Compromised Accuracy of Stereotactic Target Delineation Associated with Computed Tomography-Based Frame Registration: A Comparative Analysis of Magnetic Resonance Imaging-Computed Tomography Fusion

INTRODUCTION

Recent advancements in stereotactic neurosurgical techniques have become increasingly reliant on image-based target planning. We devised a case-phantom comparative analysis to evaluate the target registration errors arising during the magnetic resonance imaging (MRI)-computed tomography (CT) image fusion process.

METHODS

For subjects whose preoperative MRI and CT images both contained fiducial frame localizers, we investigated discrepancies in target coordinates derived from frame registration based on either MRI or CT. We generated a phantom target through an image fusion process, merging the framed CT images with their corresponding reference MRIs after masking their fiducial indicators. This phantom target was then compared with the original during each instance of target planning.

RESULTS

In our investigative study with 26 frame registrations, a systematic error in the y-axis was observed as -0.89 ± 0.42 mm across cases using either conventional CT and/or cone-beam CT (O-arm). For the z-axis, errors varied on a case-by-case basis, recording at +0.64 ± 1.09 mm with a predominant occurrence in those merged with cone-beam CT. Collectively, these errors resulted in an average Euclidean error of 1.33 ± 0.93 mm.

CONCLUSION

Our findings suggest that the accuracy of frame-based stereotactic planning is potentially compromised during MRI-CT fusion process. Practitioners should recognize this issue, underscoring a pressing need for strategies and advancements to optimize the process.

Robot-assisted transcerebellar stereotactic approach to the posterior fossa in pediatric patients: a technical note

PURPOSE

During the last decade, there has been renewed interest in stereotactic approaches to diffuse intrinsic pontine gliomas (DIPGs) in children, due to the development of new concepts in molecular biology and management, and subsequent need for tissue sampling. Stereotactic frame-based and robot-assisted techniques are associated with reduced target error and have been incorporated into standard practice at our institution.

METHODS

Four children (age 2-7 years) underwent a robot-assisted frame-based transcerebellar approach using the Leksell G frame coupled with Renishaw's neuromate® stereotactic robot. The procedures included 3 biopsies (two brainstem tumors and one cerebellar hemispheric lesion) and 1 depth electrode implantation into a low-grade tumor remnant (ganglioglioma) of the middle cerebellar peduncle causing drug-resistant epilepsy in a young girl. Targeting was based on MRI, and in one case, 18F-FET-PET was coregistered to MRI to improve sampling accuracy. The frame was applied 180° rotated compared to standard orientation, and patients were positioned prone during surgery and stereotactic preoperative CT scan. Postoperative CT scan ruled out complications and was coregistered to preoperative MRI to check the target accuracy.

RESULTS

No complications occurred, and targeting was accurate in all cases. All tissue samplings provided proper histology; depth electrode EEG exploration was diagnostic and led subsequent resective surgery.

CONCLUSIONS

According to our experience, the transcerebellar frame-based robotic stereotactic approach to the cerebellum and the brainstem is feasible, safe, and effective even in young children.

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.

Intraoperative Stereotactic Frame Registration Using a Three-Dimensional Imaging System with and without Preoperative Computed Tomography for Image Fusion

BACKGROUND

The O-arm O2 imaging system (OAO2) is an intraoperative cone beam 3D tomogram imaging tool with a wide enough field of view to perform intraoperative fiducial registration with standard stereotactic frames. However, the OAO2 3D images (cone beam CT) provide limited tissue contrast, which may reduce the accuracy of fusion to a preoperative targeting MRI for planning awake deep brain stimulation (DBS) surgeries. Therefore, most users obtain a preoperative CT scan to use as the reference exam for computational fusion with the preoperative targeting MRI and the intraoperative OAO2 cone beam CT.

OBJECTIVE

In this study, we retrospectively analyzed the discrepancy between stereotactic coordinates of deep brain targets on MRI derived from intraoperative OAO2 fiducial registration with and without the use of preoperative CT as the reference for image fusion.

METHODS

Preoperative stereotactic CT/MRI and intraoperative OAO2 cone beam CT were retrospectively evaluated for 27 consecutive DBS patients, using two commercial surgical planning software packages (BrainLab Elements and Medtronic Stealth 8). The anterior commissure, posterior commissure, and left subthalamic nucleus were identified on preoperative MRI. Each patient had intraoperative fiducial registration using the OAO2 with a Leksell headframe. For each subject, the reference scan for image fusion was set as either the preoperative CT or the preoperative MRI (volumetric T1 with contrast). Computed stereotactic coordinates for each target were then compared.

RESULTS

For 8 of 27 subjects, a discrepancy greater than 1.0 mm for at least one designated target was observed utilizing the Medtronic Stealth S8 planning station when a preoperative CT scan was not used. An additional 5 (5/27) had a discrepancy greater than 2 mm. The most common discrepancy was in the z axis. No coordinate discrepancies greater than 1 mm were observed utilizing BrainLab Elements.

CONCLUSIONS

Caution is advised in fusing intraoperative OAO2 images directly to preoperative MRI without a preoperative CT as the reference exam for image fusion, as the specific fusion algorithm employed may unpredictably affect targeting accuracy.

