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Outcomes of Minimally Invasive Transforaminal Lumbar Interbody Fusion With Expandable Lordotic Devices

Neurosurgery, Volume 86, Issue 2, February 2020, Pages E147–E155

Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is a well-accepted procedure for the treatment of degenerative lumbar disease. However, its ability to restore lumbar lordosis has been limited. Development of expandable lordotic interbody devices has challenged this limitation, furthering the scope ofminimally invasive surgery.

OBJECTIVE: To evaluate the radiographic and clinical effects of expandable lordotic interbody devices placed through an MIS-TLIF approach.

METHODS: We conducted a retrospective review of 32 1-level and 18 2-level MIS-TLIFs performed using lordotic expandable interbody devices. Lumbar radiographic measurements, Oswestry Disability Index scores (ODI), and Visual Analogue Scale scores (VAS)were obtained at preoperative, 6 wk follow up, and last follow up time points. Last follow up occurred at a mean of 11.5 ± 7.6 mo (mean ± SD).

RESULTS: At 6-wk follow-up, segmental lordosis, disc height, and foraminal height increased by an average of 3.4◦, 6.4 mm, and 4.4 mm, respectively. Only the 2-level group showed a significant increase in lumbar lordosis of 5.8◦. No significant changes occurred in sacral slope, pelvic tilt, or pelvic incidence. Average ODI and VAS decreased by −12.0 and −4.5, respectively. Postoperative lumbar lordosis inversely correlated with preoperative lordosis in patients with an initial Pelvic Incidence to Lumbar Lordosis mismatch (PI-LL) of >10◦, (r=−0.5, P = .009).

CONCLUSION: When applied across 2-levels, MIS-TLIF using expandable lordotic interbody devices produced a significant increase in lumbar lordosis. Preoperative lumbar lordosis was found to be a predictor of postoperative lumbar lordotic change in patients with sagittal imbalance.

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An Online Calculator for the Prediction of Survival in Glioblastoma Patients Using Classical Statistics and Machine Learning

Neurosurgery, Volume 86, Issue 2, February 2020, Pages E184–E192

Although survival statistics in patients with glioblastoma multiforme (GBM) are well-defined at the group level, predicting individual patient survival remains challenging because of significant variation within strata.

OBJECTIVE: To compare statistical and machine learning algorithms in their ability to predict survival in GBM patients and deploy the best performing model as an online survival calculator.

METHODS: Patients undergoing an operation for a histopathologically confirmed GBM were extracted from the Surveillance Epidemiology and End Results (SEER) database (2005-2015) and split into a training and hold-out test set in an 80/20 ratio. Fifteen statistical and machine learning algorithms were trained based on 13 demographic, socioeconomic, clinical, and radiographic features to predict overall survival, 1-yr survival status, and compute personalized survival curves.

RESULTS: In total, 20 821 patients met our inclusion criteria. The accelerated failure time model demonstrated superior performance in terms of discrimination (concordance index = 0.70), calibration, interpretability, predictive applicability, and computational efficiency compared to Cox proportional hazards regression and other machine learning algorithms. This model was deployed through a free, publicly available software interface (https://cnoc-bwh.shinyapps.io/gbmsurvivalpredictor/).

CONCLUSION: The development and deployment of survival prediction tools require a multimodal assessment rather than a single metric comparison. This study provides a framework for the development of prediction tools in cancer patients, as well as an online survival calculator for patients with GBM. Future efforts should improve the interpretability, predictive applicability, and computational efficiency of existing machine learning algorithms, increase the granularity of population-based registries, and externally validate the proposed prediction tool.

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3-Tesla MRI of deep brain stimulation patients: safety assessment of coils and pulse sequences

J Neurosurg 132:586–594, 2020

Physicians are more frequently encountering patients who are treated with deep brain stimulation (DBS), yet many MRI centers do not routinely perform MRI in this population. This warrants a safety assessment to improve DBS patients’ accessibility to MRI, thereby improving their care while simultaneously providing a new tool for neuromodulation research.

METHODS A phantom simulating a patient with a DBS neuromodulation device (DBS lead model 3387 and IPG Activa PC model 37601) was constructed and used. Temperature changes at the most ventral DBS electrode contacts, implantable pulse generator (IPG) voltages, specific absorption rate (SAR), and B1+rms were recorded during 3-T MRI scanning. Safety data were acquired with a transmit body multi-array receive and quadrature transmit-receive head coil during various pulse sequences, using numerous DBS configurations from “the worst” to “the most common.” In addition, 3-T MRI scanning (T1 and fMRI) was performed on 41 patients with fully internalized and active DBS using a quadrature transmit-receive head coil. MR images, neurological examination findings, and stability of the IPG impedances were assessed.

