A Prospective Validation Study of the First 3D Digital Exoscope for Visualization of 5-ALA-Induced Fluorescence in High-Grade Gliomas.

BACKGROUND: We report on the first use of a digital 3-dimensional (3D) exoscope equipped with a 5-aminolevulinic acid (5-ALA) fluorescence visual system. METHODS: We conducted a prospective clinical trial to evaluate the utility and sensitivity/specificity of the Olympus Orbeye 3D digital exoscope when used to visualize 5-ALA-induced fluorescence in patients with high-grade glioma undergoing a clinically indicated craniotomy. At least 2 tissue samples were each obtained from regions of strong, weak. and no fluorescence and evaluated in a blinded manner by a neuropathologist. RESULTS: Twenty patients were enrolled. Intraoperative fluorescence was observed in 100% of subjects. One hundred twenty-one surgical specimens were collected for histopathological analysis; 40 with strong, 40 weak, and 41 with no visible fluorescence. Histopathology demonstrated 62.8% of samples (n = 76) contained abundant, 20.7% (n = 25) scarce, and 16.5% (n = 20) no tumor cells. Thirty-three of the 40 specimens (82.5%) in the strong fluorescence group correlated with abundant tumor cells and 7 (17.5%) with scarce. Twenty-nine of the 40 specimens (72.5%) in the weak fluorescence group correlated with abundant tumor cells, 7 (17.5%) with scarce, and 4 (10%) with none. Fourteen of the 41 (34.2%) specimens in the no fluorescence group had abundant tumor cells, 11 (26.8%) had scarce, and 16 (39%) had none. The sensitivity was 75% and specificity was 80%. The positive predictive value was 95% and negative predictive value was 39%. CONCLUSIONS: Visualization of 5-ALA-induced tumor fluorescence with use of the Orbeye 3D digital exoscope was feasible and associated with a high positive predictive value.

Navigated Deep Brain Stimulation Surgery: Evaluating the Combined Use of a Frame-Based Stereotactic System and a Navigation System.

Deep brain stimulation (DBS) is a complex surgical procedure that requires detailed anatomical knowledge. In many fields of neurosurgery navigation systems are used to display anatomical structures during an operation to aid performing these surgeries. In frame-based DBS, the advantage of visualization has not yet been evaluated during the procedure itself. In this study, we added live visualization to a frame-based DBS system, using a standard navigation system and investigated its accuracy and potential use in DBS surgery. As a first step, a phantom study was conducted to investigate the accuracy of the navigation system in conjunction with a frame-based approach. As a second step, 5 DBS surgeries were performed with this combined approach. Afterwards, 3 neurosurgeons and 2 neurologists with different levels of experience evaluated the potential use of the system with a questionnaire. Moreover, the additional personnel, costs and required set up time were noted and compared to 5 consecutive standard procedures. In the phantom study, the navigation system showed an inaccuracy of 2.1 mm (mean SD 0.69 mm). In the questionnaire, a mean of 9.4/10 points was awarded for the use of the combined approach as a teaching tool, a mean of 8.4/10 for its advantage in creating a 3-dimensional (3-D) map and a mean of 8/10 points for facilitating group discussions. Especially neurosurgeons and neurologists in training found it useful to better interpret clinical results and side effects (mean 9/10 points) and neurosurgeons appreciated its use to better interpret microelectrode recordings (mean 9/10 points). A mean of 6/10 points was awarded when asked if the benefits were worth the additional efforts. Initially 2 persons, then one additional person was required to set up the system with no relevant added time or costs. Using a navigation system for live visualization during frame-based DBS surgery can improve the understanding of the complex 3-D anatomy and many aspects of the procedure itself. For now, we would regard it as an excellent teaching tool rather than a necessity to perform DBS surgeries.

Use of Intraoperative CT Improves Accuracy of Spinal Navigation During Screw Fixation in Cervico-thoracic Region.

