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Abstract: Sensors for an electromagnetical neuronavigation system have been miniaturized for direct implantation into vertebral bodies in order to track the vertebral body motion during cervical instrumentation. For this purpose different surgical techniques were performed on cervical spine models, and the movement of the vertebral bodies was registered and visualized. Realtime visualization of vertebral body movements during surgical maneuvers was archived by the implanted microsensors. [Copyright &y& Elsevier]

Diffuse gliomas in adults encompass a heterogenous group of central nervous system neoplasms. In recent years, extensive (epi-)genomic profiling has identified several glioma subgroups characterized by distinct molecular characteristics, most importantly IDH1/2 and histone H3 mutations. A group of 16 diffuse gliomas classified as "adult-type diffuse high-grade glioma, IDH-wildtype, subtype F (HGG-F)" was identified by the DKFZ v12.5 Brain Tumor Classifier . Histopathologic characterization, exome sequencing, and review of clinical data was performed in all cases. Based on unsupervised t -distributed stochastic neighbor embedding and clustering analysis of genome-wide DNA methylation data, HGG-F shows distinct epigenetic profiles separate from established central nervous system tumors. Exome sequencing demonstrated frequent TERT promoter (12/15 cases), PIK3R1 (11/16), and TP53 mutations (5/16). Radiologic characteristics were reminiscent of gliomatosis cerebri in 9/14 cases (64%). Histopathologically, most cases were classified as diffuse gliomas (7/16, 44%) or were suspicious for the infiltration zone of a diffuse glioma (5/16, 31%). None of the cases demonstrated microvascular proliferation or necrosis. Outcome of 14 patients with follow-up data was better compared to IDH-wildtype glioblastomas with a median progression-free survival of 58 months and overall survival of 74 months (both P <0.0001). Our series represents a novel type of adult-type diffuse glioma with distinct molecular and clinical features. Importantly, we provide evidence that TERT promoter mutations in diffuse gliomas without further morphologic or molecular signs of high-grade glioma should be interpreted in the context of the clinicoradiologic presentation as well as epigenetic profile and may not be suitable as a standalone marker for glioblastoma, IDH-wildtype., Competing Interests: Conflicts of Interest and Source of Funding: Supported by a Deutsches Konsortium für Translationale Krebsforschung (DKTK) Young Investigator grant to L.S. The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Competing Interests: Disclosure The authors report no conflicts of interest in this work.

Background: Anterior cervical diskectomy and fusion (ACDF) is a well-established surgical treatment for radiculopathy and myelopathy. Previous studies showed that empty PEEK cages have lower radiographic fusion rates, but the clinical relevance remains unclear. This paper's aim is to provide high-quality evidence on the outcomes of ACDF with empty PEEK cages and on the relevance of radiographic fusion for clinical outcomes., Methods: This large prospective multicenter clinical trial performed single-level ACDF with empty PEEK cages on patients with cervical radiculopathy or myelopathy. The main clinical outcomes were VAS (0-10) for pain and NDI (0-100) for functioning. Radiographic fusion was evaluated by two investigators for three different aspects., Results: The median (range) improvement of the VAS pain score was: 3 (1-6) at 6 months, 3 (2-8) at 12 months, and 4 (2-8) at 18 months. The median (range) improvement of the NDI score was: 12 (2-34) at 6 months, 18 (4-46) at 12 months, and 22 (2-44) at 18 months. Complete radiographic fusion was reached by 126 patients (43%) at 6 months, 214 patients (73%) at 12 months, and 241 patients (83%) at 18 months. Radiographic fusion was a highly significant ( p  < 0.001) predictor of the improvement of VAS and NDI scores., Conclusion: This study provides strong evidence that ACDF is effective treatment, but the overall rate of radiographic fusion with empty PEEK cages is slow and insufficient. Lack of complete radiographic fusion leads to less improvement of pain and disability. We recommend against using empty uncoated pure PEEK cages in ACDF., Trial Registration: ISRCTN42774128. Retrospectively registered 14 April 2009.

