[Treatment of intrinsic brain tumors located in motor eloquent areas. Results of a protocol based in navigation, tractography and neurophysiological monitoring of cortical and subcortical structures].

OBJECTIVES

The role of the microsurgical management of intrinsic brain tumors is to maximize the volumetric resection of the tumoral tissue minimizing the postoperative morbidity. The purpose of our paper has been to study the benefits of an original protocol developed for the microsurgical treatment of tumors located in eloquent motor areas where the navigation and electrical stimulation of motor subcortical pathways have been implemented.

MATERIALS AND METHODS

A total of 17 patients operated on for resection of cortical or subcortical tumors in motor areas were included in the series. Preoperative planning for multimodal navigation was done integrating anatomic studies, motor functional MRI (f-MRI) and subcortical pathways volumes generated by diffusion tensor imaging (DTI). Intraoperative neuromonitorization included motor mapping by direct cortical and subcortical electrical stimulation (CS and sCS) and localization of the central sulcus using cortical multipolar electrodes and the N20 wave inversion technique. The location of all cortical and subcortical stimulated points with positive motor response was stored in the navigator and correlated with the cortical or subcortical motor functional structures defined preoperatively.

RESULTS

The mean tumoral volumetric resection was 89.1±14.2% of the preoperative volume, with a total resection (≥100%) in twelve patients. Preoperatively a total of 58.8% of the patients had some motor deficit, increasing 24 hours after surgery to 76.5% and decreasing to 41.1% a month later. There was a great correlation between anatomic and functional data, both cortically and subcortically. However, in six cases it was not possible to identify the central sulcus and in many cases fMRI gave contradictory information. A total of 52 cortical points submitted to CS had positive motor response, with a positive correlation of 83.7%. Also, a total of 55 subcortical points had positive motor response, being in these cases 7.3±3.1 mm the mean distance from the stimulated point to the subcortical tract.

CONCLUSIONS

The integration of preoperative and intraoperative anatomic and functional studies allows a safe functional resection of the brain tumors located in eloquent areas, compared to the tumoral resection based on anatomic imaging studies. Multimodal navigation allows the integration and correlation among preoperative and intraoperative anatomic and functional data. Cortical motor functional areas are anatomically and functionally located preoperatively thanks to MRI and fMRI and subcortical motor pathways with TDI and tractography. Intraoperative confirmation is done with CS and N20 inversion wave for cortical structures and with sCS for subcortical pathways. With this protocol we achieved a mean of 90% of volumetric resection in cortical and subcortical tumors located in eloquent motor areas with an increase of neurological deficits in the immediate postoperative period that significantly decreased one month later. Ongoing studies will define the safe limits for functional resection taking into account the intraoperative brain shift. Finally, it must be demonstrated if this protocol has any benefit for patients concerning disease free or overall survival.