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.

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.

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.

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 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.

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.

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.

Frameless Functional Stereotactic Approaches

The stereotactic frame has served as the gold standard apparatus for accurate and precise targeting of deep brain structures since 1947. Despite passing the test of time, the stereotactic frame has several limitations from the perspective of both neurosurgeons and patients. Therefore, there was a need to develop a frameless system that had equivalent accuracy and reliability to the frame. This need was met with 3 commercially available frameless stereotactic systems designed specifically for deep brain stimulation surgery: Nexframe, STarFix, and ClearPoint. Over the past decade, the frameless and frame-based systems have been extensively investigated by numerous studies and found to be equivalent in experimental and clinical accuracy as well as in clinical outcomes. This chapter summarizes the findings of those studies along with the discussion of sources of stereotactic errors. The procedural aspects, advantages, and disadvantages of each frameless system are reviewed. Frameless stereotaxy is a safe, accurate, and effective technique for functional stereotactic approaches and provides a viable alternative to the frame-based systems.

Merits and Limits of Tractography Techniques for the Uninitiated

The implementation of fiber tracking or tractography modules in commercial navigation systems resulted in a broad availability of visualization possibilities for major white matter tracts in the neurosurgical community. Unfortunately the implemented algorithms and tracking approaches do not represent the state of the art of tractography strategies and may lead to false tracking results. The application of advanced tractography techniques for neurosurgical procedures poses even additional challenges that relate to effects of the individual anatomy that might be altered by edema and tumor, to stereotactic inaccuracies due to image distortion, as well as to registration inaccuracies and brain shift.

Linear array ultrasound in low-grade glioma surgery: histology-based assessment of accuracy in comparison to conventional intraoperative ultrasound and intraoperative MRI

INTRODUCTION

In low-grade glioma (LGG) surgery, intraoperative differentiation between tumor and most likely tumor-free brain tissue can be challenging. Intraoperative ultrasound can facilitate tumor resection. The aim of this study is to evaluate the accuracy of linear array ultrasound in comparison to conventional intraoperative ultrasound (cioUS) and intraoperative high-field MRI (iMRI).

METHODS

We prospectively enrolled 13 patients harboring a LGG of WHO Grade II. After assumed near total removal, a resection control was performed using navigated cioUS, navigated lioUS, and iMRI. We harvested 30 navigated biopsies from the resection cavity and compared the histopathological findings with the respective imaging results. Spearman's rho was calculated to test for significant correlations. Sensitivity and specificity as well as receiver operating characteristics (ROC) were calculated to assess test performance of each imaging modality.

RESULTS

Imaging results of lioUS correlated significantly (p < 0.009) with iMRI. Both iMRI and lioUS correlated significantly with final histopathological diagnosis (p < 0.006, p < 0.014). cioUS did not correlate with other imaging findings or with final diagnosis. The highest sensitivity for residual tumor detection was found in iMRI (83 %), followed by lioUS (79 %). The sensitivity of cioUS was only 21 %. Specificity was highest in cioUS (100 %), whereas iMRI and lioUS both achieved 67 %. ROC curves showed fair results for iMRI and lioUS and a poor result for cioUS.

CONCLUSIONS

Intraoperative resection control in LGGs using lioUS reaches a degree of accuracy close to iMRI. Test results of lioUS are superior to cioUS. cioUS often fails to discriminate solid tumors from "normal" brain tissue during resection control. Only in lesions <10 cc cioUS does show good accuracy.

Endoscopic lateral orbitotomy

Background

Lateral orbitotomy can be minimalized using contemporary endoscopy.

Methods

Anatomy of the temporal fossa/orbital wall junction is described. The attachment of the temporal fascia is cut off from the orbital rim through a 1.5 cm skin incision in the lateral orbital wrinkle. The temporal muscle is detached from the bone to create a space for the telescope. An appropriate bone opening in the lateral orbital wall is created with the aid of neuronavigation to handle intraorbital pathology.

Conclusion

Endoscopic lateral orbitotomy is an original alternative to the microsurgical Krönlein approach and yields good functional and cosmetic results.

Electronic supplementary material

The online version of this article (doi:10.1007/s00701-014-2205-7) contains supplementary material, which is available to authorized users.

