Impact of target depth on safety and efficacy outcomes in MR-guided focused ultrasound thalamotomy for tremor patients.

OBJECTIVE: Target depth, defined by the z-coordinate in the dorsoventral axis relative to the anterior commissure-posterior commissure axial plane of the MR-guided focused ultrasound (MRgFUS) lesion, is considered to be critical for tremor improvement and the occurrence of side effects such as gait impairment. However, although different z-coordinates are used in the literature, there are no comparative studies available with information on optimal lesion placement. This study aimed to compare two different MRgFUS lesion targets (z = +2 mm vs z = 0 mm) regarding efficacy and safety outcomes. METHODS: The authors conducted a retrospective analysis of 52 patients with pharmacoresistant tremor disorders who received unilateral MRgFUS thalamotomy in the ventral intermediate nucleus for the first time between 2017 and 2022 by one neurosurgeon, with two different z-coordinates, either z = +2 mm (+2-mm group; n = 17) or z = 0 mm (0-mm group; n = 35), but otherwise identical parameters. Standardized video-recorded assessments of efficacy (including the Washington Heights-Inwood Genetic Study of Essential Tremor scale) and safety (using a standardized grading system) outcomes at baseline and at 6 months posttreatment were reviewed and compared. Moreover, overall patient satisfaction was extracted as documented by the examiner at 6 months. RESULTS: Based on a multiple logistic regression analysis, the authors found that a more dorsal target with a z-coordinate of +2 mm as compared with 0 mm was associated with a higher incidence of any persistent side effect at 6 months (p = 0.02). Most consistently, sensory disturbances, although mild and nondisturbing in most cases, occurred more frequently in the +2-mm group (35% vs 11%, p = 0.007), while no significant differences were found for gait impairment (29% vs 35%) and arm ataxia (24% vs 11%). On the other hand, average tremor suppression was similar (63.6% vs 60.2%) between the groups. Here, higher efficacy was associated with a higher side effect burden in the 0-mm group but not in the +2-mm group. Despite the occurrence of side effects, general patient satisfaction was high (87% would undergo MRgFUS again) as most patients valued tremor suppression more. CONCLUSIONS: A more ventral MRgFUS target of z = 0 mm seems to be associated with a more favorable safety and a comparable efficacy profile as compared with a more dorsal target of z = +2 mm, but prospective studies are warranted.

Gait pattern analysis in the home environment as a key factor for the reliable assessment of shunt responsiveness in patients with idiopathic normal pressure hydrocephalus.

Background: The identification of patients with gait disturbance associated with idiopathic normal pressure hydrocephalus (iNPH) is challenging. This is due to the multifactorial causes of gait disturbance in elderly people and the single moment examination of laboratory tests. Objective: We aimed to assess whether the use of gait sensors in a patient's home environment could help establish a reliable diagnostic tool to identify patients with iNPH by differentiating them from elderly healthy controls (EHC). Methods: Five wearable inertial measurement units were used in 11 patients with iNPH and 20 matched EHCs. Data were collected in the home environment for 72 h. Fifteen spatio-temporal gait parameters were analyzed. Patients were examined preoperatively and postoperatively. We performed an iNPH sub-group analysis to assess differences between responders vs. non-responders. We aimed to identify parameters that are able to predict a reliable response to VP-shunt placement. Results: Nine gait parameters significantly differ between EHC and patients with iNPH preoperatively. Postoperatively, patients with iNPH showed an improvement in the swing phase (p = 0.042), and compared to the EHC group, there was no significant difference regarding the cadence and traveled arm distance. Patients with a good VP-shunt response (NPH recovery rate of ≥5) significantly differ from the non-responders regarding cycle time, cycle time deviation, number of steps, gait velocity, straight length, stance phase, and stance to swing ratio. A receiver operating characteristic analysis showed good sensitivity for a preoperative stride length of ≥0.44 m and gait velocity of ≥0.39 m/s. Conclusion: There was a significant difference in 60% of the analyzed gait parameters between EHC and patients with iNPH, with a clear improvement toward the normalization of the cadence and traveled arm distance postoperatively, and a clear improvement of the swing phase. Patients with iNPH with a good response to VP-shunt significantly differ from the non-responders with an ameliorated gait pattern.

[Trigeminal Neuralgia - What Do We Know about the Causes, Diagnosis and Treatment?] / Trigeminusneuralgie ­ was wissen wir über die Ursachen, Diagnostik und Therapie?