RESULTS In the phantom study, temperature rises at the DBS electrodes were less than 2°C for both coils during 3D SPGR, EPI, DTI, and SWI. Sequences with intense radiofrequency pulses such as T2-weighted sequences may cause higher heating (due to their higher SAR). The IPG did not power off and kept a constant firing rate, and its average voltage output was unchanged. The 41 DBS patients underwent 3-T MRI with no adverse event.

CONCLUSIONS Under the experimental conditions used in this study, 3-T MRI scanning of DBS patients with selected pulse sequences appears to be safe. Generally, T2-weighted sequences (using routine protocols) should be avoided in DBS patients. Complementary 3-T MRI phantom safety data suggest that imaging conditions that are less restrictive than those used in the patients in this study, such as using transmit body multi-array receive coils, may also be safe. Given the interplay between the implanted DBS neuromodulation device and the MRI system, these findings are specific to the experimental conditions in this study.

 

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Sex-dependent posterior fossa anatomical differences in trigeminal neuralgia patients with and without neurovascular compression: a volumetric MRI age- and sex-matched case-control study

J Neurosurg 132:631–638, 2020

The pathophysiology of trigeminal neuralgia (TN) in patients without neurovascular compression (NVC) is not completely understood. The objective of this retrospective study was to evaluate the hypothesis that TN patients without NVC differ from TN patient with NVC with respect to brain anatomy and demographic characteristics.

METHODS Six anatomical brain measurements from high-resolution brain MR images were tabulated; anterior-posterior (AP) prepontine cistern length, cerebellopontine angle (CPA) cistern volume, nerve-to-nerve distance, symptomatic nerve length, pons volume, and posterior fossa volume were assessed on OsiriX. Brain MRI anatomical measurements from 232 patients with either TN type 1 or TN type 2 (TN group) were compared with measurements obtained in 100 age- and sex-matched healthy controls (control group). Two-way ANOVA tests were conducted on the 6 measurements relative to group and NVC status. Bonferroni adjustments were used to correct for multiple comparisons. A nonhierarchical k-means cluster analysis was performed on the TN group using age and posterior fossa volume as independent variables.

RESULTS Within the TN group, females were found to be younger than males and less likely to have NVC. The odds ratio (OR) of females not having NVC compared to males was 2.7 (95% CI 1.3–5.5, p = 0.017). Patients younger than 30 years were much less likely to have NVC compared to older patients (OR 4.9, 95% CI 1.3–18.4, p = 0.017). The mean AP prepontine cistern length and symptomatic nerve length were smaller in the TN group than in the control group (5.3 vs 6.5 mm and 8.7 vs 9.7 mm, respectively; p < 0.001). The posterior fossa volume was significantly smaller in TN patients without NVC compared to those with NVC. A TN group cluster analysis suggested a sex-dependent difference that was not observed in those without NVC. Factorial ANOVA and post hoc testing found that findings in males without NVC were significantly different from those in controls or male TN patients with NVC and similar to those in females (female controls as well as female TN patients with or without NVC).

CONCLUSIONS Posterior fossa volume in males was larger than posterior fossa volume in females. This finding, along with the higher incidence of TN in females, suggests that smaller posterior fossa volume might be an independent factor in the pathophysiology of TN, which warrants further study.

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Nucleus basalis of Meynert neuronal activity in Parkinson’s disease

J Neurosurg 132:574–582, 2020

Neuronal loss within the cholinergic nucleus basalis of Meynert (nbM) correlates with cognitive decline in dementing disorders such as Alzheimer’s disease and Parkinson’s disease (PD). In nonhuman primates, the nbM firing pattern (5–40 Hz) has also been correlated with working memory and sustained attention. In this study, authors performed microelectrode recordings of the globus pallidus pars interna (GPi) and the nbM immediately prior to the implantation of bilateral deep brain stimulation (DBS) electrodes in PD patients to treat motor symptoms and cognitive impairment, respectively. Here, the authors evaluate the electrophysiological properties of the nbM in patients with PD.

METHODS Five patients (4 male, mean age 66 ± 4 years) with PD and mild cognitive impairment underwent bilateral GPi and nbM DBS lead implantation. Microelectrode recordings were performed through the GPi and nbM along a single trajectory. Firing rates and burst indices were characterized for each neuronal population with the patient at rest and performing a sustained-attention auditory oddball task. Action potential (AP) depolarization and repolarization widths were measured for each neuronal population at rest.

