Revascularization surgery for symptomatic non-moyamoya intracranial arterial stenosis or occlusion.

OBJECTIVE: Previous trials rejected a role of extracranial-to-intracranial bypass surgery for managing symptomatic atheromatous disease. However, hemodynamic insufficiency may still be a rationale for surgery, provided the bypass can be performed with low morbidity and patency is robust. METHODS: Consecutive patients undergoing bypass surgery for symptomatic non-moyamoya intracranial arterial stenosis or occlusion were retrospectively identified. The clinical course and surgical outcomes of the cohort were evaluated at 6 weeks, 6 months, and annually thereafter. RESULTS: From 1992 to 2017, 112 patients underwent 127 bypasses. The angiographic abnormality was arterial occlusion in 80% and stenosis in 20%. Procedures were performed to prevent future stroke (76%) and stroke reversal (24%), with revascularization using an arterial pedicle graft in 80% and venous interposition graft (VIG) in 20%. A poor outcome (bypass occlusion, new stroke, new neurological deficit, or worsening neurological deficit) occurred in 8.9% of patients, with arterial pedicle grafts (odds ratio [OR] 0.15), bypass for prophylaxis against future stroke (OR 0.11), or anterior circulation bypass (OR 0.17) identified as protective factors. Over the first 8 years following surgery the 66 cases exhibiting all three of these characteristics had minimal risk of a poor outcome (95% confidence interval 0%-6.6%). CONCLUSIONS: Prophylactic arterial pedicle bypass surgery for anterior circulation ischemia is associated with high graft patency and low stroke and surgical complication rates. Higher risks are associated with acute procedures, typically for posterior circulation pathology and requiring VIGs. A carefully selected subgroup of individuals with hemodynamic insufficiency and ischemic symptoms is likely to benefit from cerebral revascularization surgery.

Does evidence-based medicine training improve doctors' knowledge, practice and patient outcomes? A systematic review of the evidence.

Courses in Evidence-Based Medicine (EBM) for doctors have consistently demonstrated short-term improvements in knowledge. However, there is no strong evidence linking EBM training to changes in clinical practice or patient outcomes. This systematic review investigates whether EBM training leads to sustained improvements in doctors' knowledge and practice behaviors that may also facilitate changes in patient outcomes and experiences. A literature search was undertaken in Ovid Medline, Ovid Embase, The Cochrane Library, ERIC and Scopus. Studies published from 1997 to 2016 that assessed outcomes of EBM educational interventions amongst doctors and used measures of knowledge, skills, attitudes, practice or patient outcomes were included. Fifteen studies were included in the analysis: four randomized controlled trials (RCTs), three non-RCTs, and eight before-after (longitudinal cohort) studies. Heterogeneity among studies prevented meaningful comparisons. Varying degrees of bias due to the use of subjective measures were identified, limiting study validity. Results showed that EBM interventions can improve short-term knowledge and skills, but there is little reliable evidence of changes in long-term knowledge, attitudes, and clinical practice. No study measured improvement in patient outcomes or experiences. EBM training for medical practitioners needs to incorporate measures of behavioral changes while incorporating patient outcomes and experience measures.

Comparing outcome scales for unruptured intracranial aneurysms: A prospective cohort study.

Outcomes on the modified Rankin Scale (mRS) are commonly used to guide and evaluate the management of unruptured intracranial aneurysms (uIA). However, the mRS is unlikely to measure all the relevant aspects of the clinical health of a patient. The current study therefore investigated the relationship between the mRS and additional measures of outcome. Between January 2011 and January 2016 patients with a new diagnosis of uIA were prospectively examined at referral and 12-month follow-up. Assessment included the Physical and Mental Component Scores of the Short Form 36 (SF-36), the computerized driver screening instrument DriveSafe (DS), and the mRS. Minimally Important Change (MIC) for each outcome measure was used to identify adverse outcomes for individual patients. A total of 128 patients (98 surgery; 30 untreated) completed the minimal dataset for analysis. In the surgical group, 6% (95% CI 3-14%) experienced morbidity at 12-months, as defined by the MIC for mRS. This risk rate increased to 51% (95% CI 41-61%) when defined as an MIC on any outcome. A combined MIC also identified a downgrade in outcomes, not detectable on the mRS, in 42% (95% CI 26-61%) of untreated patients. Correlation and regression analyses were unable to identify any significant relationships between the different outcomes instruments. In sum, there were considerably more adverse outcomes reported by quality of life (SF-36) and functional (DS) instruments than by the mRS for either treated or untreated uIA. To obtain a more complete representation of patient outcomes requires administration of a multi-dimensional assessment.