Background. Posterior lumbar interbody fusion (PLIF) is a common surgical treatment for degenerative spinal instability, but many surgeons consider obesity a contraindication for elective spinal fusion. The aim of this study was to analyze whether obesity has any influence on hospitalization parameters, change in clinical status, or complications. Methods. In this prospective study, regression analysis was used to analyze the influence of the body mass index (BMI) on operating time, postoperative care, hospitalization time, type of postdischarge care, change in paresis or sensory deficits, pain level, wound complications, cerebrospinal fluid leakage, and implant complications. Results. Operating time increased only 2.5 minutes for each increase of BMI by 1. The probability of having a wound complication increased statistically with rising BMI. Nonetheless, BMI accounted for very little of the variation in the data, meaning that other factors or random chances play a much larger role. Conclusions. Obesity has to be considered a risk factor for wound complications in patients undergoing elective PLIF for degenerative instability. However, BMI showed no significant influence on other kinds of peri- or postoperative complications, nor clinical outcomes. So obesity cannot be considered a contraindication for elective PLIF.

Background: Lipomas in the lower spinal canal can lead to progressive neurological deficits, so they may have to be surgically removed. Intraoperative neurophysiological monitoring serves to minimize the morbidity of the surgical procedure. However, so far there are no evidence-based recommendations which type of monitoring procedure or combination of procedures to choose., Methods: The aim of this study was to evaluate the feasibility and value of various intraoperative monitoring techniques: motor and sensory evoked potentials (MEP, SEP), free-running and triggered electromyography (EMG). Thirty cases of spinal lipomas of the Conus medullaris (dorsal Type A: 20.0%; caudal Type B: 33.3%; transitional Type C: 46.7%) were retrospectively evaluated over a 12-year period., Results: The patients were mostly pediatric and suffered from persistent pain (73.3%), pareses (56.7%), sensory deficits (43.4%), and/or urogenital dysfunctions (60.0%). SEPs were successfully evoked in 66.7% of cases, MEPs in 86.7% of cases, and EMGs in 100%. MEP alterations correlated with direct mechanical maneuvers in the operating site. SEP changes correlated mostly with physiological events, such as rinsing/cooling of the operating site. Spike-, burst- or tonic train-activity was found in the free-running EMG that occurred only with certain manipulation patterns. Irreversible MEP changes and signal loss in the triggered EMG correlated with post-operative deficits., Conclusions: The results of this study showed, that intraoperative monitoring could be considered a helpful tool during lipoma tumor surgery near the Conus medullaris. Most reliable results were obtained from transcranial MEPs, free-running EMGs, and triggered EMGs. That's why the authors favor a routine set-up consisting of at least these three techniques, as this enables mapping at the beginning of the operation, continuous functional testing during surgery, and prognosis of the post-operative symptomology.

Object: Intraoperative neurophysiological monitoring (IONM) represents an established tool in neurosurgery to increase patient safety. Its application, however, is controversial. Its use has been described as helpful in avoiding neurological deterioration during intracranial aneurysm surgery. Its impact on extracranial-intracranial (EC-IC) bypass surgery involving parent artery occlusion for the treatment of complex aneurysms has not yet been studied. The authors therefore sought to evaluate the effects of IONM on patient safety, the surgeon's intraoperative strategies, and functional outcome of patients after cerebral bypass surgery. Intraoperative neurophysiological monitoring results were compared with those of intraoperative blood flow monitoring to assess bypass graft perfusion., Methods: Compound motor action potentials (CMAPs) were generated using transcranial electrical stimulation in patients undergoing EC-IC bypass surgery. Preoperative and postoperative motor function was analyzed. To assess graft function, intraoperative flowmetry and indocyanine green fluorescence angiography were performed. Special care was taken to compare the relevance of electrophysiological and blood flow monitoring in the detection of critical intraoperative ischemic episodes., Results: The study included 31 patients with 31 aneurysms and 1 bilateral occlusion of the internal carotid arteries, undergoing 32 EC-IC bypass surgeries in which radial artery or saphenous vein grafts were used. In 11 cases, 15 CMAP events were observed, helping the surgeon to determine the source of deterioration and to react to it: 14 were reversible and only 1 showed no recovery. In all cases, blood flow monitoring showed good perfusion of the bypass grafts. There were no false-negative results in this series. New postoperative motor deficits were transient in 1 case, permanent in 1 case, and not present in all other cases., Conclusions: Intraoperative neurophysiological monitoring is a helpful tool for continuous functional monitoring of patients undergoing large-caliber vessel EC-IC bypass surgery. The authors' results suggest that continuous neurophysiological monitoring during EC-IC bypass surgery has relevant advantages over flow-oriented monitoring techniques such as intraoperative flowmetry or indocyanine green-based angiography.

