Image-guided biopsy of intracranial lesions in children, with a small robotic device: a case series.

BACKGROUND AND OBJECTIVES: Robot-assisted biopsies have gained popularity in the last years. Most robotic procedures are performed with a floor-based robotic arm. Recently, Medtronic Stealth Autoguide, a miniaturized robotic arm that work together with an optical neuronavigation system, was launched. Its application in pediatric cases is relatively unexplored. In this study, we retrospectively report our experience using the Stealth Autoguide, for frameless stereotactic biopsies in pediatric patients. METHODS: Pediatric patients who underwent stereotactic biopsy using the Stealth Autoguide cranial robotic platform from July 2020 to May 2023 were included in this study. Clinical, neuroradiological, surgical, and histological data were collected and analyzed. RESULTS: Nineteen patients underwent 20 procedures (mean age was 9-year-old, range 1-17). In four patients, biopsy was part of a more complex surgical procedure (laser interstitial thermal therapy - LITT). The most common indication was diffuse intrinsic brain stem tumor, followed by diffuse supratentorial tumor. Nine procedures were performed in prone position, eight in supine position, and three in lateral position. Facial surface registration was adopted in six procedures, skull-fixed fiducials in 14. The biopsy diagnostic tissue acquisition rate was 100% in the patients who underwent only biopsy, while in the biopsy/LITT group, one case was not diagnostic. No patients developed clinically relevant postoperative complications. CONCLUSION: The Stealth Autoguide system has proven to be safe, diagnostic, and highly accurate in performing stereotactic biopsies for both supratentorial and infratentorial lesions in the pediatric population.

Automatic Path-Planning Techniques for Minimally Invasive Stereotactic Neurosurgical Procedures-A Systematic Review.

This review systematically examines the recent research from the past decade on diverse path-planning algorithms tailored for stereotactic neurosurgery applications. Our comprehensive investigation involved a thorough search of scholarly papers from Google Scholar, PubMed, IEEE Xplore, and Scopus, utilizing stringent inclusion and exclusion criteria. The screening and selection process was meticulously conducted by a multidisciplinary team comprising three medical students, robotic experts with specialized knowledge in path-planning techniques and medical robotics, and a board-certified neurosurgeon. Each selected paper was reviewed in detail, and the findings were synthesized and reported in this review. The paper is organized around three different types of intervention tools: straight needles, steerable needles, and concentric tube robots. We provide an in-depth analysis of various path-planning algorithms applicable to both single and multi-target scenarios. Multi-target planning techniques are only discussed for straight tools as there is no published work on multi-target planning for steerable needles and concentric tube robots. Additionally, we discuss the imaging modalities employed, the critical anatomical structures considered during path planning, and the current status of research regarding its translation to clinical human studies. To the best of our knowledge and as a conclusion from this systematic review, this is the first review paper published in the last decade that reports various path-planning techniques for different types of tools for minimally invasive neurosurgical applications. Furthermore, this review outlines future trends and identifies existing technology gaps within the field. By highlighting these aspects, we aim to provide a comprehensive overview that can guide future research and development in path planning for stereotactic neurosurgery, ultimately contributing to the advancement of safer and more effective neurosurgical procedures.

Comparison of Navigated and Frame-Based Stereotactic Biopsy-A Single-Center Cohort Study.

