gms | German Medical Science

Objective: Skull base tumors, especially meningiomas, sometimes involve vital structures, arteries, veins and nerves. To prevent postoperative motor paresis, it is very important to monitor the functions of corticospinal tract (CST) with motor evoked potentials (MEP) during skull base surgery. We report our experience of intraoperative monitoring for skull base surgery by transcranial MEP.

Methods: Twenty-four patients (26 surgeries) were enrolled this study.

To stimulate hand motor cortex, we screw “Corkscrew electrodes” into the skin just above C3 and C4 points, which prescribed international 10–20 system. The five rectangular train pulse, 200 microsecond duration and 2 millisecond interval was applied by a constant voltage stimulator. The stimulation intensity, we use threshold +40 V, usually 150–200 V.

Results: The transcranial MEP monitoring was possible in all cases. The motor paralysis did not appear in 12 cases whose MEP was stable during surgery. In 11 cases, MEP remained at the end of surgery even if the MEP amplitude decreases or lost. Mild or moderate motor paresis was developed after surgery. Some patients had a motor paresis due to tumor or previous cerebral infarction. The mild or moderate motor paresis existed after surgery. The motor paresis almost recovered until preoperative level or more by 3 months rehabilitation after surgery. In 3 cases whose MEP disappeared and not recovered, they appeared a serious long lasting motor paralysis.

Conclusions: We have some problems to be solved. First, it was difficult to predict that which maneuver affect the CST itself or perforators which supplied to CST. Because in aneurysm surgery, we can predict and understand that MEP should change during temporary clip application or premature. But tumor section surgery, it is very difficult. Second, the timing to give a warning is controversial. From our experience of aneurysm surgery, we use 50% decrease from the control value as a warning point, but is it true or not. Finally, a prediction of the outcome of the motor function is also unclear. Transcranial MEP change is well correlated to postoperative motor function. If MEP restored at the end of the surgery, motor paresis should be transient or none and be expected full recovery in a few months. Further study with a large number of patients is required to estimate the significance of this method as a means of monitoring to predict motor function.