Frameless Stereotactic System Research Articles

Chronic Evaluation of a Clinical System for Deep Brain Stimulation and Recording of Neural Network Activity

Background/Aims: In conjunction with therapeutic stimulation, next-generation deep brain stimulation (DBS) devices may offer the ability to record and analyze neural signals, providing for unprecedented insight into DBS effects on neural networks. This work was conducted to evaluate an implantable, clinical-grade system that permits concurrent stimulation and recording using a large animal (ovine) model recently developed to study DBS for epilepsy. Methods: Following anesthesia and 1.5-tesla MRI acquisition, unilateral anterior thalamic and hippocampal DBS leads were implanted (n = 3) using a frameless stereotactic system. Chronic, awake recordings of evoked potentials (EPs) and local field potentials were collected with the implanted device and analyzed off-line. Results: Hippocampal EPs were stable over long-term (>1 year) recording and consistent in morphology and latency with prior acute results. Thalamic and hippocampal DBS produced both excitatory and inhibitory network effects that were stimulation site and parameter dependent. Free roaming recordings illustrated periods of highly correlated activity between these two structures within the circuit of Papez. Conclusions: These results provide further insight into mechanisms of DBS therapy for epilepsy and an encouraging demonstration of the capabilities of this new technology, which in the future, may afford unique opportunities to study human brain function and neuromodulation mechanism of action.

A systematic review of functional magnetic resonance imaging and diffusion tensor imaging modalities used in presurgical planning of brain tumour resection

Historically, brain tumour resection has relied upon standardised anatomical atlases and classical mapping techniques for successful resection. While these have provided adequate results in the past, the emergence of new technologies has heralded a wave of less invasive, patient-specific techniques for the mapping of brain function. Functional magnetic resonance imaging (fMRI) and, more recently, diffusion tensor imaging (DTI) are two such techniques. While fMRI is able to highlight localisation of function within the cortex, DTI represents the only technique able to elucidate white matter structures in vivo. Used in conjunction, both of these techniques provide important presurgical information for thorough preoperative planning, as well as intraoperatively via integration into frameless stereotactic neuronavigational systems. Together, these techniques show great promise for improved neurosurgical outcomes. While further research is required for more widespread clinical validity and acceptance, results from the literature provide a clear road map for future research and development to cement these techniques into the clinical setup of neurosurgical departments globally.

Investigation of 3-dimensional Optical Image Guided Frameless Stereotactic Radiosurgery Using Homegrown Volumetric Modulated Arc Therapy

Recently, powerful on-board imaging technologies have propelled SRS into the frameless era. Yet, all the mainstream on-board imaging systems resort to ionizing X-rays as imaging sources. Moreover, most SRS procedures are planned with IMRT, a modality that suffers from an elevated MU, a reduced MU-to-cGy coefficient, and a prolonged treatment time. To tackle these issues, we commissioned a novel frameless stereotactic system for intracranial SRS immobilization, a 3D optical surface imaging system for target localization and real-time patient monitoring, and a homegrown VMAT system for SRS planning. Here, we present our initial results of a feasibility study. The frameless stereotactic system includes carbon fiber base boards, a cranial stereotactic localizer frame, a support bridge, patient-specific mouthpiece assemblies, and a portable vacuum pump. The portable vacuum pump applies a negative pressure to the patient mouthpiece. The resulting vacuum suction seals the mouthpiece precisely into the palate of the mouth. VMAT-SRS plans were computed with a single 360° arc containing 180 equally-spaced beams, optimized incrementally using a differentiated optimization scheme. The target localization was accomplished with a video-based 3D optical surface imaging system, consisting of three 3D camera units and fast 3D image registration software. After the patient had been initially setup, the 3D optical surface imaging system acquired a verification skin surface of the patient. This verification image was registered to a reference skin surface created from the planning 3DCT in a user-defined region of interest. The registration software calculated three translational shifts (ΔVRT, ΔLNG, and ΔLAT), and three rotational shifts (ΔPITCH, ΔROLL, and ΔYAW) for patient re-positioning. The frameless system was found to be able to secure a sustained immobilization accuracy of ∼ ±1.0 mm and 1.0° for intracranial SRS as measured by CBCT and 3D real-time optical surface imaging. With this system, the patient could be simulated, planned, and treated on different days. VMAT-SRS plan optimization converged in 10 minutes for a PTV of ∼ 35 cm3 and 6 other critical structures. VMAT-SRS plans exhibited superior dose distribution to IMRT-SRS plans as measured by conformality and homogeneity indices. The target dose inhomogeneity was less than 17% compared to about 30% for conventional SRS plans. The doses to the critical structures for VMAT-SRS plans were less than or comparable to those for conventional SRS plans. With this new approach, the treatment time was reduced by more than one hour. Our initial data revealed that the synergistic combination of the frameless system, VMAT-SRS, and the 3D real-time optical surface imaging could be an optimal intracranial SRS sub-modality.

