Neurosurgery Blog

Acta Neurochir (2011) 153:1087–1095 DOI 10.1007/s00701-011-0953-1

Microelectrode recording (MER) is widely used during deep brain stimulation (DBS) procedures because MER can identify structural borders and eloquent structures, localize somatotopic arrangements, and provide an outline of the three-dimensional shapes of target nuclei. However, MER may cause intracranial hemorrhage. We performed single track MER during DBS procedures, analyzed the accuracy of electrode positioning with MRI, and compared the amount of air and the potential risk of intracranial hemorrhage.

Method A total of 46 electrodes were placed in 23 patients who suffered from advanced Parkinson’s disease and who underwent bilateral subthalamic nucleus DBS using single track MER. Each patient’s Unified Parkinson’s Disease Rating Scale (UPDRS) score and levo-dopa equivalent dosage (LED) were estimated pre- and postoperatively. The accuracy of electrode positioning and fontal air thickness was measured by a pre- or postoperative magnetic resonance imaging (MRI) merging technique.

Findings The mean electrode positioning error was 0.92 mm (0.3–2.94 mm). The mean frontal air thickness on postoperative MRI was 3.85 mm (0–10.3 mm), which did not affect the electrode accuracy statistically (p=0.730). A total of nine electrodes required repositioning after single-track MER because they affected microstimulation or because an abnormally short STN length was observed during MER. In this series, one patient suffered from an intracranial hemorrhage after surgery that appeared to be due to venous infarction rather than related to MER.

Conclusions Although MER can facilitate accurate positioning of electrodes, multi-track MER may increase the risk of intracranial hemorrhage. The accuracy of electrode positioning appears to be acceptable under single track MER during STN DBS with careful electrophysiological and neurological monitoring. The risk of intracranial hemorrhage appears to be minimal, especially in elderly patients with atrophic brains.

Acta Neurochir (2011) 153:1111–1122. DOI 10.1007/s00701-010-0936-7

Recent improvements in imaging-based diagnosis, the broader application of neuroendoscopic techniques and advances in open surgery techniques mean that the need for stereotactic biopsies in the management of pineal region tumours must be reevaluated. The primary aim of this retrospective study was to establish whether stereotactic biopsy is still of value in the modern management of pineal region tumours.

Methods From 1985 to 2009, 88 consecutive patients underwent a stereotactic biopsy in our institution (51 males and 37 females; median age at presentation 30; range 2–74).

Results Accurate tissue diagnoses were obtained in all but one case (i.e. 99%). In one case (1%), three distinct stereotactic procedures were necessary to obtain a tissue diagnosis. There was no mortality or permanent morbidity associated with stereotactic biopsy. One patient (1%) presented an intra-parenchymal hematoma but no related clinical symptoms. Five patients (6%) presented transient morbidity, which lasted for between 2 days and 3 weeks after the biopsy.

Conclusions To guide subsequent treatment, we believe that histological diagnosis is paramount. Stereotactic biopsies are currently the safest and the most efficient way of obtaining this essential information. Recent improvements in stereotactic technology (particularly robotic techniques) appear to be very valuable, with almost no permanent morbidity or mortality risk and no decrease in the accuracy rate. In our opinion, other available neurosurgical techniques (such as endoscopic neurosurgery, stereotactic neurosurgery and open microsurgery) are complementary and not competitive.

Neurosurgery 68[ONS Suppl 1]:ons114–ons124, 2011. DOI: 10.1227/NEU.0b013e31820781bc

The efficacy of deep brain stimulation (DBS) is highly dependent on the accuracy of lead placement.

OBJECTIVE: To describe the use of intraoperative computed tomography (iCT) to confirm lead location before surgical closure and to study the accuracy of this technique.

METHODS: Fifteen patients underwent awake microelectrode-guided DBS surgery in a stereotactic frame. A portable iCT scanner (Medtronic O-arm) was positioned around the patient’s head throughout the procedure and was used to confirm lead location before fixation of the lead to the skull. Images were computationally fused with preoperative magnetic resonance imaging (MRI), and lead tip coordinates with respect to the midpoint of the anterior commissure-posterior commissure line were measured. Tip coordinates were compared with those obtained from postoperative MRI.