Trigeminal Neuralgia - What Do We Know about the Causes, Diagnosis and Treatment? Abstract. Classical trigeminal neuralgia is typically characterized by a stimulus-evoked, recurrent and intense short-lasting stabbing pain in the innervation area of the trigeminal nerve. Its intensity is among the most severe pain imaginable in humans, and yet it is often misdiagnosed and undertreated. Triggers are common activities of daily life like talking or eating. The classical trigeminal neuralgia is due to a neurovascular compression at the nerve root entry zone. The secondary form is related to an underlying neurological disease (caused for example by multiple sclerosis or compression by a brain tumor); the etiology of the idiopathic trigeminal neuralgia is unknown. Treatment options include both medication (mostly antiepileptic drugs) and escalated interventional approaches (microvascular decompression, neurolesional percutaneous procedures, neuromodulative therapeutic options and radiosurgery).

Comparison Between Flow-Regulated and Gravitational Shunt Valves in the Treatment of Normal Pressure Hydrocephalus: Flow-Grav Study.

BACKGROUND: Normal pressure hydrocephalus (NPH) is frequently treated with ventriculoperitoneal shunt (VPS) surgery. However, VPS implantation can lead to overdrainage and complications such as headaches, hygroma, and subdural hematoma due to a siphon effect in an upright position. Gravitational valves prevent overdrainage through position-dependent adjustment of valve resistance. Flow-regulated valves that increase resistance in presence of high cerebrospinal fluid flow may provide similar protection against overdrainage and present an alternative to gravitational valves. OBJECTIVE: To compare gravitational and flow-regulated shunt valves in patients with symptomatic NPH. METHODS: We performed a retrospective analysis of 97 patients suffering from NPH who underwent VPS implantation with a gravitational or a flow-regulated valve. The primary endpoint was the occurrence of hygroma or subdural hematoma. Secondary endpoints were neurological outcome (Kiefer score, Stein and Langfitt score, and NPH recovery rate), frequency of valve adjustments, and reoperations. RESULTS: No significant differences in the occurrence of hygroma and subdural hematoma (11.4% for flow-regulated valves vs 5.7% for gravitational valves, P = .462) or response to treatment (77.3% vs 81.1%, P = .802) were found. Patients with flow-regulated valves required fewer valve adjustments (1.12 vs 2.02, P < .001) to reach their optimal neurological outcome and underwent fewer surgical revisions (11.4% vs 28.3%, P = .047). CONCLUSION: Our data suggest that shunt therapy in NPH patients with a flow-regulated instead of a gravitational valve is safe and effective with a comparable clinical outcome and risk of overdrainage complications. Moreover, patients with flow-regulated valves may need fewer valve adjustments and reoperations.

How to avoid pneumocephalus in deep brain stimulation surgery? Analysis of potential risk factors in a series of 100 consecutive patients.

BACKGROUND: Accuracy of lead placement is the key to success in deep brain stimulation (DBS). Precise anatomic stereotactic planning usually is based on stable perioperative anatomy. Pneumocephalus due to intraoperative CSF loss is a common procedure-related phenomenon which could lead to brain shift and targeting inaccuracy. The aim of this study was to evaluate potential risk factors of pneumocephalus in DBS surgery. METHODS: We performed a retrospective single-center analysis in patients undergoing bilateral DBS. We quantified the amount of pneumocephalus by postoperative CT scans and corrected the data for accompanying brain atrophy by an MRI-based score. Automated computerized segmentation algorithms from a dedicated software were used. As potential risk factors, we evaluated the impact of trephination size, the number of electrode tracks, length of surgery, intraoperative blood pressure, and brain atrophy. RESULTS: We included 100 consecutive patients that underwent awake DBS with intraoperative neurophysiological testing. Systolic and mean arterial blood pressure showed a substantial impact with an inverse correlation, indicating that lower blood pressure is associated with higher volume of pneumocephalus. Furthermore, the length of surgery was clearly correlated to pneumocephalus. CONCLUSION: Our analysis identifies intraoperative systolic and mean arterial blood pressure as important risk factors for pneumocephalus in awake stereotactic surgery.

Intraoperative Neurophysiologic Assessment in Deep Brain Stimulation Surgery and its Impact on Lead Placement.

