22. Implementation of multimodal intraoperative neuromonitoring into an established setting of awake craniotomy

Abstract

Bipolar 60 Hz-stimulation-mapping and clinical evaluation are commonly used for patient assessment in awake neurosurgical procedures. Stimulation related seizures, afterdischarges, delayed wake-up or malcompliance interfere with successful testing. Somatosensory (SEPs) and motor evoked potentials (MEPs) are objective tools for mapping and monitoring independent of patients’ compliance. Their introduction into an established ‘awake setting’ were prospectively analysed for feasibility, reliability and effect on surgical strategy. Multimodal intraoperative neuromonitoring consisting of contralateral SEPs, transcranially (TES) and direct cortically (DCS) elicited MEPs (monopolar, train-of-five-technique with 250 Hz) were implemented in a 13 month period. 105 patients (53 ± 14 years, 60 male) with frontal/precentral (48), postcentral/parietal (33), temporal (16) and trigonal (8) located lesions (glioma (81), metastasis (18), others (6)) were analysed. SEPs and TES-MEPs were present in all 105 patients, as well as DCS for cortical and subcortical motor mapping. There were no serious side effects despite the description of tingling pain during direct cortical stimulation. After 5 months, a bias towards motor mapping with the monopolar stimulation was seen, such monopolar vs. bipolar stimulation was only compared in the first 70 patients: DCS-MEPs were elicited in all 70 patients, whereas the 60 Hz-stimulation elicited motor responses in 60/70 patients (p = 0.0016; Fisher’̃s-test). 90/105 patients (86%) were cooperative for the awake setting. In 4 of the 15 remaining patients (4%) language testing was considered essential and surgery was prematurely terminated. In the other 11 patients (10%), surgery was continued asleep with monopolar cortical and subcortical mapping and continuous monitoring of SEPs and MEPs. Multimodal monitoring is feasible in awake craniotomies and was well tolerated. Despite malcompliance and clinical deterioration it allows for objective assessment of somatosensory and motor pathways and proceeding with the surgical tumour resection. In conclusion, the inclusion of multimodal monitoring might be essential for pericentral surgery.