Simultaneous Motor and Visual Intraoperative Neuromonitoring in Asleep Parietal Lobe Surgery: Dual Strip Technique

Abstract

The role played by the non-dominant parietal lobe in motor cognition, attention and spatial awareness networks has potentiated the use of awake surgery. When this is not feasible, asleep monitoring and mapping techniques should be used to achieve an onco-functional balance. Objective: This study aims to assess the feasibility of a dual-strip method to obtain direct cortical stimulation for continuous real-time cortical monitoring and subcortical mapping of motor and visual pathways simultaneously in parietal lobe tumour surgery. Methods: Single-centre prospective study between 19 May–20 November of patients with intrinsic non-dominant parietal-lobe tumours. Two subdural strips were used to simultaneously map and monitor motor and visual pathways. Results: Fifteen patients were included. With regards to motor function, a large proportion of patients had abnormal interhemispheric resting motor threshold ratio (iRMTr) (71.4%), abnormal Cortical Excitability Score (CES) (85.7%), close distance to the corticospinal tract—Lesion-To-Tract Distance (LTD)—4.2 mm, Cavity-To-Tract Distance (CTD)—7 mm and intraoperative subcortical distance—6.4 mm. Concerning visual function, the LTD and CTD for optic radiations (OR) were 0.5 mm and 3.4 mm, respectively; the mean intensity for positive subcortical stimulation of OR was 12 mA ± 2.3 mA and 5/6 patients with deterioration of VEPs > 50% had persistent hemianopia and transgression of ORs. Twelve patients remained stable, one patient had a de-novo transitory hemiparesis, and two showed improvements in motor symptoms. A higher iRMTr for lower limbs was related with a worse motor outcome (p = 0.013) and a longer CTD to OR was directly related with a better visual outcome (p = 0.041). At 2 weeks after hospital discharge, all patients were ambulatory at home, and all proceeded to have oncological treatment. Conclusion: We propose motor and visual function boundaries for asleep surgery of intrinsic non-dominant parietal tumours. Pre-operative abnormal cortical excitability of the motor cortex, deterioration of the VEP recordings and CTD < 2 mm from the OR were related to poorer outcomes.

Harnessing Advanced Tractography in Neurosurgical Practice

“…This chapter underscores the importance of these neuroimaging techniques' ongoing development and clinical integration. Author's original based on data from Rajashekar et al (2022)…”

Intraoperative Neurophysiological Monitoring in Neurosurgery

“…VEPs are captured through active electrodes (O1, O2, and Oz), referencing the vertex to the Cz reference electrode on the scalp over the occipital cortex in response to light stimuli [48]. When dealing with occipital brain lesions, subdural strip electrodes may be employed for recording [49][50][51]. Recent attention to VEP monitoring has been sparked by the growing utilization of simultaneous electroretinogram (ERG) recording, progress in light-emitting diodes (LEDs) manufacturing, and the adoption of white light stimulation [26,52].…”

Transcranial Magnetic Stimulation–Based Machine Learning Prediction of Tumor Grading in Motor-Eloquent Gliomas

“…Different results were observed when the cortical region of interest was provided by functional MRI and nTMS, favoring nTMS with higher plausibility in the tumor side and similar results in the healthy side. 7 This technique provided a significant step forward 8,9 by allowing individualized motor risk stratification, 10,11 identification of safe surgical corridors, 12,13 correlation with neurological outcomes, 8,14 and better oncological results. 15 The third stage-the clinical correlation-is preoperative mapping-driven predictors of clinical outcomes, such as neurological deficits and neuropathology findings.…”