RESULTS In PD patients off medication, the authors identified neuronal discharge rates that were specific to each area populated by GPi cells (92.6 ± 46.1 Hz), border cells (34 ± 21 Hz), and nbM cells (13 ± 10 Hz). During the oddball task, firing rates of nbM cells decreased (2.9 ± 0.9 to 2.0 ± 1.1 Hz, p < 0.05). During baseline recordings, the burst index for nbM cells (1.7 ± 0.6) was significantly greater than those for GPi cells (1.2 ± 0.2, p < 0.05) and border cells (1.1 ± 0.1, p < 0.05). There was no significant difference in the nbM burst index during the oddball task relative to baseline (3.4 ± 1.7, p = 0.20). With the patient at rest, the width of the depolarization phase of APs did not differ among the GPi cells, border cells, and nbM cells (p = 0.60); however, during the repolarization phase, the nbM spikes were significantly longer than those for GPi high-frequency discharge cells (p < 0.05) but not the border cells (p = 0.20).

CONCLUSIONS Neurons along the trajectory through the GPi and nbM have distinct firing patterns. The profile of nbM activity is similar to that observed in nonhuman primates and is altered during a cognitive task associated with cholinergic activation. These findings will serve to identify these targets intraoperatively and form the basis for further research to characterize the role of the nbM in cognition.

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Lumboperitoneal and Ventriculoperitoneal Shunting for Idiopathic Intracranial Hypertension Demonstrate Comparable Failure and Complication Rates

Neurosurgery 86:272–280, 2020

Idiopathic intracranial hypertension results in increased intracranial pressure leading to headache and visual loss. This disease frequently requires surgical intervention through lumboperitoneal (LP) or ventriculoperitoneal (VP) shunting.

OBJECTIVE: To compare postoperative outcomes between LP and VP shunts, including failure and complication rates.

METHODS: A retrospective analysis was conducted using a national administrative database (MarketScan) to identify idiopathic intracranial hypertension (IIH) patients who underwent LP or VP shunting from 2007 to 2014. Multivariate logistic and Cox regressions were performed to compare rates of shunt failure and time to shunt failure between LP and VP shunts while controlling for demographics and comorbidities.

RESULTS: The analytic cohort included 1082 IIH patients, 347 of whom underwent LP shunt placement at index hospitalization and 735 of whom underwent VP shunt placement. Rates of shunt failure were similar among patients with LP and VP shunt (34.6% vs 31.7%; P=.382). Among patients who experienced shunt failure, the mean number of shunt failures was 2.1±1.6 and was similar between LP and VP cohorts. Ninety-day readmission rates, complication rates, and costs did not differ significantly between LP and VP shunts. Patients who experienced more than two shunt failures tended to have an earlier time to first shunt failure (hazard ratio 1.41; 95% confidence interval 1.08-1.85; P = .013).

CONCLUSION: These findings suggest that LP and VP shunts may have comparable rates of shunt failure and complication. Regardless of shunt type, earlier time to first shunt failure may be associated with multiple shunt failures.

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NTMS mapping of non-primary motor areas in brain tumour patients and healthy volunteers

Acta Neurochirurgica (2020) 162:407–416

Navigated transcranial magnetic stimulation (nTMS) has been increasingly used for presurgical cortical mapping of the primary motor cortex (M1) but remains controversial for the evaluation of non-primary motor areas (NPMA). This study investigates clinical and neurophysiological parameters in brain tumour patients and healthy volunteers to decide whether singlepulse biphasic nTMS allows to reliably elicite MEP outside from M1 or not.

Materials and methods Twelve brain tumour patients and six healthy volunteers underwent M1 nTMS mapping. NPMA nTMS mapping followed using 120% and 150% M1 resting motor threshold (RMT) stimulation intensity. Spearman’s correlation analysis tested the association of clinical and neurophysiological parameters between M1 and NPMA mapping.

Results A total of 88.81% of nTMS stimulations in NPMA in patients/83.87% in healthy volunteers in patients/83.87% in healthy volunteers did not result in MEPs ≥ 50 μV. Positive nTMS mapping in NPMA correlated with higher stimulation intensity and larger M1 areas in patients (120% M1 RMT SI p = 0.005/150%M1 RMT SI p = 0.198).

Conclusion Our findings indicate that in case of positive nTMS mapping in NPMA, MEPs originate mostly from M1. For future studies, MEP parameters and TMS coil rotation should be studied closely to assess the risk for postoperative motor deterioration.

