Robotic alignment system Cirq (Brainlab) for navigated brain tumor biopsies in children.

INTRODUCTION: The Cirq robotic alignment system (Brainlab, Munich, Germany) is a manually adjustable electronic arm with a robotic alignment module on its distal end, enabling the neurosurgeon to automatically and accurately align surgical instruments to a preoperatively planned trajectory. In this study, we share our first experiences and results using Cirq for intracranial tumor biopsy in children. METHODS: From May 2021 until October 2022, all consecutive patients that underwent a brain tumor biopsy using Cirq were included and compared to a historical cohort of patients biopsied with the non-robotic system Varioguide (Brainlab, Munich, Germany). Patient-related data, tumor-related data, and surgery-related data were collected. Registration accuracy was calculated for different patient-to-image registration methods. Pre- and postoperative images were fused, and entry error, target error, and angulation error were calculated. RESULTS: Thirty-seven patients, aged 1-19 years, were included (14 with Cirq and 23 with Varioguide). An integrated histopathological and molecular diagnosis was acquired in all cases. Patient-to-image registration was significantly more accurate when based on bone screw fiducials combined with intraoperative CT, as compared to surface matching or skin fiducials. The target error (Euclidian distance) was 5.3 mm for Cirq as compared to 8.3 mm for Varioguide, but this was not statistically significant. Entry error and angulation error were also not significantly different between both groups. CONCLUSION: Intracranial biopsy with the Cirq robotic system is feasible and safe, and its accuracy does not differ from the Varioguide system.

Patient-reported outcome measures more than fifteen years after treatment of sagittal or metopic craniosynostosis: a prospective cohort study.

PURPOSE: To evaluate the long-term anthropometric measurements, cosmetic satisfaction, and other patient-reported outcome measures (PROMs) of patients who underwent surgical treatment or observation only of sagittal or metopic single-suture craniosynostosis (SSC). METHODS: A prospective study was designed for all patients diagnosed with non-syndromic sagittal and metopic craniosynostosis at the British Columbia Children's Hospital, Vancouver, Canada, in the period July 1986 to July 2006. After a minimum of 15 years post-diagnosis, all eligible patients were invited to fill out the Craniofacial Surgery Outcomes Questionnaire (CSO-Q) and to attend a scheduled follow-up appointment for the collection of anthropometric measurements. A descriptive analysis of the cosmetic results was performed. Statistical analyses compared the differences in anthropometric measurements between treated and non-treated patients. RESULTS: Of the 253 eligible patients, 52 participants were willing to share patient data for use in the study. Of those 52 former patients, 36 (69.2%) filled out and returned the CSO-Q and 23 (44.2%) attended the follow-up appointment. The mean follow-up period between surgical treatment and the CSO-Q was 20.2 ± 2.5 years and between surgical treatment and the follow-up appointment was 20.9 ± 2.7 years. In patients with sagittal SSC, the mean cephalic index (CI) was significantly larger in treated than in non-treated patients (74.6 versus 69.1, p = 0.04), while the mean pupillary distance and forehead to back index were significantly smaller (pupillary distance 6.0 cm versus 6.7 cm [p = 0.04] and forehead to back index 19.6 cm versus 21.1 cm [p = 0.03]). Focusing more on the patient reported outcome measures, overall cosmetic satisfaction was found to be high (80.6%) and no differences were found between sagittal and metopic synostosis patients, nor between treated or non-treated craniosynostosis patients. Overall outcomes regarding self-esteem (RSES) and fear of negative evaluation (FNE) were comparable with population based outcomes. CONCLUSION: This is the first prospective study of sagittal and metopic craniosynostosis patients regarding long-term anthropometric outcome and patient reported outcome measures, including patients who were treated surgically and those who received observation only. Although study participation two decades after initial diagnosis was difficult to obtain, our data provide a platform from which one can develop an inclusive and uniform approach to assess patients' subjective cosmetic satisfaction using the CSO-Questionnaire and might be useful in preoperative counseling and psychosocial care for patients and their families.

Cosmetic satisfaction and patient-reported outcome measures following cranioplasty after craniectomy - A prospective cohort study.

