Sven Mularski

Navigated transcranial magnetic stimulation for preoperative functional diagnostics in brain tumor surgery.

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.

Functional Magnetic Resonance Imaging and Cortical Mapping in Motor Cortex Tumor Surgery: Complementary Methods

Functional magnetic resonance imaging (fMRI) and direct electrocortical stimulation (DES) are the most commonly used means of analyzing the functional brain topography prior to surgery in the vicinity of Brodmann area 4. No consensus has been established in the literature about the significance of both procedures in reducing operative morbidity. The study presented here was conducted in 30 patients with tumors in the area of the primary motor cortex. Blood oxygen level dependent (BOLD) sequences were preoperatively established with a standardized paradigm. Intraoperatively motor mapping was performed with DES. The results of both methods were digitally matched with a frameless image-guidance system. Correlations between the results of fMRI and of DES were analyzed. Furthermore, the potential influences of the size, position, and histology of the lesions on the mapping results were analyzed and the motor outcome was evaluated. The mean deviation between the results of fMRI and of DES was 13.8 mm (range: 7-28 mm). This deviation was independent of the histology, size, or location of the corresponding lesion. The individual variability of the analysis threshold value for the evaluation of the BOLD sequences led to a considerable topographical inaccuracy. As complementary methods, fMRI contributes to estimating the operational risk, while DES is performed when the results of MRI and fMRI suggest an immediate proximity of the tumor to motor areas.

Neuronavigation without rigid pin fixation of the head in left frontotemporal tumor surgery with intraoperative speech mapping.

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 patients 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 patients 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 patients head. The mean registration error achieved with this technique was 1.53 ± 0.51 mm (fiducial registration error ± standard deviation). The systems 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 patients 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 patients head.

Evaluierung eines DC-gepulsten magnetischen Trackingsystems im Rahmen der neurochirurgischen Navigation: Technik, Genauigkeiten und Einflussparameter / Evaluation of a DC pulsed magnetic tracking system in neurosurgical navigation: technique, accuracies, and influencing factors

Zusammenfassung Navigationssysteme haben sich als hilfreiches Instrument in der kraniellen Neurochirurgie etabliert. So genannte sensorbasierte Navigationsverfahren nutzen zur Positionsbestimmung: (a) einen Signalgeber, welcher ein definiertes elektromagnetisches Feld im Bereich des Operationssitus erzeugt; und (b) kleine Sensorenspulen, welche die Position verschiedener Operationsinstrumente im elektromagnetischen Feld detektieren. Aufgrund fehlender klinischer Daten und Langzeitergebnisse wurden elektromagnetische Systeme jedoch lange als störanfällig und ungenau angesehen. Mit der Entwicklung einer gepulsten direct current (DC)-Technik können nun jedoch auch Genauigkeiten erreicht werden, die mit den bereits etablierten optischen und mechanischen Messverfahren vergleichbar sind. Zu beachten ist jedoch, dass auch bei diesen Systemen die Beeinflussung der Messgenauigkeit innerhalb des Arbeitsbereiches mit der Magnetisierbarkeit der unterschiedlichen Metalle (Titan<Aluminium<hochlegierte Stähle<niedriglegierte Stähle) steigt. Die Arbeitsweise, die zu erzielenden Genauigkeiten, äußere Einflüsse und technische Grenzen eines solchen Systems wurden anhand von mehr als 200 Fällen untersucht. Abstract 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<aluminium<high-alloy steels<low-allow steels). The technique, accuracy, and influencing factors of a DC pulsed magnetic tracking system were investigated in more than 200 cases.

Study on the clinical application of pulsed DC magnetic technology for tracking of intraoperative head motion during frameless stereotaxy

BackgroundTracking 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 patients 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.MethodsA new sensor-based reference tool, the so-called Dynamic Reference Frame (DRF) which is designed to allow an unrestricted, 360° 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.ResultsApart 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.ConclusionRigid 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.

Neurophysiological intraoperative monitoring in neurosurgery: aid or handicap? An international survey.

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 surgeons 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.

Sensor-based neuronavigation: Evaluation of a large continuous patient population

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 patients 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.

Real-time tracking of vertebral body movement with implantable reference microsensors

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 5 × 2 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° 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.

The value of intraoperative neurophysiological monitoring for microsurgical removal of conus medullaris lipomas: a 12-year retrospective cohort study

BackgroundLipomas 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.MethodsThe 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.ResultsThe 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.ConclusionsThe 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. Thats 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.