Transcranial sonography (TCS) of brain parenchyma in movement disorders: quality standards, diagnostic applications and novel technologies

Transcranial B-mode sonography (TCS) of brain parenchyma is being increasingly used as a diagnostic tool in movement disorders. Compared to other neuroimaging modalities such as magnetic resonance imaging (MRI) and computed tomography, TCS can be performed today with portable machines and has the advantages of noninvasiveness and high resistance to movement artifacts. In distinct brain disorders TCS detects abnormalities that cannot be visualized or can only be visualized with significant effort with other imaging methods. In the field of movement disorders, TCS has been established mainly as a tool for the early and differential diagnosis of Parkinson's disease. The postoperative position control of deep brain stimulation electrodes, especially in the subthalamic nucleus, can reliably and safely be performed with TCS.  The present update review summarizes the current methodological standards and defines quality criteria of adequate TCS imaging and assessment of diagnostically relevant deep brain structures such as substantia nigra, brainstem raphe, basal ganglia and ventricles. Finally, an overview is given on recent technological advances including TCS-MRI fusion imaging and upcoming technologies of digitized image analysis aiming at a more investigator-independent assessment of deep brain structures on TCS.

Is MRI a reliable tool to locate the electrode after deep brain stimulation surgery? Comparison study of CT and MRI for the localization of electrodes after DBS

PURPOSE

MRI has been utilized to localize the electrode after deep brain stimulation, but its accuracy has been questioned due to image distortion. Under the hypothesis that MRI is not adequate for evaluation of electrode position after deep brain stimulation, this study is aimed at validating the accuracy of MRI in electrode localization in comparison with CT scan.

METHODS

Sixty one patients who had undergone STN DBS were enrolled for the analysis. Using mutual information technique, CT and MRI taken at 6 months after the operation were fused. The x and y coordinates of the centers of electrodes shown of CT and MRI were compared in the fused images to calculate average difference at five different levels. The difference of the tips of the electrodes, designated as the z coordinate, was also calculated.

RESULTS

The average of the distance between the centers of the electrodes in the five levels estimated in the fused image of brain CT and MRI taken at least 6 months after STN DBS was 1.33 mm (0.1-5.8 mm). The average discrepancy of x coordinates for all five levels between MRI and CT was 0.56 ± 0.54 mm (0-5.7 mm), the discrepancy of y coordinates was 1.06 ± 0.59 mm (0-3.5 mm), and for the z coordinate, it was 0.98 ± 0.52 mm (0-3.1 mm) (all p values < 0.001). Notably, the average discrepancy of x coordinates at 3.5 mm below AC-PC level, i.e., at the STN level between MRI and CT, was 0.59 ± 0.42 mm (0-2.4 mm); the discrepancy of y coordinates was 0.81 ± 0.47 mm (0-2.9 mm) (p values < 0.001).

CONCLUSIONS

The results suggest that there was significant discrepancy between the centers of electrodes estimated by CT and MRI after STN DBS surgery.

The peripeduncular nucleus: a novel target for deep brain stimulation?

The pedunculopontine nucleus, a promising new target for deep brain stimulation in Parkinson's disease, straddles the pontomesencephalic junction--unfamiliar territory to most functional neurosurgeons. This contribution reviews the anatomy of the pedunculopontine and peripeduncular nuclei. Given the reported findings of Mazzone et al. in NeuroReport, the authors postulate that the peripeduncular nucleus might be of previously unexpected clinical relevance.

Image-Guided Microneurosurgical Management of Small Arteriovenous Malformation: Role of Neuronavigation and Intraoperative Doppler Sonography

INTRODUCTION

The goal of this study was to evaluate the efficacy and reliability of neuronavigation and intraoperative microvascular Doppler sonography (MDS) for identifying afferent (feeding) and efferent (draining) vessels as well as for controlling the totality of the surgical resection of arteriovenous malformations (AVMs).