Introduction: Evaluating patient-reported outcomes (PROMs) helps optimize preoperative counseling and psychosocial care for patients who underwent cranioplasty. Research question: This study aimed to evaluate cosmetic satisfaction, level of self-esteem, and fear of negative evaluation (FNE) of patients who underwent cranioplasty. Material and methods: Patients who underwent cranioplasty from 1 January 2014 to 31 December 2020 â€‹at University Medical Center Utrecht and a control group consisting of our center' employees were invited to fill out the Craniofacial Surgery Outcomes Questionnaire (CSO-Q), consisting of an assessment of cosmetic satisfaction, the Rosenberg Self-Esteem Scale (RSES), and the FNE scale. To test for differences in results, chi-square tests and T-tests were performed. Logistic regression was used to study the effect of cranioplasty-related variables on cosmetic satisfaction. Results: Cosmetic satisfaction was seen in 44/80 patients (55.0%) and 52/70 controls (74.3%) (p â€‹= â€‹0.247). Thirteen patients (16.3%) and 8 controls (11.4%) had high self-esteem (p â€‹= â€‹0.362), 51 patients (63.8%) and 59 controls (84.3%) had normal self-esteem (p â€‹= â€‹0.114), and 7 patients (8.8%) and 3 controls (4.3%) had low self-esteem (p â€‹= â€‹0.337). Forty-nine patients (61.3%) and 39 controls (55.7%) had low FNE (p â€‹= â€‹0.012), 8 patients (10.0%) and 18 controls (25.7%) had average FNE (p â€‹= â€‹0.095), and 6 patients (7.5%) and 13 controls (18.6%) had high FNE (p â€‹= â€‹0.215). Cosmetic satisfaction was associated with glass fiber-reinforced composite implants (OR 8.20, p-value â€‹= â€‹0.04). Discussion and conclusion: This study prospectively evaluated PROMs following cranioplasty, for which we found favorable results.

Development of a Prediction Model for Cranioplasty Implant Survival Following Craniectomy.

BACKGROUND: Cranioplasty after craniectomy can result in high rates of postoperative complications. Although determinants of postoperative outcomes have been identified, a prediction model for predicting cranioplasty implant survival does not exist. Thus, we sought to develop a prediction model for cranioplasty implant survival after craniectomy. METHODS: We performed a retrospective cohort study of patients who underwent cranioplasty following craniectomy between 2014 and 2020. Missing data were imputed using multiple imputation. For model development, multivariable Cox proportional hazards regression analysis was performed. To test whether candidate determinants contributed to the model, we performed backward selection using the Akaike information criterion. We corrected for overfitting using bootstrapping techniques. The performance of the model was assessed using discrimination and calibration. RESULTS: A total of 182 patients were included (mean age, 43.0 ± 19.7 years). Independent determinants of cranioplasty implant survival included the indication for craniectomy (compared with trauma-vascular disease: hazard ratio [HR], 0.65 [95% confidence interval (CI), 0.36-1.17]; infection: HR, 0.76 [95% CI, 0.32-1.80]; tumor: HR, 1.40 [95% CI, 0.29-6.79]), cranial defect size (HR, 1.01 per cm2 [95% CI, 0.73-1.38]), use of an autologous bone flap (HR, 1.63 [95% CI, 0.82-3.24]), and skin closure using staples (HR, 1.42 [95% CI, 0.79-2.56]). The concordance index of the model was 0.60 (95% CI, 0.47-0.73). CONCLUSIONS: We have developed the first prediction model for cranioplasty implant survival after craniectomy. The findings from our study require external validation and deserve further exploration in future studies.

Cranial decompression and expansion surgery for the treatment of refractory idiopathic intracranial hypertension: case report and systematic review.