De novo brain arteriovenous malformation after tumor resection: case report and literature review.

The congenital origin of brain arteriovenous malformations (bAVMs) has been increasingly challenged by reports of de novo bAVMs in patients previously confirmed to have no vascular malformation. We describe the oldest patient reported in the English language literature harboring a de novo bAVM. An uneventful frontal convexity meningioma resection was performed for a 60-year-old woman, and at 67 years of age, a bAVM was detected by MRI and confirmed by digital subtraction angiography at the site of the previous meningioma resection. This case adds to the growing literature that the etiology of bAVMs is most likely multifactorial.

Cohort studies, trials, and tribulations: systematic review and an evidence-based approach to arteriovenous malformation treatment.

INTRODUCTION: There is uncertainty as to the best management of arteriovenous malformations of the brain (bAVM). However, the Spetzler-Martin grade (SMG) has been validated as an effective determinant of surgical risks. We performed a systematic review for the best evidence regarding the management of bAVM for series that incorporate an analysis based upon SMG. EVIDENCE ACQUISITION: Medline, Embase, Scopus and Cochrane databases were searched for series between January 2000 and January 2018, with a minimum of 100 cases and that incorporated SMG stratification. From this primary search, series were selected for analysis that dichotomized outcomes at modified Rankin Scale (mRS) scores between 1 and 2 due to complications of treatment or reported favorable outcome (FO) (i.e. complete occlusion, no neurological deterioration and no post treatment hemorrhage). Case series that used a subset of the population other than SMG or had a prior history of hemorrhage were excluded. The series finally analyzed were explored for outcomes that reported: complications of treatment that led to a new permanent neurological deficit with mRS score >1 (adverse outcome); post treatment hemorrhage; occlusion rate; and FO. A comparison of treatment outcomes was made when more than one modality of treatment (surgery, radiosurgery, embolization or multiple treatment modalities) could be examined with results for specific Spetzler-Ponce class (SPC) A (i.e. SMG I and II), B (i.e. SMG III) or C (i.e. SMG IV and V). EVIDENCE SYNTHESIS: The primary search produced 116 papers. After reviewing each publication and eliminating papers that had patient outcomes duplicated, 11 publications met the criteria for analysis (including: 5 exclusively surgery; 4 exclusively radiosurgery; 1 exclusively endovascular; and, 1 multi-modality). The following outcome comparisons analyzed were significant. For SPC A and B bAVM, there was a significantly higher rate of FO following treatment by surgery (98.6%; 95% CI: 97.5-99.2% and 76.4%; 95% CI: 70.0-81.7%, respectively) than radiosurgery (70.8%; 95% CI: 66.8-74.6% and 61.0%; 95% CI: 56.0-65.8%, respectively)(P<0.01). For SPC A and B bAVM, there were significantly fewer unobliterated bAVM following treatment by surgery (0.5%; 95% CI: 0.2-1.4% and 3.0%; 95% CI: 1.4-5.8%, respectively) than radiosurgery (23.9%; 95% CI: 20.4-27.8% and 30.9%; 95% CI: 27.9-34.0%, respectively) or embolization (7.6%; 95% CI: 4.3-12.9% SPC A) (P<0.01). Adverse outcomes from treatment were significantly higher for surgery (15.6%; 95% CI: 11.8-20.0%) than radiosurgery (3.3%; 95% CI: 2.3-4.8%) for SPC B (P<0.01) but not SPC A bAVM. No analysis of SPC C was possible. CONCLUSIONS: Surgery remains, in general, the best choice for treating SPC A bAVM. For SPC B bAVM the decision as to best treatment should hinge on the likelihood of obliteration by radiosurgery. In cases where obliteration rate is expected to be high, radiosurgery should be the preferred treatment. There is insufficient information to make a recommendation from this analysis with regards the role of embolization for cure. There is no satisfactory standardized treatment for SPC C bAVM and treatment must remain individualized.

The role of embolization before surgery for Spetzler-Ponce Class B and C brain AVMs: a prospective cohort series.

