Continuous subcortical monitoring of motor pathways during glioma surgery with ultrasonic surgical aspirator: technical description in a single institute experience.

Background: Actual challenge in surgical treatment of intra-axial gliomas involving eloquent areas is maximal safe resection. Mapping and monitoring of cortical and subcortical motor functions are important tools to avoid postoperative deficits. In the present study, we present our experience with a continuous dynamic motor mapping technique pairing a traditional monopolar stimulator with a Cavitron ultrasonic surgical aspirator (CUSA) to perform a continuous stimulation of the white matter avoiding removal interruption.

Methods: We describe a single center retrospective analysis of 1-year consecutive patients with intraxial tumors located adjacent to corticospinal tract and treated with surgical resection adopting "continuous dynamic mapping technique." With the support of a reconstruction software (3D Slicer), we classified the extent of resection (EOR) as gross total resection (GTR) (>98%), sub-total resection (STR) (from 90% to 97%), and partial resection (<90%). Medical Research Council (MRC) grading was adopted to evaluate neurological outcomes (from 0 to 5), assessed on first postoperative day, at 1 week, 1 month and 3 months.

Results: From July 2017 to July 2018, 29 patients underwent to surgical removal of intraxial tumor adjacent to motor areas, using continuous dynamic subcortical mapping. Median age was 54 years old (range 12-75 years). At preoperative MRI tractography reconstruction, mean distance between tumor and corticospinal tract was 4.4 mm (range At 1 week postoperative assessment, motor deficits were still present in 12 patients (41%). At 1 month, 10 patients (35%) had persisting deficits, which required admission to rehabilitation department. At 3 months, 4 patients (14%) had persistent motor impairment and overall 28 patients (98%) were able to walk by themselves.

Conclusions: Our early experience showed that a combination of dynamic subcortical mapping with transcranial and cortical strip MEP (motor evoked potentials) monitoring is useful in tumors close to motor eloquent areas to extend surgical resection avoiding permanent consequences. However, we need for further experience to consolidate and improve this technique.