Background and Objectives: As brain lesions present complex diagnostic challenges, accurate tissue sampling via biopsy is critical for effective treatment planning. Traditional frame-based stereotactic biopsy has been complemented by navigated biopsy techniques, leveraging advancements in imaging and navigation technology. This study aims to compare the navigated and frame-based stereotactic biopsy methods in a clinical setting, evaluating their efficacy, safety, and diagnostic outcomes to determine the optimal approach for precise brain lesion targeting. Materials and Methods: retrospective analysis was conducted on patients who underwent brain biopsies between January 2017 and August 2023 at an academic medical center. Data on patient demographics, clinical characteristics, biopsy technique (navigated vs. frame-based), and outcomes including accuracy, complications, and hospital stay duration were analyzed. Results: The cohort comprised 112 patients, with no significant age or gender differences between groups. Symptoms leading to biopsy were predominantly diminished muscle strength (42.0%), cognitive issues (28.6%), and aphasia (24.1%). Tumors were most common in the deep hemisphere (24.1%). The median hospital stay was 5 days, with a rehospitalization rate of 27.7%. Complications occurred in 4.47% of patients, showing no significant difference between biopsy methods. However, navigated biopsies resulted in fewer samples (p < 0.001) but with comparable diagnostic accuracy as frame-based biopsies. Conclusions: Navigated and frame-based stereotactic biopsies are both effective and safe, with comparable accuracy and complication rates. The choice of technique should consider lesion specifics, surgeon preference, and technological availability. The findings highlight the importance of advanced neurosurgical techniques in enhancing patient care and outcomes.

Anterior cingulate cortex is necessary for adaptation of action plans.

Previous research has focused on the anterior cingulate cortex (ACC) as a key brain region in the mitigation of the competition that arises from two simultaneously active signals. However, to date, no study has demonstrated that ACC is necessary for this form of behavioral flexibility, nor have any studies shown that ACC acts by modulating downstream brain regions such as the dorsal medial striatum (DMS) that encode action plans necessary for task completion. Here, we performed unilateral excitotoxic lesions of ACC while recording downstream from the ipsilateral hemisphere of DMS in rats, performing a variant of the STOP-signal task. We show that on STOP trials lesioned rats perform worse, in part due to the failure of timely directional action plans to emerge in the DMS, as well as the overrepresentation of the to-be-inhibited behavior. Collectively, our findings suggest that ACC is necessary for the mitigation of competing inputs and validates many of the existing theoretical predictions for the role of ACC in cognitive control.

Imaging of focal seizures with Electrical Impedance Tomography and depth electrodes in real time.

Intracranial EEG is the current gold standard technique for localizing seizures for surgery, but it can be insensitive to tangential dipole or distant sources. Electrical Impedance Tomography (EIT) offers a novel method to improve coverage and seizure onset localization. The feasibility of EIT has been previously assessed in a computer simulation, which revealed an improved accuracy of seizure detection with EIT compared to intracranial EEG. In this study, slow impedance changes, evoked by cell swelling occurring over seconds, were reconstructed in real time by frequency division multiplexing EIT using depth and subdural electrodes in a swine model of epilepsy. EIT allowed to generate repetitive images of ictal events at similar time course to fMRI but without its significant limitations. EIT was recorded with a system consisting of 32 parallel current sources and 64 voltage recorders. Seizures triggered with intracranial injection of benzylpenicillin (BPN) in five pigs caused a repetitive peak impedance increase of 3.4 ± 1.5 mV and 9.5 ± 3% (N =205 seizures); the impedance signal change was seen already after a single, first seizure. EIT enabled reconstruction of the seizure onset 9 ± 1.5 mm from the BPN cannula and 7.5 ± 1.1 mm from the closest SEEG contact (p<0.05, n =37 focal seizures in three pigs) and it could address problems with sampling error in intracranial EEG. The amplitude of the impedance change correlated with the spread of the seizure on the SEEG (p <<0.001, n =37). The results presented here suggest that combining a parallel EIT system with intracranial EEG monitoring has a potential to improve the diagnostic yield in epileptic patients and become a vital tool in improving our understanding of epilepsy.

Subthalamic Nucleus Stimulation Modulates Motor Epileptic Activity in Humans.