Objective: Transcranial magnetic stimulation (TMS) is a noninvasive method for analyzing cortical function. To utilize TMS for presurgical functional diagnostics, the magnetic impulse must be precisely targeted by stereotactically positioning the coil. The aim of this study was to evaluate the usefulness of TMS for operation planning when combined with a sensor-based electromagnetic navigation system (nTMS)., Methods: Preoperative functional mapping with nTMS was performed in 10 patients with rolandic tumors. Intraoperative mapping was performed with the "gold standard" of direct cortical stimulation. Stimulation was performed in the same predefined 5-mm raster for both modalities, and the results were compared., Results: In regard to the 5-mm mapping raster, the centers of gravity of nTMS and direct cortical stimulation were located at the same spot in 4 cases and at neighboring spots in the remaining 6 cases. The mean distance between the tumor and the nearest motor response ("safety margin") was 7.9 mm (range, 5-15 mm; standard deviation, 3.2 mm) for nTMS and 6.6 mm (range, 0-12 mm; standard deviation, 3.4 mm) for direct cortical stimulation., Conclusion: nTMS allowed for reliable, precise application of the magnetic impulse, and the peritumoral somatotopy corresponded well between the 2 modalities in all 10 cases. nTMS is a promising method for preoperative functional mapping in motor cortex tumor surgery.

Object: Neurophysiological intraoperative monitoring (IOM) is regarded as a useful tool to provide information about physiological changes during surgery in eloquent areas of the nervous system, to increase safety and reduce morbidity. Nevertheless, numerous older studies report that very few patients benefit from IOM, and that there are high rates of false-positive and false-negative changes of neurophysiological parameters during surgery. There is an ongoing discussion about the effectiveness of neurophysiological IOM. This questionnaire study was performed to evaluate the attitude of neurosurgeons toward neurophysiological IOM and the availability of this tool., Methods: One hundred fifty neurosurgeons from 60 institutions in 16 countries were asked to answer anonymously a questionnaire with 11 questions. The questionnaire covered aspects of personal experience, the neurosurgical institution, and availability of neurophysiological IOM as well as asking the surgeon's opinion of the procedure., Results: One hundred nine questionnaires were returned (73%). Seven questionnaires were excluded because of failure to complete the form correctly or completely, leaving 102 respondents from 44 institutions in 16 countries in the study; 79.5% of the included institutions provided neurophysiological IOM. Young neurosurgeons did not put more trust in IOM than experienced neurosurgeons. With growing IOM experience, surgeons seem to allow less influence of the findings on the course of their operation. At large institutions in which > 1500 operations per year are done, IOM is performed by the neurosurgeons themselves in most cases. In institutions with fewer operations, the IOM team consists mostly of nonneurosurgeons. Regardless of the availability of neurophysiological IOM, all surgeons stated that IOM is gaining increasing importance., Conclusions: Neurophysiological IOM represents an established tool in neurosurgery. Although the importance of IOM is emphasized by the majority of neurosurgeons, the relevance of this tool to the course of the operation changes with increasing neurophysiological IOM experience.

Intraoperative electrical stimulation of the motor cortex is a sensitive method for intraoperative mapping and monitoring of this region. Two different stimulation techniques have been established, the bipolar and monopolar techniques. Controversy exists regarding the most suitable method. Both methods have advantages and disadvantages and different electrophysiological backgrounds. The present study is a review of the electrophysiological basis of direct cortical electrical stimulation of the motor cortex. Both methods are discussed and their field of application is presented.

Object: The treatment of insular tumors is controversial. Surgical treatment is associated with a higher morbidity rate than other therapies. The present work presents a new method in which the descending motor pathways are monitored during surgery for insular tumors., Methods: Intraoperative monitoring was performed in a combination of 2 techniques. The motor cortex was stimulated with a transcranial electrical stimulus. In addition, direct subcortical stimulation was performed with an electrical anodal monopolar stimulus. Compound motor action potentials (CMAPs) were recorded from target muscles., Results: Fifteen patients were included in this preliminary study. Following transcranial stimulation, CMAPs were recorded in all cases. Subcortical stimulation was successful in 12 cases. Significant CMAP alterations were recorded in 5 patients. There were no false-negative results in the series., Conclusions: The technique presented here is a safe method. It allows a quantitative monitoring of motor function and functional mapping of the pyramidal tract during insular surgery.