Frameless image-guided stereotaxy with real-time visual feedback for brain biopsy

Frame-based stereotaxy remains the "gold standard" for cerebral biopsies and functional neurosurgery though new frameless stereotactic systems are evolving continually. As the technique of frameless stereotaxy gains increasing acceptance among neurosurgeons, this study assesses the feasibility of a system for frameless image-guided stereotaxy. All patients biopsied for intracranial lesions between February 2007 and August 2010 using the BrainLAB VarioGuide frameless stereotactic system were evaluated prospectively. Prior to surgery, patients underwent magnetic resonance (MR) imaging; additionally, fluoroethyl-tyrosine (FET)-positron emission tomography (PET) images were acquired and fused to MR images in selected cases. Biopsy trajectory length, lesion volume, procedure duration, and diagnostic yield were assessed. Ninety-six diagnostic biopsies in 91 patients were evaluated. Lesion volume ranged from 0.17 to 121.8 cm(3); trajectory length from 25.3 to 101.9 mm. Diagnostic yield was 93.8%. Mean operation time from skin incision to wound closure was 42 min; in the operating room, it was 99 min. Clinical experience indicates VarioGuide to be safe and accurate. Reachable range of lesion localisation appears to be comparable to a frame-based stereotaxy system. Operation times are brief. The unique design of this frameless stereotactic system allows real-time visual feedback of needle positioning.

Assessment of Hippocampal Adeno-Associated Viral Vector Gene Delivery via Frameless Stereotaxis in a Nonhuman Primate

Background/Aims: Expression of the neuropeptide galanin in hippocampal neurons reduces seizures in the kainic acid rodent model of epilepsy. In order to translate these findings into a human clinical trial, the safety and feasibility of hippocampal adeno-associated viral (AAV) vector expression must be demonstrated in a nonhuman primate model. Methods: The Stealth Frameless Stereotactic System and Navigus Biopsy Appliance (Medtronic) were used to inject self-complementary AAV2 carrying the gene for green fluorescent protein (GFP) into monkey hippocampi. Using a single occipital trajectory per side (n = 8 trajectories), multiple injections spaced by 5 mm were delivered to each hippocampus. Results: GFP was expressed in both neuronal and glial cells. Injections led to nonhomogeneous gene expression, suggesting closer spacing of injections may lead to more gene expression. Increasing injection volumes entailed a general increase in volume of expression, but there was no overlap of expression within the 5-mm injection interval. Efforts to avoid the occipital horn failed to prevent leaking of vector into the ventricle, and resulted in deviation of the trajectory at proximal points from the hippocampus. Conclusion: Using the occipital approach, adequate cannulation of the monkey hippocampus will require transventricular trajectories.

