Deep learning to predict risk of lateral skull base cerebrospinal fluid leak or encephalocele.

PURPOSE: Skull base features, including increased foramen ovale (FO) cross-sectional area, are associated with lateral skull base spontaneous cerebrospinal fluid (sCSF) leak and encephalocele. Manual measurement requires skill in interpreting imaging studies and is time consuming. The goal of this study was to develop a fully automated deep learning method for FO segmentation and to determine the predictive value in identifying patients with sCSF leak or encephalocele. METHODS: A retrospective cohort study at a tertiary care academic hospital of 34 adults with lateral skull base sCSF leak or encephalocele were compared with 815 control patients from 2013-2021. A convolutional neural network (CNN) was constructed for image segmentation of axial computed tomography (CT) studies. Predicted FO segmentations were compared to manual segmentations, and receiver operating characteristic (ROC) curves were constructed. RESULTS: 295 CTs were used for training and validation of the CNN. A separate dataset of 554 control CTs was matched 5:1 on age and sex with the sCSF leak/encephalocele group. The mean Dice score was 0.81. The sCSF leak/encephalocele group had greater mean (SD) FO cross-sectional area compared to the control group, 29.0 (7.7) mm2 versus 24.3 (7.6) mm2 (P = .002, 95% confidence interval 0.02-0.08). The area under the ROC curve was 0.69. CONCLUSION: CNNs can be used to segment the cross-sectional area of the FO accurately and efficiently. Used together with other predictors, this method could be used as part of a clinical tool to predict the risk of sCSF leak or encephalocele.

Safety and Efficacy of Riluzole in Traumatic Spinal Cord Injury: A Systematic Review With Meta-Analyses.

Traumatic spinal cord injury (SCI) is a cause of significant morbidity, often resulting in long-term disability. We aimed to compare outcomes after riluzole versus patients who received placebo or standard of care with no specific intervention. MEDLINE, Embase, Scopus, and Cochrane Library database searches yielded 92 records, and five met the study inclusion criteria. Fixed-effect and random-effects models were used to establish odds ratios (ORs) and mean difference (MD) with 95% confidence intervals (CIs) for each outcome. The results of the pooled analysis showed that in patients with acute traumatic SCI, riluzole resulted in increased American Spinal Injury Association (ASIA) motor scores at 3 months (MD 0.26, 95% CI [-0.10,0.61], I2 = 0%; p = 0.157) and 6 months (MD 0.21, 95% CI [-0.17,0.60], I2 = 0%; p = 0.280) and change in ASIA Impairment Scale (AIS) at 3 months (OR 0.59, 95% CI [-0.12,1.30], I2 = 0%, p = 0.101) and 6 months (OR 0.28, 95% CI [-0.50,1.06], I2 = 0%, p = 0.479) in comparison to the control groups, though not to a level of statistical significance. Riluzole resulted in fewer adverse events than the control groups (OR -0.12, 95% CI [-1.59,1.35], I2 = 0%, p = 0.874) and lower mortality (OR -0.20, 95% CI [-1.03,0.63], I2 = 0%, p = 0.640), though also not to a level of statistical significance. These meta-analyses suggest that riluzole for the treatment of traumatic SCI is safe and results in improved neurological outcomes when compared to controls, though not to a level of statistical significance. More robust prospective, randomized studies are necessary to help inform the safety and efficacy of riluzole for traumatic SCI.

The complete anterior petrosectomy: an expanded extended-middle fossa approach with removal of the infratrigeminal petrous apex and drilling of the lateral clivus.

Intradural exposure in the extended middle fossa anterior transpetrosal approach is traditionally limited to the inferior petrosal sinus inferomedially. Expanding bone removal of the petrous apex around the petrous internal carotid artery (ICA), underneath the trigeminal ganglion/mandibular nerve, and into the lateral component of the clivus can significantly expand the limits of this approach beyond the inferior petrosal sinus and allows for exposure of the midline structures, aspects of the contralateral inferior clival region, and, when high riding, the vertebrobasilar junction. To date, no descriptive techniques for drilling into the lateral clivus in this approach have been published. The authors provide a detailed stepwise description of their complete anterior petrosectomy, in use at their institution, that involves skeletonization of the posteromedial petrous ICA, gentle elevation of the trigeminal ganglion/mandibular nerve, removal of the infratrigeminal petrous apex, and two techniques for drilling into the lateral clivus along the petroclival fissure. These techniques provide a direct and unobstructed corridor to the midpetroclival region and ventral brainstem with greater maneuverability and enhanced control of the midline structures, which is especially useful for resection of petroclival meningiomas, chondrosarcomas, and giant vascular lesions of the mid- and upper basilar artery and its proximal branches.