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Embolization of brain arteriovenous malformations with intent to cure: a systematic review

J Neurosurg 132:388–399, 2020

Endovascular embolization has been established as an adjuvant treatment strategy for brain arteriovenous malformations (AVMs). A growing body of literature has discussed curative embolization for select lesions. The transition of endovascular embolization from an adjunctive to a definitive treatment modality remains controversial. Here, the authors reviewed the literature to assess the lesional characteristics, technical factors, and angiographic and clinical outcomes of endovascular embolization of AVMs with intent to cure.

METHODS Electronic databases—Ovid MEDLINE, Ovid Embase, and PubMed—were searched for studies in which there was evidence of AVMs treated using endovascular embolization with intent to cure. The primary outcomes of interest were angiographic obliteration immediately postembolization and at follow-up. The secondary outcomes of interest were complication rates. Descriptive statistics were used to calculate rates and means.

RESULTS Fifteen studies with 597 patients and 598 AVMs treated with intent-to-cure embolization were included in this analysis. Thirty-four percent of AVMs were Spetzler-Martin grade III. Complete obliteration immediately postembolization was reported in 58.3% of AVMs that had complete treatment and in 45.8% of AVMs in the entire patient cohort. The overall clinical complication rate was 24.1%. The most common complication was hemorrhage, occurring in 9.7% of patients. Procedure-related mortality was 1.5%.

CONCLUSIONS While endovascular embolization with intent to cure can be an option for select AVMs, the reported complication rates appear to be increased compared with those in studies in which adjunctive embolization was the goal. Given the high complication rate related to a primary embolization approach, the risks and benefits of such a treatment strategy should be discussed among a multidisciplinary team. Curative embolization of AVMs should be considered an unanticipated benefit of such therapy rather than a goal.

 

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Biomechanics of a novel reversibly expandable dynamic craniotomy bone flap fixation plate

J Neurosurg 132:560–567, 2020

Biomechanical evaluation of a novel expandable cranial fixation plate was assessed in cadavers. The dynamic craniotomy procedure uses low-profile reversibly expandable plates that allow cranial decompression by providing for intracranial volume expansion without removal of the bone flap. The plates allow reversible outward movement of the bone flap upon an increase in intracranial pressure (ICP) and also retract the bone flap and prevent it from sinking inside the cranium once the ICP normalizes.

METHODS A comparative evaluation of the extent of ICP control with an increase in intracranial volume between various bone flap fixation techniques was undertaken along with testing of the expandable plate compliance. Static compression tests of the plates were performed to assess bone flap fixation and prevention of sinking. Quasi-static shear tension testing of the plates was undertaken to test the tolerance of the plates for expansion. Fatigue shear tension evaluation of the plates was undertaken to assess tolerance for repetitive expansion and contraction.

RESULTS The dynamic craniotomy provided superior control of ICP with an increase in intracranial volume compared to the hinged craniotomy and standard craniotomy techniques (p < 0.001). Static compression results revealed that the plates withstood bone flap sinkage with a mean peak load of 643.3 ± 26.1 N and a mean inward bone flap displacement of 1.92 ± 0.09 mm. Static shear tension results indicated that the plates could withstand a peak expansion of 71.6 mm. Dynamic shear tension testing of the plates with repetitive 15-mm outward expansion and retraction for a total of up to 500 cycles revealed no cracking and no failure points.

CONCLUSIONS The reversibly expandable plates provide for a low-profile bone flap fixation with rigid restriction of bone flap sinking and also enable cranial decompression with a high tolerance for repetitive expansion and contraction.

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The temporoinsular projection system: an anatomical study

J Neurosurg 132:615–623, 2020

Connections between the insular cortex and the amygdaloid complex have been demonstrated using various techniques. Although functionally well connected, the precise anatomical substrate through which the amygdaloid complex and the insula are wired remains unknown. In 1960, Klingler briefly described the “fasciculus amygdaloinsularis,” a white matter tract connecting the posterior insula with the amygdala. The existence of such a fasciculus seems likely but has not been firmly established, and the reported literature does not include a thorough description and documentation of its anatomy. In this fiber dissection study the authors sought to elucidate the pathway connecting the insular cortex and the mesial temporal lobe.

METHODS Fourteen brain specimens obtained at routine autopsy were dissected according to Klingler’s fiber dissection technique. After fixation and freezing, anatomical dissections were performed in a stepwise progressive fashion.