STUDY DESIGN: A retrospective analysis of a single-center consecutive series of patients. OBJECTIVE: To test the hypothesis that using a mobile intraoperative computed tomography in combination with spinal navigation would result in better accuracy of lateral mass and pedicle screws between C3 and T5 levels, compared to cone-beam computed tomography and traditional 2D fluoroscopy. SUMMARY OF BACKGROUND DATA: Use of spinal navigation associated with 3D imaging has been shown to improve accuracy of screw positioning in the cervico-thoracic region. However, use of iCT imaging compared to a cone-beam CT has not been fully investigated in these types of surgical interventions. METHODS: We retrospectively analyzed a series of patients who underwent posterior cervico-thoracic fixations using different intraoperative imaging systems in a single hospital. We identified three different groups of patients: Group A, operated under 2D-fluoroscopic guidance without navigation; Group B: O-arm guidance with navigation; Group C: iCT AIRO guidance with navigation. Primary outcome was the rate of accurately placed screws, measured on intra or postoperative CT scan with Neo et al. classification for cervical pedicles screws and Gertzbein et al. for thoracic pedicle screws. Screws in cervical lateral masses were evaluated according to a new classification created by the authors. RESULTS: Data on 67 patients and 495 screws were available. Overall screw accuracy was 92.8% (95.6% for lateral mass screws, 81.6% for cervical pedicle screws, and 90% for thoracic pedicle screws). Patients operated with iCT AIRO navigation had significantly fewer misplaced screws (2.4%) compared to 2D-fluoroscopic guidance (9.1%) and O-arm navigation (9.7%) (P = 0.0152). Accuracy rate of iCT navigation versus O-arm navigation was significantly higher (P = 0.0042), and there was no statistically significant difference in surgical time between the three Groups (P = 0.5390). CONCLUSION: Use of high-quality CT associated with spinal navigation significantly improved accuracy of screw positioning in the cervico-thoracic region.Level of Evidence: 3.

Invasive versus non-invasive mapping of the motor cortex.

Precise and comprehensive mapping of somatotopic representations in the motor cortex is clinically essential to achieve maximum resection of brain tumours whilst preserving motor function, especially since the current gold standard, that is, intraoperative direct cortical stimulation (DCS), holds limitations linked to the intraoperative setting such as time constraints or anatomical restrictions. Non-invasive techniques are increasingly relevant with regard to pre-operative risk-assessment. Here, we assessed the congruency of neuronavigated transcranial magnetic stimulation (nTMS) and functional magnetic resonance imaging (fMRI) with DCS. The motor representations of the hand, the foot and the tongue regions of 36 patients with intracranial tumours were mapped pre-operatively using nTMS and fMRI and by intraoperative DCS. Euclidean distances (ED) between hotspots/centres of gravity and (relative) overlaps of the maps were compared. We found significantly smaller EDs (11.4 ± 8.3 vs. 16.8 ± 7.0 mm) and better spatial overlaps (64 ± 38% vs. 37 ± 37%) between DCS and nTMS compared with DCS and fMRI. In contrast to DCS, fMRI and nTMS mappings were feasible for all regions and patients without complications. In summary, nTMS seems to be the more promising non-invasive motor cortex mapping technique to approximate the gold standard DCS results.

Superior accuracy and precision of SEEG electrode insertion with frame-based vs. frameless stereotaxy methods.

BACKGROUND: Stereotactic electroencephalography (SEEG) has largely become the preferred method for intracranial seizure localization in epileptic patients due to its low morbidity and minimally invasive approach. While robotic placement is gaining popularity, many centers continue to use manual frame-based and frameless methods for electrode insertion. However, it is unclear how these methods compare in regard to accuracy, precision, and safety. Here, we aim to compare frame-based insertion using a CRW frame (Integra®) and frameless insertion using the StealthStation™ S7 (Medtronic®) navigation system for common temporal SEEG targets. METHODS: We retrospectively examined electrode targets in SEEG patients that were implanted with either frame-based or frameless methods at a level 4 epilepsy center. We focused on two commonly used targets: amygdala and hippocampal head. Stealth station software was used to merge pre-operative MR with post-operative CT images for each patient, and coordinates for each electrode tip were calculated in relation to the midcommissural point. These were compared to predetermined ideal coordinates in regard to error and directional bias. RESULTS: A total of 81 SEEG electrodes were identified in 23 patients (40 amygdala and 41 hippocampal head). Eight of 45 electrodes (18%) placed with the frameless technique and 0 of 36 electrodes (0%) placed with the frame-based technique missed their target and were not clinically useful. The average Euclidean distance comparing actual to ideal electrode tip coordinates for frameless vs. frame-based techniques was 11.0 mm vs. 7.1 mm (p < 0.001) for the amygdala and 12.4 mm vs. 8.5 mm (p < 0.001) for the hippocampal head, respectively. There were no hemorrhages or clinical complications in either group. CONCLUSIONS: Based on this series, frame-based SEEG insertion is significantly more accurate and precise and results in more clinically useful electrode contacts, compared to frameless insertion using a navigation guidance system. This has important implications for centers not currently using robotic insertion.