OBJECTIVE: The purpose of this study is to systematically review the literature on the clinical outcomes following different surgical techniques in patients with refractory idiopathic intracranial hypertension (IIH). BACKGROUND: IIH is a condition characterised by increased cranial pressure (ICP) in the absence of an intracranial lesion that does not adequately respond to different medical and surgical therapies. Cranial decompression or expansion surgeries are a last resort therapy for patients with refractory IIH. METHODS: A systematic literature search of the databases of PubMed, Embase and Medline from inception to 2019 was performed. Searches were limited to the English language and to clinical studies. Studies were included if clinical outcomes following different cranial decompression or expansion techniques were reported. We also add one case of our own experience with performing a bilateral frontoparietal expansion craniotomy and subtemporal craniectomy. RESULTS: Five manuscripts, describing 38 procedures, met the inclusion criteria. Thirty-one patients were female (82%). The mean age was 26.2 years. The techniques studied included subtemporal craniectomy (27/38, 71%), internal cranial expansion (10/38, 26%), and cranial morcellation decompression (1/38, 3%). Thirty-five patients presented with headaches of which 17 noted postoperative improvement or resolution (49%). Visual deficits were documented in 30 patients and 25 reported postoperative improvement (83%). Papilledema disappeared in 23 of 32 patients with this sign at presentation (72%). In our patient, symptoms completely resolved postoperatively and a 6% increase in intracranial volume was measured. CONCLUSIONS: Cranial vault decompression or expansion surgeries may be an effective last resort therapy for patients with refractory IIH. These surgeries expand the intracranial volume, and thus may normalise ICP, leading to clinical improvement.

Distance Control and Virtual Drilling Improves Anatomical Orientation During Anterior Petrosectomy.

BACKGROUND: A combined drill distance control and virtual drilling image guidance feedback method was developed. OBJECTIVE: To investigate whether first-time usage of the proposed method, during anterior petrosectomy (AP), improves surgical orientation and surgical performance. The accuracy of virtual drilling and the clinical practicability of the method were also investigated. METHODS: In a simulated surgical setting using human cadavers, a trial was conducted with 5 expert skull base surgeons from 3 different hospitals. They performed 10 AP approaches, using either the feedback method or standard image guidance. Damage to critical structures was assessed. Operating time, drill cavity sizes, and proximity of postoperative drill cavities to the cochlea and the acoustic meatus, were measured. Questionnaires were obtained postoperatively. Errors in the virtual drill cavities as compared with actual postoperative cavities were calculated. In a clinical setup, the method was used during AP. RESULTS: Surgeons rated their intraoperative orientation significantly better with the feedback method compared with standard image guidance. During the cadaver trial, the cochlea was harmed on 1 occasion in the control group, while surgeons drilled closer to the cochlea and meatus without injuring them in the group using feedback. Virtual drilling under- and overestimation errors were 2.2 ± 0.2 and -3.0 ± 0.6 mm on average. The method functioned properly during the clinical setup. CONCLUSION: The proposed feedback method improves orientation and surgical performance in an experimental setting. Errors in virtual drilling reflect spatial errors of the image guidance system. The feedback method is clinically practicable during AP.

Cranioplasty after craniectomy in pediatric patients-a systematic review.

INTRODUCTION: Complications following cranioplasty with either autografts or cranial implants are commonly reported in pediatric patients. However, data regarding cranioplasty strategies, complications and long-term outcomes are not well described. This study systematically reviews the literature for an overview of current cranioplasty practice in children. METHODS: A systematic review of articles published from inception to July 2018 was performed. Studies were included if they reported the specific use of cranioplasty materials following craniectomy in patients younger than 18 years of age, and had a minimum follow-up of at least 1 year. RESULTS: Twenty-four manuscripts, describing a total of 864 cranioplasty procedures, met the inclusion criteria. The age of patients in this aggregate ranged from 1 month to 20 years and the weighted average was 8.0 years. The follow-up ranged from 0.4 months to 18 years and had a weighted average of 40.4 months. Autologous bone grafts were used in 484 cases (56.0%). Resorption, infection and/or hydrocephalus were the most frequently mentioned complications. In this aggregate group, 61 patients needed a revision cranioplasty. However, in 6/13 (46%) papers studying autologous cranioplasties, no data was provided on resorption, infection and revision cranioplasty rates. Cranial implants were used in 380 cases (44.0%), with custom-made porous hydroxyapatite being the most commonly used material (100/380, 26.3%). Infection and migration/fracturing/loosening were the most frequently documented complications. Eleven revision cranioplasties were reported. Again, no data was reported on infection and revision cranioplasty rates, in 7/16 (44%) and 9/16 (56%) of papers, respectively. CONCLUSION: Our systematic review illuminates that whether autografts or cranial implants are used, postcranioplasty complications are quite common. Beyond this, the existing literature does not contain well documented and comparable outcome parameters, suggesting that prospective, long-term multicenter cohort studies are needed to be able to optimize cranioplasty strategies in children who will undergo cranioplasty following craniectomy.