BACKGROUND: There is uncertainty of the benefit of preoperative embolization for Spetzler-Ponce Class (SPC) B and C arteriovenous malformations of the brain (bAVM). We examined whether or not preoperative embolization reduces the risk of permanent neurological deficits in SPC B and C bAVM surgery. METHODS: A prospective bAVM database (between1989 and 2015) was analyzed by regression for factors associated with a new permanent neurological deficit arising as a consequence of surgery or preoperative embolization with a modified Rankin Scale (mRS) score >1 at 12 months after surgery (adverse outcome). RESULTS: From a cohort of 785 patients with bAVM, 277 patients with SPC B or C bAVM were planned for treatment by surgery with (N.=67) or without (N.=210) preoperative embolization. There were significant differences (embolization versus no embolization) in: permanent neurological deficits leading to a mRS>1 (45% versus 20%, P<0.01); permanent neurological deficits leading to a mRS>2 (22% versus 8.1%, P=0.04); perioperative transfusion of 2.5 liters of blood or more (31% versus 16%, P<0.01); and, delayed postoperative hemorrhage (19% versus 8.1%, P=0.01). Regression analysis identified the following factors to be associated with increased likelihood of an adverse outcome: infratentorial location (odds ratio 0.441, P=0.045); SPC C bAVM (OR=0.501, P=0.034); earlier rank order of surgery (OR=0.994, P<0.01); and, preoperative embolization (OR=0.313, P<0.01). CONCLUSIONS: The use of preoperative embolization does not reduce adverse outcomes in SPC B and C bAVM. The role of embolization in the preoperative management of complex bAVM by surgery deserves further study.

Quantitative assessment of changes in hemodynamics of the internal carotid artery after bypass surgery for moyamoya disease.

OBJECTIVE Although intracranial vessel remodeling has been observed in moyamoya disease, concerns remain regarding the effect of bypass surgery on hemodynamic changes within the internal carotid artery (ICA). The authors aimed to quantify the surgical effect of bypass surgery on bilateral ICAs in moyamoya disease and to estimate pressure drop (PD) along the length of the ICA to predict surgical outcomes. METHODS Records of patients who underwent bypass surgery for treatment of moyamoya disease and in whom flow rates were obtained pre- and postsurgery by quantitative MR angiography were retrospectively reviewed. Quantitative MR angiography and computational fluid dynamics were applied to measure morphological and hemodynamic changes during pre- and postbypass procedures. The results for vessel diameter, volumetric flow, PD, and mean wall shear stress along the length of the ICA were analyzed. Subgroup analysis was performed for the circle of Willis (CoW) configurations. RESULTS Twenty-three patients were included. The PD in ICAs on the surgical side (surgical ICAs) decreased by 21.18% (SD ± 30.1%) and increased by 11.75% (SD ± 28.6%) in ICAs on the nonsurgical side (contralateral ICAs) (p = 0.001). When the PD in contralateral ICAs was compared between patients with a complete or incomplete CoW, the authors found that the PDI in the former group decreased by 2.45% and increased by 20.88% in the latter (p = 0.05). Regression tests revealed that a greater postoperative decrease in PD corresponded to shrinking of ICAs (R2 = 0.22, p = 0.02). CONCLUSIONS PD may be used as a reliable biomechanical indicator for the assessment of surgical treatment outcomes. The vessel remodeling characteristics of contralateral ICA were related to CoW configurations.

Surgical management.

Surgical management includes selection of patients for surgery, performing the technical procedure of brain arteriovenous malformation (bAVM) resection and perioperative management that maximize the chance for the best outcome. In general the Spetzler-Ponce class (SPC) can divide patients into those with good evidence that surgery is appropriate in most cases (SPC A), those in whom surgery should only be considered occasionally with highly nuanced indications (SPC C), and surgery may be appropriate having made a detailed analysis of patient (including age), clinical (including mode of presentation), and AVM characteristics (including diffuseness), and a comparative analysis of outcomes with alternate management pathways for SPC B cases. The underlying competent performance of surgery must successfully achieve: consideration of the physiology; correct identification of vessel; protection of the arterial supply to normal brain; understanding of the expected anatomic relationship between feeding arteries and draining veins; and recognition and management of complex arterial feeding patterns from transdural and transosseous sources. Aggressive blood pressure management is required for bAVM with significant changes to brain vascular physiology as a consequence of surgery. For such cases, brain vascular remodeling will take approximately 1 week after surgery. During this period, protection against elevation of blood pressure must be strictly achieved.

European consensus conference on unruptured brain AVMs treatment (Supported by EANS, ESMINT, EGKS, and SINCH).