Patient-reported experience measures in patients undergoing navigated transcranial magnetic stimulation (nTMS): the introduction of nTMS-PREMs.

BACKGROUND: Patient-reported experience measures (PREMs) are a unique measure of experience of patients which can help address the quality of care of the patients. OBJECTIVE: Our aim of the study is to collect quality of care outcomes with our newly navigated transcranial magnetic stimulation patient-reported experience measure (nTMS-PREMs) questionnaire among neurosurgical patients undergoing nTMS. METHODS: A single-centre prospective nTMS-PREMs 19-item questionnaire study was performed between February 2018 and December 2018 on patient referred for nTMS at our hospital. The Data was analysed using Likert scale, linear and logistic regression using statistical software (STATA 13.0®). RESULTS: Fifty patient questionnaires were collected (30 males, 20 females, mean age of 47.6 ± 2.1 years) among which 74% of patients underwent both motor and language mapping with a mean duration of 103.3 ± 5.1 min. An overall positive response was noted from the results of the questionnaire, tiredness and anxiety being the common effects noted. Patients with the left-sided disease appreciated more the conditions provided in our laboratory (Q4, p = 0.040) and increasing age was related to less confidence and trust (Q6, p = 0.038) in the staff performing the exam. Younger patients tolerated nTMS better than older patients (> 65 years). PubMed literature search resulted in no relevant articles on the use of PREMs in nTMS patients. CONCLUSION: nTMS is a well-tolerated non-invasive tool and nTMS-PREMS provides a promising role in identifying the unmet needs of the patients and improving the quality of their care.

Surface-Based Registration of MR Scan versus Refined Anatomy-Based Registration of CT Scan: Effect on the Accuracy of SEEG Electrodes Implantation Performed in Prone Position under Frameless Neuronavigation.

INTRODUCTION: Stereoelectroencephalography (SEEG) refers to a commonly used diagnostic procedure to localise and define the epileptogenic zone of refractory focal epilepsies, by means of minimally invasive operation techniques without large craniotomies. OBJECTIVE: This study aimed to investigate the influence of different registration methods on the accuracy of SEEG electrode implantation under neuronavigation for paediatric patients with refractory epilepsy. METHODS: The clinical data of 18 paediatric patients with refractory epilepsy were retrospectively analysed. The SEEG electrodes were implanted under optical neuronavigation while the patients were in the prone position. Patients were divided into two groups on the basis of the surface-based registration of MR scan method and refined anatomy-based registration of CT scan. Registration time, accuracy, and the differences between electrode placement and preoperative planned position were analysed. RESULTS: Thirty-six electrodes in 7 patients were placed under surface-based registration of MR scan, and 45 electrodes in 11 patients were placed under refined anatomy-based registration of CT scan. The registration time of surface-based registration of MR scan and refined anatomy-based registration of CT scan was 45 ± 12 min and 10 ± 4 min. In addition, the mean registration error, the error of insertion point, and target error were 3.6 ± 0.7 mm, 2.7 ± 0.7 mm, and 3.1 ± 0.5 mm in the surface-based registration of MR scan group, and 1.1 ± 0.3 mm, 1.5 ± 0.5 mm, and 2.2 ± 0.6 mm in the refined anatomy-based registration of CT scan group. The differences between the two registration methods were statistically significant. CONCLUSIONS: The refined anatomy-based registration of CT scan method can improve the registration efficiency and electrode placement accuracy, and thereby can be considered as the preferred registration method in the application of SEEG electrode implantation under neuronavigation for treatment of paediatric intractable epilepsy.