The angular gyrus (AG) is a circumscribed area between the parietal and temporal lobes and its exact function is not clear. The purpose of the present study was to investigate the feasibility of intraoperative electrical stimulation of the AG in humans. The AG was electrically stimulated in five cases with the assistance of neuronavigation. Two different stimulation techniques were applied: bipolar cortical stimulation and monopolar cortical stimulation. After monopolar cortical stimulation, a compound muscle action potential was recorded from the contralateral arm muscles in three patients. In the remaining two patients no compound muscle action potential was elicited after monopolar cortical stimulation. The latency of the recorded compound muscle action potential from the thenar muscle ranged from 30.3 to 32.7 milliseconds and from the two forearm flexors was 28.7 and 29.7. Bipolar stimulation generated a motor response in the contralateral extremity in three research subjects but no motor response in two. Response was obtained in all three research subjects with the combination of 40 Hz and a duration of 4 or 6 seconds. Because this is to their knowledge the first report demonstrating a functional output of Exner's area to the motor cortex, it would be difficult to suggest all the pathways and functions of this complex connectivity. The aim of the pilot study presented here was to investigate the feasibility of electrical stimulation of the AG. The findings presented here show that intraoperative electrical stimulation of the AG is possible. Although the results are limited by the small number of patients investigated, they are encouraging and suggest that it is worthwhile to continue research in this area.

Objective: Navigation systems enable neurosurgeons to guide operations with imaging data. Sensor-based neuronavigation uses an electromagnetic field and sensors to measure the positions of the patient's brain anatomy and the surgical instruments. The aim of this investigation was to determine the accuracy level of sensor-based tracking in a large patient collection., Methods: This study covers 250 patients operated upon during a continuous 5.5-year period. The patients had a wide range of indications and surgical procedures. The operations were performed with a direct current (DC) pulsed sensor-based electromagnetic navigation system. Four kinds of errors were measured: the fiducial registration error (FRE), the target registration error (TRE), brain shift, and the position error (PE). These errors were calculated for five subgroups of indications: target determination and trajectory guidance, functional navigation, skull base and neurocranium, determination of resection volume, and transnasal and transsphenoidal access., Results: The overall mean FRE was 1.66mm (+/-0.61mm). The overall mean TREs were 1.33mm (+/-0.51mm) centroid and 1.59mm (+/-0.57mm) lesional. The overall mean brain shift for applicable cases was 1.61mm (+/-1.14mm). The overall mean PE was 0.92mm (+/-0.54mm)., Conclusions: By and large, modern sensor-based neuronavigation operates within an acceptable and commonplace degree of error. However, the neurosurgeon must remain critical in cases of small lesions, and must exert caution not to introduce further interference from metal objects or electromagnetic devices.

Objective: Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system., Methods: Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision(®), Stryker). The accuracy of placement was assessed postoperatively by CT scan, and the patients were followed-up clinically for a mean of 16 months., Results: The total medio-caudal pedicle wall perforation rate was 9.2% (30/326). In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more) was 3.37% (11/326). Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period., Conclusion: We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.

Navigation systems are useful instruments in cranial neurosurgery. For specification of position, so-called sensor-based navigation techniques use: (a) a signal emitter that generates a defined electromagnetic field in the area of the operation site; and (b) small sensors that detect the position of various operating instruments in the electromagnetic field. For a long time, owing to a lack of clinical data and long-term studies, electromagnetic systems have been regarded as error-prone and imprecise. With the development of a pulsed direct current (DC) technique, precision levels can now be reached that are comparable with those of established optical and mechanical measuring procedures. However, it must be noted that the influence on the measuring accuracy within the operating field increases with increasing susceptibility of the various metals used in the operating theatre (titanium

Objective: Intraoperative speech mapping has evolved into the "gold standard" for neurosurgical removal of lesions near the language cortex. The integration of neuronavigation into a multimodal protocol can improve the reliability of this type of operation, but most systems require rigid fixation of the patient's head throughout the operation. This article describes and evaluates a new noninvasively attached sensor-based reference tool, which can replace rigid pin fixation of the patient's head during awake craniotomies., Methods: The attachment technique and the resulting application accuracy were investigated under clinical conditions in 13 patients undergoing awake craniotomy with intraoperative mapping of cortical language sites., Results: Spatial information was used for updating the image guidance by continuously adjusting the image planes relative to the position of the patient's head. The mean registration error achieved with this technique was 1.53 +/- 0.51 mm (fiducial registration error +/- standard deviation). The system's median application accuracy between dura opening and closure ranged from 0.83 to 1.85 mm (position error)., Conclusion: The use of a reference sensor can replace uncomfortable pin fixation of the patient's head during navigation-supported awake craniotomies. Application accuracy is not affected by repositioning of the patient or by unavoidable head movements. Thus, this technique enables full exploitation of the benefits of navigation in a multimodal operative protocol without the need to rigidly fix the patient's head.