RESULTS: iCT was integrated into standard frame-based microelectrode-guided DBS surgery with a minimal increase in surgical time or complexity. Technically adequate 2-dimensional and 3-dimensional images were obtained in all cases. Head positioning and fixation techniques that allow unobstructed imaging are described. Lead tip measurements on iCT fused with preoperative MRI were statistically indistinguishable from those obtained with postoperative MRI.

CONCLUSION: iCT can be easily incorporated into standard DBS surgery, replaces the need for C-arm fluoroscopy, and provides accurate intraoperative 3-dimensional confirmation of electrode tip locations relative to preoperative images and surgical plans. iCT fused to preoperative MRI may obviate the need for routine postoperative MRI in DBS surgery. Technical nuances that must be mastered for the efficient use of iCT during DBS implantation are described.

Acta Neurochir (2011) 153:517–526.DOI 10.1007/s00701-010-0933-x

Endoscopic and stereotactic surgery have gained widespread acceptance as minimally invasive tools for the diagnosis of intracerebral pathologies. We investigated the specific advantages and disadvantages of each technique in the assessment of periventricular lesions.

Method This study included a retrospective series of 70 patients with periventricular lesions. Endoscopic surgery was performed in 17 patients (mean age, 37 years; range, 4 months–78 years) and stereotactic biopsy in 55 patients (mean age, 63 years; range, 23–80 years), including two patients who underwent both procedures.

Results Hydrocephalus was present in 13/17 patients in the endoscopic group (77%) and in 11/55 patients in the stereotactic group (20%). Diagnosis was achieved in all patients in the endoscopic group and in all but one patient in the stereotactic group, in whom histological diagnosis was obtained by endoscopic biopsy during a second operation. In the endoscopic group, additional procedures performed included ventriculostomy (2/17), cyst fenestration (3/17), endoscopic shunt revision (3/17) and placement of Rickham reservoirs or external cerebrospinal fluid drains (6/17). Adverse events occurred in one patient after endoscopy (chronic subdural hematoma) and in two patients after stereotactic surgery (one mild hemiparesis and one transitory paresis of the contralateral leg).

Conclusions Endoscopic and stereotactic surgery have distinct advantages and disadvantages in approaching periventricular lesions. The advantages of endoscopy encompass the possibility to perform additional surgical procedures during the same session (e.g. tumour reduction, third ventriculostomy, fenestration of a cyst). The visual control reduces the hazard of injury to anatomical structures and allows for a better control of bleeding although there is a considerable blind-out in such situations. The advantages of stereotactic surgery include a smaller approach and precise planning of the trajectory. It is usually performed under local anaesthesia. Both methods provide a safe and efficient therapeutic option in periventricular lesions with low surgical-related morbidity.

Neurosurgery 67:1745–1756, 2010 DOI: 10.1227/NEU.0b013e3181f74105

Deep brain stimulation (DBS) surgery is used for treating movement disorders, including Parkinson disease, essential tremor, and dystonia. Successful DBS surgery is critically dependent on precise placement of DBS electrodes into target structures. Frequently, DBS surgery relies on normalized atlas-derived diagrams that are superimposed on patient brain magnetic resonance imaging (MRI) scans, followed by microelectrode recording and macrostimulation to refine the ultimate electrode position. Microelectrode recording carries a risk of hemorrhage and requires active patient participation during surgery.

OBJECTIVE: To enhance anatomic imaging for DBS surgery using high-field MRI with the ultimate goal of improving the accuracy of anatomic target selection.

METHODS: Using a 7-T MRI scanner combined with an array of acquisition schemes using multiple image contrasts, we obtained high-resolution images of human deep nuclei in healthy subjects.

RESULTS: Superior image resolution and contrast obtained at 7 T in vivo using susceptibility-weighted imaging dramatically improved anatomic delineation of DBS targets and allowed the identification of internal architecture within these targets. A patient-specific, 3-dimensional model of each target area was generated on the basis of the acquired images.

CONCLUSION: Technical developments in MRI at 7 T have yielded improved anatomic resolution of deep brain structures, thereby holding the promise of improving anatomicbased targeting for DBS surgery. Future study is needed to validate this technique in improving the accuracy of targeting in DBS surgery.