OBJECTIVE: Pharmaco-refractory focal motor epileptic seizures pose a significant challenge. Deep brain stimulation (DBS) is a recently recognized therapeutic option for the treatment of refractory epilepsy. To identify the specific target for focal motor seizures, we evaluate the modulatory effects of the subthalamic nucleus (STN) stimulation because of the critical role of STN in cortico-subcortical motor processing. METHODS: Seven patients with epilepsy with refractory seizures who underwent chronic stereoelectroencephalography (SEEG) monitoring were studied in presurgical evaluation. Seizure onset zone was hypothesized to be partially involved in the motor areas in 6 patients. For each patient, one electrode was temporally implanted into the STN that was ipsilateral to the seizure onset zone. The cortical-subcortical seizure propagation was systemically evaluated. The simultaneously electrophysiological responses over distributed cortical areas to STN stimulation at varied frequencies were quantitatively assessed. RESULTS: We observed the consistent downstream propagation of seizures from the motor cortex toward the ipsilateral STN and remarkable cortical responses on motor cortex to single-pulse STN stimulation. Furthermore, we showed frequency-dependent upstream modulatory effect of STN stimulation on motor cortex specifically. In contrast to the enhanced effects of low frequency stimulation, high-frequency stimulation of the STN can significantly reduce interictal spikes, high-frequency oscillations over motor cortex disclosing effective connections to the STN. INTERPRETATION: This result showed that the STN is not only engaged in as a propagation network of focal motor seizures but STN stimulation can profoundly modulate the epileptic activity of motor cortex in humans, suggesting a mechanism-based alternative for patients suffering from refractory focal motor seizures. ANN NEUROL 2020;88:283-296.

Diagnostic yield of fluorescence-assisted frame-based stereotactic biopsies of intracerebral lesions in comparison with frozen-section analysis.

PURPOSE: Stereotactic biopsies are routinely used to establish a histological diagnosis of unclear cerebral pathologies. Intraoperatively, frozen-section analysis often confirms diagnostic tissue but also exhibits methodological pitfalls. Intraoperative five-aminolevulinic acid (5-ALA)-fluorescence has been described not only in gliomas but also in other cerebral pathologies. In this study, we assessed the 5-ALA contribution to the intraoperative confirmation of diagnostic tissue in frame-based stereotactic biopsies of unclear intracerebral lesions in direct comparison with frozen-section analysis. METHODS: Patients scheduled for stereotactic biopsies of unclear intracerebral pathologies received 5-ALA preoperatively. Obtained samples were intraoperatively analyzed for the presence of 5-ALA-fluorescence. One sample was used for frozen-section and a second one for permanent histopathological analysis. The diagnostic yield of frozen-section and intraoperative 5-ALA-fluorescence was calculated. The inclusion criteria for this retrospective analysis were unclear intracerebral lesions with inconclusive imaging findings and several differential diagnoses. RESULTS: A total of 39 patients with 122 obtained specimens were included. The overall diagnostic yield was 92.3%. 5-ALA-positive samples were obtained in 74.3% (29/39) of patients and all these samples contained diagnostic tissue. 5-ALA-fluorescence confirmed diagnostic tissue with a sensitivity of 100%, a specificity of 27%, a positive predictive value (PPV) of 78%, and a negative predictive value (NPV) of 100%. A clear diagnosis could be predicted by frozen section with a sensitivity of 80%, a specificity of 100%, a PPV of 100%, and NPV of 30%; Fisher's exact test p = 0.01. CONCLUSION: The 5-ALA-fluorescence in stereotactic biopsies of unclear intracerebral pathologies exhibits a high PPV/NPV for intraoperative confirmation of diagnostic tissue and might increase the diagnostic yield of the procedure by overcoming some of the limitations of frozen-section.

Comparison between 1.5- and 3-T Magnetic Resonance Acquisitions for Direct Targeting Stereotactic Procedures for Deep Brain Stimulation: A Phantom Study.

