Stimulation threshold potentials of intraoperative cortical motor mapping using monopolar trains of five in pediatric epilepsy surgery

Abstract

Objective

Direct cortical stimulation in commonly used for the accurate localization of the motor cortex but the electrical threshold stimulation parameters with this technique had not been fully established.

Patients and methods

A retrospective review of 15 cases of pediatric surgical cases were performed. The patients consisted of nine male patients and six female patients with age range from 2 to 18 years (mean: 10.8 years; median: 14 years). The most common pathology was cortical dysplasia (nine cases). Stimulation was performed with a train of five stimulations (range five–seven stimulations; <5% of stimulations required more than five stimulations) applied, each train of 50 μs pulse duration, with an interstimulus interval of 1.1 msec. Stimulation intensity commenced at 25 V and this was increased at 5–10 V increments until motor evoked potentials waveforms of sufficient duration and morphology were consistently generated.

Results

Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were found to be more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate (83.7%) and required the lowest stimulation voltage (36.0 V). The stimulation voltage was found to be statistically significant compared to threshold values for abductor hallucis, tibialis anterior, deltoid, and orbicularis oris with respective p values of 0.006, 0.021, 0,027, and 0.015. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds when compared to other pathology (p = 0.067).

Conclusion

Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate and required the lowest stimulation voltage. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds.