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Sandro M. Krieg and Bernhard Meyer

Since spinal navigation became applicable, including robotic assistance into standard navigational setups seems reasonable. A newly released modular robotic assistance for drill stabilization (Cirq, Brainlab) was used in a 74-year-old man undergoing dynamic stabilization of L3–4 via navigated transfascial pedicle screws. The authors demonstrate the second worldwide surgery with this device and the second case performed in their department. They provide insight in its applicability to estimate its further potential in spinal robotics. Although being just the first step of this universal platform, the authors already see clinical benefit by its ease of use and drill support.

The video can be found here: https://youtu.be/oN2ZiHFRFkU.

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Malte Ottenhausen, Sandro M. Krieg, Bernhard Meyer and Florian Ringel

Greater extent of resection (EOR) of low-grade gliomas is associated with improved survival. Proximity to eloquent cortical regions often limits resectability and elevates the risk of surgery-related deficits. Therefore, functional localization of eloquent cortex or subcortical fiber tracts can enhance the EOR and functional outcome. Imaging techniques such as functional MRI and diffusion tensor imaging fiber tracking, and neurophysiological methods like navigated transcranial magnetic stimulation and magnetoencephalography, make it possible to identify eloquent areas prior to resective surgery and to tailor indication and surgical approach but also to assess the surgical risk. Intraoperative monitoring with direct cortical stimulation and subcortical stimulation enables surgeons to preserve essential functional tissue during surgery. Through tailored pre- and intraoperative mapping and monitoring the EOR can be maximized, with reduced rates of surgery-related deficits.

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Sebastian Ille, Jens Gempt, Bernhard Meyer and Sandro M. Krieg

Navigated transcranial magnetic stimulation (nTMS) allows for preoperative mapping for eloquent gliomas. Besides surgical planning, it also guides intraoperative stimulation mapping. The authors’ routine includes preoperative nTMS plus nTMS-based tractography for motor and language to consult patients, plan surgery, craniotomy, and guide cortical and subcortical stimulation.

Here, the authors present this routine in a 48-year-old woman with a glioma of the left middle and superior frontal gyrus reaching the precentral gyrus and superior longitudinal fascicle. Gross-total resection via awake surgery was achieved without deficit.

The nTMS data and nTMS-based tractography augment eloquent glioma management far beyond its current application.

The video can be found here: https://youtu.be/h4ldgMXL1ys.

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Vicki M. Butenschoen, Mirja Seifert, Bernhard Meyer and Sandro M. Krieg

OBJECTIVE

Autologous bone graft reimplantation remains the standard treatment after decompressive hemicraniectomy. Unfortunately, some patients present with signs of bone resorption without any visible signs of infection; the reasons remain unknown. Contamination with Propionibacterium acnes has been discussed as a potential source of the osteolytic process. The aim of this study was to investigate the microbial spectrum detected in samples of grafts from patients with aseptic bone resorption and compare them to septic bone graft infections in order to identify P. acnes as the specific pathogen of aseptic bone resorption.

METHODS

The authors retrospectively reviewed all patients treated for aseptic bone resorption between 2012 and 2017 in their neurosurgical department. Septic infections were used as a control group to gain information on the present bacterial spectrum. Perioperative data such as demographics, number of surgeries, and complications were assessed and compared with the microbiological analyses conducted in order to detect differences and potential sources for aseptic bone resorption and possible differences in bacterial contamination in septic and aseptic bone infection.

RESULTS

In total, 38 patients underwent surgery between 2012 and 2017 for septic bone infection—14 for aseptic bone resorption. In 100% of the septic bone infection cases in which bone flap removal was needed, bacteria could be isolated from the removed bone flap (55% Staphylococcus aureus, 13.2% Enterococcus faecalis, and 18.4% Staphylococcus epidermidis). The microbial spectrum from samples of aseptic bone flaps with resorption was examined in 10 of 14 patients and revealed contamination with P. acnes in 40% (n = 4, the other 6 bone grafts were sterile), especially in sonication analysis, whereas visible septic bone infection was mainly caused by S. aureus without detection of P. acnes.

CONCLUSIONS

Aseptic bone resorption may be caused by low-grade infections with P. acnes. However, further analysis needs to be conducted in order to understand its clinical relevance and treatment perspective.

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Ehab Shiban, Sandro M. Krieg, Thomas Obermueller, Maria Wostrack, Bernhard Meyer and Florian Ringel

OBJECT

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

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Vicki M. Butenschön, Sebastian Ille, Nico Sollmann, Bernhard Meyer and Sandro M. Krieg

OBJECTIVE

Navigated transcranial magnetic stimulation (nTMS) is used to identify the motor cortex prior to surgery. Yet, there has, until now, been no published evidence on the economic impact of nTMS. This study aims to analyze the cost-effectiveness of nTMS, evaluating the incremental costs of nTMS motor mapping per additional quality-adjusted life year (QALY). By doing so, this study also provides a model allowing for future analysis of general cost-effectiveness of new neuro-oncological treatment options.

METHODS

The authors used a microsimulation model based on their cohort population sampled for 1000 patients over the time horizon of 2 years. A health care provider perspective was used to assemble direct costs of total treatment. Transition probabilities and health utilities were based on published literature. Effects were stated in QALYs and established for health state subgroups.

RESULTS

In all scenarios, preoperative mapping was considered cost-effective with a willingness-to-pay threshold < 3*per capita GDP (gross domestic product). The incremental cost-effectiveness ratio (ICER) of nTMS versus no nTMS was 45,086 Euros/QALY. Sensitivity analyses showed robust results with a high impact of total treatment costs and utility of progression-free survival. Comparing the incremental costs caused by nTMS implementation only, the ICER decreased to 1967 Euros/QALY.