Intravascular ultrasound to aid in the diagnosis and revision of an intra-aortic pedicle screw: illustrative case.

BACKGROUND: Pedicle screw impingement on vessel walls has the potential for complications due to pulsatile effects and wall erosion. Artifacts from spinal instrumentation create difficulty in accurately evaluating this interface. The authors present the first case of intravascular ultrasound (IVUS) used to characterize a pedicle screw breach into the aortic lumen. OBSERVATIONS: A 21-year-old female with surgically corrected scoliosis underwent computed tomography angiography (CTA) 3 years postoperatively, which revealed a pedicle screw within the thoracic aorta lumen. Metal artifact distorted the CTA images, which prompted the decision to use intraoperative IVUS. The IVUS confirmed the noninvasive imaging findings and guided final decisions regarding aortic endograft size and location during spine hardware revision. LESSONS: For asymptomatic patients presenting with pedicle screws malpositioned in or near the aorta, treatment decisions revolve around the extent of vessel wall penetration. Intraluminal depth can be obscured by artifact on computed tomography or magnetic resonance imaging or inadequately evaluated by a transesophageal echocardiogram. In our intraoperative experience, IVUS confirmed the depth of vessel lumen violation by a single pedicle screw and no wall penetration by two additional screws of concern. This was useful in deciding on thoracic endovascular aortic repair graft size and landing zone and facilitated safe spinal instrumentation removal and revision.

Neuroendoscopic Evacuation Improves Outcomes Compared with External Ventricular Drainage in Patients with Spontaneous Intraventricular Hemorrhage: A Systematic Review with Meta-Analyses.

BACKGROUND: Spontaneous intraventricular hemorrhage (IVH) is a cause of significant morbidity and mortality. Treatment for resulting obstructive hydrocephalus has traditionally been via an external ventricular drain (EVD). We aimed to compare patient outcomes after neuroendoscopic surgery (NES) evacuation of IVH versus EVD management. METHODS: MEDLINE, Embase, and Cochrane Library databases were searched on October 8, 2022. Of the 252 records remaining after removal of duplicates, 12 met study inclusion criteria. After extraction of outcomes data, fixed-effect and random-effects models were used to establish odds ratios (ORs) with 95% confidence intervals (CIs) for intensive care unit length of stay, rate of permanent cerebrospinal fluid diversion, Glasgow Outcome Scale score, and mortality rate. RESULTS: The results of the pooled analysis showed that intensive care unit length of stay was shorter (OR -2.61 [95% CI -5.02, -0.19]; I2 = 97.76%; P = 0.034), permanent cerebrospinal fluid diversion was less likely (OR -0.79, 95% CI [-1.17, -0.41], I2 = 46.96%, P < 0.001), higher Glasgow Outcome Scale score was more likely (OR 0.48, 95% CI [0.04, 0.93], I2 = 60.12%, P = 0.032), and all-cause mortality was less likely (OR -1.11, 95% CI [-1.79, -0.44], I2 = 0%, P = 0.001) in the NES evacuation group compared with the EVD group. CONCLUSIONS: NES for evacuation of spontaneous IVH results in reduced intensive care unit length of stay, reduced permanent cerebrospinal fluid diversion rates, improved Glasgow Outcome Scale score, and reduced mortality when compared with EVD. More robust prospective, randomized studies are necessary to help inform the safety and utility of NES for IVH.

Frailty in middle cranial fossa approach for encephalocele or cerebrospinal fluid leak repair.