In December of 2016, a Consensus Conference on unruptured AVM treatment, involving 24 members of the three European societies dealing with the treatment of cerebral AVMs (EANS, ESMINT, and EGKS) was held in Milan, Italy. The panel made the following statements and general recommendations: (1) Brain arteriovenous malformation (AVM) is a complex disease associated with potentially severe natural history; (2) The results of a randomized trial (ARUBA) cannot be applied equally for all unruptured brain arteriovenous malformation (uBAVM) and for all treatment modalities; (3) Considering the multiple treatment modalities available, patients with uBAVMs should be evaluated by an interdisciplinary neurovascular team consisting of neurosurgeons, neurointerventionalists, radiosurgeons, and neurologists experienced in the diagnosis and treatment of brain AVM; (4) Balancing the risk of hemorrhage and the associated restrictions of everyday activities related to untreated unruptured AVMs against the risk of treatment, there are sufficient indications to treat unruptured AVMs grade 1 and 2 (Spetzler-Martin); (5) There may be indications for treating patients with higher grades, based on a case-to-case consensus decision of the experienced team; (6) If treatment is indicated, the primary strategy should be defined by the multidisciplinary team prior to the beginning of the treatment and should aim at complete eradication of the uBAVM; (7) After having considered the pros and cons of a randomized trial vs. a registry, the panel proposed a prospective European Multidisciplinary Registry.

Microsurgery for Spetzler-Ponce Class A and B arteriovenous malformations utilizing an outcome score adopted from Gamma Knife radiosurgery: a prospective cohort study.

OBJECTIVE The purpose of this study was to adapt and apply the extended definition of favorable outcome established for Gamma Knife radiosurgery (GKRS) to surgery for brain arteriovenous malformations (bAVMs). The aim was to derive both an error around the point estimate and a model incorporating angioarchitectural features in order to facilitate comparison among different treatments. METHODS A prospective microsurgical cohort was analyzed. This cohort included patients undergoing embolization who did not proceed to microsurgery and patients denied surgery because of perceived risk of treatment. Data on bAVM residual and recurrence during long-term follow-up as well as complications of surgery and preoperative embolization were analyzed. Patients with Spetzler-Ponce Class C bAVMs were excluded because of extreme selection bias. First, patients with a favorable outcome were identified for both Class A and Class B lesions. Patients were considered to have a favorable outcome if they were free of bAVM recurrence or residual at last follow-up, with no complication of surgery or preoperative embolization, and a modified Rankin Scale score of more than 1 at 12 months after treatment. Patients who were denied surgery because of perceived risk, but would otherwise have been candidates for surgery, were included as not having a favorable outcome. Second, the authors analyzed favorable outcome from microsurgery by means of regression analysis, using as predictors characteristics previously identified to be associated with complications. Third, they created a prediction model of favorable outcome for microsurgery dependent upon angioarchitectural variables derived from the regression analysis. RESULTS From a cohort of 675 patients who were either treated or denied surgery because of perceived risk of surgery, 562 had Spetzler-Ponce Class A or B bAVMs and were included in the analysis. Logistic regression for favorable outcome found decreasing maximum diameter (continuous, OR 0.62, 95% CI 0.51-0.76), the absence of eloquent location (OR 0.23, 95% CI 0.12-0.43), and the absence of deep venous drainage (OR 0.19, 95% CI 0.10-0.36) to be significant predictors of favorable outcome. These variables are in agreement with previous analyses of microsurgery leading to complications, and the findings support the use of favorable outcome for microsurgery. The model developed for angioarchitectural features predicts a range of favorable outcome at 8 years following microsurgery for Class A bAVMs to be 88%-99%. The same model for Class B bAVMs predicts a range of favorable outcome of 62%-90%. CONCLUSIONS Favorable outcome, derived from GKRS, can be successfully used for microsurgical cohort series to assist in treatment recommendations. A favorable outcome can be achieved by microsurgery in at least 90% of cases at 8 years following microsurgery for patients with bAVMs smaller than 2.5 cm in maximum diameter and, in the absence of either deep venous drainage or eloquent location, patients with Spetzler-Ponce Class A bAVMs of all diameters. For patients with Class B bAVMs, this rate of favorable outcome can only be approached for lesions with a maximum diameter just above 6 cm or smaller and without deep venous drainage or eloquent location.

The unruptured intracranial aneurysm treatment score: a multidisciplinary consensus.