Clinical accuracy of ExacTrac intracranial frameless stereotactic system

In this paper, the authors assess the accuracy of the Brainlab ExacTrac system for frameless intracranial stereotactic treatments in clinical practice. They recorded couch angle and image fusion results (comprising lateral, longitudinal, and vertical shifts, and rotation corrections about these axes) for 109 stereotactic radiosurgery and 166 stereotactic radiotherapy patient treatments. Frameless stereotactic treatments involve iterative 6D image fusion corrections applied until the results conform to customizable pass criteria, theirs being 0.7 mm and 0.5° for each axis. The planning CT slice thickness was 1.25 mm. It has been reported in the literature that the CT slices' thickness impacts the accuracy of localization to bony anatomy. The principle of invariance with respect to patient orientation was used to determine spatial accuracy. The data for radiosurgery comprised 927 image pairs, of which 532 passed (pass ratio of 57.4%). The data for radiotherapy comprised 15983 image pairs, of which 10 050 passed (pass ratio of 62.9%). For stereotactic radiotherapy, the combined uncertainty of ExacTrac calibration, image fusion, and intrafraction motion was (95% confidence interval) 0.290-0.302 and 0.306-0.319 mm in the longitudinal and lateral axes, respectively. The combined uncertainty of image fusion and intrafraction motion in the anterior-posterior coordinates was 0.174-0.182 mm. For stereotactic radiosurgery, the equivalent ranges are 0.323-0.393, 0.337-0.409, and 0.231-0.281 mm. The overall spatial accuracy was 1.24 mm for stereotactic radiotherapy (SRT) and 1.35 mm for stereotactic radiosurgery (SRS). The ExacTrac intracranial frameless stereotactic system spatial accuracy is adequate for clinical practice, and with the same pass criteria, SRT is more accurate than SRS. They now use frameless stereotaxy exclusively at their center.

Microsurgical resection of deep-seated lesions using transparent tubular retractor: pediatric case series

To facilitate effective resection of deep-seated brain lesions without causing significant trauma to the overlying cortex, the authors used a transparent plastic tubular retractor to approach these lesions. Between July 2009 and January 2011, we used an 11-mm diameter transparent plastic tubular retractor in combination with a frameless stereotactic navigation system to remove 18 deep lesions. Gross total resection of the lesions was achieved in 14 of 18 patients, and subtotal removal occurred in four patients. Effective resection of lesions was achieved in all patients through small size craniotomy window and small cortical incision. The histopathologic diagnosis was established in all 18 patients: 3 hematomas, 3 cavernous angioma, 7 low-grade glioma, 2 dysembryoplastic neuroepithelial tumor, 1 choroid plexus papilloma, 1 abscess, and 1 meningioma. Microsurgery using a transparent tubular retractor guided by a neuronavigation system facilitated accurate and effective removal of these deep-seated brain lesions.

Frameless Stereotactic Cerebral Biopsy: Our Experience in 296 Cases

Aims: To evaluate the reliability, safety and accuracy of a the frameless stereotactic system in our clinical series and the differences between head fixation by means of a standard Mayfield head holder and the pinless FESS frame, and to evaluate the usefulness of biopsy targeting on the basis of magnetic resonance spectroscopy (MRS) data. Methods: The spectroscopic analysis was used to facilitate the targeting of the lesion. The fusion image function embedded in the Neuronavigation Unit was used postoperatively to assess the level of accuracy of the biopsy. The grading of the glioma specimens was correlated to the spectroscopic data. Results: 296 patients underwent cerebral biopsy in 8 years. The diagnostic yield was 99.7%. The spectroscopic choline/N-acetyl aspartate ratio in different areas of the same tumor correlated well with the histological grading of the lesion. Conclusion: The frameless stereotactic systems guarantee excellent biopsy results. Advanced imaging, in particular MRS, facilitates the correct targeting of nonenhancing lesions.