Acta Neurochir (2010) 152:2029–2036. DOI 10.1007/s00701-010-0779-2

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.

Neurosurgery 67:957–963, 2010 DOI: 10.1227/NEU.0b013e3181ec49c7

Bilateral globus pallidus internus (GPi) deep brain stimulation (DBS) was shown to be effective in cervical dystonia refractory to medical treatment in several small short-term and 1 long-term follow-up series. Optimal stimulation parameters and their repercussions on the cost/benefit ratio still need to be established.

OBJECTIVE: To report our long-term outcome with bilateral GPi deep brain stimulation in cervical dystonia.

METHODS: The Toronto Western Spasmodic Torticollis Rating Scale was evaluated in 10 consecutive patients preoperatively and at last follow-up. The relationship of improvement in postural severity and pain was analyzed and stimulation parameters noted and compared with those in a similar series in the literature.

RESULTS: The mean (standard deviation) follow-up was 37.6 (16.9) months. Improvement in the total Toronto Western Spasmodic Torticollis Rating Scale score as evaluated at latest follow-up was 68.1% (95% confidence interval: 51.5-84.6). In 4 patients, there was dissociation between posture severity and pain improvement. Prevalently bipolar stimulation settings and high pulse widths and amplitudes led to excellent results at the expense of battery life.

CONCLUSION: Improvement in all 3 subscale scores of the Toronto Western Spasmodic Torticollis Rating Scale with bilateral GPi deep brain stimulation seems to be the rule. Refinement of stimulation parameters might have a significant impact on the cost/ benefit ratio of the treatment. The dissociation of improvement in posture severity and pain provides tangible evidence of the complex nature of cervical dystonia and offers interesting insight into the complex functional organization of the GPi.

Neurosurgery 67:1088–1093, 2010 DOI: 10.1227/NEU.0b013e3181ecc887

Image-guided neuronavigation has largely replaced stereotactic frames when precise, real-time anatomic localization is required during neurosurgical procedures. However, some procedures, including placement of deep-brain stimulation (DBS) leads for the treatment of movement disorders, are still performed using frame-based stereotaxy. Despite the demonstration of comparable accuracy between frame-based and ‘‘frameless’’ image-guided approaches, the clinical efficacy of frameless DBS placement has never been reported.

OBJECTIVE: To analyze the outcomes of subthalamic nucleus (STN) DBS using the frameless technique for the treatment of Parkinson’s disease (PD).

METHODS: Of 31 subjects (20 men) with PD for 10 6 4 years, 28 had bilateral STN DBS and 3 had unilateral STN DBS. The Unified Parkinson’s Disease Rating Scale (UPDRS) motor scale (III) and total medication doses were assessed before surgery on and off medication and off medication/ON DBS (off/ON) after 6 to 12 months of STN DBS.

RESULTS: There was a 58% improvement from bilateral STN DBS in the UPDRS III (40 6 16 preoperatively off, 17 6 11 off/ON) 9.6 6 1.9 months after surgery (P , .001). This compared favorably with the published outcomes using the frame-based technique. All motor subscores improved significantly (P , .01). The mean reduction in medication was 50%. No intraoperative complications occurred, but one subject with hypertension died of a delayed hemorrhage postoperatively. Two subjects developed postoperative infections that required lead removal and antibiotics.

CONCLUSIONS: Bilateral STN DBS for PD performed by an experienced team using a frameless approach results in outcomes comparable to those reported with the use of the frame-based technique.

J Neurosurg 113:639–647, 2010.DOI: 10.3171/2010.3.JNS091385

A challenge associated with deep brain stimulation (DBS) in treating advanced Parkinson disease (PD) is the direct visualization of brain nuclei, which often involves indirect approximations of stereotactic targets. In the present study, the authors compared T2*-weighted images obtained using 7-T MR imaging with those obtained using 1.5- and 3-T MR imaging to ascertain whether 7-T imaging enables better visualization of targets for DBS in PD.

Methods. The authors compared 1.5-, 3-, and 7-T MR images obtained in 11 healthy volunteers and 1 patient with PD.