OBJECTIVE: We endeavored to develop an unruptured intracranial aneurysm (UIA) treatment score (UIATS) model that includes and quantifies key factors involved in clinical decision-making in the management of UIAs and to assess agreement for this model among specialists in UIA management and research. METHODS: An international multidisciplinary (neurosurgery, neuroradiology, neurology, clinical epidemiology) group of 69 specialists was convened to develop and validate the UIATS model using a Delphi consensus. For internal (39 panel members involved in identification of relevant features) and external validation (30 independent external reviewers), 30 selected UIA cases were used to analyze agreement with UIATS management recommendations based on a 5-point Likert scale (5 indicating strong agreement). Interrater agreement (IRA) was assessed with standardized coefficients of dispersion (vr*) (vr* = 0 indicating excellent agreement and vr* = 1 indicating poor agreement). RESULTS: The UIATS accounts for 29 key factors in UIA management. Agreement with UIATS (mean Likert scores) was 4.2 (95% confidence interval [CI] 4.1-4.3) per reviewer for both reviewer cohorts; agreement per case was 4.3 (95% CI 4.1-4.4) for panel members and 4.5 (95% CI 4.3-4.6) for external reviewers (p = 0.017). Mean Likert scores were 4.2 (95% CI 4.1-4.3) for interventional reviewers (n = 56) and 4.1 (95% CI 3.9-4.4) for noninterventional reviewers (n = 12) (p = 0.290). Overall IRA (vr*) for both cohorts was 0.026 (95% CI 0.019-0.033). CONCLUSIONS: This novel UIA decision guidance study captures an excellent consensus among highly informed individuals on UIA management, irrespective of their underlying specialty. Clinicians can use the UIATS as a comprehensive mechanism for indicating how a large group of specialists might manage an individual patient with a UIA.

ICA aneurysm surgically treated utilizing a choroidal to PCOM bypass and vein bypass.

This video shows the surgical repair of a 2.3 cm ICA aneurysm found in a 58-year-old woman, who presented for right eye vision changes. The patient underwent a right modified orbitozygomatic craniotomy and saphenous vein bypass from the common carotid to the temporal M2. The aneurysm was then opened and repaired. However, since the anterior choroidal artery was not filling, a salvage bypass between the anterior choroidal and the PCOM was done. Both bypasses were patent and the patient has done well with a mRS of 1 for vision symptoms. The video can be found here: http://youtu.be/ciMyzfXgo8l.

Brain arteriovenous malformations.

An arteriovenous malformation is a tangle of dysplastic vessels (nidus) fed by arteries and drained by veins without intervening capillaries, forming a high-flow, low-resistance shunt between the arterial and venous systems. Arteriovenous malformations in the brain have a low estimated prevalence but are an important cause of intracerebral haemorrhage in young adults. For previously unruptured malformations, bleeding rates are approximately 1% per year. Once ruptured, the subsequent risk increases fivefold, depending on associated aneurysms, deep locations, deep drainage and increasing age. Recent findings from novel animal models and genetic studies suggest that arteriovenous malformations, which were long considered congenital, arise from aberrant vasculogenesis, genetic mutations and/or angiogenesis after injury. The phenotypical characteristics of arteriovenous malformations differ among age groups, with fistulous lesions in children and nidal lesions in adults. Diagnosis mainly involves imaging techniques, including CT, MRI and angiography. Management includes observation, microsurgical resection, endovascular embolization and stereotactic radiosurgery, alone or in any combination. There is little consensus on how to manage patients with unruptured malformations; recent studies have shown that patients managed medically fared better than those with intervention at short-term follow-up. By contrast, interventional treatment is preferred following a ruptured malformation to prevent rehaemorrhage. Management continues to evolve as new mechanistic discoveries and reliable animal models raise the possibility of developing drugs that might prevent the formation of arteriovenous malformations, induce obliteration and/or stabilize vessels to reduce rupture risk. For an illustrated summary of this Primer, visit: http://go.nature.com/TMoAdn.

Validation of the supplemented Spetzler-Martin grading system for brain arteriovenous malformations in a multicenter cohort of 1009 surgical patients.