Frameless stereotactic procedures in pediatric patients: safety and diagnostic efficacy

The aim of our retrospective study was to evaluate the feasibility, safety, and diagnostic yield of a frameless method for stereotactic neurosurgical procedures in pediatric patients. Twenty-two frameless stereotactic neurosurgical procedures (18 biopsies, 4 catheter placements), using a modified frameless stereotactic navigational system, were performed in 21 pediatric patients in our institution from 2004 to 2009. All procedures were performed by the senior authors (AAK, SC). We completed 18 biopsy procedures in 18 patients, yielding usable diagnostic specimens in 100% of the procedures. Of this biopsy group, two patients experienced an asymptomatic hemorrhage per CT, and one patient experienced a transient hemiparesis, recovering to baseline within 1week after surgery. Four catheter placement procedures were completed in three patients, including one patient who had to have the procedure repeated. We had no peri-operative mortality or technical difficulties related to the catheter placements. Frameless stereotactic neurosurgical procedures in the pediatric population are feasible and can be completed safely for histological tumor diagnosis as well as for accurate placement of intracranial catheters. This method has low rates of morbidity comparable to frame-based procedures, with the advantage of greater operative convenience.

Development of a Large Animal Model for Investigation of Deep Brain Stimulation for Epilepsy

Background/Objectives: To better understand the mechanism of action of deep brain stimulation (DBS) for epilepsy and to investigate implantable device features, it is desirable to have a large animal model to evaluate clinical-grade systems. This study assessed the suitability of an ovine model of epilepsy for this purpose. Methods: Animals were anesthetized for surgery and 1.5 T MRIs collected. Unilateral anterior thalamic DBS leads, hippocampal depth electrodes and catheters were implanted using a frameless stereotactic system. Evoked responses and local field potentials were collected and stored for off-line analysis. Results: Despite limited neuroanatomic information for this species, it was possible to reliably implant leads into the target structures using MR-guided techniques. Stimulation of these regions produced robust evoked potentials within this circuit that were dependent on stimulus location and parameters. High-frequency thalamic DBS produced a clear inhibition of both spontaneous and penicillin-induced ictal activity in the hippocampus which far outlasted the duration of the stimulation. Conclusions: These preliminary results suggest that the sheep model may be useful for further investigation of DBS for epilepsy. The demonstration of marked suppression of network excitability with high-frequency stimulation supports a potential therapeutic mechanism for this DBS therapy.

Stereotactic Irradiation of the Postoperative Resection Cavity for Brain Metastasis: A Frameless Linear Accelerator-Based Case Series and Review of the Technique

Whole-brain radiation therapy (WBRT) is the standard of care after resection of a brain metastasis. However, concern regarding possible neurocognitive effects and the lack of survival benefit with this approach has led to the use of stereotactic radiosurgery (SRS) to the resection cavity in place of WBRT. We report our initial experience using an image-guided linear accelerator-based frameless stereotactic system and review the technical issues in applying this technique. We retrospectively reviewed the setup accuracy, treatment outcome, and patterns of failure of the first 18 consecutive cases treated at Brigham and Women's Hospital. The target volume was the resection cavity without a margin excluding the surgical track. The median number of brain metastases per patient was 1 (range, 1-3). The median planning target volume was 3.49 mL. The median prescribed dose was 18 Gy (range, 15-18 Gy) with normalization ranging from 68% to 85%. In all cases, 99% of the planning target volume was covered by the prescribed dose. The median conformity index was 1.6 (range, 1.41-1.92). The SRS was delivered with submillimeter accuracy. At a median follow-up of 12.7 months, local control was achieved in 16/18 cavities treated. True local recurrence occurred in 2 patients. No marginal failures occurred. Distant recurrence occurred in 6/17 patients. Median time to any failure was 7.4 months. No Grade 3 or higher toxicity was recorded. A long interval between initial cancer diagnosis and the development of brain metastasis was the only factor that trended toward a significant association with the absence of recurrence (local or distant) (log-rank p = 0.097). Frameless stereotactic irradiation of the resection cavity after surgery for a brain metastasis is a safe and accurate technique that offers durable local control and defers the use of WBRT in select patients. This technique should be tested in larger prospective studies.