Objective: The modified 5-item frailty index (mFI-5) is a concise, comorbidity-based risk stratification tool that can predict adverse outcomes after surgery. The goal of this study was to understand the frailty of patients undergoing surgery for temporal encephalocele or cerebrospinal fluid (CSF) leak and the utility of mFI-5 for predicting increased post-operative outcomes. Methods: A retrospective review of adults with temporal encephalocele or CSF leak who underwent middle cranial fossa (MCF) approach craniotomies with or without mastoidectomy from January 2015 through August 2021 at a tertiary care academic medical center was performed. Patients who underwent additional surgeries or extended surgical approaches were excluded. The mFI-5 was calculated for all patients. Demographic and clinical data were obtained from the medical record. Results: Thirty-six patients underwent 40 MCF approach craniotomies for temporal encephalocele or CSF leak, including three revision cases and one patient with sequential bilateral operations. Mean age was 54.1 ± 10.8 years, and 66.7% were female. In the univariable regression analysis, mFI-5 score, age, and procedure time use were significantly associated with increased hospital length of stay (LOS) but not increased intensive care unit (ICU) LOS. Anesthesia time and lumbar drain were significantly associated with increased hospital LOS and ICU LOS, and they remained significantly associated with increased hospital LOS in the multivariable model. Conclusion: Frailty is associated with increased hospital LOS stay among patients undergoing MCF approach for CSF leak or encephalocele. Reducing anesthesia time and avoiding lumbar drain use are potentially modifiable risk factors that can reduce the LOS and associated costs. Level of Evidence: 4.

Presacral mature cystic teratoma associated with Currarino syndrome in an adolescent with androgen insensitivity: illustrative case.

BACKGROUND: Currarino syndrome is a rare disorder that classically presents with the triad of presacral mass, anorectal malformation, and spinal dysraphism. The presacral mass is typically benign, although malignant transformation is possible. Surgical treatment of the mass and exploration and repair of associated dysraphism are indicated for diagnosis and symptom relief. There are no previous reports of Currarino syndrome in an androgen-insensitive patient. OBSERVATIONS: A 17-year-old female patient presented with lack of menarche. Physical examination and laboratory investigation identified complete androgen insensitivity. Imaging analysis revealed a presacral mass lesion, and the patient was taken to surgery for resection of the mass and spinal cord untethering. Intraoperative ultrasound revealed a fibrous stalk connecting the thecal sac to the presacral mass, which was disconnected without the need for intrathecal exploration. The presacral mass was then resected, and pathological analysis revealed a mature cystic teratoma. Postoperatively, the patient recovered without neurological or gastrointestinal sequelae. LESSONS: Diagnosis of incomplete Currarino syndrome may be difficult but can be identified via work-up of other disorders, such as androgen insensitivity. Intraoperative ultrasound is useful for surgical decision making and may obviate the need for intrathecal exploration during repair of dysraphism in the setting of Currarino syndrome.

Expansion of the Foramen Ovale in Patients With Cerebrospinal Fluid Leak or Encephalocele.

OBJECTIVE: Spontaneous cerebrospinal fluid (CSF) leaks are associated with elevated intracranial pressure and idiopathic intracranial hypertension (IIH). Skull base erosion and widening of the foramen ovale have been reported in patients with IIH. This study sought to investigate changes in the size of the foramen ovale and foramen spinosum in patients with IIH, spontaneous CSF leak, and encephalocele. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary care academic medical center. PATIENTS: Adult patients treated from 2014 to 2018 with computed tomographic imaging of the head and who were diagnosed with IIH, encephalocele, or CSF leak. INTERVENTION: Two blinded observers measured the long and short axes of the foramen ovale and foramen spinosum on axial computed tomographic images. Measurements were used to calculate the approximate elliptical cross-sectional area of the foramina. MAIN OUTCOME MEASURES: Length, width, and area of the foramen ovale and foramen spinosum. RESULTS: A total of 264 patients were identified meeting the inclusion criteria and were placed into three groups. There were 170 patients with IIH, 48 with spontaneous CSF leak or encephalocele (CSF/E group), and 46 with traumatic or iatrogenic CSF leak (control group). Mean foramen ovale short axis (4.85 ± 1.00 mm) and cross-sectional area (30.17 ± 9.25 mm2) in the CSF/E group were significantly increased compared with measurements in patients with IIH or the control groups. Foramen ovale size was positively correlated with age in the CSF/E group. No significant difference in foramen spinosum size was found. CONCLUSION: Skull base defect resulting in spontaneous CSF leak or encephalocele is associated with enlargement of the foramen ovale on axial computed tomography.