Results. With 7-T imaging, distinct images of the brain were obtained, including the subthalamic nucleus (STN) and internal globus pallidus (GPi). Compared with the 1.5- and 3-T MR images of the STN and GPi, the 7-T MR images showed marked improvements in spatial resolution, tissue contrast, and signal-to-noise ratio.

Conclusions. Data in this study reveal the superiority of 7-T MR imaging for visualizing structures targeted for DBS in the management of PD. This finding suggests that by enabling the direct visualization of neural structures of interest, 7-T MR imaging could be a valuable aid in neurosurgical procedures.

Neurosurg Focus 29 (2):E3, 2010. (DOI: 10.3171/2010.4.FOCUS10103)

Deep brain stimulation (DBS) is the treatment of choice for otherwise healthy patients with advanced Parkinson disease who are suffering from disabling dyskinesias and motor fluctuations related to dopaminergic therapy. As DBS is an elective procedure, it is essential to minimize the risk of morbidity. Further, precision in targeting deep brain structures is critical to optimize efficacy in controlling motor features. The authors have already established an operational checklist in an effort to minimize errors made during DBS surgery. Here, they set out to standardize a strict, step-by-step approach to the DBS surgery used at their institution, including preoperative evaluation, the day of surgery, and the postoperative course. They provide careful instruction on Leksell frame assembly and placement as well as the determination of indirect coordinates derived from MR images used to target deep brain structures. Detailed descriptions of the operative procedure are provided, outlining placement of the stereotactic arc as well as determination of the appropriate bur hole location, lead placement using electrophysiology, and placement of the internal pulse generator. The authors also include their approach to preventing postoperative morbidity. They believe that a strategic, step-by-step approach to DBS surgery combined with a standardized checklist will help to minimize operating room mistakes that can compromise targeting and increase the risk of complication.

Neurosurg Focus 29 (2):E13, 2010. DOI: 10.3171/2010.5.FOCUS1094

The aim of this study was to review the indications for and results of deep brain stimulation (DBS) of the posterior hypothalamus (pHyp) in the treatment of drug-refractory and severe painful syndromes of the face, disruptive and aggressive behavior associated with epilepsy, and below-average intelligence. The preoperative clinical picture, functional imaging studies, and overall clinical results in the literature are discussed.

Methods. All patients underwent stereotactic implantation of deep-brain electrodes within the pHyp. Data from several authors have been collected and reported for each clinical entity, as have clinical results, adverse events, and neurophysiological characteristics of the pHyp.

Results. The percentage of patients with chronic cluster headache who responded to DBS was 50% in the overall reported series. The response rate was 100% for short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing and for chronic paroxysmal hemicrania, although only 2 patients and 1 patient, respectively, have been described as having these conditions. None of the 4 patients suffering from refractory neuropathic trigeminal pain benefited from the procedure (0% response rate), whereas all 5 patients (100%) affected with refractory trigeminal neuralgia (TN) due to multiple sclerosis (MS) and undergoing pHyp DBS experienced a significant decrease in pain attacks within the first branch of cranial nerve V. Six (75%) of 8 patients presenting with aggressive behavior and mental retardation benefited from pHyp stimulation; 6 patients were part of the authors’ series and 2 were reported in the literature.

Conclusions. In carefully selected patients, DBS of the pHyp can be considered an effective procedure for the treatment of refractory trigeminal autonomic cephalalgias, aggressive behavior, and MS-related TN in the first trigeminal branch. Only larger and prospective studies along with multidisciplinary approaches (including, by necessity, neuroimaging studies) can lead us to better patient selection that would reduce the rate of nonresponders.