METHODS

Between June 2000 and November 2005, twenty-five patients with small arteriovenous malformations (grades I-III) underwent microsurgical removal at our institution. A passive-marker-based neuronavigation system (Brain Lab, Munich, Germany), and an intraoperative MDS (Multi Dop X system, DWL, Germany) were used in this surgery. Blood flow velocities (BFV) in afferent and efferent vessels were recorded before and after removal of AVM. The preoperative neurological status and postoperative outcome were recorded. Patient follow-up monitoring ranged from 4 months to 3 years (mean: 16 months).

RESULTS

The calculated registration accuracy of the neuronavigation computer ranged between 0.2-1.7 mm (mean: 1.1 mm). Before AVM removal the mean BFV of afferent vessels was 56.5+/-13.4 (28-98 cm/s) and the PI varied by 0.40+/-0.11 (0.25-0.66), after AVM removal these values reduced to 4.8+/-0.8 cm/s and 0.26+/-0.05, respectively. Similarly, before AVM removal, the mean BFV of efferent vessels was 13.5+/-4.5 (4-20 cm/s) and PI was 0.4+/-0.2 (0.34-0.56), after AVM removal both BFV and PI were not recorded. Complete removal of the AVMs was accomplished in 24 (96%) out of 25 patients which was confirmed with postoperative digital subtraction angiography (DSA). While there was no mortality, three patients (12%) had a worsening in their neurological status after surgery.

CONCLUSION

Image-guided microneurosurgery with intraoperative MDS is a safe, effective, and reliable method for identifying the afferent and efferent vessels and for confirming the complete resection of AVMs. These benefits of image-guided microsurgery were most apparent for small, deep-seated AVMs that were not visible on the surface of the brain. In addition these techniques reduce the operative time and blood loss during AVM resection.

Comparison of Accuracy and Precision between Frame-Based and Frameless Stereotactic Navigation for Deep Brain Stimulation Electrode Implantation

The accuracy and precision of frameless neuronavigation as compared to conventional frame-based stereotaxy for implantation of deep brain stimulation (DBS) electrodes were studied in 14 patients with essential tremor. DBS electrodes were implanted bilaterally in the ventrolateral thalamus [ventrointermediate nucleus (VIM)] in one procedure. Frameless neuronavigation was used on one side and the conventional frame-based technique on the other. Targeting was guided by MRI and CT imaging. Intraoperative stereotactic plain X-ray verified final electrode positions and electrode deviations from the planned target were measured. Clinical outcome was evaluated with the Essential Tremor Rating Scale. Thirteen of the patients were eligible for measuring electrode deviations and 10 of them were available for a clinical follow-up. Electrode deviations from target were larger using the frameless technique in the medial-lateral (x: 1.9 +/- 1.3 mm) and anterior-posterior (y:0.9 +/- 0.8 mm) directions as compared to the frame-based technique (x: 0.5 +/- 0.5 and y: 0.4 +/- 0.4 mm) but similar in the superior-inferior direction (z). The vector of deviation was 2.5 +/- 1.4 mm with the frameless technique and 1.2 +/- 0.6 with the frame-based technique. The differences were statistically significant (p < 0.05-0.001). The dispersion was larger with the frameless technique as represented by the larger standard deviations in all three planes. At clinical follow-ups, tremor reduction was similar irrespective of the implantation technique. It is concluded that conventional frame-based stereotaxy has higher accuracy/precision for hitting a small brain target than the frameless technique. However, the difference is relatively small and does not influence the clinical result of DBS electrode implantations in the VIM when treating tremor.

Using the Magnetic Resonance Three-Dimensional Volume Rendering for Tissues Technique in the Planning of Craniotomy Flaps with Linear Scalp Incision

Preoperative three-dimensional images with surface venous anatomy may be used in the planning of a linear scalp incision and the opening site of the dura mater for protection of surface veins during surgical dissection, and to find the splitting site of the brain according to the lesion. In 45 patients who had a brain tumor, linear scalp incision planning was done by regarding the three-dimensional images derived from post-contrast time-of-flight (TOF) sequence raw data. The findings of correspondence and the quality of routine contrast-enhanced magnetic resonance imaging (MRI) and three-dimensional volume rendering for tissues (VRT) images were analyzed separately with the surgical findings according to a visual grading system. Our experience revealed that the surgical findings correlated well with the three-dimensional VRT images. According to a visual surgical grading system, a grade III correlation was found in 20 (45%), grade II in 15 (33%), grade I in 7 (15%), and grade 0 in 3 (7%) patients in our study population. At the end of our research we conclude that this method is useful in terms of the preoperative determination of brain surface anatomy and may be used in the determination of the site of a linear scalp incision according to the localization of an intracranial lesion.