INTRODUCTION: Deep brain stimulation (DBS) is a well-established treatment for movement disorders. High magnetic fields could have an impact on distortion. We evaluated 1.5- and 3-T magnetic resonance imaging (MRI) sequences for accuracy, precision, and trueness of our MRI-guided direct targeting protocol. METHODS: Effects of distortion on MR sequences (T1- and T2-weighted sequences) can be evaluated using a dedicated phantom (Elekta). Field strength capabilities were assessed on Siemens Avanto (1.5 T) and Skyra (3 T) scanners. We assessed the precision of our stereotactic MRI-guided procedure. RESULTS: We focused on the risk of error due to a high field strength. Error values on the localizer box were between 0.4 and 0.7 mm at 1.5 T and between 0.6 and 2 mm at 3 T. The most accurate 1.5-T sequence is the 3D FLASH T1-weighted sequence, which had an accuracy value of 0.6 mm. At 3 T, the accuracy value of the isotropic 3D FLASH T1-weighted sequence was 1.6 mm. CONCLUSION: Given the millimetric size of stereotactic targets and electrodes, lead implantation for neuromodulation therapy needs to be accurate. We demonstrate that 3-T imaging could not be used for stereotaxy in our MRI-guided direct targeting protocol because of a risk of error induced by distortion.

CT-Guided Percutaneous Trigeminal Tractotomy-Nucleotomy for Intractable Craniofacial Pain.

OBJECT: In this report, we aimed to analyze the outcome results of our patients who underwent percutaneous trigeminal tractotomy (TR) and nucleotomy (NC) procedures, which are defined as destructive procedures targeting the descending trigeminal tractus and nucleus caudalis of the spinal trigeminal nucleus, respectively, for intractable craniofacial pain. METHODS: The medical records of a total of 12 patients who underwent a total of 14 computed tomography (CT)-guided TR-NC procedures at our clinics between 2005 and 2017 were retrospectively reviewed. RESULTS: A significant increase in patients' performance status (p = 0.015) as well as a significant decrease in the VAS score (p < 0.001) were achieved. Grade I pain relief (VAS = 0, no pain) was established in 66.7% of the patients, whereas grade II pain relief was observed in the remaining patients. Two of the patients suffered from recurrent pain after the initial procedure. Both patients underwent a second trigeminal TR-NC procedure, and grade I pain relief was re-established. The mean VAS score at 3-month follow-up was 1.4 ± 1.1, whereas this score at 6-month follow-up was 2 ± 1.3. The trigeminal TR-NC procedure resulted in a significant decrease in patients' VAS scores at 3- and 6-month follow-up visits compared with preoperative VAS scores (p < 0.001). Transient ataxia was noted in only one patient (8.3%) early after the procedure. CONCLUSIONS: The results presented in the current study support the efficacy of the percutaneous CT-guided trigeminal TR-NC procedure in the management of intractable facial pain in selected patients. The use of CT guidance allows direct visualization of the target area, thereby enhancing the safety and success of the procedure.

The repertoire of seizure onset patterns in human focal epilepsies: Determinants and prognostic values.

OBJECTIVE: In this study, we seek to analyze the determinants of the intracranial electroencephalography seizure onset pattern (SOP) and the impact of the SOP in predicting postsurgical seizure outcome. METHODS: To this end, we analyzed 820 seizures from 252 consecutive patients explored by stereo-electroencephalography (total of 2148 electrodes), including various forms of focal refractory epilepsies. We used a reproducible method combining visual and time-frequency analyses. RESULTS: We described eight SOPs: low-voltage fast activity (LVFA), preictal spiking followed by LVFA, burst of polyspikes followed by LVFA, slow wave/DC shift followed by LVFA, sharp theta/alpha waves, beta sharp waves, rhythmic spikes/spike-waves, and delta-brush. LVFA occurred in 79% of patients. The seizure onset pattern was significantly associated with (1) underlying etiology (burst of polyspikes followed by LVFA with the presence of a focal cortical dysplasia, LVFA with malformation of cortical development, postvascular and undetermined epilepsies), (2) spatial organization of the epileptogenic zone (EZ; burst of polyspikes followed by LVFA with focal organization, slow wave/DC shift followed by LVFA with network organization), and (3) postsurgical seizure outcome (better outcome when LVFA present). SIGNIFICANCE: This study demonstrates that the main determinants of the SOP are the underlying etiology and the spatial organization of the EZ. Concerning the postsurgical seizure outcome, the main determinant factor is the spatial organization of the EZ, but the SOP plays also a role, conferring better prognosis when LVFA is present.