Cranioplasties following craniectomies in children-a multicenter, retrospective cohort study.

OBJECTIVE: Complications following pediatric cranioplasty after craniectomy with either autologous bone flaps or cranial implants are reported to be common, particularly bone flap resorption. However, only sparse data are available regarding cranioplasty strategies, complications, and outcomes. This manuscript describes a Canadian-Dutch multicenter pediatric cohort study with autografts and cranial implant cranioplasties following craniectomies for a variety of indications. METHODS: The study included all children (< 18 years) who underwent craniectomy and subsequent cranioplasty surgeries from 2008 to 2014 (with a minimum of 1-year follow-up) at four academic hospitals with a dedicated pediatric neurosurgical service. Data were collected regarding initial diagnosis, age, time interval between craniectomy and cranioplasty, bone flap storage method, type of cranioplasty for initial procedure (and redo if applicable), and the postoperative outcome including surgical site infection, wound breakdowns, bone flap resorption, and inadequate fit/disfigurement. RESULTS: Sixty-four patients (46 males, average age 9.7 ± 5.5 years) were eligible for inclusion, with mean follow-up of 82.3 ± 31.2 months after craniectomy. Forty cranioplasties (62.5%) used autologous bone re-implant, 23 (57.5%) of which showed resorption. On average, resorption was documented at 434 days (range 62-2796 days) after reimplantation. In 20 cases, a revision cranioplasty was needed. In 24 of the post-craniectomy cases (37.5%), a cranial implant was used with one of ten different implant types. Implant loosening prompted a complete revision cranioplasty in 2 cases (8.3%). Cranial implants were associated with low morbidity and lower reoperation dates compared to the autologous cranioplasties. CONCLUSION: The most prominent finding in this multicenter cohort study was that bone flap resorption in children remains a common and widespread problem following craniectomy. Cranioplasty strategies varied between centers and evolved over time within centers. Cranial implants were associated with low morbidity and low reoperation rates. Still, longer term and prospective multicenter cohort studies are needed to optimize cranioplasty strategies in children after craniectomies.

Benchmarking Distance Control and Virtual Drilling for Lateral Skull Base Surgery.

BACKGROUND: Novel audiovisual feedback methods were developed to improve image guidance during skull base surgery by providing audiovisual warnings when the drill tip enters a protective perimeter set at a distance around anatomic structures ("distance control") and visualizing bone drilling ("virtual drilling"). OBJECTIVE: To benchmark the drill damage risk reduction provided by distance control, to quantify the accuracy of virtual drilling, and to investigate whether the proposed feedback methods are clinically feasible. METHODS: In a simulated surgical scenario using human cadavers, 12 unexperienced users (medical students) drilled 12 mastoidectomies. Users were divided into a control group using standard image guidance and 3 groups using distance control with protective perimeters of 1, 2, or 3 mm. Damage to critical structures (sigmoid sinus, semicircular canals, facial nerve) was assessed. Neurosurgeons performed another 6 mastoidectomy/trans-labyrinthine and retro-labyrinthine approaches. Virtual errors as compared with real postoperative drill cavities were calculated. In a clinical setting, 3 patients received lateral skull base surgery with the proposed feedback methods. RESULTS: Users drilling with distance control protective perimeters of 3 mm did not damage structures, whereas the groups using smaller protective perimeters and the control group injured structures. Virtual drilling maximum cavity underestimations and overestimations were 2.8 ± 0.1 and 3.3 ± 0.4 mm, respectively. Feedback methods functioned properly in the clinical setting. CONCLUSION: Distance control reduced the risks of drill damage proportional to the protective perimeter distance. Errors in virtual drilling reflect spatial errors of the image guidance system. These feedback methods are clinically feasible.

Thulium laser-assisted endoscopic third ventriculostomy: Determining safe laser settings using in vitro model and 2 year follow-up results in 106 patients.