Evaluation of Patient Perspectives Toward Awake, Frame-Based Deep-Brain Stimulation Surgery

BACKGROUND

Deep brain stimulation (DBS) is an effective therapeutic modality; however, only a percentage of eligible patients undergo the procedure.

OBJECTIVES

To study patients' perspectives toward DBS surgery.

METHODS

A survey was sent to 95 consecutive adult patients who underwent DBS surgery for Parkinson disease, essential tremor, or dystonia; the response rate was 73% (69 patients). Post-hoc analyses were performed to evaluate factors that led to favorable outcomes. The average time between surgical procedure to survey completion was 16 months.

RESULTS

Awake surgery, use of a rigid head frame, and having hair clipped were seldom reported as major deterrents to surgery. Patients retrospectively reported an average comfort level of 8.3 ± 1.8 during surgery. The average comfort level with head frame placement was reported as 5.2 ± 3.15, and patients reporting discomfort with the frame nonetheless reported overall comfort with the procedure (8.7 ± 1.8). An analysis of satisfaction revealed that 90% of patients would recommend the procedure to a family member or friend and that 78% of patients would undergo the procedure again. A post-hoc analysis of patients who were not satisfied with the procedure revealed that this subset reported significantly less overall comfort (6.9 ± 1.7, P = 0.0003) and were less likely to report that the goals and expectations of surgery were clearly discussed before surgery (P = 0.0004).

CONCLUSIONS

Frame placement, awake surgery, and head shaving did not appear to play a significant role in most patients' decision-making process to undergo DBS, as analyzed in this retrospective cohort. The majority of patients were satisfied with the procedure and reported being comfortable. Managing goals and expectations preoperatively played a significant role in ultimate overall satisfaction.

Accuracy of VarioGuide Frameless Stereotactic System Against Frame-Based Stereotaxy: Prospective, Randomized, Single-Center Study

INTRODUCTION

Frameless stereotactic brain biopsy systems are widely used today. VarioGuide (VG) is a relatively novel frameless system. Its accuracy was studied in a laboratory setting but has not yet been studied in the clinical setting. The purpose of this study was to determine its accuracy and diagnostic yield and to compare this with frame-based (FB) stereotaxy.

MATERIAL AND METHODS

Overall, 53 patients (33 males and 20 females, 60 ± 15 years old) were enrolled into this prospective, randomized, single-center study. Twenty-six patients were randomized into the FB group and 27 patients into the VG group. Real trajectory was pointed on intraoperative magnetic resonance. The distance of the targets and angle deviation between the planned and real trajectories were computed. The overall discomfort of the patient was subjectively assessed by the visual analog scale score.

RESULTS

The median lesion volume was 5 mL (interquartile range [IQR]: 2-16 mL) (FB) and 16 mL (IQR: 2-27 mL) (VG), P = 0.133. The mean distance of the targets was 2.7 ± 1.1 mm (FB) and 2.9 ± 1.3 mm (VG), P = 0.456. Mean angle deviation was 2.6 ± 1.3 deg (FB) and 3.5 ± 2.1 deg (VG), P = 0.074. Diagnostic yield was 93% (25/27) in VG and 96% (25/26) in FB, P = 1.000. Mean operating time was 47 ± 26 minutes (FB) and 59 ± 31 minutes (VG), P = 0.140. One minor bleeding was encountered in the VG group. Overall patient discomfort was significantly higher in the FB group (visual analog scale score 2.5 ± 2.1 vs. 1.2 ± 0.6, P = 0,004).

CONCLUSIONS

The VG system proved to be comparable in terms of the trajectory accuracy, rate of complications and diagnostic yield compared with the "gold standard" represented by the traditional FB stereotaxy for patients undergoing brain biopsy. VG is also better accepted by patients.

Frame-based stereotactic neurosurgery in children under the age of seven: Freiburg University's experience from 99 consecutive cases

INTRODUCTION

Stereotactic frame-based procedures proved to be precise, safe and are of widespread use among adult patients. Regarding pediatric patients few data is available, therefore the use of the stereotactic frame remains controversial in this population. This motivated us to report our experience in stereotactic procedures in the youngest patients and review the literature concerning this subject.

METHODS

All frame-based procedures performed in patients younger than seven years in the University of Freiburg during the last 10 years were retrospectively analyzed and discussed under the light of the current literature.

RESULTS

The studied population was composed of 72 patients under the age of seven (mean 3.4±2.1 years-old), in whom 99 stereotactic procedures were performed. Brain tumor was present in 60 patients, hydrocephalus in five, cystic lesions in three, intracranial abscess in three and epilepsy in one patient. Stereotactic surgery was performed in 36 cases for brachytherapy, in 29 for biopsy, in 20 cases for cyst puncture, in eight for stereotactically guided endoscopic ventriculostomy, in five for catheter placement and in one case for depth electrode insertion. The overall complication rate was 5%. There were three cases of pin penetration through the skull, one case of frame dislocation after extensive cyst drainage and two skull fractures. Neurologic deficit related to frame fixation was observed in none of the cases. In disagreement with other authors, no case of pin related infection, air embolism, hematoma or CSF leak was observed.

CONCLUSION

Frame-based stereotactic neurosurgery is a safe technique also in the youngest patients. Rather than the simple use of torque-limiting devices training and experience in the manual adjustment of the stereotactic frame in children have been proven to be crucial factors that contribute to reducing pin related complications.