Postictal electroencephalographic (EEG) suppression: A stereo-EEG study of 100 focal to bilateral tonic-clonic seizures.

OBJECTIVES: We aimed to describe intracerebral aspects of postictal generalized electroencephalography suppression (PGES) following focal to bilateral tonic-clonic ("secondarily generalized tonic-clonic") seizures (GTCS) recorded using stereoelectroencephalographic (SEEG), and to correlate these with electroclinical features. METHODS: Three independent observers scored semiologic and SEEG features. Patient and epilepsy characteristics were collected. Descriptive statistics and multivariate analysis were performed. The operational definition of PGES on SEEG used strict criteria (absence of visible signal at 20 µV/mm amplitude, in all readable channels). Postictal regional suppression (RS) was identified if only a subset of implanted electrodes showed absence of signal. RESULTS: We evaluated 100 seizures in 52 patients. Interobserver agreement was good (κ 0.72 for clinical features and 0.73 for EEG features). PGES was present in 27 of 100 and RS without PGES present in 42 of 100 seizures. Region of RS included epileptogenic zone in 43 of 51 (86%). No effect of sampling (multilobar or bilateral exploration) was seen. Oral tonicity (mouth opening and/or tonic vocalization during the tonic phase of GTCS) was associated with the presence of PGES (P = 0.029; negative predictive value [NPV] 0.91). Bilateral upper limb extension during the tonic phase correlated with PGES (P = 0.041; NPV 0.85). Association of both oral tonicity and bilateral upper limb extension had a high NPV of 0.96. SIGNIFICANCE: SEEG recordings confirm true absence of signal during postictal EEG suppression. PGES is unlikely when both upper limb extension and oral tonicity are absent. We hypothesize that bilateral tonic seizure discharge at bulbar level brainstem regions is associated with the production of oral signs and may relate to mechanisms of PGES.

Utilization of the Intraoperative Mobile AIRO® CT Scanner in Stereotactic Surgery: Workflow and Effectiveness.

BACKGROUND: In frame-based stereotactic surgery, intraoperative imaging is crucial. It generally follows a workflow including preoperative MRI and intraoperative frame-based CT. The intraoperative transport of the anesthetized and intubated patient to and from the CT unit can be time-consuming and cumbersome. Here, we report the first 50 patients who underwent stereotactic biopsies using the mobile AIRO® intraoperative CT (iCT) scanner. METHODS: A conventional stereotactic frame was mounted to the AIRO® carbon table via carbon adapter. 0°gantry thin-slice iCT was performed. The imaging data were transferred to a conventional stereotaxy working unit. After fusion of the preoperative MRI and AIRO® iCT, the stereotactic system was built based on the iCT, and trajectories were calculated accordingly. RESULTS: The frame-based stereotactic iCT was easy to implement and successfully accomplished in all patients. The MRI/iCT image fusion was feasible in all of the studies. A conclusive histological result was obtained in 46 of the 50 cases included. There was no bleeding complication. Net surgery time was reduced by 38 min, on average. CONCLUSION: We conclude that the AIRO® system is a safe, easy-to-use, and sufficiently accurate iCT for CT frame-based stereotactic biopsy planning that results in a considerable reduction of surgery time. In the future, it remains to be evaluated if the accuracy rates and intraoperative workflow will permit its application in deep brain stimulation and other functional procedures as well.

A Comparative Study of Fiducial-Based and Fiducial-Less Registration Utilizing the O-Arm.