Modification of Existing Human Motor Memories Is Enabled by Primary Cortical Processing during Memory Reactivation

One of the most challenging tasks of the brain is to constantly update the internal neural representations of existing memories. Animal studies have used invasive methods such as direct microfusion of protein inhibitors to designated brain areas, in order to study the neural mechanisms underlying modification of already existing memories after their reactivation during recall [1-4]. Because such interventions are not possible in humans, it is not known how these neural processes operate in the human brain. In a series of experiments we show here that when an existing human motor memory is reactivated during recall, modification of the memory is blocked by virtual lesion [5] of the related primary cortical human brain area. The virtual lesion was induced by noninvasive repetitive transcranial magnetic stimulation guided by a frameless stereotactic brain navigation system and each subject's brain image. The results demonstrate that primary cortical processing in the human brain interacting with pre-existing reactivated memory traces is critical for successful modification of the existing related memory. Modulation of reactivated memories by noninvasive cortical stimulation may have important implications for human memory research and have far-reaching clinical applications.

Stereotaxy: Breaking the limits of current radiofrequency ablation techniques

Radiofrequency ablation (RFA) allows for local curative tumor treatment by inducing coagulation necrosis with high-frequency alternating current. However, the tumor size is the major limiting factor due to a mismatch of the tumor volume and the induced necrotic zone. RFA probes have to be optimally distributed in and around the tumor in order to produce overlapping ablation zones. Due to different guidance and ablation strategies the result is strongly operator dependent and there is a lack of reliability. These challenges can be managed by 3D-planning using a frameless stereotactic navigation system, allowing for the simultaneous display of multiple trajectories. The spatial information gained from 3D imaging is available in coordinates and thus forms an accurate input for performing the intervention. Stereotaxy enables highly accurate probe positioning. Stereotactic radiofrequency ablation (SRFA) may substantially improve the safety and efficacy in clinical practice, especially in the treatment of large and irregularly shaped tumors. The proposed methods may also be used for similar percutaneous local tumor treatments.

Precision of navigated stereotactic probe implantation into the brainstem

The indications for stereotactic biopsies or implantation of probes for local chemotherapy in diffuse brainstem tumors have recently come under debate. The quality of performing these procedures significantly depends on the precision of the probes' placement in the brainstem. The authors evaluated the precision of brainstem probe positioning using a navigated frameless stereotactic system in an experimental setting. Using the VarioGuide stereotactic system, 33 probes were placed into a specially designed model filled with agarose. In a second experimental series, 8 anatomical specimens were implanted with a total of 32 catheters into the pontine brainstem using either a suboccipital or a precoronal entry point. Before intervention in both experimental settings, a thin-sliced CT scan for planning was obtained and fused to volumetric T1-weighted MR imaging data. After the probe positioning procedures, another CT scan and an MR image were obtained to compare the course of the catheters versus the planned trajectory. The deviation between the planned and the actual locations was measured to evaluate the precision of the navigated intervention. Using the VarioGuide system, mean total target deviations of 2.8 +/- 1.2 mm on CT scanning and 3.1 +/- 1.2 mm on MR imaging were detected with a mean catheter length of 151 +/- 6.1 mm in the agarose model. The catheter placement in the anatomical specimens revealed mean total deviations of 1.95 +/- 0.6 mm on CT scanning and 1.8 +/- 0.7 mm on MR imaging for the suboccipital approach and a mean catheter length of 59.5 +/- 4.1 mm. For the precoronal approach, deviations of 2.2 +/- 1.2 mm on CT scanning and 2.1 +/- 1.1 mm on MR imaging were measured (mean catheter length 85.9 +/- 4.7 mm). The system-based deviation of frameless stereotaxy using the VarioGuide system reveals good probe placement in deep-seated locations such as the brainstem. Therefore, the authors believe that the system can be accurately used to conduct biopsies and place probes in patients with brainstem lesions.