RESULTS The insula is connected with the opercula of the frontal, parietal, and temporal lobes through the extreme capsule, which represents a network of short association fibers. At the limen insulae, white matter fibers from the extreme capsule converge and loop around the uncinate fasciculus toward the temporal pole and the mesial temporal lobe, including the amygdaloid complex.

CONCLUSIONS The insula and the mesial temporal lobe are directly connected through white matter fibers in the extreme capsule, resulting in the appearance of a single amygdaloinsular fasciculus. This apparent fasciculus is part of the broader network of short association fibers of the extreme capsule, which connects the entire insular cortex with the temporal pole and the amygdaloid complex. The authors propose the term “temporoinsular projection system” (TIPS) for this complex.

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Pain Outcomes Following Microvascular Decompression for Drug-Resistant Trigeminal Neuralgia: A Systematic Review and Meta-Analysis

Neurosurgery, Volume 86, Issue 2, February 2020, Pages 182–190

Microvascular decompression (MVD) is a potentially curative surgery for drug-resistant trigeminal neuralgia (TN). Predictors of pain freedom after MVD are not fully understood. OBJECTIVE: To describe rates and predictors for pain freedom following MVD.

METHODS: Using preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, PubMed, Cochrane Library, and Scopus were queried for primary studies examining pain outcomes after MVD for TN published between 1988 and March 2018. Potential biases were assessed for included studies. Pain freedom (ie, Barrow Neurological Institute score of 1) at last follow-up was the primary outcome measure. Variables associated with pain freedom on preliminary analysis underwent formal meta-analysis. Odds ratios (OR) and 95% confidence intervals (CI) were calculated for possible predictors.

RESULTS: Outcome data were analyzed for 3897 patients from 46 studies (7 prospective, 39 retrospective). Overall, 76.0% of patients achieved pain freedom afterMVD with amean follow-up of 1.7 ± 1.3 (standard deviation) yr. Predictors of pain freedom on meta-analysis using random effectsmodels included (1) disease duration≤5 yr (OR=2.06, 95% CI=1.08- 3.95); (2) arterial compression over venous or other (OR = 3.35, 95% CI = 1.91-5.88); (3) superior cerebellar artery involvement (OR = 2.02, 95% CI = 1.02-4.03), and (4) type 1 Burchiel classification (OR = 2.49, 95% CI = 1.32-4.67).

CONCLUSION: Approximately three-quarters of patients with drug-resistant TN achieve pain freedom after MVD. Shorter disease duration, arterial compression, and type 1 Burchiel classification may predict more favorable outcome. These results may improve patient selection and provider expectations.

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Is There a Need for a 6-Month Postradiosurgery Magnetic Resonance Imaging in the Treatment of Vestibular Schwannoma?

Neurosurgery, Volume 86, Issue 2, February 2020, Pages 250–256

Stereotactic radiosurgery (SRS) is a common treatment modality for vestibular schwannoma (VS), with a role in primary and recurrent/progressive algorithms. At our institution, routine magnetic resonance imaging (MRI) is obtained at 6 and 12 mo following SRS for VS.

OBJECTIVE: To analyze the safety and financial impact of eliminating the 6-mo post-SRS MRI in asymptomatic VS patients. METHODS: A prospectively maintained SRS database was retrospectively reviewed for VS patients with 1 yr of post-treatment follow-up, 2005 to 2015. Decisions at 6-mo MRI were binarily categorized as routine follow-up vs clinical action—defined as a clinical visit, additional imaging, or an operation as a direct result of the 6-mo study.

RESULTS: A total of 296 patients met screening criteria, of whom 53 were excluded for incomplete follow-up and 8 for NF-2. Nine were reimaged prior to 6 mo due to clinical symptoms. Routine 6-mo post-SRS MRI was completed by 226 patients (76% of screened cohort), following from which zero instances of clinical action occurred.When scaled using national insurance database-derived financials—which estimated the mean per-study charge for MRI of the brain with and without contrast at $1767—the potential annualized national charge reduction was approximated as $1 611 504.

CONCLUSION: For clinically stable VS, 6-mo post-SRS MRI does not contribute significantly to management. We recommend omitting routine MRI before 12 mo, in patients without new or progressive neurological symptoms. If extrapolated nationally to the more than 100 active SRS centers, thousands of patients would be spared an inconvenient, nonindicated study, and national savings in health care dollarswouldbe on the order ofmillions annually.