Validation of High Precision Robot-Assisted Methods for Intracranial Applications: Preliminary Study.

BACKGROUND: This work attempts to simulate a robot-based autonomous targeted neurosurgical procedure such as biopsy on a vegetable specimen. The objective of the work is to validate the robot-based autonomous neuroregistration and neuronavigation for neurosurgery in terms of stereotactic navigation and target accuracy. CASE DESCRIPTION: A vegetable (carrot) fixed in a tray was used as a model. The tray was affixed with multiple markers. The robot autonomously registers the subject precisely and subsequently accesses the target. The navigation trajectory closely follows the path from the entry point to the target point, as specified in the medical image. The replication of procedures reveals that the target accuracies are within 1 mm. The results based on the case studies are presented. Intricate cases in terms of entry hole size, depth, and size of the target are considered for both phantom and vegetable trials. CONCLUSIONS: The results of the case studies show enhanced and consistent performance characteristics in terms of accuracy, precision, and repeatability with the added advantage of the economy of time. The case studies serve as validation for a high precision robot-assisted neuroregistration and neuronavigation task for neurosurgery and pave the way for further animal and human trials.

Identifying the Sources of Error When Using 3-Dimensional Printed Head Models with Surgical Navigation.

OBJECTIVES: The evaluation of sources of error when preparing, printing, and using 3-dimensional (3D) printed head models for training purposes. METHODS: Two 3D printed models were designed and fabricated using actual patient imaging data with reference marker points embedded artificially within these models that were then registered to a surgical navigation system using 3 different methods. The first method uses a conventional manual registration, using the actual patient's imaging data. The second method is done by directly scanning the created model using intraoperative computed tomography followed by registering the model to a new imaging dataset manually. The third is similar to the second method of scanning the model but eventually uses an automatic registration technique. The errors for each experiment were then calculated based on the distance of the surgical navigation probe from the respective positions of the embedded marker points. RESULTS: Errors were found in the preparation and printing techniques, largely depending on the orientation of the printed segment and postprocessing, but these were relatively small. Larger errors were noted based on a couple of variables: if the models were registered using the original patient imaging data as opposed to using the imaging data from directly scanning the model (1.28 mm vs. 1.082 mm), and the accuracy was best using the automated registration techniques (0.74 mm). CONCLUSION: Spatial accuracy errors occur consistently in every 3D fabricated model. These errors are derived from the fabrication process, the image registration process, and the surgical process of registration.

Safety and accuracy of frameless electromagnetic-navigated (AXIEMTM)-guided brain lesion biopsies: a large single-unit study.

BACKGROUND: Brain biopsies are required to establish a definitive histological diagnosis for brain lesions that have been identified on imaging in order to guide further treatment for patients. OBJECTIVE: Various navigation systems are in use but little up to date evidence is available regarding the safety and accuracy of a frameless, electromagnetic technique to target brain lesions. METHODS: Data was collected retrospectively on all patients that had brain biopsies at our institution from 01/01/2010 to 31/12/2017. Operation notes, neuropathology reports, and clinical notes on electronic patient record were used to determine whether biopsy of adequate identifiable abnormal tissue was achieved, whether a definitive diagnosis was established, any adverse events occurred, and if a repeat biopsy was carried out. RESULTS: Three hundred seventy-one AxiEM (Medtronic, Minneapolis, USA)-guided brain tumor biopsies were performed in this 8-year period. Three hundred forty-nine (94.07%) procedures provided definitive tissue diagnosis, 22 (5.93%) were non diagnostic; in 6 cases (1.62%), repeat biopsy was performed and adverse events which caused clinical compromise were observed in 4 patients (1.08%). CONCLUSIONS: The AxiEM is a fast, effective, and safe frameless and pinless neuronavigational system. It offers a high degree of accuracy required for the establishment of a definitive diagnosis, permitting optimal further treatment, and thus improving patient outcomes.

Technical note: accuracy and precision in stereotactic stem cell transplantation.

