Direct motor evoked potentials and cortical mapping using the NIM® nerve monitoring system: A technical note

Removal of Perirolandic Cavernoma with Direct Cortical Stimulation and Neuronavigation with DTI

Background and Introduction

Intraoperative neuromonitoring for eloquent cortical lesions is irreplaceable in present-day neurosurgery.

Objective

We report a novel technique of combining awake craniotomy with direct cortical stimulation of the motor cortex using the NIM^© nerve monitoring system.

Technique

A 17-year-old boy presenting with focal motor seizures, diagnosed with left perirolandinc cavernoma, underwent awake craniotomy and complete excision under direct cortical stimulation with NIM monopolar stimulator electrode to locate the motor cortex.

Result

The patient developed transient weakness of handgrip during surgery, which improved by the same day evening. At 3 months follow-up, he could perform all the activities with his dominant right hand.

Conclusion

Cortical stimulation using a nerve monitoring system is a useful technique in case of nonavailability of standard evoked potential monitoring system for motor cortex mapping.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.