Ehab Shiban, Sandro M. Krieg, Thomas Obermueller, Maria Wostrack, Bernhard Meyer and Florian Ringel
Resection of a motor eloquent lesion has become safer because of intraoperative neurophysiological monitoring (IOM). Stimulation of subcortical motor evoked potentials (scMEPs) is increasingly used to optimize patient safety. So far, scMEP stimulation has been performed intermittently during resection of eloquently located lesions. Authors of the present study assessed the possibility of using a resection instrument for continuous stimulation of scMEPs.
An ultrasonic surgical aspirator was attached to an IOM stimulator and was used as a monopolar subcortical stimulation probe. The effect of the aspirator’s use at different ultrasound power levels (0%, 25%, 50%, 75%, and 100%) on stimulation intensity was examined in a saline bath. Afterward monopolar stimulation with the surgical aspirator was used during the resection of subcortical lesions in the vicinity of the corticospinal tract in 14 patients in comparison with scMEP stimulation via a standard stimulation electrode. During resection, the stimulation current at which an MEP response was still measurable with subcortical stimulation using the surgical aspirator was compared with the corresponding stimulation current needed using a standard monopolar subcortical stimulation probe at the same location.
The use of ultrasound at different energy levels did result in a slight but irrelevant increase in stimulation energy via the tip of the surgical aspirator in the saline bath. Stimulation of scMEPs using the surgical aspirator or monopolar probe was successful and almost identical in all patients. One patient developed a new permanent neurological deficit. Transient new postoperative paresis was observed in 28% (4 of 14) of cases. Gross-total resection was achieved in 64% (9 of 14) cases and subtotal resection (> 80% of tumor mass) in 35% (5 of 14).
Continuous motor mapping using subcortical stimulation via a surgical aspirator, in comparison with the sequential use of a standard monopolar stimulation probe, is a feasible and safe method without any disadvantages. Compared with the standard probe, the aspirator offers continuous information on the distance to the corticospinal tract.
Ehab Shiban, Sandro M. Krieg, Bernhard Haller, Niels Buchmann, Thomas Obermueller, Tobias Boeckh-Behrens, Maria Wostrack, Bernhard Meyer and Florian Ringel
Subcortical stimulation is a method used to evaluate the distance from the stimulation site to the corticospinal tract (CST) and to decide whether the resection of an adjacent lesion should be terminated to prevent damage to the CST. However, the correlation between stimulation intensity and distance to the CST has not yet been clearly assessed. The objective of this study was to investigate the appropriate correlation between the subcortical stimulation pattern and the distance to the CST.
Monopolar subcortical motor evoked potential (MEP) mapping was performed in addition to continuous MEP monitoring in 37 consecutive patients with lesions located in motor-eloquent locations. The proximity of the resection cavity to the CST was identified by subcortical MEP mapping. At the end of resection, the point at which an MEP response was still measurable with minimal subcortical MEP intensity was marked with a titanium clip. At this location, different stimulation paradigms were executed with cathodal or anodal stimulation at 0.3-, 0.5-, and 0.7-msec pulse durations. Postoperatively, the distance between the CST as defined by postoperative diffusion tensor imaging fiber tracking and the titanium clip was measured. The correlation between this distance and the subcortical MEP electrical charge was calculated.
Subcortical MEP mapping was successful in all patients. There were no new permanent motor deficits. Transient new postoperative motor deficits were observed in 14% (5/36) of cases. Gross-total resection was achieved in 75% (27/36) and subtotal resection (> 80% of tumor mass) in 25% (9/36) of cases. Stimulation intensity with various pulse durations as well as current intensity was plotted against the measured distance between the CST and the titanium clip on postoperative MRI using diffusion-weighted imaging fiberitracking tractography. Correlational and regression analyses showed a nonlinear correlation between stimulation intensity and the distance to the CST. Cathodal stimulation appeared better suited for subcortical stimulation.
Subcortical MEP mapping is an excellent intraoperative method to determine the distance to the CST during resection of motor-eloquent lesions and is highly capable of further reducing the risk of a new neurological deficit.
Jens Gempt, Julia Gerhardt, Vivien Toth, Stefanie Hüttinger, Yu-Mi Ryang, Maria Wostrack, Sandro M. Krieg, Bernhard Meyer, Annette Förschler and Florian Ringel
Brain metastases occur in 10% to 40% of patients harboring cancer. In cases of neurosurgical metastasis resection, all postoperative neurological deterioration should be avoided. Reasons for postoperative deficits can be direct tissue damage due to resection, hemorrhage, venous congestive infarcts, or arterial ischemic events leading to tissue infarction. The aim of this study was to evaluate whether postoperative ischemic infarctions occur in surgery for brain metastasis and to determine their influence on new postoperative neurological deficits.
Patients who underwent resection of brain metastases and had preoperative and early postoperative (within 48 hours) MRI scans, including diffusion-weighted imaging sequences and apparent diffusion coefficient maps, between January 2009 and May 2012 were included in this study. Clinical and histopathological data (histopathological results, pre- and postoperative neurological status, and previous tumor-specific therapy) were recorded.
One hundred twenty-two patients (56 male, 66 female) who underwent resection of brain metastases were included. The patients' mean age was 60 years (range 21–89 years). The mean time span from initial tumor diagnosis to resection of brain metastasis was 44 months (range 0–338 months). The mean preoperative Karnofsky Performance Status was 80% (exact mean 76% ± 17% [SD]), and the mean postoperative value was 80% (exact mean 78% ± 17%). Twelve (9.8%) of the 122 patients had postoperative permanent worsening of a neurological deficit or a new permanent neurological deficit; 44 (36.1%) of the 122 patients had postoperative ischemic lesions. When comparing patients with and without previous brain irradiation, 53.8% of patients with previous brain irradiation had ischemic lesions on postoperative imaging compared with 31.3% of patients without previous brain irradiation (p = 0.033). There was a significant association between ischemia and postoperative neurological status deterioration (transient or permanent); 13 (29.5%) of 44 patients with ischemic lesions had deterioration of their neurological status compared with 7 (9%) of the 78 patients who did not have ischemic lesions (p = 0.003).
This study demonstrates a high prevalence of vascular incidents in patients undergoing resection for metastatic brain disease. Patients harboring postoperative ischemic lesions detected by MRI have a higher rate of neurological deficits (transient or permanent). Patients who had previous irradiation therapy are at higher risk of developing postoperative ischemic lesions. A large number of postoperative neurological deficits are caused by ischemic incidents.