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Kathrin Machetanz, Florian Grimm, Thomas V. Wuttke, Josua Kegele, Holger Lerche, Marcos Tatagiba, Sabine Rona, Alireza Gharabaghi, Jürgen Honegger, and Georgios Naros

OBJECTIVE

There is an increasing interest in stereo-electroencephalography (SEEG) for invasive evaluation of insular epilepsy. The implantation of insular SEEG electrodes, however, is still challenging due to the anatomical location and complex functional segmentation in both an anteroposterior and ventrodorsal (i.e., superoinferior) direction. While the orthogonal approach (OA) is the shortest trajectory to the insula, it might insufficiently cover these networks. In contrast, the anterior approach (AOA) or posterior oblique approach (POA) has the potential for full insular coverage, with fewer electrodes bearing a risk of being more inaccurate due to the longer trajectory. Here, the authors evaluated the implantation accuracy and the detection of epilepsy-related SEEG activity with AOA and POA insular trajectories.

METHODS

This retrospective study evaluated the accuracy of 220 SEEG electrodes in 27 patients. Twelve patients underwent a stereotactic frame-based procedure (frame group), and 15 patients underwent a frameless robot-assisted surgery (robot group). In total, 55 insular electrodes were implanted using the AOA or POA considering the insular anteroposterior and ventrodorsal functional organization. The entry point error (EPE) and target point error (TPE) were related to the implantation technique (frame vs robot), the length of the trajectory, and the location of the target (insular vs noninsular). Finally, the spatial distribution of epilepsy-related SEEG activity within the insula is described.

RESULTS

There were no significant differences in EPE (mean 0.9 ± 0.6 for the nonsinsular electrodes and 1.1 ± 0.7 mm for the insular electrodes) and TPE (1.5 ± 0.8 and 1.6 ± 0.9 mm, respectively), although the length of trajectories differed significantly (34.1 ± 10.9 and 70.1 ± 9.0 mm, repsectively). There was a significantly larger EPE in the frame group than in the robot group (1.5 ± 0.6 vs 0.7 ± 0.5 mm). However, there was no group difference in the TPE (1.5 ± 0.8 vs 1.6 ± 0.8 mm). Epilepsy-related SEEG activity was detected in 42% (23/55) of the insular electrodes. Spatial distribution of this activity showed a clustering in both anteroposterior and ventrodorsal directions. In purely insular onset cases, subsequent insular lesionectomy resulted in a good seizure outcome.

CONCLUSIONS

The implantation of insular electrodes via the AOA or POA is safe and efficient for SEEG implantation covering both anteroposterior and ventrodorsal functional organization with few electrodes. In this series, there was no decrease in accuracy due to the longer trajectory of insular SEEG electrodes in comparison with noninsular SEEG electrodes. The results of frame-based and robot-assisted implantations were comparable.

Free access

Felipe Branco de Paiva, Brett A. Campbell, Leonardo A. Frizon, Adriana Martin, Andres Maldonado-Naranjo, André G. Machado, and Kenneth B. Baker

OBJECTIVE

Deep brain stimulation (DBS) is an effective therapy for different neurological diseases, despite the lack of comprehension of its mechanism of action. The use of nonhuman primates (NHPs) has been historically important in advancing this field and presents a unique opportunity to uncover the therapeutic mechanisms of DBS, opening the way for optimization of current applications and the development of new ones. To be informative, research using NHPs should make use of appropriate electrode implantation tools. In the present work, the authors report on the feasibility and accuracy of targeting different deep brain regions in NHPs using a commercially available frameless stereotactic system (microTargeting platform).

METHODS

Seven NHPs were implanted with DBS electrodes, either in the subthalamic nucleus or in the cerebellar dentate nucleus. A microTargeting platform was designed for each animal and used to guide implantation of the electrode. Imaging studies were acquired preoperatively for each animal, and were subsequently analyzed by two independent evaluators to estimate the electrode placement error (EPE). The interobserver variability was assessed as well.

RESULTS

The radial and vector components of the EPE were estimated separately. The magnitude of the vector of EPE was 1.29 ± 0.41 mm and the mean radial EPE was 0.96 ± 0.63 mm. The interobserver variability was considered negligible.

CONCLUSIONS

These results reveal the suitability of this commercial system to enhance the surgical insertion of DBS leads in the primate brain, in comparison to rigid traditional frames. Furthermore, our results open up the possibility of performing frameless stereotaxy in primates without the necessity of relying on expensive methods based on intraoperative imaging.

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Michael L. Levy, Joseph C. T. Chen, Arun P. Amar, Shinya Yamada, Koji Togo, Yoshiro Iizuka, and Murwarid Mura Assifi

Modern radiographic techniques have allowed the creation of high-definition planar images that can provide important anatomical as well as physiological data. Planar imaging sets can be reformatted into three-dimensional (3-D) data sets that can then be manipulated to demonstrate important anatomical or gross pathological features. Three-dimensional data sets have been used with success in modern image-guided or frameless stereotactic surgery. Another potential application is so-called "virtual endoscopy" or "scopeless endoscopy," in which a 3-D anatomical data set is reformatted into a volume-rendered image that can then be viewed. By reformatting images in this way, a "surgeon's-eye" view can be obtained, which can aid in presurgical planning and diagnosis. The use of virtual endoscopy has the potential to increase our understanding of the appropriate anatomy and the anatomical relationships most apparent during neurosurgical approaches. In so doing, virtual endoscopy may serve as an important means of planning for therapeutic interventions.