BACKGROUND: Frameless stereotactic surgery utilizing fiducial-based (FB) registration is an established tool in the armamentarium of deep brain stimulation (DBS) surgeons. Fiducial-less (FL) registration via intraoperative CT, such as the O-arm, has been routinely used in spine surgery, but its accuracy for DBS surgery has not been studied in a clinical setting. OBJECTIVE: We undertook a study to analyze the accuracy of the FL technique in DBS surgery and compare it to the FB method. METHODS: In this prospective cohort study, 97 patients underwent DBS surgery using the NexFrame and the O-arm registration stereotactic system. Patients underwent FB (n = 50) registration from 2015 to 2016 and FL (n = 47) O-arm registration from 2016 to 2017. RESULTS: The radial errors (RE) and vector/euclidean errors of FB and FL registration were not significantly different. There was no difference in additional passes between methods, but there was an increase in the number of RE ≥2.5 mm in the FL method. CONCLUSION: Although there was no statistically significant difference in RE or the need for additional passes, the increased number of errors ≥2.5 mm with the FL method (17 vs. 4% in FB) indicates the need for further study. We concluded that O-arm images of the implants should be utilized to assess and correct for this error.

Targeting inaccuracy caused by mechanical distortion of the Leksell stereotactic frame during fixation.

BACKGROUND: The stereotactic frame represents the mainstay of accuracy for targeting in stereotactic procedures. Any distortion of the frame may induce a significant source of error for the stereotactic coordinates. OBJECTIVE: To analyze the sources of distortion of the Leksell frame G induced by fixation to the patient's head and to evaluate the clinical impact of frame distortion on the accuracy of targeting in stereotactic procedures. METHODS: We analyzed the torques exerted on the fixation screws after frame placement in a series of patients treated stereotactically by an experienced team. We studied the risk for frame bending in an experimental model of stereotactic frame fixation, with increasing torque of fixation screws in a homogeneous and heterogeneous distribution of torques between the four screws. We assessed the impact of expanding dimensions of bending of the Leksell frame both on surgeries utilizing the stereotactic frame, and on radiosurgical procedures with the Gamma Knife. RESULTS: Frames were fixed clinically at a range of torques of 0.147-0.522 Nm (mean = 0.348 Nm). The torques did not vary significantly with time. Heterogeneity between the two opposite pairs of screws is often limited, but can reach 96.3%. Distortion of the frame may occur even at minimal levels of torque. Heterogeneity between the two opposite pairs of screws will significantly raise the amount of frame distortion. We found a direct correlation between measures of the frame distortion and extend of the deviation from the stereotactic target in clinical models of stereotactic procedures. CONCLUSION: Stereotactic frames were subjected to distortion due to the torque used for frame fixation. The risk of distortion increased with the torque used and the heterogeneity between the torques of the fixation screws. Distortion of the frame was a significant source of inaccuracy of targeting for stereotactic procedures in clinical practice.

Comparative Study of Robot-Assisted versus Conventional Frame-Based Deep Brain Stimulation Stereotactic Neurosurgery.

BACKGROUND/AIMS: Technological advancements had a serious impact on the evolution of robotic systems in stereotactic neurosurgery over the last three decades and may turn robot-assisted stereotactic neurosurgery into a sophisticated alternative to purely mechanical guiding devices. OBJECTIVES: To compare robot-assisted and conventional frame-based deep brain stimulation (DBS) surgery with regard to accuracy, precision, reliability, duration of surgery, intraoperative imaging quality, safety and maintenance using a standardized setup. METHODS: Retrospective evaluation of 80 consecutive patients was performed who underwent DBS surgery using either a frame-based mechanical stereotactic guiding device (n = 40) or a stereotactic robot (ROSA Brain, MedTech, Montpellier, France) (n = 40). RESULTS: The mean accuracy of robot-assisted and conventional lead implantation was 0.76 mm (SD: 0.37 mm, range: 0.17-1.52 mm) and 1.11 mm (SD: 0.59 mm, range: 0.10-2.90 mm), respectively. We observed a statistically significant difference in accuracy (p < 0.001) when comparing lateral deviations between both modalities. Furthermore, a statistical significance was observed when investigating the proportion of values exceeding 2.00 mm between both groups (p = 0.013). In 8.75% (n = 7) of conventionally implanted leads, lateral deviations were greater than 2.0 mm. With a maximum value of 1.52 mm, this threshold was never reached during robot-guided DBS. The mean duration of DBS surgery could be reduced significantly (p < 0.001) when comparing robot-guided DBS (mean: 325.1 ± 81.6 min) to conventional lead implantation (mean: 394.8 ± 66.6 min). CONCLUSIONS: Robot-assisted DBS was shown to be superior to conventional lead implantation with respect to accuracy, precision and operation time. Improved quality control, continuous intraoperative monitoring and less manual adjustment likely contribute to the robotic system's reliability allowing high accuracy during lead implantation despite limited experience. Hence, robot-assisted lead implantation can be considered an appropriate and reliable alternative to purely mechanical devices.