CONCLUSIONS

Motor mapping prior to surgery provides a cost-effective tool to improve the clinical outcome and overall survival of high-grade glioma patients in a resource-limited setting. Moreover, the model used in this study can be used in the future to analyze new treatment options in neuro-oncology in terms of their general cost-effectiveness.

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Sandro M. Krieg, Lukas Bobinski, Lucia Albers and Bernhard Meyer

OBJECTIVE

Lateral lumbar interbody fusion (LLIF) is frequently used for anterior column stabilization. Many authors have reported that intraoperative neuromonitoring (IONM) of the lumbar plexus nerves is mandatory for this approach. However, even with IONM, the reported motor and sensory deficits are still considerably high. Thus, the authors’ approach was to focus on the indication, trajectory, and technique instead of relying on IONM findings per se. The objective of this study therefore was to analyze the outcome of our large cohort of patients who underwent LLIF without IONM.

METHODS

The authors report on 157 patients included from 2010 to 2016 who underwent LLIF as an additional stabilizing procedure following dorsal instrumentation. LLIF-related complications as well as clinical outcomes were evaluated.

RESULTS

The mean follow-up was 15.9 ± 12.0 months. For 90.0% of patients, cage implantation by LLIF was the first retroperitoneal surgery. There were no cases of surgery-related hematoma, vascular injury, CSF leak, or any other visceral injury. Between 1 and 4 cages were implanted per surgery, most commonly at L2–3 and L3–4. The mean length of surgery was 92.7 ± 35 minutes, and blood loss was 63.8 ± 57 ml. At discharge, 3.8% of patients presented with a new onset of motor weakness, a new sensory deficit, or the deterioration of leg pain due to LLIF surgery. Three months after surgery, 3.5% of the followed patients still reported surgery-related motor weakness, 3.6% leg pain, and 9.6% a persistent sensory deficit due to LLIF surgery.

CONCLUSIONS

The results of this series demonstrate that the complication rates for LLIF without IONM are comparable, if not superior, to those in previously reported series using IONM. Hence, the authors conclude that IONM is not mandatory for LLIF procedures if the surgical approach is tailored to the respective level and if the visualization of nerves is performed.

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Nico Sollmann, Thomas Picht, Jyrki P. Mäkelä, Bernhard Meyer, Florian Ringel and Sandro M. Krieg

Up to now, navigated transcranial magnetic stimulation (nTMS) has been used for motor mapping in the vicinity of rolandic brain lesions. Recently, nTMS has also been suggested to be useful in mapping human language areas.

The authors describe the case of a left-handed patient with a left-side glioblastoma within the opercular inferior frontal gyrus who presented with severe motor aphasia. Preoperative functional MRI (fMRI) indicated speech dominance of the right hemisphere and did not show any language-related activation in the vicinity of the tumor. Navigated TMS, however, showed a significantly higher rate of induced speech arrests for the left than for the right. Left-side direct cortical stimulation induced clear speech arrests during awake surgery.

This case suggests that nTMS may be useful for preoperative speech mapping in tumors affecting the anatomy, vasculature, and brain oxygen levels and therefore impairing fMRI reliability.

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Sandro M. Krieg, Lisa Kempf, Doris Droese, Steffen K. Rosahl, Bernhard Meyer and Jens Lehmberg

Object

Recording the auditory brainstem response (ABR) is a common method for monitoring the integrity of auditory pathways during surgery in the cerebellopontine angle. Electrocochleography (ECochG) is an alternative means of intraoperative neuromonitoring. In the present study the authors compared the practicability and prognostic significance of these two methods by performing simultaneous recordings in the operating room.

Methods

Between 2006 and 2011, 125 patients (mean age 55 years) underwent surgery in the cerebellopontine angle. Seventy-one percent of the patients presented with a hearing deficit, and 37% had useful hearing but with slight functional impairment. Auditory brainstem response was recorded with a subdermal needle electrode at the mastoid. For ECochG recording, a noninvasive ball electrode was attached to the tympanic membrane. Amplitudes obtained from both ECochG and ABR audiometry were compared and correlated to pre- and postoperative hearing deficits.

Results

Simultaneous intraoperative monitoring via ABR and ECochG was possible in 114 cases (91%). Postoperatively, 42% of patients showed some degree of new hearing deficit, whereas 4% had improvement. The mean amplitudes in ECochG monitoring were significantly higher (0.18 ± 0.04 μV) than the ABR potentials (0.08 ± 0.006 μV; p < 0.05). All waves recorded at the mastoid needle electrode could be recognized in the potentials of the tympanic ball electrode. Hearing outcome correlated more reliably with the relative amplitude changes in Waves III and V in ECochG (III: p = 0.0008, V: p = 0.0015) than in ABR monitoring (III: p = 0.2075, V: p = 0.0398).

Conclusions

Intraoperative monitoring of the auditory system by recording with noninvasive tympanic ball electrodes is more practicable than with subcutaneous needle electrodes at the tragus. Since there is also a reliable correlation between ECochG and clinical outcome, the method can replace common ABR recording during surgery in the cerebellopontine angle.

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Ehab Shiban, Sandro M. Krieg, Bernhard Haller, Niels Buchmann, Thomas Obermueller, Tobias Boeckh-Behrens, Maria Wostrack, Bernhard Meyer and Florian Ringel

OBJECT

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.