gms | German Medical Science

Objective: Presumed eloquence has been shown to be a modifiable risk factor in low-grade glioma (LGG) resection. Two intraoperative neurophysiological methods are accepted to guide the intraoperative decision making: mapping and monitoring. We demonstrate our neurophysiological management strategy in LGG resection focusing on motor function.

Method: 32 patients (2009 - 2014) with LGG of less than 10 mm to the corticospinal tract (CST) shown in preoperative fiber tracking were analyzed. Simultaneous direct cortical stimulation MEP monitoring (DCS-MEP) and subcortical mapping was performed applying monopolar stimulation, train of 5 stimuli, inter-stimulus-interval 4.0 ms and pulse duration 0.5 ms. From 2010 continuous dynamic mapping was realized by integrating the mapping probe at the tip of a suction device coupled with an acoustic MEP alarm.

Results: Lowest mapping thresholds (MT) were as follows (MT, number of patients): >20 mA, n= 1; 11-20 mA, n= 8; 6-10 mA, n= 6; 4-5 mA, n= 8; 1-3 mA, n= 9. DCS-MEP showed stable signals in 23 patients, unspecific changes in 8, irreversible alterations or loss in 1 patient. At 3 months, 1 patient (3 %) had a persisting postoperative motor deficit, which was caused by a vascular injury. None had a permanent motor deficit caused by a mechanical injury of the CST.

Conclusions: DCS-MEP predicts the integrity of the CST and therefore postoperative motor outcome. Only DCS-MEP is able to predict vascular injury. Mapping predicts the proximity to the CST. The continuous dynamic mapping technique improves the accuracy. This combined approach may increase the safety of motor eloquent LGG surgery.