BACKGROUND: The supplementary grading system for brain arteriovenous malformations (AVMs) was introduced in 2010 as a tool for improving preoperative risk prediction and selecting surgical patients. OBJECTIVE: To demonstrate in this multicenter validation study that supplemented Spetzler-Martin (SM-Supp) grades have greater predictive accuracy than Spetzler-Martin (SM) grades alone. METHODS: Data collected from 1009 AVM patients who underwent AVM resection were used to compare the predictive powers of SM and SM-Supp grades. Patients included the original 300 University of California, San Francisco patients plus those treated thereafter (n = 117) and an additional 592 patients from 3 other centers. RESULTS: In the combined cohort, the SM-Supp system performed better than SM system alone: area under the receiver-operating characteristics curve (AUROC) = 0.75 (95% confidence interval, 0.71-0.78) for SM-Supp and AUROC = 0.69 (95% confidence interval, 0.65-0.73) for SM (P < .001). Stratified analysis fitting models within 3 different follow-up groupings (<6 months, 6 months-2 years, and >2 years) demonstrated that the SM-Supp system performed better than SM system for both medium (AUROC = 0.71 vs 0.62; P = .003) and long (AUROC = 0.69 vs 0.58; P = .001) follow-up. Patients with SM-Supp grades ≤6 had acceptably low surgical risks (0%-24%), with a significant increase in risk for grades >6 (39%-63%). CONCLUSION: This study validates the predictive accuracy of the SM-Supp system in a multicenter cohort. An SM-Supp grade of 6 is a cutoff or boundary for AVM operability. Supplemented grading is currently the best method of estimating neurological outcomes after AVM surgery, and we recommend it as a starting point in the evaluation of AVM operability.

Multidisciplinary consensus on assessment of unruptured intracranial aneurysms: proposal of an international research group.

BACKGROUND AND PURPOSE: To address the increasing need to counsel patients about treatment indications for unruptured intracranial aneurysms (UIA), we endeavored to develop a consensus on assessment of UIAs among a group of specialists from diverse fields involved in research and treatment of UIAs. METHODS: After composition of the research group, a Delphi consensus was initiated to identify and rate all features, which may be relevant to assess UIAs and their treatment by using ranking scales and analysis of inter-rater agreement (IRA) for each factor. IRA was categorized as very high, high, moderate, or low. RESULTS: Ultimately, 39 specialists from 4 specialties agreed (high or very high IRAs) on the following key factors for or against UIA treatment decisions: (1) patient age, life expectancy, and comorbid diseases; (2) previous subarachnoid hemorrhage from a different aneurysm, family history for UIA or subarachnoid hemorrhage, nicotine use; (3) UIA size, location, and lobulation; (4) UIA growth or de novo formation on serial imaging; (5) clinical symptoms (cranial nerve deficit, mass effect, and thromboembolic events from UIAs); and (6) risk factors for UIA treatment (patient age and life expectancy, UIA size, and estimated risk of treatment). However, IRAs for features rated with low relevance were also generally low, which underlined the existing controversy about the natural history of UIAs. CONCLUSIONS: Our results highlight that neurovascular specialists currently consider many features as important when evaluating UIAs but also highlight that the appreciation of natural history of UIAs remains uncertain, even within a group of highly informed individuals.

The risk of meningitis following expanded endoscopic endonasal skull base surgery: a systematic review.

Objective To examine the risk of postoperative meningitis following expanded endoscopic endonasal skull base (EESB) surgery. Setting A systematic analysis of publications identified through searches of the electronic databases from Embase (1980-July 17, 2012), Medline (1950-July 17, 2012), and references of review articles. Main Outcome Measures Incidence of meningitis following EESB surgery. Results A total of 2,444 manuscripts were selected initially, and full-text analysis produced 67 studies with extractable data. Fifty-two contained data regarding the frequency of postoperative meningitis. The overall risk of postoperative meningitis following EESB surgery was 1.8% (36 of 2,005). For those reporting a cerebrospinal fluid (CSF) leak, meningitis occurred in 13.0% (35 of 269). For those not reporting a CSF leak, meningitis occurred in 0.1% (1 of 1,736). The odds ratio for the development of meningitis in the presence of a postoperative CSF leak was 91.99 (95% confidence interval, 11.72-721.88; p < 0.01). There was no difference in reported incidence of meningitis or CSF leak between anterior and posterior cranial fossa surgery. There was one reported case of meningitis-related mortality following EESB surgery. Conclusion The evidence in skull base surgery is limited. This study demonstrates a low incidence of meningitis (1.8%) following EESB procedures. The incidence of meningitis from EESB surgery without an associated CSF leak is uncommon.