Abstract
ObjectiveThe intraoperative monitoring of cranial nerve function records evoked responses at latencies of a few milliseconds. Unfortunately, these responses may be masked by the electrical artifact of the stimulation pulse. In electrical stimulation, the return discharge of the stimulation pulse significantly contributes to the width of the electrical artifact. MethodsWe have generated stimulation pulses with an ISIS Neurostimulator (inomed Medizintechnik GmbH) providing a novel stimulation artifact reduction technique. It delays the return discharge of the stimulating pulse beyond the latency of the expected physiological response. This delayed return discharge is controlled such that no unintended physiological response is evoked. ResultsIn 21 neurosurgical interventions with motor evoked potentials of the facial nerve (FNMEP), the stimulation method generated a stimulation pulse artifact with reduced tail duration. Compared to conventional stimulation with immediate return discharge, the signal-to-noise ratio of the physiological response may improve with the novel stimulation method. In some surgeries, only the novel stimulation method generated clearly identifiable response signals. ConclusionsThe reduced width of the stimulation artifact extends the toolbox of intraoperative monitoring modalities by rendering the interpretation of cranial nerve evoked potentials more reliable. SignificanceThe novel technique enhances the number of patients for whom intraoperative monitoring may aid in cranial neurosurgery.
Highlights
Microneurosurgery of the skull base carries a significant risk of impairing cranial nerve function (Yaßsargil, 1984)
The reduced width of the stimulation artifact extends the toolbox of intraoperative monitoring modalities by rendering the interpretation of cranial nerve evoked potentials more reliable
The novel technique enhances the number of patients for whom intraoperative monitoring may aid in cranial neurosurgery
Summary
Microneurosurgery of the skull base carries a significant risk of impairing cranial nerve function (Yaßsargil, 1984). For continuous monitoring of cranial nerve motor function, transcranial electrical stimulation (TES) allows activation of the motor cortex and the motor pathway proximal to the surgical field and, the recording of the motor evoked potential (MEP) in cranial nerve target muscles, for example the facial nerve MEP (FNMEP) (Akagami et al, 2005; Sarnthein et al, 2013; Bozinov et al, 2015; Seidel et al, 2020). Despite these advantages, cranial nerve MEP monitoring has not become a standard tool of IONM yet.
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