Localization of Deep Brain Stimulation Electrode by Image Registration Is Software Dependent: A Comparative Study between Four Widely Used Software Programs.

BACKGROUND: The control of the anatomic position of the active contacts is essential to understand the effects and adapt the settings of the neurostimulation. The localization is commonly assessed by a registration between the preoperative MRI and the postoperative CT scan. However, its accuracy depends on the quality of the registration algorithm and many software programs are available. OBJECTIVE: To compare the localization of implanted deep brain stimulation (DBS) leads in the subthalamic nucleus (STN) between four registration devices. METHODS: The preoperative stereotactic MRI was co-registered and fused with the 3-month postoperative CT scan in 27 patients implanted in the STN for Parkinson's disease (53 leads). Localizations of the active contacts were calculated in the stereotactic frame space and compared between software programs. RESULTS: The coordinates of the active contacts were different between software programs in the 3 axes (p < 0.001) with a mean vectorial error between the deepest contact locations of 1.17 mm (95% CI 1.09-1.25). CONCLUSION: We found a small but significant difference in the coordinates calculated on four different devices. These results have to be considered when performing studies comparing active contact locations or when following patients with an implanted DBS lead.

Method to perform safety stereotactic procedures in children under 2 years of age.

INTRODUCTION: Stereotactic procedures have been used in neurosurgery for many years. In children especially, care should be considered to avoid complication caused by fixation of the frame in a not fully developed skull bone. We present our method to adapt the frame in children under 2 years of age. METHODS: Twelve procedures in patients under 24 months were performed between 2003 and 2015. Micromar frame was used. It was adapted with a small pillow made of gauss attached to the posterior part to hold the head, then four pins were fixed without adjustment. We analyze for each patient age, indication, histopathology, and complications. RESULTS: Eleven patients with a mean age of 13.5 months (range 9 to 22 months) underwent 12 stereotactic procedures. In all cases, biopsy samples were obtained, histopathology was positive in 11/12 cases. No complications occurred. CONCLUSION: Stereotactic frame procedures need special attention in small children where the skull bones are not fully developed. We present a simple method to perform this surgery in patients under 2 years of age.

Frameless robot-assisted stereoelectroencephalography for refractory epilepsy in pediatric patients: accuracy, usefulness, and technical issues.

BACKGROUND: Stereoelectroencephalography (SEEG) is an effective technique to help to locate and to delimit the epileptogenic area and/or to define relationships with functional cortical areas. We intend to describe the surgical technique and verify the accuracy, safety, and effectiveness of robot-assisted SEEG in a newly created SEEG program in a pediatric center. We focus on the technical difficulties encountered at the early stages of this program. METHODS: We prospectively collected SEEG indication, intraoperative events, accuracy calculated by fusion of postoperative CT with preoperative planning, complications, and usefulness of SEEG in terms of answering preimplantation hypothesis. RESULTS: Fourteen patients between the ages of 5 and 18 years old (mean 10 years) with drug-resistant epilepsy were operated on between April 2016 and April 2018. One hundred sixty-four electrodes were implanted in total. The median entry point localization error (EPLE) was 1.57 mm (1-2.25 mm) and the median target point localization error (TPLE) was 1.77 mm (1.2-2.6 mm). We recorded seven intraoperative technical issues. Two patients suffered complications: meningitis without demonstrated germ in one patient and a right frontal hematoma in the other. In all cases, the SEEG was useful for the therapeutic decision-making. CONCLUSION: SEEG has been useful for decision-making in all our pediatric patients. The robotic arm is an accurate tool for the insertion of the deep electrodes. Nevertheless, it is an invasive technique not risk-free and many problems can appear at the beginning of a robotic arm-assisted SEEG program that must be taken into account beforehand.

