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.

Ahead of Print: Intraoperative Neuromonitoring in Glioma Surgery

Background: Resection of gliomas in or adjacent to the motor system is widely performed using intraoperative neuromonitoring (IOM). Despite the fact that data on the safety of IOM are available, the significance and predictive value of the procedure is still under discussion. Moreover, cases of false negative monitoring affect the surgeon’s confidence in IOM.

Objective: To examine cases of false negative IOM to reveal structural explanations.

Methods: Between 2007 and 2010 we resected 115 consecutive supratentorial gliomas in or close to eloquent motor areas using direct cortical stimulation for monitoring of motor evoked potentials (MEPs). The monitoring data were reviewed and related to new postoperative motor deficit and postoperative imaging. Clinical outcomes were assessed during follow-up.