Background: Brain tumor surgery is limited by the risk of postoperative neurological deficits. Intraoperative neurophysiological examination techniques, which are based on the electrical excitability of the human brain cortex, are thus still indispensable for surgery in eloquent areas such as the primary motor cortex (Brodman Area 4)., Methods: This study analyzed the data obtained from a total of 255 cerebral interventions for lesions with direct contact to (121) or immediately adjacent to (134) Brodman Area 4 in order to optimize stimulation parameters and to search for direct correlation between intraoperative potential changes and specific surgical maneuvers when using monopolar cortex stimulation (MCS) for electrocortical mapping and continuous intraoperative neurophysiological monitoring., Results: Compound muscle action potentials (CMAPs) were recorded from the thenar muscles and forearm flexors in accordance with the large representational area of the hand and forearm in Brodman Area 4. By optimizing the stimulation parameters in two steps (step 1: stimulation frequency and step 2: train sequence) MCS was successful in 91% (232/255) of the cases. Statistical analysis of the parameters latency, potential width and amplitude showed spontaneous latency prolongations and abrupt amplitude reductions as a reliable warning signal for direct involvement of the motor cortex or motor pathways., Conclusion: MCS must be considered a stimulation technique that enables reliable qualitative analysis of the recorded potentials, which may thus be regarded as directly predictive. Nevertheless, like other intraoperative neurophysiological examination techniques, MCS has technical, anatomical and neurophysiological limitations. A variety of surgical and non-surgical influences can be reason for false positive or false negative measurements.

Objective: In the spine, navigation techniques serve mainly to control and accurately target insertion of implants. The main source of error is that the spine is not a rigid organ, but rather a chain of semiflexible movement segments. Any intraoperative manipulation of the patient alters the geometry and volumetry as compared to the 3D volume model created from the image data. Thus, the objective of the study was to implement the theoretical principle of microsensor referencing in a model experiment and to clarify which anatomical structures are suitable for intermittent implantation of positional sensors, as illustrated with cervical vertebral bodies., Materials and Methods: Laboratory tests were conducted using 70 models of human cervical vertebral bodies. The first experiment investigated whether arbitrary movements of vertebral bodies can be tracked with the positional information from the implanted microsensors. The accuracy of this movement monitoring was determined quantitatively on the basis of positional error measurement. In the second experiment, different ventral and dorsal surgical operations were simulated on five models of the cervical spine. Quantifiable measurement values such as the spatial extension of the intervertebral space and the relative positions of the planes of the upper plates were determined., Results: With respect to the differing anatomy of the individual vertebral bodies of the cervical spine, the sensors could be placed securely with a 5x2 mm drill. The registration error (RE) was determined as a root mean square error. The mean value was 0.9425 mm (range: 0.57-1.2 mm; median: 0.9400 mm; SD: 0.1903 mm). The precision of the movement monitoring of the vertebral body was investigated along its three main axes. The error tolerance between post-interventional 3D reconstruction and direct measurement on the model did not exceed 1.3 mm in the distance measurements or 2.5 degrees in the angular measurements. The tomograms on the system monitor could be updated in close to real time on the basis of the positional information from the reference sensor., Conclusions: Motion sensors implanted into the vertebral bodies communicated any change in position to the navigation system in close to real time, thus enabling the preoperative image data set to be updated. The experiments described could ultimately show that continuous real-time visualization of individual vertebral body movements along the movement axes (flexion-extension, tilting and rotation) is possible with high accuracy using implantable microsensors. A future application of such microsensors might be the integration of robot systems into spinal microsurgery.