OBJECTIVES: While the efficacy of deep brain stimulation (DBS) to treat various neurological disorders is undisputed, the surgical methods differ widely and the importance of intraoperative microelectrode recording (MER) or macrostimulation (MS) remains controversially debated. The objective of this study is to evaluate the impact of MER and MS on intraoperative lead placement. PATIENTS AND METHODS: We included 101 patients who underwent awake bilateral implantation of electrodes in the subthalamic nucleus with MER and MS for Parkinson's disease from 2009 to 2017 in a retrospective observational study. We analyzed intraoperative motor outcomes between anatomically planned stimulation point (PSP) and definite stimulation point (DSP), lead adjustments and Unified Parkinson's Disease Rating Scale Item III (UPDRS-III), levodopa equivalent daily dose (LEDD), and adverse events (AE) after 6 months. RESULTS: We adjusted 65/202 leads in 47/101 patients. In adjusted leads, MS results improved significantly when comparing PSP and DSP (p < 0.001), resulting in a number needed to treat of 9.6. After DBS, UPDRS-III and LEDD improved significantly after 6 months in adjusted and nonadjusted patients (p < 0.001). In 87% of leads, the active contact at 6 months still covered the optimal stimulation point during surgery. In total, 15 AE occurred. CONCLUSION: MER and MS have a relevant impact on the intraoperative decision of final lead placement and prevent from a substantial rate of poor stimulation outcome. The optimal stimulation points during surgery and chronic stimulation strongly overlap. Follow-up UPDRS-III results, LEDD reductions, and DBS-related AE correspond well to previously published data.

Introduction of a self-holding retractor for optimized abdominal visualization in ventriculoperitoneal shunt surgery: first experiences at a single center.

OBJECTIVE: Ventriculoperitoneal shunt implantation is a common procedure in general neurosurgery. The patient population is often fragile, ranging from elderly to pediatric patients, and avoidance of perioperative complication is of utmost importance. Abdominal catheter dislocation has been found to be a common cause for early shunt dysfunction and needs to be avoided by optimal visualization of the abdominal catheter insertion zone. Here, we introduce a self-holding wound retractor system Alexis® and demonstrate its use for abdominal shunt surgery in a series of patients. METHODS: We explain the use of the Alexis® self-holding wound retractor during open ventriculoperitoneal shunt surgery in a series of 16 patients operated at our institution. RESULTS: The self-holding retractor consists of two polymer rings connected by a polymer membrane. The deep ring is easily placed on the internal fascia of the straight muscle and circular retraction is achieved by twisting the upper ring. Free hand working can then be performed by a single surgeon with good abdominal exposure. No case of abdominal dislocation or infection occurred in our series, although no properly powered statistical analysis can be performed regarding the sample size. CONCLUSION: We demonstrate the Alexis® Wound Retractor, which is an easy tool for optimal visualization of the abdominal catheter insertion zone. We believe it can facilitate surgical practice of shunt surgery, especially in obese patients.

ACE-inhibitors: a preventive measure for bone flap resorption after autologous cranioplasty?

OBJECTIVEDecompressive craniectomy (DC) is an established treatment for refractory intracranial hypertension. It is usually followed by autologous cranioplasty (AC), the reinsertion of a patient's explanted bone flap. A frequent long-term complication of AC is bone flap resorption (BFR), which results in disfigurement as well as loss of the protective covering of the brain. This study investigates risk factors for BFR after AC, including medical conditions and antihypertensive drug therapies, with a focus on angiotensin-converting enzyme inhibitors (ACEIs), which have been associated with a beneficial effect on bone healing and bone preservation in orthopedic, osteoporosis, and endocrinology research.METHODSIn this single-center, retrospective study 183 consecutive cases were evaluated for bone flap resorption after AC. Information on patient demographics, medical conditions, antihypertensive therapy, and BFR-defined as an indication for revision surgery established by a neurosurgeon based on clinical or radiographic assessments-was collected. A Kaplan-Meier analysis of time from AC to diagnosis of BFR was performed, and factors associated with BFR were investigated using the log-rank test and Cox regression.RESULTSA total of 158 patients were considered eligible for inclusion in the data analysis. The median follow-up time for this group was 2.2 years (95% CI 1.9-2.5 years). BFR occurred in 47 patients (29.7%), with a median time to event of 3.7 years (95% CI 3.3-4.1 years). An ACEI prescription was recorded in 57 cases (36.1%). Univariate Kaplan-Meier analysis and the log-rank test revealed that ACEI therapy (2-year event free probability [EFP] 83.8% ± 6.1% standard error vs 63.9% ± 5.6%, p = 0.02) and ventriculoperitoneal (VP) shunt treatment (2-year EFP 86.9% ± 7.1% vs 66% ± 5.0%, p = 0.024) were associated with a lower probability of BFR. Multiple Cox regression analysis showed ACEI therapy (HR 0.29, p = 0.012), VP shunt treatment (HR 0.278, p = 0.009), and male sex (HR 0.500, p = 0.040) to be associated with a lower risk for BFR, whereas bone fragmentation (HR 1.92, p = 0.031) was associated with a higher risk for BFR.CONCLUSIONSHypertensive patients treated with ACEIs demonstrate a lower rate of BFR than patients treated with other hypertensive medications and nonhypertensive patients. Our results are in line with previous reports on the positive influence of ACEIs on bone healing and preservation. Further analysis of the association between ACEI treatment and BFR development is needed and will be evaluated in a multicenter prospective trial.