Acta Neurochir DOI 10.1007/s00701-010-0742-2

The safe and reversible nature of deep brain stimulation (DBS) has allowed movement disorder neurosurgery to become commonplace throughout the world. Fundamental understanding of individual patient’s anatomy is critical for optimizing the effects and side effects of DBS surgery. Three patients undergoing stereotactic surgery for movement disorders, at the institution’s intraoperative magnetic resonance imaging operating suite, were studied with fiber tractography. Stereotactic targets and fiber tractography were determined on preoperative magnetic resonance imagings using the Schaltenbrand–Wahren atlas for definition in the BrainLab iPlan software (BrainLAB Inc., Feldkirchen, Germany). Subthalamic nucleus, globus pallidus interna, and ventral intermediate nucleus targets were studied. Diffusion tensor imaging parameters used ranged from 2 to 8 mm for volume of interest in the x/y/z planes, fiber length was kept constant at 30 mm, and fractional anisotropy threshold varied from 0.20 to 0.45. Diffusion tensor imaging tractography allowed reliable and reproducible visualization and correlation between frontal eye field, premotor, primary motor, and primary sensory cortices via corticospinal tracts and corticopontocerebellar tracts. There is an apparent increase in the number of cortical regions targeted by the fiber tracts as the region of interest is enlarged. This represents a possible mechanism of the increased effects and side effects observed with higher stimulation voltages. Currently available diffusion tensor imaging techniques allow potential methods to characterize the effects and side effects of DBS. This technology has the potential of being a powerful tool to optimize DBS neurosurgery

J Neurosurg 112:497–502, 2010. DOI: 10.3171/2009.7.JNS09572

With the expanding indications and increasing number of patients undergoing deep brain stimulation (DBS), postoperative MR imaging is becoming even more important in guiding clinical care and practice-based learning; important safety concerns have recently emerged, however. Although phantom model studies have driven conservative recommendations regarding imaging parameters, highlighted by 2 recent reports describing adverse neurological events associated with MR imaging in patients with implanted DBS systems, the risks of MR imaging in such patients in clinical practice has not been well addressed. In this study, the authors capitalized on their large experience with serial MR imaging (3 times per patient) to use MR imaging itself and clinical outcomes to examine the safety of MR imaging in patients who underwent staged implantation of DBS electrodes for Parkinson disease, tremor, and dystonia.

Methods. Sixty-four patients underwent staged bilateral lead implantations between 1997 and 2006, and each patient underwent 3 separate MR imaging sessions subsequent to DBS placement. The first of these was performed after the first DBS placement, the second occurred prior to the second DBS placement, and third was after the second DBS placement. Follow-up was conducted to examine adverse events related either to MR imaging or to DBSinduced injury.

Results. One hundred and ninety-two MR images were obtained, and the mean follow-up time was 3.67 years. The average time between the first and second, and second and third MR imaging sessions was 19.4 months and 14.7 hours, respectively. Twenty-two MR imaging–detected new findings of hemorrhage were documented. However, all new findings were related to acute DBS insertion, whereas there were no new findings after imaging of the chronically implanted electrode.

Conclusions. Although potential risks of MR imaging in patients undergoing DBS may be linked to excessive heating, induced electrical currents, disruption of the normal operation of the device, and/or magnetic field interactions, MR imaging can be performed safely in these patients and provides useful information on DBS lead location to inform patient-specific programming and practice-based learning

J Neurosurg 112:479–490, 2010. DOI: 10.3171/2009.6.JNS081161

The authors discuss their method for placement of deep brain stimulation (DBS) electrodes using interventional MR (iMR) imaging and report on the accuracy of the technique, its initial clinical efficacy, and associated complications in a consecutive series of subthalamic nucleus (STN) DBS implants to treat Parkinson disease (PD).

Methods. A skull-mounted aiming device (Medtronic NexFrame) was used in conjunction with real-time MR imaging (Philips Intera 1.5T). Preoperative imaging, DBS implantation, and postimplantation MR imaging were integrated into a single procedure performed with the patient in a state of general anesthesia. Accuracy of implantation was assessed using 2 types of measurements: the “radial error,” defined as the scalar distance between the location of the intended target and the actual location of the guidance sheath in the axial plane 4 mm inferior to the commissures, and the “tip error,” defined as the vector distance between the expected anterior commissure–posterior commissure (AC-PC) coordinates of the permanent DBS lead tip and the actual AC-PC coordinates of the lead tip. Clinical out- come was assessed using the Unified Parkinson’s Disease Rating Scale part III (UPDRS III), in the off-medication

state.Results. Twenty-nine patients with PD underwent iMR imaging–guided placement of 53 DBS electrodes into the STN. The mean (± SD) radial error was 1.2 ± 0.65 mm, and the mean absolute tip error was 2.2 ± 0.92 mm. The tip error was significantly smaller than for STN DBS electrodes implanted using traditional frame-based stereotaxy (3.1 ± 1.41 mm). Eighty-seven percent of leads were placed with a single brain penetration. No hematomas were visible on MR images. Two device infections occurred early in the series. In bilaterally implanted patients, the mean improvement on the UPDRS III at 9 months postimplantation was 60%.