A modified stereotactic frame as an instrument holder for frameless stereotaxis: Technical note

Background:In order to improve the targeting capability and trajectory planning and provide a more secure probe-holding system, a simple method to use a stereotactic frame as an instrument holder for the frameless stereotactic system was devised.Methods:A modified stereotactic frame and BrainLab vector vision neuronavigation sys¬tem were used together. The patient was placed in the stereotactic head-holder to which a reference array of the neuronavigation system was attached. The pointer of the frameless system was placed in the probe-holder of the frame. An offset in distances was kept between the radius of the arch of the frame and the tip of the pointer so that the pointer was always outside the head during navigation. The offset correction was made on the BrainLab monitor so that the center of the arc of the frame was at the tip of the probe line on the monitor. Then, using the frame’s coordinate adjuster system, the center of the arc was positioned on the target. This method was used to insert depth electrodes (seven procedures) and gain access to the temporal horn (three procedures).Results:Post-operative scans showed that the accuracy was within 2.5 mm in all three planes for depth electrode placement, and easy access to the temporal horn was obtained in two other patients.Conclusion:This is a simple method to use a stereotactic frame to improve coordinate and trajectory adjustments and provides a better method to stabilize the pointer and the probe-holder during frameless stereotactic procedures.

Development of a frameless stereotactic radiosurgery system based on real-time 6D position monitoring and adaptive head motion compensation

Stereotactic radiosurgery delivers radiation with great spatial accuracy. To achieve sub-millimeter accuracy for intracranial SRS, a head ring is rigidly fixated to the skull to create a fixed reference. For some patients, the invasiveness of the ring can be highly uncomfortable and not well tolerated. In addition, placing and removing the ring requires special expertise from a neurosurgeon, and patient setup time for SRS can often be long. To reduce the invasiveness, hardware limitations and setup time, we are developing a system for performing accurate head positioning without the use of a head ring. The proposed method uses real-time 6D optical position feedback for turning on and off the treatment beam (gating) and guiding a motor-controlled 3D head motion compensation stage. The setup consists of a central control computer, an optical patient motion tracking system and a 3D motion compensation stage attached to the front of the LINAC couch. A styrofoam head cast was custom-built for patient support and was mounted on the compensation stage. The motion feedback of the markers was processed by the control computer, and the resulting motion of the target was calculated using a rigid body model. If the target deviated beyond a preset position of 0.2 mm, an automatic position correction was performed with stepper motors to adjust the head position via the couch mount motion platform. In the event the target deviated more than 1 mm, a safety relay switch was activated and the treatment beam was turned off. The feasibility of the concept was tested using five healthy volunteers. Head motion data were acquired with and without the use of motion compensation over treatment times of 15 min. On average, test subjects exceeded the 0.5 mm tolerance 86% of the time and the 1.0 mm tolerance 45% of the time without motion correction. With correction, this percentage was reduced to 5% and 2% for the 0.5 mm and 1.0 mm tolerances, respectively.

Quality Assessment of FSRT using CBCT

Clinical application of frameless stereotactic localization systems requires precise target localization. We assessed localization accuracy and setup uncertainty for frameless fractioned stereotactic radiotherapy (FSRT) patients based on two CBCT systems.

Frameless Stereotactic Radiosurgery with a Bite-plate: Our Experience with Brain Metastases