BACKGROUND: While multiple trials have employed stereotactic stem cell transplantation, injection techniques have received little critical attention. Precise cell delivery is critical for certain applications, particularly when targeting deep nuclei. METHODS: Ten patients with a history of ischemic stroke underwent CT-guided stem cell transplantation. Cells were delivered along 3 tracts adjacent to the infarcted area. Intraoperative air deposits and postoperative T2-weighted MRI fluid signals were mapped in relation to calculated targets. RESULTS: The deepest air deposit was found 4.5 ± 1.0 mm (mean ± 2 SEM) from target. The apex of the T2-hyperintense tract was found 2.8 ± 0.8 mm from target. On average, air pockets were found anterior (1.2 ± 1.1 mm, p = 0.04) and superior (2.4 ± 1.0 mm, p < 0.001) to the target; no directional bias was noted for the apex of the T2-hyperintense tract. Location and distribution of air deposits were variable and were affected by the relationship of cannula trajectory to stroke cavity. CONCLUSIONS: Precise stereotactic cell transplantation is a little-studied technical challenge. Reflux of cell suspension and air, and the structure of the injection tract affect delivery of cell suspensions. Intraoperative CT allows assessment of delivery and potential trajectory correction.

Frameless stereotactic biopsy for precision neurosurgery: diagnostic value, safety, and accuracy.

BACKGROUND: Stereotactic biopsy is consistently employed to characterize cerebral lesions in patients who are not suitable for microsurgical resection. In the past years, technical improvement and neuroimaging advancements contributed to increase the diagnostic yield, the safety, and the application of this procedure. Currently, in addition to histological diagnosis, the molecular analysis is considered essential in the diagnostic process to properly select therapeutic and prognostic algorithms in a personalized approach. The present study reports our experience with frameless stereotactic brain biopsy in this molecular era. METHODS: One hundred forty consecutive patients treated from January 2013 to September 2018 were analyzed. Biopsies were performed using the Brainlab Varioguide® frameless stereotactic system. Patients' clinical and demographic data, the time of occupation of the operating room, the surgical time, the morbidity, and the diagnostic yield in providing a histological and molecular diagnosis were recorded and evaluated. RESULTS: The overall diagnostic yield was 93.6% with nine procedures resulting non-diagnostic. Among 110 patients with glioma, the IDH-1 mutational status was characterized in 108 cases (98.2%), resulting wild-type in all subjects but 3; MGMT methylation was characterized in 96 cases (87.3%), resulting present in 60 patients, and 1p/19q codeletion was founded in 6 of the 20 cases of grade II-III gliomas analyzed. All the specimens were apt for molecular analysis when performed. Bleeding requiring surgical drainage occurred in 2.1% of the cases; 8 (5.7%) asymptomatic hemorrhages requiring no treatment were observed. No biopsy-related mortality was recorded. Median length of hospital stay was 5 days (IQR 4-8) with mean surgical time of 60.77 min (± 23.12) and 137.44 ± 24.1 min of total occupation time of the operative room. CONCLUSIONS: Stereotactic frameless biopsy is a safe, feasible, and fast procedure to obtain a histological and molecular diagnosis.

Current accuracy of surface matching compared to adhesive markers in patient-to-image registration.

OBJECT: In the past, the accuracy of surface matching has been shown to be disappointing. We aimed to determine whether this had improved over the years by assessing application accuracy of current navigation systems, using either surface matching or point-pair matching. METHODS: Eleven patients, scheduled for intracranial surgery, were included in this study after a power analysis had shown this small number to be sufficient. Prior to surgery, one additional fiducial marker was placed on the scalp, the "target marker," where the entry point of surgery was to be expected. Using one of three different navigation systems, two patient-to-image registration procedures were performed: one based on surface matching and one based on point-pair matching. Each registration procedure was followed by the digitization of the target marker's location, allowing calculation of the target registration error. If the system offered surface matching improvement, this was always used; and for the two systems that routinely offer an estimate of neuronavigation accuracy, this was also recorded. RESULTS: The error in localizing the target marker using point-pair matching or surface matching was respectively 2.49 mm and 5.35 mm, on average (p < 0.001). In those four cases where an attempt was made to improve the surface matching, the error increased to 6.35 mm, on average. For the seven cases where the system estimated accuracy, this estimate did not correlate with target registration error (R2 = 0.04, p = 0.67). CONCLUSION: The accuracy of navigation systems has not improved over the last decade, with surface matching consistently yielding errors that are twice as large as when point-pair matching with adhesive markers is used. These errors are not reliably reflected by the systems own prediction, when offered. These results are important to make an informed choice between image-to-patient registration strategies, depending on the type of surgery at hand.

