82. Motor evoked potentials are very sensitive to blood pressure in insular glioma surgery: A case report

Abstract

Since many years Motor Evoked potentials (MEPs) have been considered as a valuable tool to assess the integrity of motor pathways (Deletis, 1993). In brain tumor surgery, MEP are of particular value during the removal of insular glioma where the mechanism of injury is mainly vascular (Neuloh et al., 2007). We present and discuss the case of an insular glioma where MEP were lost during continuous monitoring through Direct Cortical Stimulation (DCS). A 47 year old female was operated on a left insular glioma. After the central sulcus was identified through the phase reversal technique, we performed continuous MEP monitoring (train of 4, ISI 2.5 ms, baseline intensity of stimulation 20 mA) from contra lateral upper and lower extremity muscles, through a 8 channels strip electrode placed over the motor cortex. A sudden disappearance of all MEPs occurred during tumor resection. Before MEPs loss, blood pressure dropped from 120 to 88 mm Hg. At this point stimulation intensity was increased up to 30 mA without any recovery of MEPs. To follow, papaverine was locally instilled to counteract vasospastic changes but this also carried no effect on MEPs. Finally, blood pressure progressively recovered to 110 mmHg and only at that time MEPs started to recover at 20 mA of stimulation intensity. At closing, MEPs completely recovered to baseline. Post-operative outcome was negative for motor impairment. Muscle MEPs are very sensitive to subcortical ischemia. Among corrective measures, to increase blood pressure proved to be more effective than papaverine and increased stimulation intensity to facilitate MEP recovery.