Ahead of Print: Low Threshold Mapping Motor Cortex

Background: Microsurgery within eloquent cortex is a controversial approach due to the high-risk of permanent neurological deficit. Few data exist showing the relationship between mapping stimulation intensity required for eliciting a muscle motor evoked potential (MEP) and distance to the motor neurons; furthermore, the motor threshold at which no deficit occurs remains to be defined.

Objective: To evaluate the safety of low threshold MEP mapping for tumor resection close to the primary motor cortex.

Methods: Fourteen patients undergoing tumor surgery were included. Motor threshold was defined as the stimulation intensity that elicited MEPs from target muscles (amplitude >30[mu]V). Monopolar high-frequency motor mapping with train-of-five stimuli (HF-TOF) (pulse duration=500[mu]s; interstimulus interval=4.0ms; frequency=250Hz) was used to determine motor response negative sites where incision and dissection could be performed. At sites negative to 3mA HF-TOF stimulation, the tumor was resected.

Editor Choice: Surgery of Insular Nonenhancing Gliomas

Background: Despite intraoperative technical improvements, the insula remains a challenging area for surgery because of its critical relationships with vascular and neurophysiological functional structures.

Objective: To retrospectively investigate the morbidity profile in insular nonenhancing gliomas, with special emphasis on volumetric analysis of tumoral resection.

Methods: From 2000 to 2010, 66 patients underwent surgery. All surgical procedures were conducted under cortical-subcortical stimulation and neurophysiological monitoring. Volumetric scan analysis was applied on T2-weighted magnetic resonance images (MRIs) to establish preoperative and postoperative tumoral volume.

Video: Brain Mapping With Resting-State Signals

This video illustrates the anatomy-based approach to systematic seed selection and resting-state SCP network identification. It also demonstrates qualitative correspondence between stimulation mapping and resting-state SCP mapping results.

Ahead of Print: Safe Resection of Arteriovenous Malformations in Eloquent Motor Areas Aided by Functional Imaging and Intraoperative Monitoring

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BACKGROUND: Arteriovenous malformations (AVMs) proximal to motor cortical areas or motor projection systems are challenging to manage due to the risk of severe sensory and motor impairment. Surgical indication in these cases therefore remains controversial.

OBJECTIVE: To propose a standardized approach for centrally situated AVMs, based on functional imaging and intraoperative electrophysiological evaluation.

METHODS: We conducted a retrospective analysis of 15 patients who underwent surgical treatment for AVMs in motor cortical areas or proximal to motor projections. Preoperative assessment included fMRI and 3D-tractography. Operations were performed under continuous electrophysiological monitoring aided by direct brain stimulation. We identified critical bloody supply to the motor areas by temporary occluding the feeding vessels under electrophysiological monitorization. Clinical outcome was evaluated using the modified Rankin Scale.

Ahead of Print: Electrostimulation Mapping of Spatial Neglect

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BACKGROUND: Cortical and subcortical electrostimulation mapping during awake brain surgery for tumor removal is usually used in order to minimize deficits.

OBJECTIVE: Electrostimulation was used to study neuronal substrates involved in spatial awareness in humans.

METHODS: Spatial neglect was studied using a line bisection task in combination with electrostimulation mapping of the right hemisphere in 50 cases. Stimulation sites were identified using Talairach’s coordinates. The behavioral effects induced by stimulation, especially eye movements and deviations from the median, were quantified and compared to pre-operative data and to a control group.