Transoral Approach to the Craniovertebral Junction: A Neuronavigated Cadaver Study.

More than 100 years after the first description by Kanavel of a transoral-transpharyngeal approach to remove a bullet impacted between the atlas and the clivus [1], the transoral approach (TOA) still represents the 'gold standard' for surgical treatment of a variety of conditions resulting in anterior craniocervical compression and myelopathy [2, 3]. Nevertheless, some concerns-such as the need for a temporary tracheostomy and a postoperative nasogastric tube, and the increased risk of infection resulting from possible bacterial contamination and nasopharyngeal incompetence [4-6]-led to the introduction of the endoscopic endonasal approach (EEA) by Kassam et al. [7] in 2005. Although this approach, which was conceived to overcome those surgical complications, soon gained wide attention, its clear predominance over the TOA in the treatment of craniovertebral junction (CVJ) pathologies is still a matter of debate [3]. In recent years, several papers have reported anatomical studies and surgical experience with the EEA, targeting different areas of the midline skull base, from the olfactory groove to the CVJ [8-19]. Starting from these preliminary experiences, further anatomical studies have defined the theoretical (radiological) and practical (surgical) craniocaudal limits of the endonasal route [20-25]. Our group has done the same for the TOA [26, 27] and compared the reliability of the radiological and surgical lines of the two different approaches. Very recently, a cadaver study, with the aid of neuronavigation, tried to define the upper and lower limits of the endoscopic TOA [28].

Current status of training environments in neuro-interventional practice: are animal models still contemporary?

PURPOSE: Several different training environments for practicing neurointerventional procedures have been realized in silico, in vitro, and in vivo. We seek to replace animal-based training with suitable alternatives. In an effort to determine present training model distribution and preferences, we interviewed interventional neuroradiologists from 25 different countries about their experience in distinct training environments. METHODS: A voluntary online survey comprising 24 questions concerning the different training facilities was designed and electronically conducted with the members of the European Society for Minimally Invasive Neurological Therapy. RESULTS: Seventy-one physicians with an average experience of 11.8 (±8.7) years completed the survey. The majority of participants had experience with animal-based training (eg, stroke intervention: 36; 50.7%). Overall, animal-based training was rated as the most suitable environment to practice coil embolization (20 (±6)), flow diverter placement (13 (±7)), and stroke intervention (13.5 (±9)). In-vitro training before using a new device in patients was supported by most participants (35; 49.3%). Additionally, preference for certain training models was related to the years of experience. CONCLUSION: This survey discloses the preferred training modalities in European neurointerventional centers with the majority of physicians supporting the general concept of in-vitro training, concomitantly lacking a standardized curriculum for educating neurointerventional physicians. Most suitable training modalities appeared to be dependent on procedure and experience. As animal-based training is still common, alternate artificial environments meeting these demands must be further developed.

Frameless Deep Brain Stimulation Surgery: A Single-Center Experience and Retrospective Analysis of Placement Accuracy of 220 Electrodes in a Series of 110 Patients.

BACKGROUND: Proper lead placement is considered one of the key factors in achieving a good clinical outcome in deep brain stimulation (DBS), but there is still considerable controversy surrounding the accuracy of the frameless in comparison to the frame-based technique. OBJECTIVE: We report our single-center experience with DBS electrode placement to evaluate the accuracy of the frameless stereotactic system. METHODS: We prospectively analyzed the data of 110 patients who underwent DBS surgery for Parkinson disease, dystonia, essential tremor, or refractory epilepsy. The final targets (FTs) of the 220 leads were: subthalamic nucleus, globus pallidus pars interna, ventralis intermedius nucleus, and anterior nuclei of thalamus in thalamus. A bilateral stereotactic approach using a combined identification of target based on preoperative images (MRI and CT scan fusion) and intra-operative micro-electrode recording (MER) were done. We collected and compared the coordinates of planned target (PT), the definitive expected target (ET) during MER, and the effective final location (FT) of the lead using the postoperative CT. Accuracy was assessed by both vector error (VE) and deviation from the PT. RESULTS: The mean and SD from PTs was 0.78 ± 0.43 mm in the x direction, 0.68 ± 0.41 mm in the y direction, and 0.76 ± 0.41 mm in the z direction. Global VE was 1.43 ± 0.37. CONCLUSION: Frameless systems appear to be a reliable and accurate technique.

