Introduction of a novel connection clip for the ultrasonic aspirator for subcortical continuous motor mapping

A connection clip to the ultrasonic aspirator handpiece was introduced for simultaneous resection and mapping of corticospinal motor tract (CST) (Kombos et al., 2001).

To report retrospectively the use of this clip in cerebral surgery with CST mapping.

Eight women and four men were included (mean: 55.8 years, SD 17.3 years). The ultrasonic aspirator handpiece was stimulated every second (5 biphasic pulses, 0.4 ​ms per phase, max 14 ​mA). Motor evoked potentials (MEPs) (Taniguchi et al., 1993), with transcranial and direct cortical stimulation, were alternated with CST mapping. The distances between the stimulus locations to the CST (diffusion tensor imaging based fibre tractography) were determined postoperatively. Muscle strength was evaluated pre-operatively, at discharge and 3 months.

Motor mapping thresholds ranged between 2 and 13 ​mA, in 12 consecutive patients (7 post-central, 5 insular). The distance of the stimulation site to the CST was fitted (y ​= ​0.63x+2.33, R² ​= ​0.33; x, mA; y, mm), approximating the rule of thumb of 1 ​mA indicating 1 ​mm (R² ​= ​0.22). One patient presented with a deterioration of motor function (wrist, M4+). No intraoperative seizures were observed.

The concept that 1 ​mA corresponds to 1 ​mm from the CST, was roughly observed within this low current range. This rule must be applied, integrating the confidence limits, when getting close to the CST, in conjunction with MEPs.

The standardization of this clip, for continuous stimulation of the ultrasonic aspirator with simultaneous tissue resection, made the guided surgical flow smoother, more refined and very natural.