BACKGROUND AND OBJECTIVE: Endoscopic third ventriculostomy is used to treat hydrocephalus. Different laser wavelengths have been proposed for laser-assisted endoscopic third ventriculostomies over the last decades. The aim of this study was to evaluate Thulium laser endoscopic third ventriculostomy heat penetration in the surrounding environment of the floor of the third ventricle in an in vitro setting with visualization of thermal distribution. Subsequently 106 Thulium laser endoscopic third ventriculostomy procedures were retrospectively analyzed to demonstrate safety. METHODS: The in vitro visualization was based on the color Schlieren method. The heat penetration was measured beneath a tissue phantom of the floor of the third ventricle with a fiber of 365 µm in diameter at different energy settings; 1.0W (956 J/cm2 ), 2.0W (1,912 J/cm2 ), 4.0W (3,824 J/cm2 ), and 7.0W (6,692 J/cm2 ), with a pulse duration of 1.0 second. All experiments were repeated five times. In addition, 106 Thulium laser endoscopic third ventriculostomy procedures between 2005 and 2015 were retrospectively analysed for etiology, sex, complications, and laser parameters. RESULTS: In the energy settings from 1.0 to 4.0 W, heat penetration depth beneath the phantom of the third ventricle did not exceed 1.5 mm. The heat penetration depth at 7 W, exceeded 6 mm. The clinical overall success rate was 80% at the 2-year follow-up study. Complications occurred in 5% of the procedures. In none of the 106 investigated clinical patients bleeding or damage to the basilar artery was encountered due to Thulium laser ablation. CONCLUSIONS: The in vitro experiments show that under 4.0W the situation is considered safe, due to low penetration of heat, thus the chance of accidentally damaging critical structures like the basilar artery is very small. The clinical results show that the Thulium laser did not cause any bleeding of the basilar artery, and is a safe technique for laser endoscopic third ventriculostomy. Lasers Surg. Med. © 2017 Wiley Periodicals, Inc.

Minimally Invasive Strip Craniectomy Simplifies Anesthesia Practice in Patients With Isolated Sagittal Synostosis.

BACKGROUND: Traditional open corrective surgery for isolated sagittal synostosis entails significant blood loss, transfusion rates, morbidity, and a lengthy hospitalization. Minimally invasive strip craniectomy (MISC) was introduced to avoid the disadvantages of open techniques. OBJECTIVES: The aim of the study was, first, to compare the anesthesia practice in MISC and open extended strip craniectomy (OESC), and, second, to evaluate the incidence of perioperative complications in both surgical procedures. METHODS: A retrospective analysis was conducted for all consecutive patients receiving either OESC or MISC for nonsyndromic isolated sagittal synostosis between January 2006 and February 2014. The primary endpoints were the volume of blood loss, the volume of infused blood products, the duration of surgery, the anesthesia time, the intubation time, and the length of admission to high care units and the hospital. RESULTS: In MISC, the median duration of surgery (90 versus 178 min.), anesthesia time (178 versus 291 min), and intubation time (153 versus 294 min) were all significantly (P < 0.001) shorter than in OESC. Intraoperative blood loss was less in MISC than in OESC (3.8 versus 29.7 mL/kg, P < 0.001), requiring less crystalloids (33.3 versus 76.9 mL/kg, P < 0.001) as well as less erythrocyte transfusions (0.0 versus 19.7 mL/kg, P < 0.001) in a smaller number of patients (2/20 versus 13/15). The improved hemodynamic stability in MISC allowed for placement of less arterial and central venous catheters. After OESC all 15 patients were admitted to high care units, compared with 9 of 20 in MISC. The overall median hospital stay was shorter in MISC than in OESC (4 versus 6 d, P < 0.001). Although the incidence of technical complications was similar in both techniques, patients in MISC were less affected by perioperative electrolyte and acid-base disturbances and postoperative pyrexia. CONCLUSIONS: Minimally invasive strip craniectomy simplifies anesthesia practice relative to OESC with shorter operative times, decreased needs for replacement fluids and blood products, lessened requirements for invasive monitoring, and reduced demands for postoperative high care beds.

Frameless image-guided stereotactic brain biopsies: emphasis on diagnostic yield.