Conclusions. The authors’ technical approach to placement of DBS electrodes adapts the procedure to a standard configuration 1.5-T diagnostic MR imaging scanner in a radiology suite. This method simplifies DBS implantation by eliminating the use of the traditional stereotactic frame and the subsequent requirement for registration of the brain in stereotactic space and the need for physiological recording and patient cooperation. This method has improved accuracy compared with that of anatomical guidance using standard frame-based stereotaxy in conjunction with pre- operative MR imaging.

J Neurosurg 111:1209–1215, 2009.(DOI: 10.3171/2008.10.JNS08763)

Object. Deep brain stimulation (DBS) of the subcallosal cingulate gyrus (SCG), including Brodmann area 25, is currently being investigated for the treatment of major depressive disorder (MDD). As a potential emerging therapy, optimal target selection within the SCG has still to be determined. The authors compared the location of the electrode contacts in responders and nonresponders to DBS of the SCG and correlated the results with clinical outcome to help in identifying the optimal target within the region. Based on the location of the active contacts used for long-term stimulation in responders, the authors suggest a standardized method of targeting the SCG in patients with MDD.

Methods. Postoperative MR imaging studies of 20 patients with MDD treated with DBS of the SCG were ana- lyzed. The authors assessed the location of the active contacts relative to the midcommissural point and in relation to anatomical landmarks within the medial aspect of the frontal lobe. For this, a grid with 2 main lines was designed, with 1 line in the anterior-posterior and 1 line in the dorsal-ventral axis. Each of these lines was divided into 100 units, and data were converted into percentages. The anterior-posterior line extended from the anterior commissure (AC) to the projection of the anterior aspect of the corpus callosum (CCa). The dorsal-ventral line extended from the inferior portion of the CC (CCi) to the most ventral aspect of the frontal lobe (abbreviated “Fr” for the formula).

Results. Because the surgical technique did not vary across patients, differences in stereotactic coordinates between responders and nonresponders did not exceed 1.5 mm in any axis (x, y, or z). In patients who responded to the procedure, contacts used for long-term stimulation were in close approximation within the SCG. In the anterior- posterior line, these contacts were located within a 73.2 ± 7.7 percentile distance from the AC (with the AC center being 0% and the line crossing the CCa being 100%). In the dorsal-ventral line, active contacts in responders were located within a 26.2 ± 13.8 percentile distance from the CCi (with the CCi edge being 0% and the Fr inferior limit being 100%). In the medial-lateral plane, most electrode tips were in the transition between the gray and white matter of SCG.

Conclusions. Active contacts in patients who responded to DBS were relatively clustered within the SCG. Be- cause of the anatomical variability in the size and shape of the SCG, the authors developed a method to standardize the targeting of this region.

Neurosurgery 64:654–663, 2009 DOI: 10.1227/01.NEU.0000340684.60443.55

OBJECTIVE: To conduct a prospective, open, nonrandomized study of treatment- associated morbidity in patients undergoing microsurgery or gamma knife radiosurgery (GKRS) for vestibular schwannomas.

METHODS: Ninety- one patients with vestibular schwannomas with a maximum tumor diameter of 25 mm in the cerebellopontine angle were treated according to a prospective protocol either by GKRS (63 patients) or open microsurgery (28 patients) using the suboccipital approach. Primary end points included hearing function, according to the Gardner- Robertson scale, and facial nerve function, according to the House- Brackmann scale at 2 years. Clinical data included a balance platform test, score for tinnitus and vertigo using a visual analog scale, and working ability. Patients responded to the qualityof- life questionnaires Short- Form 36 and Glasgow Benefit Inventory.