Better Hemodynamics and Less Antihypertensive Medication: Comparison of Scalp Block and Local Infiltration Anesthesia for Skull-Pin Placement in Awake Deep Brain Stimulation Surgery.

OBJECTIVE: In deep brain stimulation (DBS) surgery, acute high blood pressure (BP) is a risk factor for intracranial hemorrhage. To minimize pain and hypertensive conditions, sufficient local anesthesia is mandatory. We evaluated whether local instillation of anesthetics (LA) or a scalp block (SB) is superior concerning intraoperative hemodynamics and analgesia. METHODS: We retrospectively analyzed intraoperative cardiovascular parameters and perioperative medication in 47 patients (LA = 29, SB = 18) undergoing DBS surgery. Primary study end points were intraoperative systolic BP and heart rate. Secondary end points were use of intraoperative antihypertensives and perioperative analgesics. RESULTS: Patients who had SB showed lower mean systolic BP and heart rate compared with patients who had LA. Patients who had LA required more antihypertensive medication to stabilize BP. BP was higher, particularly during the first 90 minutes of surgery, in patients who had LA. Thereafter, more antihypertensives were necessary to achieve sufficient BP control in the LA group. The dose of analgesics did not differ significantly between both groups during and after surgery. CONCLUSIONS: Our data suggest that SB might be superior to LA for DBS surgery with respect to BP control and hemodynamics. The need for analgesics does not differ substantially between both anesthetic treatment options.

Progressive Functional Underdrainage in Cerebrospinal Fluid Shunt-Dependent Women During Pregnancy: Case Report and Review of the Literature.

BACKGROUND: Since the 1950s cerebrospinal fluid (CSF) shunt dependency has no longer been a contradiction to normal life, including sexuality and pregnancy in women, because of advances in the understanding of hydrocephalus and shunt technology. Although pregnancy in shunt-dependent women is rare, it causes uncertainty among treating physicians. CASE DESCRIPTION: We report the case of a 34-year-old pregnant woman with a ventriculoperitoneal shunt. Throughout her pregnancy she experienced progressive symptoms of CSF underdrainage without any signs of other pregnancy-related complications. After the delivery of a healthy infant, shunt resistance had to be readjusted to prepregnancy levels. A comprehensive review of the literature reports in English, listed in PubMed, is provided. CONCLUSIONS: Conservative treatment of pregnancy-related functional underdrainage by consecutive valve pressure adjustment is possible, easy, and safe.

[How Reliable is Neuronavigation?]. / Wie zuverlässig ist Neuronavigation?

Neuronavigation plays a central role in modern neurosurgery. It allows visualizing instruments and three-dimensional image data intraoperatively and supports spatial orientation. Thus it allows to reduce surgical risks and speed up complex surgical procedures. The growing availability and importance of neuronavigation makes clear how relevant it is to know about its reliability and accuracy. Different factors may influence the accuracy during the surgery unnoticed, misleading the surgeon. Besides the best possible optimization of the systems themselves, a good knowledge about its weaknesses is mandatory for every neurosurgeon.

Simple Accuracy Enhancing Techniques in Neuronavigation.

BACKGROUND: Neuronavigation is an essential tool in cranial neurosurgery. Despite continuing improvements in the technologies used for neuronavigation, certain events can lead to unacceptable mismatches. To provide the best possible outcome for the patients, surgeons need to do everything possible to reduce mismatches. METHODS AND RESULTS: Some simple techniques can greatly improve neuronavigation accuracy and patient safety. We describe two simple methods that were developed or refined in the Department of Neurosurgery at Inselspital, Bern, Switzerland: the transdermal navigation landmark and use of bone screws for co-registration. CONCLUSIONS: Both techniques are easy to use, do not require expensive additional instruments, and are helpful in procedures involving neuronavigation.

