The purpose of this study was to achieve a more radical resection of tumors in the area of the motor cortex via minimal craniotomy using a combination of neuronavigation and neurophysiological monitoring with direct electrical cortical stimulation and to compare retrospectively the clinical outcome and postoperative magnetic resonance imaging with a control group that was operated on in our service when the combination of these monitoring techniques was not available. A total of 42 patients with tumors in or near the central region underwent surgery with neuronavigation guidance and neurophysiological monitoring. The primary motor cortex was identified intraoperatively by the somatosensory evoked phase reversal method and direct cortical stimulation. The functional areas were transferred into the neuronavigation system. By stimulating the identified primary motor cortex and displaying the motor area in the operating microscope a permanent control of the motor function was possible during the whole operation. Using these techniques a more radical tumor resection - evaluated by postoperative MRI - was achieved in the study group (p = 0.04) and also a trend toward a better neurological outcome.
Intraoperative motor evoked potential (MEP) monitoring in patients with spinal and cranial lesions is thought to be a valuable tool for prevention of postoperative motor deficits. Aim of this study was to investigate its diagnostic value in a spinal and a cranial patient group. Ninety-six patients, 31 with spinal and 65 with intracranial lesions, were studied. Transcranial stimulation was performed with a high-frequency electrical train stimulation using two subdermal needle electrodes. MEPs were recorded from the pathology-related muscles. Decreasing amplitudes of 50% or more, increasing stimulus intensities of 20% or more or increased latencies were taken as warning criteria. MEP recording was possible in 90% of the spinal and 98% of the cranial group. With two further exclusions, 28 patients of the spinal and 62 of the cranial group were analyzed. We saw a temporary maximum amplitude reduction of 50% or more and an increase in stimulation intensity of 20% or more in 8 spinal and 29 cranial patients. Five of the spinal and nine of the cranial patients deteriorated in motor function postoperatively. One patient with normal MEP monitoring showed a temporary motor weakness postoperatively. Latencies were normal in all patients. Given both warning criteria, intraoperative MEP changes had a sensitivity of 83%/ 100% and a specificity of 86%/ 62% (spinal/ cranial group). The positive predictive value of MEP changes for postoperative motor function deterioration was 63%/ 31%, and the negative predictive value was 95%/ 100%. Transcranial electrical monitoring of MEP is a practicable and safe method. However, there are many events, which can cause amplitude changes of MEP independent from surgical manipulations. Although sensitivity is high for both groups, this results in a moderate specificity for the cranial group and a low positive predictive value for both groups.
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