RESULTS: Three elderly GKRS patients withdrew; all remaining patients were followed for 2 years. Both primary end points were highly significant in favor of GKRS (P<0.001). Evidence of reduced facial nerve function (House- Brackmann grade 2 or poorer) at 2 years was found in 13 of 28 open microsurgery patients and 1 of 60 GKRS patients. Thirteen of 28 patients who underwent surgery had serviceable hearing (Gardner- Robertson grade A or B) preoperatively, but none had serviceable hearing postoperatively. Twentyfive of 60 GKRS patients had serviceable hearing before treatment, and 17 (68%) of them had serviceable hearing 2 years after treatment. The tinnitus and vertigo visual analog scale score, as well as balance platform tests, did not change significantly after treatment, and working status did not differ between the groups at 2 years. Quality of life was significantly better in the GKRS group at 2 years, based on the Glasgow Benefit Inventory questionnaire. One GKRS patient required operative treatment within the 2-year study period.

CONCLUSION: This is the second prospective study to demonstrate better facial nerve and hearing outcomes from GKRS than from open surgery for small- and medium- sized vestibular schwannomas.

J Neurosurg 111:820–824, 2009. DOI: 10.3171/2009.3.JNS081695

Object. Frameless stereotactic biopsy has been shown in multiple studies to be a safe and effective tool for the diagnosis of brain lesions. However, no study has directly evaluated its safety in lesions located in eloquent regions in comparison with noneloquent locations. In this study, the authors determine whether an increased risk of neurological decline is associated with biopsy of lesions in eloquent regions of the brain.
Methods. Medical records, including imaging studies, were reviewed for 284 cases in which frameless stereotactic biopsy procedures were performed by 19 neurosurgeons at 7 institutions between January 2000 and December 2006. Lesion location was classified as eloquent or noneloquent in each patient. The incidence of neurological decline was calculated for each group.
Results. During the study period, 160 of the 284 biopsies predominately involved eloquent regions of the brain. In evaluation of the complication rate with respect to biopsy site, neurological decline occurred in 9 (5.6%) of 160 biopsies in eloquent brain areas and 10 (8.1%) of 124 biopsies in noneloquent regions; this difference was not statistically significant (p = 0.416). A higher number of needle passes was associated with the presence of a postoperative hemorrhage at the biopsy site, although not with a change in the result of neurological examination.
Conclusions. Frameless stereotactic biopsy of lesions located in eloquent brain regions is as safe and effective as biopsy of lesions in noneloquent regions. Therefore, with careful planning, frameless stereotactic biopsy remains a valuable and safe tool for diagnosis of brain lesions, independent of lesion location.

Stereotact Funct Neurosurg 2009;87:322-329 (DOI:10.1159/000235804)

After implantation of the first electrode in bilateral deep brain stimulation (DBS) lead implantation, brain shift effects in the target region and along the implantation trajectory of the second electrode are quantified with intraoperative magnetic resonance imaging (MRI). We investigated intraoperative X-ray imaging for its feasibility in indirect detection of brain shift.

Methods: In 25 patients who underwent bilateral DBS lead implantation, X-ray and MRI were performed before and after implantation of the first electrode. Two parameters of brain shift were assessed with nonrigid free-form deformation field analysis of the MRI data: global brain shift along the anterior and posterior commissure (AC-PC) line and specific brain shift along the implantation trajectory of the second electrode. Pre- and intraoperative X-ray images were geometrically and intensity corrected for detection of significant signal changes through intracranial air accumulation during implantation of the first electrode.

Results: After implantation of the first electrode, brain shift greater than 1 mm (maximum 1.3 mm) was observed at the AC and brain shift greater than 2 mm (maximum 2.5 mm) was observed along the planned implantation trajectory of the second electrode. In 1 patient, the implantation trajectory of the second electrode went through a sulcus after cortical brain shift. In 9 patients, intracranial air volume between 0.1 and 38.5 ml was observed with MRI after implantation of the first electrode. Significant X-ray absorption changes were induced by an intracranial air volume of greater than 8 ml.

Conclusion: In bilateral DBS implantation, brain shift effects can cause misallocation of the second electrode with the risk of adverse or no stimulation effects as well as unnecessary cortical damage. A lack of X-ray signal changes caused by intracranial air invasion during DBS lead implantation indicates a lack of clinically relevant brain shift.