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Ependymal fluorescence in fluorescence-guided resection of malignant glioma: a systematic review

Acta Neurochirurgica (2020) 162:365–372

Fluorescence in the ventricular wall or the ependyma during fluorescence-guided resection (FGR) of malignant glioma is commonly observed when malignant gliomas infiltrate the ventricles. However, the underlying pathophysiology and clinical importance are largely unknown but may play a role in deciding whether to continue resection into the ventricles or not. Here, we systematically review available data regarding ependymal fluorescence in FGR using five aminolevulinic acid (5-ALA) and sodium fluorescein (SF).

Methods A literature search on MEDLINE, EMBASE, and WEB OF SCIENCE was performed using the following headings and search operators: ependy* fluorescence AND (5-ALA OR five aminolevulinic acid), ventric* wall fluorescence AND (5- ALA OR five aminolevulinic acid), ependy* fluorescence AND fluorescein, and ventric* wall fluorescence AND fluorescein. Both authors analyzed abstracts independently. Included articles were further reviewed for prevalence of ependymal fluorescence, patterns of fluorescence, and histopathological characteristics of sampled tissues as well as radiological signs of ependymal fluorescence. Results are reported according to the PRISMA statement.

Results Of 202 records identified, 6 studies were included compiling a total number of 198 patients treated with FGR using 5- ALA. No study on ependymal fluorescence after administration of SF was found. Overall prevalence of ependymal fluorescence was 61.4%. A total of 54.5% of cases were found to be positive for tumor cells. A total of 25.5% of patients with ependymal fluorescence were related to contrast enhancement in ventricular walls.

Conclusions The phenomenon of ventricular wall fluorescence in 5-ALA-derived fluorescence-guided resection of malignant glioma is poorly understood and not always may fluorescence represent tumor infiltration. A larger scale prospective sampling study with molecular analyses is currently ongoing and will hopefully provide further insight into pathophysiology and clinical implications of ependymal fluorescence.

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Locating the foramen ovale by using molar and inter-eminence planes: a guide for percutaneous trigeminal neuralgia procedures

J Neurosurg 132:624–630, 2020

The first attempt to cannulate the foramen ovale is often times unsuccessful and requires subsequent reattempts, thereby increasing the risk of an adverse event and radiation exposure to the patient and surgeon. Failure in cannulation may be attributable to variation in soft-tissue–based landmarks used for needle guidance. Also, the incongruity between guiding marks on the face and bony landmarks visible on fluoroscopic images may also complicate cannulation. Therefore, the object of this study was to assess the location of the foramen ovale by way of bony landmarks, exclusive of soft-tissue guidance.

METHODS A total of 817 foramina ovalia (411 left-sided, 406 right-sided) from cranial base images of 424 dry crania were included in the study. The centroid point of each foramen ovale was identified. A sagittal plane through the posterior-most molar (molar plane) and a coronal plane passing through the articular eminences of the temporal bones (inter-eminence plane) were superimposed on images. The distances of the planes from the centroids of the foramina were measured. Also, counts were taken to assess how often the planes and their intersections crossed the boundary of the foramen ovale.

RESULTS The average distance between the molar plane and the centroid of the foramen was 1.53 ± 1.24 mm (mean ± SD). The average distance between the inter-eminence plane and the centroid was 1.69 ± 1.49 mm. The molar and inter-eminence planes crossed through the foramen ovale boundary 83.7% (684/817) and 81.6% (667/817) of the time, respectively. The molar and inter-eminence planes passed through the boundary of the foramen together 73.5% (302/411) of the time. The molar and inter-eminence planes intersected within the boundary of the foramen half of the time (49.4%; 404/817).

CONCLUSIONS The results of this study provide a novel means of identifying the location of the foramen ovale. Unlike the soft-tissue landmarks used in the many variations of the route of Härtel, the bony landmarks identified in this study can be palpated, marked on the face, appreciated fluoroscopically, and do not require any measurement from soft-tissue structures. Utilizing the molar and inter-eminence planes as cannulation guides will improve the approach to the foramen ovale and decrease the amount of radiation exposure to both the patient and surgeon.

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Intraoperative facial motor evoked potential monitoring for pontine cavernous malformation resection

J Neurosurg 132:265–271, 2020

The aim of this study was to predict postoperative facial nerve function during pontine cavernous malformation surgery by monitoring facial motor evoked potentials (FMEPs).