Decision-Making and Management in a Patient With Coexistent Colloid Cyst and Pituitary Macroadenoma: A Case Report.

The coexistence of separate and distinct primary intracranial tumors is rare. Specifically, there are no previous reports of a colloid cyst coexisting with a pituitary macroadenoma. We present the case of a 40-year-old male with a colloid cyst associated with mild enlargement of the right lateral ventricle and a coexistent pituitary macroadenoma with compression of the optic apparatus. An endoscopic endonasal transsphenoidal surgery (EETS) for resection of the pituitary mass was performed first due to the patient's complaints of acute visual changes. He then underwent a right frontal craniotomy for resection of the colloid cyst one month later. The patient recovered without residual deficits in vision, and he did not require ventricular shunting after removal of the colloid cyst. We aimed to discuss our decision-making process and the management of these coexistent lesions.

Erroneous Central Venous Catheter Placement: Multidisciplinary Primary Surgical Repair of the Vertebral Artery.

Central venous catheters are a common practice in critical care medicine. These lines are of particular importance when a patient needs large volume resuscitation or medications that cannot be infused through a peripheral line. Even though central venous catheters are frequently utilized, they are associated with potentially significant risks that one must be aware of when attempting placement. The anatomy and pertinent complications are key for any healthcare professional to be aware of during this procedure. As such, vascular injury has been described in the literature, but vertebral artery injury and common repair techniques are less common. Primary repair of the second vertebral artery segment is infrequently detailed in the literature and this report describes pertinent case details and plan of action for identification and repair of iatrogenic vertebral artery injury following catheter placement.

Low-Pressure Hydrocephalus in Spontaneous Angiogram-Negative Subarachnoid Hemorrhage Following COVID-19 Infection.

A preliminary report warned that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could have neuro-invasive potential as it was observed that some patients showed neurologic symptoms such as headache, nausea, and vomiting. Following early speculation there have been reports of neurologic manifestations involving both the central nervous system and peripheral nervous system including reports that coronavirus disease 2019 (COVID-19) may increase the risk of acute ischemic stroke. Here we present a patient with recent COVID-19 infection who experienced low-pressure hydrocephalus requiring high-output cerebrospinal fluid (CSF) diversion following spontaneous angiogram-negative subarachnoid hemorrhage. We hypothesize that patients who are either currently or who have recently been infected with SARS-CoV-2 may have altered ventricular compliance and/or altered CSF hydrodynamics from mechanisms that are not yet understood but potentially related to previously described pathophysiologic mechanisms of the virus and associated inflammatory reaction.

Enlarging Ventriculus Terminalis in a Patient With Polyarteritis Nodosa.

Ventriculus terminalis (VT) is a cystic embryological remnant within the conus medullaris that normally regresses after birth. In rare cases, it may persist into adulthood and give rise to neurologic symptoms. The pathogenesis remains unclear but is thought to be related to failed embryonic regression with other proposed possible etiologies including vascular disturbances. We present an intriguing case of a slow-growing VT in a woman with progressive neurologic symptoms who experiences symptomatic relief following thoracic laminectomy and fenestration. Our case is the first to present a unique association with polyarteritis nodosa and only the third to report a case of documented enlargement of the VT over time successfully treated with surgical fenestration.

Spontaneous Spinal Epidural Hematoma Associated With Apixaban Therapy: A Report of two Cases.

Spontaneous spinal epidural hematoma (SSEH) is a rare clinical entity that can result in severe neurological deficit and warrants emergent neurosurgical evaluation and management. The exact etiology of this entity remains unknown, but certain risk factors exist, including the use of anticoagulant medications. There are few published reports of the association of SSEH with direct factor Xa inhibitors. We aimed to present 2 cases of SSEH in patients on chronic apixaban therapy. To the best of our knowledge, there is only 1 other report of SSEH in the setting of apixaban therapy. A comparison between the cases suggests the importance of rapid recognition and management of SSEH in order to achieve favorable neurological outcomes.

Cervical Spine Aneurysmal Bone Cyst in a Pediatric Patient: Embolization Considerations and Potential Pitfalls.