Prospective Comparative Study in Spine Surgery Between O-Arm and Airo Systems: Efficacy and Radiation Exposure.

OBJECTIVE: Pedicle screw placement remains challenging. The present study focuses on the comparison between 2 intraoperative-based neuronavigation systems (O-Arm and AIRO) during thoracolumbar screw instrumentation. METHODS: This is a prospective, comparative, nonrandomized study conducted in 2 French academic centers. The O-Arm was used at the University Hospital of Bordeaux, whereas the AIRO was used at the University Hospital of Marseille. Routine computed tomography was performed on postoperative day 2 to evaluate pedicle screw placement. Measures of radiation exposure were extracted directly from reports provided by each system. The effective dose was calculated. RESULTS: Overall, 74 screws were placed in 11 patients in the O-Arm group and 84 in 11 patients in the AIRO group. In the first group, 90.8% were rated as acceptable and 92.2% in the second (P > 0.05) according to the Heary and Gertzbein classifications, respectively, for thoracic and lumbar spine. Differences between both implantation systems were significant (P < 0.05) concerning dose length product (235 and 1039 mGy/cm, in O-Arm and AIRO, respectively), overall mean radiation dose received by 1 patient (3.52 and 15.6 mSv in O-Arm and AIRO, respectively), mean radiation dose per single scan (2.58 and 8.7 mSv in O-Arm and AIRO, respectively), mean effective dose per instrumented level (1.04 and 3.9 mSv in O-Arm and AIRO, respectively), and radiation dose received by the primary surgeon (0.63 and 0 µSv in O-Arm and AIRO, respectively). CONCLUSIONS: Intraoperative computed tomography-based navigation is a major innovation that improves the accuracy of pedicle screw positioning with acceptable patient radiation exposure and reduced surgical team exposure.

Minimally invasive approaches to aneurysms of the anterior circulation: selection criteria and clinical outcomes.

Over the last few decades, cerebrovascular surgery has gravitated towards a minimally invasive philosophy without compromising the foundational principles of patient safety and surgical efficacy. Enhanced radiosurveillance modalities and increased average life expectancy have resulted in an increased reported incidence of intracranial aneurysms. Although endovascular therapies have gained popularity in the recent years, microsurgical clipping continues to be of value in the management of these aneurysms owing to its superior occlusion rates, applicability to complex aneurysms and reduced retreatment rates. The concept of keyhole transcranial procedures has advanced the field significantly leading to decreased postoperative neurological morbidity and quicker recovery. The main keyhole neurosurgical approaches include the supraorbital craniotomy (SOC), lateral supraorbital craniotomy (LSOC), mini-pterional craniotomy (MPTC), mini-orbitozygomatic craniotomy and the mini anterior interhemispheric approach (MAIA). As these minimally invasive approaches can have an inherent limitation of a narrow viewing angle and low regional illumination, the use of endoscopic assistance in such procedures is being popularized. Neuroendoscopy can aid in the visualization of hidden neurovascular structures and inspection of the parent arterial segment without undue retraction of the lesion. This review focuses on the historical progression of the surgical management of intracranial aneurysms, the technical details of various minimally invasive approaches, patient selection and clinical outcomes of the anterior circulation aneurysms and useful tenets to avoid complications during these procedures. Meticulous preoperative planning to understand the patient's vascular anatomy, the orientation and relationship of the aneurysm to adjacent structures, use of neuronavigation guidance and endoscopic assistance if needed can lead to an optimal surgical outcome while minimizing neurological morbidity and mortality.