METHODS From 2008 to 2017, 10 patients with pontine cavernous malformations underwent total resection via the trans–fourth ventricle floor approach with FMEP monitoring. House-Brackmann grades and Karnofsky Performance Scale (KPS) scores were obtained pre- and postoperatively. The surgeries were performed using one of 2 safe entry zones into the brainstem: the suprafacial triangle and infrafacial triangle approaches. Six patients underwent the suprafacial triangle approach, and 4 patients underwent the infrafacial triangle approach. A cranial peg screw electrode was used to deliver electrical stimulation for FMEP by a train of 4 or 5 pulse anodal constant current stimulation. FMEP was recorded from needle electrodes on the ipsilateral facial muscles and monitored throughout surgery by using a threshold- level stimulation method.

RESULTS FMEPs were recorded and analyzed in 8 patients; they were not recorded in 2 patients who had severe preoperative facial palsy and underwent an infrafacial triangle approach. Warning signs appeared in all patients who underwent the suprafacial triangle approach. However, after temporarily stopping the procedures, FMEP findings during surgery showed recovery of the thresholds. FMEPs in patients who underwent the infrafacial triangle approach were stable during the surgery. House-Brackmann grades were unchanged postoperatively in all patients. Postoperative KPS scores improved in 3 patients, decreased in 1, and remained the same in 6 patients.

CONCLUSIONS FMEPs can be used to monitor facial nerve function during surgery for pontine cavernous malformations, especially when the suprafacial triangle approach is performed.

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Lumbar drain trial outcomes of normal pressure hydrocephalus: a single-center experience of 254 patients

J Neurosurg 132:306–312, 2020

A short-term lumbar drain (LD) trial is commonly used to assess the response of normal pressure hydrocephalus (NPH) patients to CSF diversion. However, it remains unknown whether the predictors of passing an LD trial match the predictors of improvement after ventriculoperitoneal shunting. The aim of this study was to examine outcomes, complication rates, and associations between predictors and outcomes after an LD trial in patients with NPH.

METHODS The authors retrospectively reviewed the records of 254 patients with probable NPH who underwent an LD trial between March 2008 and September 2017. Multivariate regression models were constructed to examine predictors of passing the LD trial. Complications associated with the LD trial procedure were recorded.

RESULTS The mean patient age was 77 years and 56.7% were male. The mean durations of gait disturbance, cognitive decline, and urinary incontinence were 29 months, 32 months, and 28 months, respectively. Of the 254 patients, 30% and 16% reported objective and subjective improvement after the LD trial, respectively. Complications included a sheared LD catheter, meningitis, lumbar epidural abscess, CSF leak at insertion site, transient lower extremity numbness, slurred speech, refractory headaches, and hyponatremia. Multivariate analyses using MAX-R revealed that a prior history of stroke predicted worse outcomes, while disproportionate subarachnoid spaces (uneven enlargement of supratentorial spaces) predicted better outcomes after the LD trial (r2 = 0.12, p < 0.05).

CONCLUSIONS The LD trial is generally safe and well tolerated. The best predictors of passing the LD trial include a negative history of stroke and having disproportionate subarachnoid spaces.

 

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Overview of Different Flow Diverters and Flow Dynamics

Neurosurgery 86:S21–S34, 2020

Over the past decade, flow diverter technology for endocranial aneurysms has seen rapid evolution, with the development of new devices quickly outpacing the clinical evidence base. However, flow diversion has not yet been directly compared to surgical aneurysm clipping or other endovascular procedures. The oldest and most well-studied device is the Pipeline Embolization Device (PED; Medtronic), recently transitioned to the Pipeline Flex (Medtronic), which still has sparse data regarding outcomes.

To date, other flow diverting devices have not been shown to outperform the PED, although information comes primarily from retrospective studies with short follow-up, which are not always comparable.

Because of this lack of high-quality outcome data, no reliable recommendations can be made for choosing among flow diversion devices yet. Moreover, the decision to proceed with flow diversion should be individualized to each patient.

In this work, we wish to provide a comprehensive overview of the technical specifications of all flow diverter devices currently available, accompanied by a succinct description of the evidence base surrounding each device.

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Interlaminar contralateral endoscopic lumbar foraminotomy assisted with the O-arm navigation

Acta Neurochirurgica (2020) 162:121–125

The interlaminar contralateral endoscopic lumbar foraminotomy (ICELF) provides access to the foraminal pathology with less violation to facet than the ipsilateral approach. However, it is technically challenging even for an experienced surgeon.

Methods We introduce the step-by-step workflow of the interlaminar contralateral endoscopic lumbar foraminotomy assisted with O-arm navigation system.

Conclusion The ICELF assisted with O-arm navigation is safe, accurate, and efficient for the treatment of lumbar foraminal stenosis. The CT-based navigation reshapes the learning curve of the advanced endoscopic technique, reducing the risk of facet joint violation, and minimizes radiation exposure to surgeons.