Background: Tracking of post-registration head motion is one of the major problems in frameless stereotaxy. Various attempts in detecting and compensating for this phenomenon rely on a fixed reference device rigidly attached to the patient's head. However, most of such reference tools are either based on an invasive fixation technique or have physical limitations which allow mobility of the head only in a restricted range of motion after completion of the registration procedure., Methods: A new sensor-based reference tool, the so-called Dynamic Reference Frame (DRF) which is designed to allow an unrestricted, 360 degrees range of motion for the intraoperative use in pulsed DC magnetic navigation was tested in 40 patients. Different methods of non-invasive attachment dependent on the clinical need and type of procedure, as well as the resulting accuracies in the clinical application have been analyzed., Results: Apart from conventional, completely rigid immobilization of the head (type A), four additional modes of head fixation and attachment of the DRF were distinguished on clinical grounds: type B1 = pin fixation plus oral DRF attachment; type B2 = pin fixation plus retroauricular DRF attachment; type C1 = free head positioning with oral DRF; and type C2 = free head positioning with retroauricular DRF. Mean fiducial registration errors (FRE) were as follows: type A interventions = 1.51 mm, B1 = 1.56 mm, B2 = 1.54 mm, C1 = 1.73 mm, and C2 = 1.75 mm. The mean position errors determined at the end of the intervention as a measure of application accuracy were: 1.45 mm in type A interventions, 1.26 mm in type B1, 1.44 mm in type B2, 1.86 mm in type C1, and 1.68 mm in type C2., Conclusion: Rigid head immobilization guarantees most reliable accuracy in various types of frameless stereotaxy. The use of an additional DRF, however, increases the application scope of frameless stereotaxy to include e.g. procedures in which rigid pin fixation of the cranium is not required or desired. Thus, continuous tracking of head motion allows highly flexible variation of the surgical strategy including intraoperative repositioning of the patient without impairment of navigational accuracy as it ensures automatic correction of spatial distortion. With a dental cast for oral attachment and the alternative option of non-invasive retroauricular attachment, flexibility in the clinical use of the DRF is ensured.

Purpose: Although computer- and image-guided surgical procedures are an improvement of frame-guided stereotaxy, many navigation systems still require rigid fixation of the patient's head throughout the operation. This study describes the clinical application of a technical modification that enables cranial navigation with "free head mobility" using CT and MR images as well as the calculated 3-D reconstruction models., Material and Methods: A sensor-based electromagnetic neuronavigation system was expanded to allow the localization and position monitoring of several sensors within an electromagnetic field. One of these sensors was attached to a dental splint as an additional reference (DRF = dynamic reference frame). Thus, it was possible to determine the position of the sensor-guiding surgical instruments and to record the slightest movement of the cranium as well. This information was then used to continuously adapt the position of the imaging plane and the resultant calculated 3-D reconstructions to the actual position of the cranium., Results: The clinical application of the DRF was tested for different neurosurgical procedures. They included image-guided biopsies and endoscopic interventions using MRI data, transnasal accesses to the base of the skull using CT data and surgical removal of multilocular metastases using data from both imaging modalities. Intracranial target reference points as well as those on the skull were found with a high accuracy to the initial measurement position after arbitrary movement of the patient's head. Thus, navigation was also possible without rigid fixation of the head because of the continuous adaptation of the imaging data on the change in position of the patient's head., Conclusion: Based on these first test results, a high clinical potential for DRF application in cranial navigation is to be expected. The aim of DRF is to dispense with the rigid fixation of the patient's head. This increases the application scope of image-guided navigation procedures to include, for example, any bioptic or endoscopic intervention, in which rigid pin fixation of the cranium is not required or desired. For all other procedures, continuous position monitoring by DRF ensures automatic correction of imaging data with mechanical alteration of the head position.

Intraoperative monitoring of motor function by means of motor evoked potentials (MEPs) is a new method. The current study examines the influence of preoperative paresis on the feasibility and reliability of this method. Intraoperative monitoring of MEPs was performed in 58 patients during surgery in the central region. The patients were divided into three groups according to their preoperative strength (group I, muscle strength less than or equal to grade 4 according to the British Medical Research Council grading system [n = 17]; group II, normal strength (n = 36); and group III, muscle strength less than grade 5 but not worse than grade 4 [n = 5]). The motor cortex was stimulated directly with a high-frequency monopolar anodal train. In groups II and III, MEPs were elicited in all patients on cortical stimulation, whereas in group I a response was obtained in only 88% of patients. The MEP parameters in all groups had a broad interindividual range of variation. A correlation between individual intraoperative potential changes and surgical maneuvers was observed in seven patients in group II and in four patients in group I. No MEP changes were recorded in group III. Irreversible MEP changes (groups I and II) resulted in postoperative clinical deterioration. No postoperative deterioration of motor function was observed in patients with reversible MEP changes. Preoperative paresis reduces the feasibility of the method; however, it has no influence on the intraoperative pattern and reaction of the MEPs.