Non-invasive frameless stereotactic radiosurgical systems have recently been developed. We report our experience of frameless stereotactic radiosurgery (SRS) with a bite-plate for brain metastases. Between February 2002 and December 2005, 147 patients with brain metastases were treated with C-arm linear accelerator-based SRS and 122 patients were followed up by our institute. An optic tracking system with infrared light-emitting diodes was used for real-time monitoring. A bite-plate with fiducial markers was applied as a first-line method for frameless SRS. Head-ring fixation was used in patients lacking teeth. Lung carcinomas (63%) were the most common primary tumors, followed by breast carcinomas (13%). Ninety patients underwent radiosurgery with a bite-plate and 32 patients underwent fixation of a head ring. Males were significantly more predominant in the head-ring group (26 men and 6 women), compared with the bite-plate group (47 men and 43 women, p < 0.01). The average age (62 years) in the bite-plate group was significantly younger than that (68 years) in the head-ring group (p < 0.01). The median survival time was 12.0 months in the bite-plate group and 8.0 months in the head-ring group (p = 0.0621). Nine patients who had brain metastases in or close to the brain stem were treated with fractionated stereotactic radiotherapy. The frameless stereotactic radiosurgical system with a bite-plate is safe and effective for the treatment of brain metastasis. Elderly male patients sometimes are edentulous and require placement of a head ring for radiosurgery.

STEREOTACTIC MINIMALLY INVASIVE TUBULAR RETRACTOR SYSTEM FOR DEEP BRAIN LESIONS

Deep-seated supratentorial intraparenchymal and intraventricular brain lesions can be difficult to access without causing significant trauma to the overlying cortex and intervening white matter tracts. Traditional brain retractors use multiple blades, which do not exert pressure in an equally distributed fashion. Tubular retractors offer an advantage. Although a commercially available frame-based tubular retractor system is on the market (COMPASS; Compass, Inc., Rochester, MN), we modified existing off-the-shelf equipment at our institution into a frameless tubular brain retractor. We used 14- to 22-mm METRx (Medtronic, Minneapolis, MN) tubular retractors in combination with a frameless stereotactic navigation system to remove 10 deep lesions. Histological findings included 6 periventricular metastases, 1 insular glioblastoma multiforme, 1 periventricular glioblastoma multiforme, 1 intraventricular meningioma, and 1 hippocampal cavernous malformation. Radiographic gross total resection was achieved in all patients. One patient experienced a transient worsening of an existing preoperative Wernicke's aphasia; otherwise, there were no intra- or postoperative complications. One patient with radiographic gross total resection of a metastatic lesion experienced a local recurrence of disease, requiring stereotactic radiosurgery. A frameless stereotactic tubular retractor system for deep brain lesions can be assembled with equipment already available at many institutions. Use of this system can decrease incision and craniotomy size, decrease retractor-induced trauma to overlying cortex, and help prevent damage to underlying white matter tracts.

Corpus callosotomy in children with intractable epilepsy using frameless stereotactic neuronavigation: 12-year experience at The Hospital for Sick Children in Toronto

Although corpus callosotomy has been used effectively since the late 1930s to treat severe, medically intractable seizure disorders, particularly atonic or drop-attack seizures, controversy remains as to when, how, and how much surgery should be performed. Intraoperative determination of the extent of callosotomy, the need to stage the procedure, and the side of the interhemispheric approach represent technical issues that remain debatable. The authors report the 12-year experience of the senior author as well as surgical outcomes with corpus callosotomy using a frameless stereotactic neuronavigation system (ISG View Wand and BrainLab). Thirteen consecutive children at The Hospital for Sick Children underwent single-stage corpus callosotomy for medically intractable seizures. The mean age was 10.3 years. Five children underwent partial callosotomy, and 8 underwent complete callosotomy. The side of operative approach to avoid large parasagittal bridging veins was determined by preoperative study of 3D MR imaging/MR venography reconstructed by the neuronavigation system. The extent of callosotomy was determined using intraoperative feedback from the neuronavigation system and postoperative MR imaging. The extent of callosotomy determined by intraoperative neuronavigation and postoperative MR imaging correlated closely in all cases. There were no operative deaths. There was no significant postoperative morbidity related to venous infarction. Four of 5 patients in the partial callosotomy cohort and 7 of 8 patients in the complete callosotomy cohort showed significant improvement in seizure control. The use of frameless stereotactic neuronavigation is a safe, effective, and important surgical adjunct in the planning and execution of successful corpus callosotomy in children with intractable epilepsy.