Intraoperative visualisation of functional structures facilitates safe frameless stereotactic biopsy in the motor eloquent regions of the brain.

BACKGROUND: For stereotactic brain biopsy involving motor eloquent regions, the surgical objective is to enhance diagnostic yield and preserve neurological function. To achieve this aim, we implemented functional neuro-navigation and intraoperative magnetic resonance imaging (iMRI) into the biopsy procedure. The impact of this integrated technique on the surgical outcome and postoperative neurological function was investigated and evaluated. METHOD: Thirty nine patients with lesions involving motor eloquent structures underwent frameless stereotactic biopsy assisted by functional neuro-navigation and iMRI. Intraoperative visualisation was realised by integrating anatomical and functional information into a navigation framework to improve biopsy trajectories and preserve eloquent structures. iMRI was conducted to guarantee the biopsy accuracy and detect intraoperative complications. The perioperative change of motor function and biopsy error before and after iMRI were recorded, and the role of functional information in trajectory selection and the relationship between the distance from sampling site to nearby eloquent structures and the neurological deterioration were further analyzed. RESULTS: Functional neuro-navigation helped modify the original trajectories and sampling sites in 35.90% (16/39) of cases to avoid the damage of eloquent structures. Even though all the lesions were high-risk of causing neurological deficits, no significant difference was found between preoperative and postoperative muscle strength. After data analysis, 3mm was supposed to be the safe distance for avoiding transient neurological deterioration. During surgery, the use of iMRI significantly reduced the biopsy errors (p = 0.042) and potentially increased the diagnostic yield from 84.62% (33/39) to 94.87% (37/39). Moreover, iMRI detected intraoperative haemorrhage in 5.13% (2/39) of patients, all of them benefited from the intraoperative strategies based on iMRI findings. CONCLUSIONS: Intraoperative visualisation of functional structures could be a feasible, safe and effective technique. Combined with intraoperative high-field MRI, it contributed to enhance the biopsy accuracy and lower neurological complications in stereotactic brain biopsy involving motor eloquent areas.

Transsphenoidal surgery: accuracy of an image-guided neuronavigation system to approach the pituitary fossa (sella turcica).

OBJECTIVE: To determine the accuracy of locating the pituitary fossa with the Brainsight neuronavigation system by determining the mean target error of the rostral (tuberculum sellae) and caudal (dorsum sellae) margins of the pituitary fossa. STUDY DESIGN: Experimental cadaveric study. ANIMALS: Ten canine cadavers. METHODS: Computed tomography (CT) and MRI were performed on each cadaver with fiducials in place. Images were saved to the neuronavigation computer and used to plan the drilling approach. The cadavers were placed in the surgical head clamp of the Brainsight system and positioned for a transsphenoidal approach. On the basis of the planning, 2 localization points were drilled, 1 each at the rostral and caudal margins of the pituitary fossa, and CT was repeated. Error was assessed from the difference in millimeters between the targets identified during Brainsight planning and the actual location of the 2 points drilled on each cadaver skull as identified by postdrilling CT. RESULTS: The rostral and caudal margins of the pituitary fossa provided 2 target points per cadaver. The median target error (interquartile range) for all target sites (n = 20) was 3.533 mm (range, 2.013-4.745). CONCLUSION: This stereotactic system allowed the surgeon to locate the rostral and caudal margins of the pituitary fossa with clinically acceptable accuracy and confidence. CLINICAL SIGNIFICANCE: Using the Brainsight neuronavigation system for localization during transsphenoidal hypophysectomy may decrease morbidity and surgical time.