BACKGROUND: Studies regarding frameless stereotactic brain biopsy mainly report high diagnostic yield (DY) as opposed to relatively low diagnostic accuracy. This discrepancy raises the question of the certainty and precision of obtained diagnoses. This article proposes a DY definition encompassing diagnostic certainty and precision according to the World Health Organization (WHO) central nervous system (CNS) tumour classification system. Furthermore, our eight-year experience with this procedure is reviewed and evaluated. METHODS: A consecutive series of 235 frameless biopsy procedures was reviewed. Criteria were set up for categorising obtained diagnoses. All cases were included in a predictive factor analysis of inconclusive biopsy and postoperative complications. RESULTS: According to our predefined DY criteria, the DY was 72.8 %. The inconclusive biopsy outcome measured 21.7 %; the non-diagnostic biopsy outcome was 5.5 %. The only predictive factor found for inconclusive biopsy procedures was age under 30. Predictive factors for postoperative complications, which were found statistically significant after multivariable analysis, were glucose level and intra-operative haemorrhage. The total morbidity rate was 8.5 %, including a mortality rate of 0.9 %. CONCLUSIONS: Although frameless stereotactic brain biopsy procedures are considered to be relatively safe, the true DY is significantly less than previously reported, most probably due to the lack of standardised DY criteria. Based on our DY definition and subsequent DY findings, standardisation of DY criteria and definition is paramount for biopsy diagnosis interpretation.

Surgical instrument tracking optimizes trans-sphenoidal endoscopic treatment of petrous apex cholesterol granuloma.

During endoscopic trans-sphenoidal treatment of petrous apex cholesterol granuloma, the challenge for the surgeon is to drill the posterior wall of the sphenoid sinus to reach the lesion while attempting to avoid the internal carotid artery (ICA). A refined neuronavigation technique is presented that diminishes bonework needed for exposure and marsupialization, and simultaneously minimizes risks of accidental harm to the ICA. The technique utilizes real-time intraoperative instrument tracking of a drill, enabling safe creation of a direct canal toward the cyst just medial to the paraclival ICA and of a curette for entirely image-guided marsupialization of the cyst's deep areas through the canal.

Validation of exposure visualization and audible distance emission for navigated temporal bone drilling in phantoms.

BACKGROUND: A neuronavigation interface with extended function as compared with current systems was developed to aid during temporal bone surgery. The interface, named EVADE, updates the prior anatomical image and visualizes the bone drilling process virtually in real-time without need for intra-operative imaging. Furthermore, EVADE continuously calculates the distance from the drill tip to segmented temporal bone critical structures (e.g. the sigmoid sinus and facial nerve) and produces audiovisual warnings if the surgeon drills in too close vicinity. The aim of this study was to evaluate the accuracy and surgical utility of EVADE in physical phantoms. METHODOLOGY/PRINCIPAL FINDINGS: We performed 228 measurements assessing the position accuracy of tracking a navigated drill in the operating theatre. A mean target registration error of 1.33±0.61 mm with a maximum error of 3.04 mm was found. Five neurosurgeons each drilled two temporal bone phantoms, once using EVADE, and once using a standard neuronavigation interface. While using standard neuronavigation the surgeons damaged three modeled temporal bone critical structures. No structure was hit by surgeons utilizing EVADE. Surgeons felt better orientated and thought they had improved tumor exposure with EVADE. Furthermore, we compared the distances between surface meshes of the virtual drill cavities created by EVADE to actual drill cavities: average maximum errors of 2.54±0.49 mm and -2.70±0.48 mm were found. CONCLUSIONS/SIGNIFICANCE: These results demonstrate that EVADE gives accurate feedback which reduces risks of harming modeled critical structures compared to a standard neuronavigation interface during temporal bone phantom drilling.

Determination of a facial nerve safety zone for navigated temporal bone surgery.