The Nelaton Catheter Guard for Safe and Effective Placement of Subdural Drain for Two-Burr-Hole Trephination in Chronic Subdural Hematoma: A Technical Note.

BACKGROUND: For chronic subdural hematoma, placement of a Blake drain with a two-burr-hole craniotomy is often preferred. However, the placement of such drains carries the risk of penetrating the brain surface or damaging superficial venous structures. OBJECTIVE: To describe the use of a Nelaton catheter for the placement of a subdural drain in two-burr-hole trephination for chronic subdural hematoma. METHOD: A Nelaton catheter was used to guide placement of a Blake drain into the subdural hematoma cavity and provide irrigation of the hematoma cavity. With the two-burr-hole method, the Nelaton catheter could be removed easily via the frontal burr hole after the Blake drain was in place. RESULTS: We used the Nelaton catheters in many surgical procedures and found it a safe and easy technique. This method allows the surgeon to safely direct the catheter into the correct position in the subdural space. CONCLUSIONS: This tool has two advantages. First, the use of a small and flexible Nelaton catheter is a safe method for irrigation of a chronic subdural hematoma cavity. Second, in comparison with insertion of subdural drainage alone through a burr hole, the placement of the Nelaton catheter in subdural space is easier and the risk of damaging relevant structures such as cortical tissue or bridging veins is lower. Thus this technique may help to avoid complications when placing a subdural drain.

What happens to the bone flap? Long-term outcome after reimplantation of cryoconserved bone flaps in a consecutive series of 92 patients.

BACKGROUND: Reimplantation of cryoconserved autologous bone flaps is a standard procedure after decompressive craniotomies. Aseptic necrosis and resorption are the most frequent complications of this procedure. At present there is no consensus regarding the definition of the relevant extent and indication for surgical revision. The objective of this retrospective analysis was to identify the incidence of bone flap resorption and the optimal duration of follow-up. METHODS: Between February 2009 and March 2012, 100 cryoconserved autologous bone flaps were reimplanted at the Department of Neurosurgery, Inselspital Bern. Three patients were not available for follow-up, and five patients died before follow-up. All patients underwent follow-up at 6 weeks and a second follow-up more than 12 months postoperatively. A clinical and CT-based score was developed for judgment of relevance and decision making for surgical revision. RESULTS: Mean follow-up period was 21.6 months postoperatively (range: 12 to 47 months); 48.9 % (45/92) of patients showed no signs of bone flap resorption, 20.7 % (19/92) showed minor resorption with no need for surgical revision, and 30.4 % (28/92) showed major resorption (in 4 % of these the bone flap was unstable or collapsed). CONCLUSIONS: Aseptic necrosis and resorption of reimplanted autologous bone flaps occurred more frequently in our series of patients than in most reports in the literature. Most cases were identified between 6 and 12 months postoperatively. Clinical observation or CT scans of patients with autologous bone flaps are recommended for at least 12 months. Patient-specific implants may be preferable to autologous bone flaps.

Improved localization of implanted subdural electrode contacts on magnetic resonance imaging with an elastic image fusion algorithm in an invasive electroencephalography recording.

BACKGROUND: Accurate projection of implanted subdural electrode contacts in presurgical evaluation of pharmacoresistant epilepsy cases by invasive electroencephalography is highly relevant. Linear fusion of computed tomography and magnetic resonance images may display the contacts in the wrong position as a result of brain shift effects. OBJECTIVE: A retrospective study in 5 patients with pharmacoresistant epilepsy was performed to evaluate whether an elastic image fusion algorithm can provide a more accurate projection of the electrode contacts on the preimplantation magnetic resonance images compared with linear fusion. METHODS: An automated elastic image fusion algorithm (AEF), a guided elastic image fusion algorithm (GEF), and a standard linear fusion algorithm were used on preoperative magnetic resonance images and postimplantation computed tomography scans. Vertical correction of virtual contact positions, total virtual contact shift, corrections of midline shift, and brain shifts caused by pneumocephalus were measured. RESULTS: Both AEF and GEF worked well with all 5 cases. An average midline shift of 1.7 mm (SD, 1.25 mm) was corrected to 0.4 mm (SD, 0.8 mm) after AEF and to 0.0 mm (SD, 0 mm) after GEF. Median virtual distances between contacts and cortical surface were corrected by a significant amount, from 2.3 mm after linear fusion algorithm to 0.0 mm after AEF and GEF (P < .001). Mean total relative corrections of 3.1 mm (SD, 1.85 mm) after AEF and 3.0 mm (SD, 1.77 mm) after GEF were achieved. The tested version of GEF did not achieve a satisfying virtual correction of pneumocephalus. CONCLUSION: The technique provided a clear improvement in fusion of preimplantation and postimplantation scans, although the accuracy is difficult to evaluate.

