J Neurosurg 133:642–654, 2020
Brain mapping techniques allow one to effectively approach tumors involving the primary motor cortex (M1). Tumor resectability and maintenance of patient integrity depend on the ability to successfully identify motor tracts during resection by choosing the most appropriate neurophysiological paradigm for motor mapping. Mapping with a highfrequency (HF) stimulation technique has emerged as the most efficient tool to identify motor tracts because of its versatility in different clinical settings. At present, few data are available on the use of HF for removal of tumors predominantly involving M1.
METHODS The authors retrospectively analyzed a series of 102 patients with brain tumors within M1, by reviewing the use of HF as a guide. The neurophysiological protocols adopted during resections were described and correlated with patients’ clinical and tumor imaging features. Feasibility of mapping, extent of resection, and motor function assessment were used to evaluate the oncological and functional outcome to be correlated with the selected neurophysiological parameters used for guiding resection. The study aimed to define the most efficient protocol to guide resection for each clinical condition.
RESULTS The data confirmed HF as an efficient tool for guiding resection of M1 tumors, affording 85.3% complete resection and only 2% permanent morbidity. HF was highly versatile, adapting the stimulation paradigm and the probe to the clinical context. Three approaches were used. The first was a “standard approach” (HF “train of 5,” using a monopolar probe) applied in 51 patients with no motor deficit and seizure control, harboring a well-defined tumor, showing contrast enhancement in most cases, and reaching the M1 surface. Complete resection was achieved in 72.5%, and 2% had permanent morbidity. The second approach was an “increased train approach,” that is, an increase in the number of pulses (7–9) and of pulse duration, using a monopolar probe. This second approach was applied in 8 patients with a long clinical history, previous treatment (surgery, radiation therapy, chemotherapy), motor deficit at admission, poor seizure control, and mostly high-grade gliomas or metastases. Complete resection was achieved in 87.5% using this approach, along with 0% permanent morbidity. The final approach was a “reduced train approach,” which was the combined use of train of 2 or train of 1 pulses associated with the standard approach, using a monopolar or bipolar probe. This approach was used in 43 patients with a long clinical history and poorly controlled seizures, harboring tumors with irregular borders without contrast enhancement (low or lower grade), possibly not reaching the cortical surface. Complete resection was attained in 88.4%, and permanent morbidity was found in 2.3%.
CONCLUSIONS Resection of M1 tumors is feasible and safe. By adapting the stimulation paradigm and probe appropriately to the clinical context, the best resection and functional results can be achieved.
Neurosurgery 70:1060–1071, 2012 DOI: 10.1227/NEU.0b013e31823f5ade
Resection of gliomas in or adjacent to the motor system is widely performed with intraoperative neuromonitoring (IOM). Despite the fact that data on the safety of IOM are available, the significance and predictive value of the procedure are still under discussion. Moreover, cases of false-negative monitoring affect the surgeon’s confidence in IOM.
OBJECTIVE: To examine cases of false-negative IOM to reveal structural explanations.
METHODS: Between 2007 and 2010, we resected 115 consecutive supratentorial gliomas in or close to eloquent motor areas using direct cortical stimulation for monitoring of motor evoked potentials (MEPs). The monitoring data were reviewed and related to new postoperative motor deficit and postoperative imaging. Clinical outcomes were assessed during follow-up.
RESULTS: Monitoring of MEPs was successful in 112 cases (97.4%). Postoperatively, 30.3% of patients had a new motor deficit, which remained permanent in 12.5%. Progression- free follow-up was 9.7 months (range, 2 weeks-40.6 months). In 65.2% of all cases, MEPs were stable throughout the operation, but 8.9% showed a new temporary motor deficit, whereas 4.5% (5 patients) presented with permanently deteriorated motor function representing false-negative monitoring at first glance. However, these cases were caused by secondary hemorrhage, ischemia, or resection of the supplementary motor area.
CONCLUSION: Continuous MEP monitoring provides reliable monitoring of the motor system, influences the course of operation in some cases, and has to be regarded as the standard for IOM of the motor system. In our series, we found no false-negative MEP results.
Acta Neurochir (2012) 154:555–563. DOI 10.1007/s00701-011-1255-3
Navigated brain stimulation (NBS) is a newly evolving technique. In addition to its supposed purpose, e.g., preoperative mapping of the central region, little is known about its further use in neurosurgery. We evaluated the usefulness of diffusion tensor imaging fiber tracking (DTI-FT) based on NBS compared to conventional characterization of the seed region.
Methods We examined 30 patients with tumors in or close to the corticospinal tract (CST) using NBS with the Nexstim eXimia system. NBS was performed for motor cortex mapping, and DTI-FT was performed by three different clinicians using BrainLAB iPlan® Cranial 3.0.1 at two time points. Number of fibers, tract volume, aberrant tracts, and proximity to the tumor were compared between the two methods.
Results We recognized a higher number of fibers (1,298± 1,279 vs. 916±986 fibers; p<0.01), tract volume (23.0±15.3 vs. 18.3±14.0 cm3; p<0.01), and aberrant tracts (0.6±0.5 vs. 0.3±0.5 aberrant tracts/tracked CST; p<0.001) when the seed region was defined conventionally, while proximity of the tracts to the tumor did not differ. While NBS-based DTI-FT is independent of the planning clinician, conventional outlining of the seed region shows generally higher variability between investigators.
Conclusions Conventional DTI-FT showed significant differences between the two modalities, most likely because of the more specific definition of the seed region when DTI-FT is based on NBS. Moreover, NBS-aided DTI fiber tracking is user-independent and, therefore, a method for further standardization of DTI fiber tracking.