BACKGROUND: Transtemporal approaches require surgeons to drill the temporal bone to expose target lesions while avoiding the critical structures within it, such as the facial nerve and other neurovascular structures. We envision a novel protective neuronavigation system that continuously calculates the drill tip-to-facial nerve distance intraoperatively and produces audiovisual warnings if the surgeon drills too close to the facial nerve. Two major problems need to be solved before such a system can be realized. OBJECTIVE: To solve the problems of (1) facial nerve segmentation and (2) calculating a safety zone around the facial nerve in relation to drill-tip tracking inaccuracies. METHODS: We developed a new algorithm called NerveClick for semiautomatic segmentation of the intratemporal facial nerve centerline from temporal bone computed tomography images. We evaluated NerveClick's accuracy in an experimental setting of neuro-otologic and neurosurgical patients. Three neurosurgeons used it to segment 126 facial nerves, which were compared with the gold standard: manually segmented facial nerve centerlines. The centerlines are used as a central axis around which a tubular safety zone is built. The zone's thickness incorporates the drill tip tracking errors. The system will warn when the tracked tip crosses the safety zone. RESULTS: Neurosurgeons using NerveClick could segment facial nerve centerlines with a maximum error of 0.44 ± 0.23 mm (mean ± standard deviation) on average compared with manual segmentations. CONCLUSION: Neurosurgeons using our new NerveClick algorithm can robustly segment facial nerve centerlines to construct a facial nerve safety zone, which potentially allows timely audiovisual warnings during navigated temporal bone drilling despite tracking inaccuracies.

The impact of workflow and volumetric feedback on frameless image-guided neurosurgery.

OBJECTIVE: During image-guided neurosurgery, if the surgeon is not fully orientated to the surgical position, he or she will briefly shift attention toward the visualization interface of an image guidance station, receiving only momentary "point-in-space" information. The aim of this study was to develop a novel visual interface for neuronavigation during brain tumor surgery, enabling intraoperative feedback on the entire progress of surgery relative to the anatomy of the brain and its pathology, regardless of the interval at which the surgeon chooses to look. METHODS: New software written in Java (Sun Microsystems, Inc., Santa Clara, CA) was developed to visualize the cumulative recorded instrument positions intraoperatively. This allowed surgeons to see all previous instrument positions during the elapsed surgery. This new interactive interface was then used in 17 frameless image-guided neurosurgical procedures. The purpose of the first 11 cases was to obtain clinical experience with this new interface. In these cases, workflow and volumetric feedback (WVF) were available at the surgeons' discretion (Protocol A). In the next 6 cases, WVF was provided only after a complete resection was claimed (Protocol B). RESULTS: With the novel interactive interface, dynamics of surgical resection, displacement of cortical anatomy, and digitized functional data could be visualized intraoperatively. In the first group (Protocol A), surgeons expressed the view that WVF had affected their decision making and aided resection (10 of 11 cases). In 3 of 6 cases in the second group (Protocol B), tumor resections were extended after evaluation of WVF. By digitizing the cortical surface, an impression of the cortical shift could be acquired in all 17 cases. The maximal cortical shift measured 20 mm, but it typically varied between 0 and 10 mm. CONCLUSION: Our first clinical results suggest that the embedding of WVF contributes to improvement of surgical awareness and tumor resection in image-guided neurosurgery in a swift and simple manner.

Auditory feedback during frameless image-guided surgery in a phantom model and initial clinical experience.

In this study the authors measured the effect of auditory feedback during image-guided surgery (IGS) in a phantom model and in a clinical setting. In the phantom setup, advanced IGS with complementary auditory feedback was compared with results obtained with 2 routine forms of IGS, either with an on-screen image display or with image injection via a microscope. The effect was measured by means of volumetric resection assessments. The authors also present their first clinical data concerning the effects of complementary auditory feedback on instrument handling during image-guided neurosurgery. When using image-injection through the microscope for navigation, however, resection quality was significantly worse. In the clinical portion of the study, the authors performed resections of cerebral mass lesions in 6 patients with the aid of auditory feedback. Instrument tip speeds were slightly (although significantly) influenced by this feedback during resection. Overall, the participating neurosurgeons reported that the auditory feedback helped in decision-making during resection without negatively influencing instrument use. Postoperative volumetric imaging studies revealed resection rates of > or = 95% when IGS with auditory feedback was used. There was only a minor amount of brain shift, and postoperative resection volumes corresponded well with the preoperative intentions of the neurosurgeon. Although the results of phantom surgery with auditory feedback revealed no significant effect on resection quality or extent, auditory cues may help prevent damage to eloquent brain structures.