Frameless stereotactic subcaudate tractotomy for intractable obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic, disabling disorder. Psychosurgery may be indicated for a subset of patients for whom no conventional treatment is satisfactory. This paper focuses on the stereotactic subcaudate tractotomy (SST). Thus far, these procedures have been carried out using frame-based stereotactic techniques. However, modern - highly accurate - frameless stereotactic procedures have successfully been introduced in neurosurgical practice. We developed a novel frameless stereotactic subcaudate tractotomy procedure with promising initial results in a patient suffering from intractable OCD. This is the first report on frameless SST. Future studies should examine whether other ablative stereotactic psychosurgery procedures can be done using frameless stereotactic methods.

Intra-operative 3D ultrasound in neurosurgery

In recent years there has been a considerable improvement in the quality of ultrasound (US) imaging. The integration of 3D US with neuronavigation technology has created an efficient and inexpensive tool for intra-operative imaging in neurosurgery. In this review we present the technological background and an overview of the wide range of different applications. The technology has so far mostly been applied to improve surgery of tumours in brain tissue, but it has also been found to be useful in other procedures such as operations for cavernous haemangiomas, skull base tumours, syringomyelia, medulla tumours, aneurysms, AVMs and endoscopy guidance.

Frameless stereotactic placement of depth electrodes in epilepsy surgery

Object. Depth electrodes are useful in the identification of deep epileptogenic foci. Computerized tomography—magnetic resonance (CT/MR)— and angiography-guided frame-based techniques are safe and accurate but require four-point skull fixation that limits cranial access for the placement of additional grids and strips. The authors investigated the viability and accuracy of placing depth electrodes by using a commercially available frameless system.

Methods. A slotted, custom-designed adapter was built to interface with the StealthStation Guide Frame-DT and 960-525 StealthFighter. The Cranial Navigation software was used to plan the trajectory and entry site based on preoperative spoiled gradient MR imaging studies. Forty-one depth electrodes were placed in 51 targets in 20 patients. Thirty-one of these electrodes were inserted through the temporal neocortex following craniotomy and placement of subdural grids, whereas 10 were placed through burr holes. All electrodes had contact either within (71%) or touching (29%) the target, 50 of which (98%) provided adequate recordings. Although the mean distance of the distal electrode contact from the intended target was 3.1 ± 0.5 mm, the mean distance to the edge of the anatomical structure was 0.4 ± 0.9 mm. Placement via the laterotemporal approach was significantly (p < 0.001) more accurate than that via the occipitotemporal approach. No complication occurred.

Conclusions. Depth electrodes can be placed safely and accurately by using a commercially available frameless stereotactic navigation system and a custom-made adapter. Depth electrode placement to record ictal onsets during epilepsy surgery only requires the contacts to touch rather than to reside within the intended structure. The laterotemporal approach is a more accurate method of placing electrodes than is the occipitotemporal one, likely due to the increased distance from the entry point to the target.

Correlation of factors predicting intraoperative brain shift with successful resection of malignant brain tumors using image-guided techniques

BACKGROUND

Intraoperative brain shift may cause inaccuracy of stereotactic image guidance on the basis of preoperatively acquired imaging data. The purpose of our study was to determine whether factors predicting brain shift affect the success of image-guided resection of malignant brain tumors.

METHODS

We retrospectively studied 54 patients who underwent image-guided resections of histopathologically confirmed malignant brain tumors (9 metastases, 45 high-grade gliomas). Precautions were taken during surgery to minimize brain shift, but intraoperative imaging was not performed. The following factors predictive of intraoperative brain shift were assessed: tumor size, periventricular location, patient age, prior surgery or radiation therapy, patient positioning, use of mannitol, and length of operative time. Postoperative magnetic resonance imaging was obtained in all cases within 48 hours of surgery to assess extent of resection.