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Individual variations of the superior petrosal vein complex and their microsurgical relevance in 50 cases of trigeminal microvascular decompression

Acta Neurochirurgica (2020) 162:197–209

We investigated the understudied anatomical variations of the superior petrosal vein (SPV) complex (SPVC), which may play some role in dictating the individual complication risk following SPVC injury.

Methods Microvascular decompressions of the trigeminal nerve between September 2012 and July 2016. All operations utilized an SPVC preserving technique. Preoperative balanced fast field echo (bFFE) magnetic resonance imaging, or equivalent sequences, and operative videos were studied for individual SPVC anatomical features.

Results Applied imaging and operative SPVC anatomy were described for fifty patients (mean age, 67.18 years; female sex and right-sided operations, 58% each). An SPVC component was sacrificed intentionally in 6 and unintentionally in only 7 cases. Twenty-nine different individual variations were observed; 80% of SPVCs had either 2 SPVs with 3 or 1 SPV with 2, 3, or 4 direct tributaries. Most SPVCs had 1 SPV (64%) and 2 SPVs (32%). The SPV drainage point into the superior petrosal sinus was predominantly between the internal auditory meatus and Meckel cave (85.7% of cases). The vein of the cerebellopontine fissure was the most frequent direct tributary (86%), followed by the pontotrigeminal vein in 80% of SPVCs. Petrosal-galenic anastomosis was detected in at least 38%of cases. At least 1 SPVin 54%of the cases and at least 1 direct tributary in 90%disturbed the operative field. The tributaries were more commonly sacrificed.

Conclusions The extensive anatomical variation of SPVC is depicted. Most SPVCs fall into 4 common general configurations and can usually be preserved. BFFE or equivalent sequences remarkably facilitated the intraoperative understanding of the individual SPVC in most cases.

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Long-term outcomes of high-dose single-fraction radiosurgery for chordomas of the spine and sacrum

J Neurosurg Spine 32:79–88, 2020

The current treatment of chordomas is associated with significant morbidity, high rates of local recurrence, and the potential for metastases. Stereotactic radiosurgery (SRS) as a primary treatment could reduce the need for en bloc resection to achieve wide or marginal margins. Spinal SRS outcomes support the exploration of SRS’s role in the durable control of these conventionally radioresistant tumors. The goal of the study was to evaluate outcomes of patients with primary chordomas treated with spinal SRS alone or in combination with surgery.

METHODS Clinical records were reviewed for outcomes of patients with primary chordomas of the mobile spine and sacrum who underwent single-fraction SRS between 2006 and 2017. Radiographic local recurrence-free survival (LRFS), overall survival (OS), symptom response, and toxicity were assessed in relation to the extent of surgery.

RESULTS In total, 35 patients with de novo chordomas of the mobile spine (n = 17) and sacrum (n = 18) received SRS and had a median post-SRS follow-up duration of 38.8 months (range 2.0–122.9 months). The median planning target volume dose was a 24-Gy single fraction (range 18–24 Gy). Overall, 12 patients (34%) underwent definitive SRS and 23 patients (66%) underwent surgery and either neoadjuvant or postoperative adjuvant SRS. Definitive SRS was selectively used to treat both sacral (n = 7) and mobile spine (n = 5) chordomas. Surgical strategies for the mobile spine were either intralesional, gross-total resection (n = 5) or separation surgery (n = 7) and for the sacrum en bloc sacrectomy (n = 11). The 3- and 5-year LRFS rates were 86.2% and 80.5%, respectively. Among 32 patients (91%) receiving 24-Gy radiation doses, the 3- and 5-year LRFS rates were 96.3% and 89.9%, respectively. The 3- and 5-year OS rates were 90.0% and 84.3%, respectively. The symptom response rate to treatment was 88% for pain and radiculopathy. The extent or type of surgery was not associated with LRFS, OS, or symptom response rates (p > 0.05), but en bloc resection was associated with higher surgical toxicity, as measured using the Common Terminology Criteria for Adverse Events (version 5.0) classification tool, than epidural decompression and curettage/intralesional resection (p = 0.03). The long-term rate of toxicity ≥ grade 2 was 31%, including 20% grade 3 tissue necrosis, recurrent laryngeal nerve palsy, myelopathy, fracture, and secondary malignancy.

CONCLUSIONS High-dose spinal SRS offers the chance for durable radiological control and effective symptom relief with acceptable toxicity in patients with primary chordomas as either a definitive or adjuvant therapy.

 

 

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