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

Area of Science:

• Neurosurgery
• Neuroscience
• Oncology

Background:

• The non-dominant parietal lobe is crucial for motor cognition, attention, and spatial awareness, necessitating careful surgical approaches.
• Awake surgery is often preferred, but asleep monitoring and mapping techniques are vital for achieving an onco-functional balance when awake surgery is not feasible.

Purpose of the Study:

• To assess the feasibility of a dual-strip method for direct cortical stimulation.
• To achieve continuous real-time cortical monitoring and simultaneous subcortical mapping of motor and visual pathways during parietal lobe tumor surgery.

Main Methods:

• A single-centre prospective study involving patients with intrinsic non-dominant parietal lobe tumors.
• Utilized two subdural strips for simultaneous mapping and monitoring of motor and visual pathways.
• Collected data on interhemispheric resting motor threshold ratio (iRMTr), Cortical Excitability Score (CES), and distances to critical tracts (LTD, CTD).

Main Results:

• Fifteen patients were included, with a high proportion showing abnormal motor parameters (iRMTr 71.4%, CES 85.7%).
• Significant proximity to motor and visual tracts was observed (LTD/CTD for corticospinal tract: 4.2mm/7mm; LTD/CTD for optic radiations: 0.5mm/3.4mm).
• Higher iRMTr correlated with worse motor outcomes (p=0.013), and longer CTD to optic radiations predicted better visual outcomes (p=0.041).

Conclusions:

• The study proposes functional boundaries for asleep surgery in non-dominant parietal lobe tumors.
• Pre-operative abnormal cortical excitability, visual evoked potential (VEP) deterioration, and close proximity to optic radiations (<2mm CTD) are linked to poorer outcomes.
• The dual-strip method facilitates simultaneous motor and visual pathway monitoring, aiding in achieving onco-functional balance.