Application accuracy in frameless image-guided neurosurgery: a comparison study of three patient-to-image registration methods.

OBJECT: The aim of this study was to compare three patient-to-image registration methods in frameless stereotaxy in terms of their application accuracy (the accuracy with which the position of a target can be determined intraoperatively). In frameless stereotaxy, imaging information is transposed to the surgical field to show the spatial position of a localizer or surgical instrument. The mathematical relationship between the image volume and the surgical working space is calculated using a rigid body transformation algorithm, based on point-pair matching or surface matching. METHODS: Fifty patients who were scheduled to undergo a frameless image-guided neurosurgical procedure were included in the study. Prior to surgery, the patients underwent either computerized tomography (CT) scanning or magnetic resonance (MR) imaging with widely distributed adhesive fiducial markers on the scalp. An extra fiducial marker was placed on the head as a target, as near as possible to the intracranial lesion. Prior to each surgical procedure, an optical tracking system was used to perform three separate patient-to-image registration procedures, using anatomical landmarks, adhesive markers, or surface matching. Subsequent to each registration, the target registration error (TRE), defined as the Euclidean distance between the image space coordinates and world space coordinates of the target marker, was determined. Independent of target location or imaging modality, mean application accuracy (+/- standard deviation) was 2.49 +/- 1.07 mm when using adhesive markers. Using the other two registration strategies, mean TREs were significantly larger (surface matching, 5.03 +/- 2.30 mm; anatomical landmarks, 4.97 +/- 2.29 mm; p < 0.001 for both). CONCLUSIONS: The results of this study show that skin adhesive fiducial marker registration is the most accurate noninvasive registration method. When images from an earlier study are to be used and accuracy may be slightly compromised, anatomical landmarks and surface matching are equally accurate alternatives.

Image-guided vascular neurosurgery based on three-dimensional rotational angiography. Technical note.

Three-dimensional rotational angiography is capable of exquisite visualization of cerebral blood vessels and their pathophysiology. Unfortunately, images obtained using this modality typically show a small region of interest without exterior landmarks to allow patient-to-image registration, precluding their use for neuronavigation purposes. The aim of this study was to find an alternative technique to enable 3D rotational angiography-guided vascular neurosurgery. Three-dimensional rotational angiograms were obtained in an angiographic suite with direct navigation capabilities. After image acquisition, a navigated pointer was used to touch fiducial positions on the patient's head. These positions were located outside the image volume but could nevertheless be transformed into image coordinates and stored in the navigation system. Prior to surgery, the data set was transferred to the navigation system in the operating room, and the same fiducial positions were touched again to complete the patient-to-image registration. This technique was tested on a Perspex phantom representing the cerebral vascular tree and on two patients with an intracranial aneurysm. In both the phantom and patients, the neuronavigation system provided 3D images representing the vascular tree in its correct orientation, that is, the orientation seen by the neurosurgeon through the microscope. In one patient, tissue shift was clearly observed without significant changes in the orientation of the structures. Results in this study demonstrate the feasibility of using 3D rotational angiography data sets for neuronavigation purposes. Determining the benefit of this type of navigation should be the subject of future studies.

The effect of repetitive manual fiducial localization on target localization in image space.

OBJECTIVE: In this clinical study, we quantify intra- and interobserver variability of manual fiducial localization in image space, as the effect of repetitive manual fiducial localization is still unclear, especially on a target position. METHODS: After uploading eight imaging datasets with a total of 56 skin adhesive fiducial markers in a commercially available image-guidance system, the centroids of the fiducial markers were tagged. This task was executed repeatedly at three separate moments by six different observers. The fiducial localization variability and its target shift effect in image space were determined out of 1008 tagged fiducial markers. RESULTS: The maximal intraobserver target shift effect measured 0.72 +/- 0.14 mm in computed tomographic image space and 0.95 +/- 0.21 mm in magnetic resonance image space. CONCLUSION: If a fiducial tagging task is well understood, repetitive manual detection of fiducial markers can be done with a low intraobserver fiducial localization variability, resulting in a submillimetric effect on a target position, either in computed tomographic or magnetic resonance image space. Therefore, we think it is justified to determine the centroids of a skin adhesive fiducial marker in the image space by hand.