Background: Intraoperative neurophysiological monitoring has become the standard procedure for locating eloquent regions of the brain. Such continuous electrical stimulation of motor pathways is usually applied by means of flat silicon-embedded electrodes placed directly on the motor cortex. However, shifting of the silicon strip on the cortical surface as well as electrode displacement due to brain shift underneath the electrode can lead to inaccurate recordings not directly caused by intraoperative impairment of the motor cortex or the motor pathways., Method: This prospective study was conducted to quantify cortical brain shift during open cranial surgery and to assess its impact on electrode positioning in 31 procedures near the precentral gyrus. Three groups of different lesion volumes were distinguished. Movement of the cortex between opening of the dura and completion of tumor removal as well as cortical electrode shifting were digitally measured and analyzed., Findings: Cortical surface structures evidenced a significantly larger shift (up to 23.4 mm) in comparison to the electrode strips (up to 4.2 mm) in lesions with a volume of over 20 ml. Cortex shifting highly correlated with lesion volume, whereas strip electrode movement was almost unidirectional and did not differ significantly among the three groups. However, the way they were placed (completely on the cortex vs. partly underlying or overlapping the craniotomy borders) affected the magnitude of their intraoperative displacement. As a consequence, 3 of the 31 cases (9.3%) showed a significant change in the recorded motor responses due to intraoperative dislocation of the stimulating electrode., Interpretation: Changes in the location of cerebral structures due to intraoperative brain shift may exert a marked influence on intraoperative neurophysiological monitoring if cortical strip electrodes are used. Therefore, long-term monitoring of the central region requires continuous checking of the position of stimulating electrodes and, if necessary, correction of their location.

Introduction: A number of studies demonstrate that a significant reduction of postoperative neurological deficits can be achieved by applying intraoperative neurophysiological monitoring (IOM) methods. A cost analysis of IOM is imperative considering the strained financial situation in the public health services., Material and Methods: The calculation model presented here comprises two cost components: material and personnel. The material costs comprise consumer goods and depreciation of capital goods. The computation base was 200 IOM cases per year. Consumer goods were calculated for each IOM procedure respectively. The following constellation served as a basis for calculating personnel costs: (a) a medical technician (salary level BAT Vc) for one hour per case; (b) a resident (BAT IIa) for the entire duration of the measurement, and (c) a senior resident (BAT Ia) only for supervision., Results: An IOM device consisting of an 8-channel preamplifier, an electrical and acoustic stimulator and special software costs 66,467 euros on the average. With an annual depreciation of 20%, the costs are 13,293 euros per year. This amounts to 66.46 euros per case for the capital goods. For reusable materials a sum of 0.75 euro; per case was calculated. Disposable materials were calculate for each procedure respectively. Total costs of 228.02 euro; per case were,s a sum of 0.75 euros per case was calculated. Disposable materials were calculate for each procedure respectively. Total costs of 228.02 euros per case were, calculated for surgery on the peripheral nervous system. They amount to 196.40 euros per case for spinal interventions and to 347.63 euros per case for more complex spinal operations. Operations in the cerebellopontine angle and brain stem cost 376.63 euros and 397.33 euros per case respectively. IOM costs amount to 328.03 euros per case for surgical management of an intracranial aneurysm and to 537.15 euros per case for functional interventions. Expenses run up to 833.63 euros per case for operations near the motor cortex and to 117.65 euros per case for intraoperative speech monitoring., Discussion: Costs for inpatient medical rehabilitation have increased considerably in recent years. In view of the financial situation, it is necessary to reduce postoperative morbidity and the costs it involves. IOM leads to a reduction of morbidity. The costs for IOM calculated here justify its routine application in view of the legal and socioeconomic consequences of surgery-related neurological deficits.

Object: The repetitive application of high-frequency anodal monopolar stimulation during surgery in or near the motor cortex allows a qualitative and quantitative evaluation of motor evoked potentials (MEPs). Using this method, motor pathways and motor function can be continuously monitored during surgery., Methods: In this prospective study, 70 patients underwent MEP monitoring during surgery performed in the central region. All procedures were performed after general anesthesia had been induced without the aid of muscle relaxants. The motor pathways were monitored during the entire surgical procedure by repetitive high-frequency anodal monopolar stimulation (frequency 400-500 Hz; train 7-10 pulses; impulse duration 0.2-0.7 msec; and stimulation intensity 16.9 +/- 7.76 mA). The MEPs were continuously evaluated to assess their latency, potential duration, and amplitude. Recorded alterations in these parameters were subsequently correlated with surgical maneuvers and with postoperative neurological deterioration. The monitoring parameters (latency, potential duration, and amplitude) had a broad interindividual range of variation. A correlation between individual intraoperative changes in the potentials and surgical maneuvers or postoperative neurological deterioration was observed in eight cases. A spontaneous shift in latency greater than 15% or a sudden reduction in the amplitude of the potential greater than 80% was considered a warning criterion. In all cases in which there was an irreversible change in latency or a complete loss of potentials were observed, there was postoperative neurological deterioration., Conclusions: Improved surgical safety can be achieved using intraoperative neurophysiological monitoring procedures. Repetitive stimulation of the motor cortex proved to be a reliable method for monitoring subcortical motor pathways. Changes in MEP latency and MEP amplitude served as warning criteria during surgery and possessed prognostic value.

