gms | German Medical Science

Objective: Preserving motor function is a major challenge in surgery for intraaxial brain tumors and metastasis, which are very closed located to the corticospinal tracts (CSTs). We evaluated the contribution of the combination of diffusion tensor imaging-based fibre tracking (DTI-FT) of the CST integrated to the navigation and subcortical direct electrical stimulations (DESs). We prooved if there is a direct correlation between the value of DESs-threshold and the distance between the tumor-borderline and CST.

Method: A retrospective analysis was conducted in 348 patients undergoing brain surgery in an eloquent area between 2010 until July 2014 at the authors' institution. We excluded patients with an age between 0 and 18 and patients, who underwent epileptic surgery or surgery of cavernoma, so final number of patients that got analysed was 286. DTI-FT was coregistered to surgical navigation-derived images in all patients. Subcortical-stimulated MEPs (scrtMEPs) were recorded intraoperatively to assess function and estimate the distance from the CSTs. Preoperative clinical motor function was compared with postoperative outcome at several time points and correlated with incidences of intraoperative dcMEP alarm and low scrtMEP values.

Results: The threshold level needed to elicit scrtMEPs was plotted against the distance to the CSTs based on diffusion tensor imaging tractography, generating a trend line that demonstrated a linear order between these variables, and a relationship of 0.97 mA for every 1 mm of brain tissue distance from the CSTs. Clinically, 203 (71%) of 286 patients had no postoperative deficits, and 46 of the remaining 83 improved to baseline function within 1 month. Seven patients had varying degrees of permanent motor deficits. Subcortical stimulation was applied in all patents. At one month after surgery, only 19 patients had still a slight impairment of motor function.

Conclusions: DTI-FT is an accurate technique to map the CST in the vicinity of brain tumours, metastases and meningiomas. By combining anatomical (DTI-FT) and functional (subcortical DES) studies for intraoperative localisation oft the CST and enabled the safe resection of tumors approximating these tracts. We could evaluate the distance from the CSTs using the threshold of subcortical monopolar stimulation. The linear correlation between the distance to the CSTs and the threshold of subcortical stimulation producing a motor response provides an intraoperative technique to better preserve motor function.