On the other hand, one must always be cognizant of the technical limitations of these studies regardless of the quality of the reconstructed images. Prospective, correlative, clinical studies in which the anatomical advantages of virtual-based endoscopy are evaluated in large cadaver or patient series must be performed. Until then, the only potential ways to compensate for errors that exist in the algorithms and reconstructions of 3-D endoscopic images are based on the surgeon's understanding of the clinical state of the patient and prior experience with the anatomy in the region of question.

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Alon Y. Mogilner and Ali R. Rezai

Chronic epidural motor cortex stimulation (MCS) has been shown to have promise in the treatment of patients with refractory deafferentation pain. Precise placement of the electrode over the motor cortex region corresponding to the area of pain is essential for the success of this procedure. Whereas standard anatomical landmarks have been used in the past in conjunction with image guidance, the use of functional brain imaging can be beneficial in the precise surgical planning. The authors report the use of functional imaging–guided frameless stereotactic surgery for epidural MCS. Five patients underwent MCS in which functional imaging guidance was used. Prior to surgery, patients underwent magnetic resonance (MR) imaging with skin fiducial markers placed on standard anatomical reference prints, followed by magnetoencephalography (MEG) mapping of the sensory and motor cortices. In two patients, functional MR imaging was also performed using a motor task paradigm. The functional imaging data were integrated into a frameless stereotactic database by using a three-dimensional coregistration algorithm. Subsequently, a frameless stereotactic craniotomy was performed using the integrated anatomical and functional imaging data for surgical planning. Intraoperative somatosensory evoked potentials (SSEPs) and direct stimulation were used to confirm the target and final placement of the electrode.

Direct stimulation and SSEPs performed intraoperatively confirmed the accuracy of the functional imaging data. Trial periods of stimulation successfully reduced pain in three of the five patients who then underwent permanent internal placement of the system. At a mean 6-month follow up, these patients reported an average reduction in pain of 55% on a visual analog scale. The integration of functional and anatomical imaging data allows for precise and efficient surgical planning and may reduce the time necessary for intraoperative physiological verification.

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Robert A. Ratcheson

a collegial spirit, he was able to develop interdisciplinary programs and became a respected leader at the medical school. He served twice as interim dean and was offered the post on a permanent basis. After his retirement from Utah in 2000, he joined the faculty at Stanford University and worked to advance the field of frameless stereotactic surgery. In 2010, a lectureship and chair were endowed in his honor at the University of Utah. Peter was an active member of the Congress of Neurological Surgeons, the American Association of Neurological Surgeons, the

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Reto J. Bale, Johannes Burtscher, Wilhelm Eisner, Alois A. Obwegeser, Michael Rieger, Reinhart A. Sweeney, Andreas Dessl, Salvatore M. Giacomuzzi, Klaus Twerdy, and Werner Jaschke

obtained to spare the patient from undergoing additional imaging. Once the mouthpiece has been made, all different imaging procedures, including CT, MR, PET, and SPECT studies, may be obtained while the mouthpiece and appropriate markers are in place. Following imaging, treatments including frameless stereotactic surgery, frameless stereotactic brachytherapy, and fractionated external-beam radiation therapy may be precisely performed using this device without requiring additional imaging ( Fig. 3 ). Fig. 3. Interdisciplinary integration of diagnostic images into brain

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Promod Pillai, Abhik Ray-Chaudhury, Mario Ammirati, and E. Antonio Chiocca

consistent with a pituitary macroadenoma ( Fig. 1 ). Results of endocrine function evaluations were normal, and he was informed of the likely diagnosis of a nonsecreting pituitary tumor. The pituitary lesion was decompressed via transsphenoidal approach with the aid of frameless stereotactic surgery and intra-operative MR imaging. Intraoperative analysis of several biopsy frozen sections yielded a preliminary diagnosis of an inflammatory granulomatous lesion. Intraoperatively, the lesion was unusually rubbery and firm. Postoperatively, the patient experienced transient

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Jesse Jones and John Ruge

for resection that carries greater risk to the optic nerve. Five other studies of 8, 59 8, 4 37, 53 63, 19 and 176 10 patients with macroadenomas treated with frameless stereotactic surgery reported no postoperative visual decline. Despite extended resection with intraoperative MR imaging, including suprasellar folds, damage to the optic nerve is similarly infrequent. The authors of a study of 106 tumors describe the sole case of visual deterioration after surgery in the literature, in a patient with preexisting chiasma syndrome. 38 Six patients (5

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Stefan A. Rath, Slawomir Moszko, Petra M. Schäffner, Giuseppe Cantone, Veit Braun, Hans-Peter Richter, and Gregor Antoniadis

atlantoaxial screw arthrodesis, the occiput with special rods, and into the upper thoracic spine. In the last 4 patients treated, we used a further development of this system (StarLock, Synthes Company) with a polyaxial locking mechanism that allows independent screw placement. Frameless Stereotactic Surgery of the Cervical Spine The first 9 patients, treated at the neurosurgical department of Ulm, underwent operations using the Surgical Tool Navigator pointer-based system (Zeiss) for spinal navigation. In the following 18 patients, who underwent surgery at the

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Uwe Max Mauer, Chris Schulz, Ronny Rothe, and Ulrich Kunz

require procedures that may be of relevance in military operational settings will be treated in a specific neurological department depends on the availability of modern surgical support procedures. Frame-based and frameless stereotactic surgery and neuronavigation have been used for years. The integration of functional imaging, for example, PET, functional MR imaging, and fiber tracking, into a navigation system are likely to become standard for certain types of surgeries in the future. In addition, 5-aminolevulinic acid–induced fluorescence is used for intraoperative