Development and validation of a 3D-printed neuronavigation headset for therapeutic brain stimulation.

BACKGROUND: Accurate neuronavigation is essential for optimal outcomes in therapeutic brain stimulation. MRI-guided neuronavigation, the current gold standard, requires access to MRI and frameless stereotaxic equipment, which is not available in all settings. Scalp-based heuristics depend on operator skill, with variable reproducibility across operators and sessions. An intermediate solution would offer superior reproducibility and ease-of-use to scalp measurements, without requiring MRI and frameless stereotaxy. OBJECTIVE: We present and assess a novel neuronavigation method using commercially-available, inexpensive 3D head scanning, computer-aided design, and 3D-printing tools to fabricate form-fitted headsets for individuals that hold a stimulator, such as an rTMS coil, in the desired position over the scalp. METHODS: 20 individuals underwent scanning for fabrication of individualized headsets designed for rTMS of the left dorsolateral prefrontal cortex (DLPFC). An experienced operator then performed three trials per participant of three neuronavigation methods: MRI-guided, scalp-measurement (BeamF3 method), and headset placement, and marked the sites obtained. Accuracy (versus MRI-guidance) and reproducibility were measured for each trial of each method. RESULTS: Within-subject accuracy (against a gold-standard centroid of three MRI-guided localizations) for MRI-guided, scalp-measurement, and headset methods was 3.7 ± 1.6 mm, 14.8 ± 7.1 mm, and 9.7 ± 5.2 mm respectively, with headsets significantly more accurate (M = 5.1, p = 0.008) than scalp-measurement methods. Within-subject reproducibility (against the centroid of 3 localizations in the same modality) was 3.7 ± 1.6 mm (MRI), 4.2 ± 1.4 (scalp-measurement), and 1.4 ± 0.7 mm (headset), with headsets achieving significantly better reproducibility than either other method (p < 0.0001). CONCLUSIONS: 3D-printed headsets may offer good accuracy, superior reproducibility and greater ease-of-use for stimulator placement over DLPFC, in settings where MRI-guidance is impractical.

Ultrasound-guided brain surgery: echographic visibility of different pathologies and surgical applications in neurosurgical routine.

BACKGROUND: The use of intraoperative ultrasound (iUS) has increased in the last 15 years becoming a standard tool in many neurosurgical centers. Our aim was to assess the utility of routine use of iUS during various types of intracranial surgery. We reviewed our series to assess ultrasound visibility of different pathologies and iUS applications during the course of surgery. MATERIALS AND METHODS: This is a retrospective review of 162 patients who underwent intracranial surgery with assistance of the iUS guidance system (SonoWand). Pathologic categories were neoplastic (135), vascular (20), infectious (2), and CSF related (5). Ultrasound visibility was assessed using the Mair classification, a four-tiered grading system that considers the echogenicity of the lesion and its border visibility (from 0 to 3; grade 0, pathology not visible; grade 3, visible with clear border with normal tissue). iUS applications included lesion localization, approach planning to deep-seated lesions, and lesion removal. RESULTS: All pathologies were visible on iUS except one aneurysm. On average, extra-axial tumors were identified more easily and had clearer limits compared to intra-axial tumors (extra-axial 17% grade 2, 83% grade 3; intra-axial 5.5% grade 1, 46.5% grade 2, 48% grade 3). iUS provided precise and safe transcortical trajectories to deep-seated lesions (71 patients; tumors, hemangiomas, ICHs); iUS was judged to be less useful to approach skull base tumors and aneurysms. iUS was used to judge extent of resection in 152 cases; surgical artifacts reduced sonographic visibility in 25 cases: extent of resection was correctly checked in 127 patients (53 gliomas, 15 metastases, 39 meningiomas, 4 schwannomas, 4 sellar region tumors, 6 hemangiomas, 3 AVMs, 2 abscesses). CONCLUSIONS: iUS was highly sensitive in detecting all types of pathology, was safe and precise in planning trajectories to intraparenchymal lesions (including minimally mini-invasive approaches), and was accurate in checking extent of resection in more than 80% of cases. iUS is a versatile and feasible tool; it could improve safety and its use may be considered in routine intracranial surgery.