Background: The aim of image-guided neurosurgery is to accurately project computed tomography (CT) or magnetic resonance imaging (MRI) data into the operative field for defining anatomical landmarks, pathological structures and tumour margins. To achieve this end, different image-guided and computer-assisted, so-called "neuronavigation" systems have been developed in order to offer the neurosurgeon precise spatial information., Method: The present study reports on the experience gained with a prototype of the NEN-NeuroGuard neuronavigation system (Nicolet Biomedical, Madison, WI, USA). It utilises a pulsed DC electromagnetic field for determining the location in space of surgical instruments to which miniaturised sensors are attached. The system was evaluated in respect to its usefulness, ease of integration into standard neurosurgical procedures, reliability and accuracy., Findings: The NEN-system was used with success in 24 intracranial procedures for lesions including both gliomas and cerebral metastases. It allowed real-time display of surgical manoeuvres on pre-operative CT or MR images without a stereotactic frame or a robotic arm. The mean registration error associated with MRI was 1.3 mm (RMS error) and 1.5 mm (RMS error) with CT-data. The average intra-operative target-localising error was 3.2 mm (+/- 1.5 mm SD). Thus, the equipment was of great help in planning and performing skin incisions and craniotomies as well as in reaching deep-seated lesions with a minimum of trauma., Interpretation: The NEN-NeuroGuard system is a very user-friendly and reliable tool for image-guided neurosurgery. It does not have the limitations of a conventional stereotactic frame. Due to its electromagnetic technology it avoids the "line-of-sight" problem often met by optical navigation systems since its sensors remain active even when situated deep inside the skull or hidden, for example, by drapes or by the surgical microscope.

Retrospective analysis of 165 patients (105 males, 60 females) with a mean age of 21.2 years (range 14 to 25 years) of 6933 surgically treated patients from January 1987 to May 1999 focused on age and sex distribution, body mass, familial predisposition, trauma, histology, and clinical course. The incidence of herniated lumbar discs was 2.3% in patients aged up to 25 years. A valid family history was obtained in 121 patients and a positive history was found in 82 of these patients (67.8%). The patients had a higher body mass index compared to a group of individuals with a similar age structure. Radiography demonstrated bony changes in 124 patients (75.2%), primarily attributable to postural deformities such as scoliosis. The condition of the bony structures seems to be more important than the condition of the disc tissue in the occurrence of this disease in young patients.

Intraoperative cranial nerve monitoring has significantly improved the preservation of facial nerve function following surgery in the cerebellopontine angle (CPA). Facial electromyography (EMG) was performed in 60 patients during CPA surgery. Pairs of needle electrodes were placed subdermally in the orbicularis oris and orbicularis oculi muscles. The duration of facial EMG activity was noted. Facial EMG potentials occurring in response to mechanical or metabolic irritation of the corresponding nerve were made audible by a loudspeaker. Immediate (4-7 days after tumor excision) and late (6 months after surgery) facial nerve function was assessed on a modified House-Brackmann scale. Late facial nerve function was good (House-Brackmann 1-2) in 29 of 60 patients, fair (House-Brackmann 3-4) in 14, and poor (House-Brackmann 5-6) in 17. Postmanipulation facial EMG activity exceeding 5 minutes in 15 patients was associated with poor late function in five, fair function in six, and good function in four cases. Postmanipulation facial EMG activity of 2-5 minutes in 30 patients was associated with good late facial nerve function in 20, fair in eight, and poor in two. The loss of facial EMG activity observed in 10 patients was always followed by poor function. Facial nerve function was preserved postoperatively in all five patients in whom facial EMG activity lasted less than 2 minutes. Facial EMG is a sensitive method for identifying the facial nerve during surgery in the CPA. EMG bursts are a very reliable indicator of intraoperative facial nerve manipulation, but the duration of these bursts do not necessarily correlate with short- or long-term facial nerve function despite the fact that burst duration reflects the severity of mechanical aggression to the facial nerve.