Infection rate of emergency bolt-kit vs. non-emergency conventional implanted silver bearing external ventricular drainage catheters.

BACKGROUND: Bolt-kit systems are increasingly used as an alternative to conventional external cerebrospinal fluid (CSF) drainage systems. Since 2009 we regularly utilize bolt-kit external ventricular drainage (EVD) systems with silver-bearing catheters inserted manually with a hand drill and skull screws for emergency ventriculostomy. For non-emergency situations, we use conventional ventriculostomy with subcutaneous tunneled silver-bearing catheters, performed in the operating room with a pneumatic drill. This retrospective analysis compared the two techniques in terms of infection rates. METHODS: 152 patients (aged 17-85 years, mean=55.4 years) were included in the final analysis; 95 received bolt-kit silver-bearing catheters and 57 received conventionally implanted silver-bearing catheters. The primary endpoint combined infection parameters: occurrence of positive CSF culture, colonization of catheter tips, or elevated CSF white blood cell counts (>4/µl). Secondary outcome parameters were presence of microorganisms in CSF or on catheter tips. Incidence of increased CSF cell counts and number of patients with catheter malposition were also compared. RESULTS: The primary outcome, defined as analysis of combined infection parameters (occurrence of either positive CSF culture, colonization of the catheter tips or raised CSF white blood cell counts >4/µl)was not significantly different between the groups (58.9% bolt-kit group vs. 63.2% conventionally implanted group, p=0.61, chi-square-test). The bolt-kit group was non-inferior and not superior to the conventional group (relative risk reduction of 6.7%; 90% confidence interval: -19.9% to 25.6%). Secondary outcomes showed no statistically significant difference in the incidence of microorganisms in CSF (2.1% bolt-kit vs. 5.3% conventionally implanted; p=0.30; chi-square-test). CONCLUSIONS: This analysis indicates that silver-bearing EVD catheters implanted with a bolt-kit system outside the operating room do not significantly elevate the risk of CSF infection as compared to conventional implant methods.

Low-threshold monopolar motor mapping for resection of lesions in motor eloquent areas in children and adolescents.

OBJECT: Resection of lesions close to the primary motor cortex (M1) and the corticospinal tract (CST) is generally regarded as high-risk surgery due to reported rates of postoperative severe deficits of up to 50%. The authors' objective was to determine the feasibility and safety of low-threshold motor mapping and its efficacy for increasing the extent of lesion resection in the proximity of M1 and the CST in children and adolescents. METHODS: The authors analyzed 8 consecutive pediatric patients in whom they performed 9 resections for lesions within or close (≤ 10 mm) to M1 and/or the CST. Monopolar high-frequency motor mapping with train-of-five stimuli (pulse duration 500 µsec, interstimulus interval 4.0 msec, frequency 250 Hz) was used. The motor threshold was defined as the minimal stimulation intensity that elicited motor evoked potentials (MEPs) from target muscles (amplitude > 30 µV). Resection was performed toward M1 and the CST at sites negative to 1- to 3-mA high-frequency train-of-five stimulation. RESULTS: The M1 was identified through high-frequency train-of-five via application of varying low intensities. The lowest motor thresholds after final resection ranged from 1 to 9 mA in 8 cases and up to 18 mA in 1 case, indicating proximity to motor neurons. Intraoperative electroencephalography documented an absence of seizures during all surgeries. Two transient neurological deficits were observed, but there were no permanent deficits. Postoperative imaging revealed complete resection in 8 patients and a very small remnant (< 0.175 cm3) in 1 patient. CONCLUSIONS: High-frequency train-of-five with a minimal threshold of 1-3 mA is a feasible and safe procedure for resections in the proximity of the CST. Thus, low-threshold motor mapping might help to expand the area for safe resection in pediatric patients with lesions located within the precentral gyrus and close to the CST, and may be regarded as a functional navigational tool. The additional use of continuous MEP monitoring serves as a safety feedback for the functional integrity of the CST, especially because the true excitability threshold in children is unknown.