BACKGROUND: Aneurysmal bone cysts (ABCs) comprise 1%-2% of all bone tumors. ABCs involving the upper cervical spine in pediatric patients complicate intervention because of an immature skeleton and nearby neurovascular elements. Treatment often consists of surgical intervention with preoperative embolization to mitigate blood loss. During selective arterial embolization, it is important to be aware of extracranial-intracranial anastomoses from tumor feeding vessels. We describe a C2 vertebrae ABC that had multiple tumor arteries anastomosing with bilateral vertebral arteries. CASE DESCRIPTION: A 3-year-old healthy girl presented with 1 month of progressive neck pain and palpable posterior neck mass. Imaging was most consistent with an ABC of the C2 vertebra. Preoperative embolization was planned. Angiography demonstrated tumor arterial supply anastomosing with the left and right vertebral artery stemming from the ascending and deep cervical artery branches. Tumor embolization was therefore carried out using coils and larger embolization particles to decrease ischemic stroke risk. Follow-up angiography showed successful tumor embolization with no vertebrobasilar complications. Surgical excision was uncomplicated and the patient's cervical spine has remained stable without fusion. CONCLUSIONS: Preoperative embolization for ABC resection is common, but thorough angiography must be done to rule out dangerous extracranial-intracranial anastomoses. This case demonstrated 2 key anastomoses with the vertebral artery that if not recognized, could lead to disastrous consequences. Comprehensive angiographic evaluation is necessary because previous reports have described ischemic complications from embolization because of unrecognized vertebrobasilar anastomoses. If any angiographic evidence is seen, then larger particle size, coil embolization, or abandoning the case should be considered.

Perioperative risk factors associated with ICU intervention following select neurosurgical procedures.

BACKGROUND/OBJECTIVE: Following cranial neurosurgical procedures, intensive care unit (ICU) admission is routine; however, our institution's growing referral network has led to more frequent bed shortages. Consequently, there are increased requests to transfer our postoperative patients out of the ICU early in the monitoring window. We aimed to find risk factors to prioritize which postoperative neurosurgical patients that should remain in the unit. PATIENTS AND METHODS: An unmatched case-control study was conducted following retrospective chart review of patients who underwent common cranial procedures between August 2015 and June 2016 at our institution. Patients receiving postoperative ICU intervention were defined as cases. Several perioperative events were investigated for association with postoperative ICU level care. Individual risk factors were analyzed using Chi-squared tests for categorical variables (reported as odds ratio) and independent sample two tailed t-tests for continuous variables. Regression models were used for multivariate analysis. RESULTS: We identified 282 patients who met inclusion criteria, with 148 cases and 134 controls and no statistically significant differences between group demographics. Elective cases carried an odds ratio (OR 0.12, 95 % CI 0.05-0.26, p < 0.001), suggesting decreased likelihood of postoperative intensivist intervention. Single variable analysis showed ICU level of care was more more likely with general anesthesia (OR 3.72, 95 % CI 1.90-7.25, p < 0.001) and American Society of Anesthesiologists (ASA) class IV patients (OR 3.28, 95 % CI 1.59-6.78, p < 0.001). Continuous variables (blood loss and operative time) both demonstrated statistically significant differences (p < 0.001) between case and control groups with higher blood loss (100 ± 167 mL) and operative times (245 ± 119 min) seen in the ICU intervention group. Our regression model identified non-elective cases, operative time, and blood loss having associations with postoperative intensivist intervention. CONCLUSION: Growing demand for ICU beds at our institution has us looking for more objective data guiding decisions on lower-risk patients who could transfer early out of the ICU in times of overcapacity. Elective endovascular aneurysm treatment and DBS are cranial procedures least likely to receive postoperative ICU level intervention. Consideration to procedural blood loss of 100 cc or more and operative time greater than 4 h should also be given as these risk factors were associated with more likely needing postoperative ICU intervention. These results should not spur drastic changes in ICU protocols, but continued quality improvement projects should investigate these correlations to add more objective data for ICU utilization.

Atrioesophageal Fistula: Considerations for the neurological clinician.

Atrioesophageal fistula (AEF) is a rare complication of cardiac ablation for atrial fibrillation. It can present in many ways, but neurological signs and symptoms are common initial signs sometimes resulting in neurosurgeons and neurologists first evaluating patients with the condition. We present a case report of at 68-year-old female who presented with acute stroke symptoms and multifocal hemorrhages on MRI who was worked up through our neurosurgery department and diagnosed with AEF. This case highlights three clues to alert neurological clinicians to AEF as a possible diagnosis; clinical worsening of neurological symptoms in correlation to episodes of emesis, septic emboli on CT/MRI, and bacteremia caused by a gram positive oral or GI flora. If neurological clinicians encounter these red flags, an immediate CT of the chest and abdomen and consultation with cardiothoracic surgery may be life-saving.

