthetic chart shows how HR and BP recovered to baseline after surgical stimulation was discontinued. Blink reflex (BR) intraoperative neuromonitoring changes (b) showed decrease of the left BR iR1 from baseline coinciding timely with stretching of the left trigeminal nerve and hemodynamic disturbances. The reflex recovered to baseline after surgical stimulation was discontinued.
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F3
A dose of 1.0 mg atropine sulfate was administered to the patient to counteract the bradycardia, with returning of HR and BR responses to baseline values within 1 min after its administration [Figure 3].
Sudden drop of heart rate (HR) ( ) and blood pressure (BP) ( ) from baseline (a). Consecutive traces of the left and right laryngeal adductor reflex (LAR) (b) showing reversible reduction of both cR1 (left traces) and cR1 and cR2 (right traces) responses from baseline and simultaneous reversible reduction of the left vocal corticobulbar motor evoked potentials (CoMEPs) responses (c). All these changes correlated temporally with surgical maneuvers that stretched the left vagus nerve. All HR, BP, left-sided vocal CoMEP, and bilateral LAR side responses recovered to baseline after surgical stimulation was discontinued.
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F4
The surgical team acted immediately, neural stimulation was stopped, and 1.0 mg of atropine was given to the patient immediately, with improvement of hemodynamic parameters, bilateral LAR, and left side CoMEP responses 1 min after administering atropine [Figure 4].