Intraoperative monitoring of the facial nerve by automated categorisation of EMG-activity

• Applicant: Professor Dr. Julian Prell
• Subject Area: Clinical Neurology; Neurosurgery and Neuroradiology
• Term: from 2010 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 183849231

During surgery for vestibular schwannoma, the facial nerve can be monitored by intraoperative evaluation of the EMG from the facial muscles. With this method, particular patterns (A-trains) signify potential damage to the facial nerve. A quantitative correlation between the amount of observed A-trains activity and the degree of clinical postoperative impairment has been demonstrated. However, false negative (very few A-trains, significant postoperative deficits) and false positive results (many A-trains, few clinical deficits) have been shown to impair the reliability of the method. In the context of our first application (PR1275/1-1), methods for automated analysis of the facial nerve EMG have been developed and evaluated. It was our main goal to identify the sources of false positive and false negative results. This goal was accomplished. In accord with our assumptions, false negative findings were shown to be based on too small a sample with too small an amount of electrodes utilized. In addition, we were able to demonstrate in a consecutive series of papers published in highly ranking journals that intraoperative manipulation of the Intermedius Nerve may lead to additional pathological A-trains without a postoperative clinical correlate; thus, this intermedius nerve activity acts as an interfering signal in the context of facial nerve monitoring. This follow-up application is based on the findings as outlined above. Its goal is to develop and evaluate methods which may technically differentiate between real facial nerve A-trains and A-trains elicited by intermedius nerve manipulation in an intraoperative setting. To do so, the respective biosignals will be compared systematically in order to find divergent signal characteristics. In this context, the assumption that intraoperative manipulation of a given motor unit will lead to monomorphic and specific EMG-signals will be followed further, as this would mean that after a certain time, the specific pattern may lose significance, because the corresponding unit cannot be damaged any further. In addition, EMG-analysis will be directly compared with the two other available methods for facial nerve monitoring: Direct electrical stimulation and facial nerve motor evoked potentials. Both methods are also flawed with false positive monitoring results; however, these results should not be based on intermedius nerve activity according to our assumptions. Thus, a complementary approach may lead to new findings in this context. Finally, a technical method for documentation of the facial nerve functional status after surgery is to be evaluated. This method is based on 3D-fotography and supposed to allow for an objective evaluation in contrast to the common method of clinical assessment by paresis grades. Our finding that A-trains elicited by the intermedius nerve tend to be limited to specific parts of the facial muscles can be evaluated further with this method.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozent Dr. Stefan Rampp