Hemorrhage Rate After External Ventricular Drain Placement in Subarachnoid Hemorrhage: Time to Heparin Administration.

OBJECTIVE: The use of antiplatelet or anticoagulants has previously been shown to increase hemorrhagic complications of ventricular catheterization. Although heparin use 24 h after ventriculostomy appears safe, the safety of heparin immediately (within 4 h) after ventriculostomy is unknown. The objective of this study was to assess the safety of heparin immediately (within 4 h) after ventriculostomy in subarachnoid hemorrhage (SAH) patients undergoing endovascular treatment. PATIENTS AND METHODS: This is a retrospective cohort study of 46 patients with aneurysmal SAH secondary to aneurysm rupture who required ventriculostomy. Post-ventriculostomy imaging was carefully reviewed for tract hemorrhaging. Timing of heparinization was noted. Early heparinization was within 4 h after ventriculostomy, and intermediate heparinization was between 4 and 24 h after ventriculostomy. RESULTS: Overall, the tract hemorrhage rate was 26.1% for the study cohort-mostly grade I tract hemorrhages-consistent with the existing literature. The tract hemorrhage rate in the early (<4 h) heparin group was a remarkable 58.8%. The hemorrhages were also notably larger in the early (<4 h) heparin group. CONCLUSION: Although heparin appears to be safe after 4 h, immediate heparinization (within 4 h) after ventriculostomy significantly increases the odds of tract hemorrhage. Additional time should be afforded between ventriculostomy and heparinization to avoid potentially devastating external ventricular drain tract hemorrhage. It is advisable to wait a sufficient time (at least 4 h) after ventriculostomy before embarking on endovascular treatment of ruptured aneurysms.

Impact of a Vascular Neurosurgery Simulation-Based Course on Cognitive Knowledge and Technical Skills in European Neurosurgical Trainees.

OBJECTIVE: To assess microsurgical and diagnostic cerebral angiography modules and their corresponding objective assessment scales as educational tools for European neurosurgical residents at the European Association of Neurosurgical Societies Resident Vascular Neurosurgery course, which was held in Prague, Czech Republic, on September 2013. Microsurgical skills and cerebral angiography are fundamental skills in vascular neurosurgery. There is a need to develop a simulation-based curriculum focusing on these skills for neurosurgical trainees worldwide. METHODS: The course consisted of 2 modules: microanastomosis and diagnostic cerebral angiography. In addition to an initial screening survey, each module was divided into 3 components: 1) a before didactic cognitive knowledge and technical skills testing, 2) a didactic lecture, and 3) an after didactic cognitive knowledge and technical skills testing. We compared the trainees' cognitive and technical scores from the before and after testing phases. Wilcoxon sum rank test was used to test statistical significance. RESULTS: The knowledge test median scores increased from 63% and 68% to 80% and 88% (P < 0.01) on the microanastomosis and cerebral angiography modules, respectively. The practical hands-on simulation assessment median scores increased from 42% and 50% to 50.5% and 68% (P < 0.01) on the microanastomosis and cerebral angiography modules, respectively. CONCLUSIONS: Our course suggests that a simulation-based vascular neurosurgery curriculum is feasible and may enhance resident knowledge and technical proficiency.

Remote cerebellar hemorrhage following supratentorial cerebrovascular surgery.

Three patients with remote cerebellar hemorrhage following supratentorial cerebrovascular surgery are presented. Remote cerebellar hemorrhage is a rare surgical complication that is most often associated with aneurysm clipping or temporal lobectomies. Bleeding occurs on the superior cerebellar cortex and is believed to be venous in origin. The precise pathogenesis of remote cerebellar hemorrhage has yet to be fully elucidated but is generally considered to be a consequence of intraoperative cerebrospinal fluid loss causing caudal displacement of the cerebellum with resultant stretching of the supracerebellar veins. This case series will hopefully shed further light on the incidence, presentation, workup, and treatment of this particular complication of supratentorial surgery.