RESULTS

Perioperative mortality was 0% in our series; perioperative morbidity was 3 of 54 patients (5.5%); 1 patient required reoperation for a hematoma, and 2 had transient neurological deficits. Successful resection was accomplished in 93% of tumors less than 30 cm(3) compared with 63.6% of tumors greater than 30 cm(3) (P = .026, Fisher exact test). This difference was more pronounced for patients with malignant gliomas. However, other factors predictive of intraoperative brain shift were not associated with unsuccessful resection.

CONCLUSIONS

Intraoperative brain shift does not significantly affect the likelihood of successful resection of malignant brain tumors smaller than 30 cm(3). Larger tumors are less likely to be successfully resected, although factors other than brain shift can contribute to unsuccessful resection.

High precision radiosurgery and technical standards

BACKGROUND

A high degree of precision and accuracy in radiosurgery is a fundamental requirement for therapeutic success. Small radiation fields and steep dose gradients are clinically applied thus necessitating a dedicated quality assurance program in order to guarantee dosimetric and geometric accuracy.

MATERIAL AND METHODS

A detailed analysis of the course of treatment independent of the irradiation technique used results in the so-called chain of uncertainties in radiosurgery (immobilisation, imaging, treatment planning system, definition of regions of interest, mechanical accuracy, dose planning, dose verification). Each link in this chain is analysed for accuracy and the established quality assurance procedures are discussed. A "System Test" was used to check the whole chain of uncertainties simultaneously.

RESULTS

The tests described are compatible with published reports on quality assurance in radiosurgery. In terms of accuracy the weakest link in the chain of uncertainties is stereotactic MR imaging. Geometric overall accuracy measured in the "System Test" is less than 0.7 mm.

CONCLUSION

The established quality assurance routines have clinically been validated. MR imaging dominates geometric overall accuracy in radiosurgery, which can be limited to less than 1 mm by an adequate quality assurance protocol.

From Letterbox to Keyhole Approach for Resecting Intracranial Lesions

BACKGROUND

Computer-assisted neurosurgery systems (CANS) have the ability to translate preoperative image data sets directly to the operating field and were thought to be very useful in neurosurgery. However, key questions regarding their use remain only partially addressed.

METHODS

To answer the doubts of the skeptics, we set up a registry of all CANS and any non-CANS procedures in our institution. The results of 354 procedures are presented in this paper.

RESULTS

CANS was used in 254 procedures, with a mean accuracy of 1.9 mm and a failure rate of 2.8%. Over time, the accuracy improved to 1.6 mm and failures were abolished. The CANS was most useful in anterior skull approaches and took less time in the operating room, and the patients were discharged earlier than those who underwent non-CANS procedures.

CONCLUSION

We feel that the introduction of CANS has changed our practice for the better, with significant benefits to patients, surgeons and the hospital at large, and we recommend its usage as a standard of care.

Semiautomated registration using new markers for assessing the accuracy of a navigation system

OBJECTIVES

New markers are described that can be used for an improved registration procedure and for the exact comparison of navigation systems. The advantages of the markers are demonstrated, together with an automated segmentation algorithm for locating the centroid of the markers in image space. Compared to manual registration, this method shows an improved registration accuracy.

MATERIALS AND METHODS

The new markers are detected completely automatically within all scan images. This allows a semiautomatic registration, as a preregistration is performed via the algorithm. Furthermore, the exact coordinates within one scan slice are now determined with the calculation procedure. The calculated data from the preregistration were matched up with a manual preregistration and some reference data, so as to confirm the quality of this new algorithm. The accuracies of several manual and semiautomatic registrations were also compared.

RESULTS

The average deviation between the coordinates of the algorithm and the reference data (coordinate measuring machine) was 0.3 mm. The standard deviation amounted to 0.131 mm. Comparing several manual registrations with the reference data showed that the middle fiducial registration error (FRE) was between 0.7 and 2 mm. In comparison, the FRE remained constant at around 0.7 mm for the semiautomatic registration procedure.

CONCLUSIONS

The measured results show a significant improvement in the preregistration data using the new markers together with the algorithm. This improvement leads to a reproducible and more accurate registration. The combination of the new marker type with the automated segmentation algorithm minimizes the human error factor, and provides the opportunity to directly compare image-guided and robotic systems.