gms | German Medical Science

Objective: Intraoperative neuromonitoring (IONM)is required for resection of eloquently located cerebral lesions. Speech monitoring with bipolar stimulation is widely used during awake surgery, whereas monopolar stimulation in combination with extended IONM including SSEP, MEP and ECG monitoring most frequently is applied for motor mapping in asleep patients. In our neurooncological department both techniques are used either combined or separately for surgery of eloquent brain tumours. Here, we present data concerning assessment of intraoperative relevance of both techniques.

Methods: We prospectively enclosed data of all patients undergoing surgery using any IONM method between 01/19-11/19 (n=104). Retrospectively evaluation of relevance of the chosen intraoperative techniques was conducted. Postoperative neurological outcome and grade of resection evaluated by post-OP MRI were analysed as proof of concept.

Results: 68% of the patients underwent awake surgery. Awake surgery with 60 Hz stimulation only was assessed to be adequate in 24 % (n=25) mostly in strict left temporal lesions. 43 % (n=45) of the surgeries required either planned or additional monopolar stimulation or extended IONM mostly due to lesions of the right hemisphere in planned non-awake surgeries or non-adequate awake patients in awake surgery. In 20 % of the patients (n=21) combination of both methods was evaluated as useful or relevant mostly in patients when monopolar stimulation only showed indifferent results or lesions were located parietotemporal. In 13 % (n=13) none of the methods were relevant mostly due to indifferent or intraoperative loss of IONM signals or non-adequate awake patients when speech testing was obligate. 4 patients (4%) suffered from a permanent deficit linked to resection. Complete resection was intraoperatively evaluated in 77 patients (79%), after matching with post-OP MRI 16% showed a residual tumorvolume.

Conclusion: Adequate IONM techniques depend on various factors such as localisation, required testing parameters and patients’ compliance. Monopolar stimulation was found to be essential for eloquent tumours of the right hemisphere in non-awake or inadequately awake patients for motor mapping. 60 Hz stimulation only was sufficient for strict temporal lesions without vessel conflicts. Combination was useful in patients with parietotemporal lesions or when monopolar motor mapping showed indifferent results. Extended IONM was only crucial in lesions conflicting cerebral vessels.