Exploring the Validity and Reliability of Neurosurgery Residency Program Rankings: A Quantitative Analysis

OBJECTIVE

To evaluate the relationships between Doximity rankings (Doximity, Inc.) of residency programs and 2 new ranking systems based on publication rates and academic pursuits.

METHODS

We collected data on 550 neurosurgery graduates over 3 years. We analyzed the median number of published manuscripts per resident and the percentage of residents pursuing academic careers and compared them across the Doximity Research Productivity and Reputation Rankings. We used logistic regression to evaluate the relationships among the rankings, publication rates, and academic pursuits.

RESULTS

Neurosurgery residents published a median of 10 manuscripts per person (IQR: 6-17), and 50% (IQR: 33%-67%) of residents in a given program pursued an academic career. The distributions of the median number of published manuscripts across the Doximity Research Productivity Ranking and the Doximity Reputation Ranking tiers differed significantly (all P < 0.001). Similarly, the distribution of the percentage of residents pursuing an academic career across both published Doximity ranking systems' tiers differed significantly (all P = 0.02). Moreover, we found moderate agreement between the 2 Doximity rankings, fair agreement between the publication and the other 3 rankings, and slight agreement between the academic pursuit and the Doximity rankings.

CONCLUSIONS

We introduced 2 new methods to rank residency programs based on the number of graduates pursuing an academic position and the median number of published manuscripts per resident. By taking a comprehensive approach, neurosurgery applicants can ensure that they select a residency program that meets their needs and offers them the best opportunity for success.

Competitive neurosurgery residency programs: Predictors of matching outcome and research productivity

OBJECTIVE

The aim of this study was to provide a comprehensive assessment of preresidency research and school as predictors of competitive neurosurgery matching and to assess for any correlations between preresidency and intraresidency research productivity.

METHODS

Individuals who graduated from US neurosurgery programs from 2018 through 2020 were assessed for medical school, degree (MD, DO, or PhD), preresidency versus intraresidency publications, author order, article type, and neurosurgery matching outcomes.

RESULTS

Medical school ranking (top 50) and the number of published papers (≥3) before intern year were predictors for matching to a top-25 residency program after adjusting for other covariates (p < 0.001, p = 0.002, respectively). On average, individuals who published more papers before residency published more papers during residency. For the comprehensive clinical papers category, there was a significant difference between individuals from the top 25 residency programs and others, with a stronger correlation between the number of preresidency publications and intraresidency publications for neurosurgeons who attended a top-25 residency program (r = 0.378 and r = 0.179, respectively; p = 0.02).

CONCLUSION

Medical school ranking and research productivity as measured by the number of published papers were independently associated with matching to the top 25 residency programs. In addition, high research productivity in the preresidency years was associated with continued productivity during residency, especially in the category of comprehensive clinical papers.

Academically Inclined: Predictors of Early Career Trajectory and Avenues for Early Intervention Among Neurosurgery Trainees

BACKGROUND

The relationship of academic activities before and during neurosurgery residency with fellowship or career outcomes has not been studied completely.

OBJECTIVE

To assess possible predictors of fellowship and career outcomes among neurosurgery residents.

METHODS

US neurosurgery graduates (2018-2020) were assessed retrospectively for peer-reviewed citations of preresidency vs intraresidency publications, author order, and article type. Additional parameters included medical school, residency program, degree (MD vs DO; PhD), postgraduate fellowship, and academic employment.

RESULTS

Of 547 neurosurgeons, 334 (61.1%) entered fellowships. Fellowship training was significantly associated with medical school rank and first-author publications. Individuals from medical schools ranked 1 to 50 were 1.6 times more likely to become postgraduate fellows than individuals from medical schools ranked 51 to 92 (odds ratio [OR], 1.63 [95% CI 1.04-2.56]; P = .03). Residents with ≥2 first-author publications were almost twice as likely to complete a fellowship as individuals with <2 first-author publications (OR, 1.91 [95% CI 1.21-3.03]; P = .006). Among 522 graduates with employment data available, academic employment obtained by 257 (49.2%) was significantly associated with fellowship training and all publication-specific variables. Fellowship-trained graduates were twice as likely to pursue academic careers (OR, 1.99 [95% CI 1.34-2.96]; P < .001) as were individuals with ≥3 first-author publications ( P < .001), ≥2 laboratory publications ( P = .04), or ≥9 clinical publications ( P < .001).

CONCLUSION

Research productivity, medical school rank, and fellowships are independently associated with academic career outcomes of neurosurgeons. Academically inclined residents may benefit from early access to mentorship, sponsorship, and publishing opportunities.

Freehand frontal external ventricular drain (EVD) placement: Accuracy and complications

Ventriculostomy placement is a life-saving procedure. Our aim was to determine the predictors of inaccurate placement, our infection and hemorrhage rate. This was a retrospective study of EVD placements between January - November 2019. Data related to hemorrhage, infection and catheter misplacement were collected. Univariate and multivariate analyses of predictors of suboptimal catheter placement were performed. 131 consecutive patients underwent freehand EVD placement. The indications were subarachnoid hemorrhage in 36 (27.5%) patients, hemorrhagic stroke in 36 (27.5%), and trauma in 32 (24.4%) patients. Nine patients (6.8%) had culture-proven CSF bacterial infection. Sixteen (12.2%) patients developed small tract hemorrhage, while 8 (6.1%) patients developed large intraparenchymal hemorrhage. There was no correlation between tract hemorrhage or large hemorrhage with the use of antiplatelet or anticoagulation medicines on presentation, diagnosis or Kakarla grade. Trauma diagnosis (odds ratio 2.59, p-value 0.05), left side of EVD placement (odds ratio 2.84, p-value 0.03), increasing midline shift (odds ratio 1.09, p-value 0.03), and lower bicaudate index (odds ratio 0.56, p-value 0.02) were all predictors of Kakarla grade 3 suboptimal placement. When Kakarla grade 2 and 3 were combined, similar results were obtained except that midline shift was no longer statistically significant. The multivariable regression model predicting Kakarla 3 suboptimal placement revealed that low bicaudate index and left sided EVD were predictors of misplaced EVD.

Changes in Angioarchitecture After Stereotactic Radiosurgery for Dural Arteriovenous Fistula

INTRODUCTION

Dural arteriovenous fistulae (DAVF) are intracranial vascular abnormalities encountered in neurosurgery practice. Treatment options are microsurgical disconnection, endovascular embolization and/or radiosurgery. Past studies have reported the efficacy, safety, and predictors of success of radiosurgery. In this study, we investigated the angioarchitecture of fistulae at the time of radiosurgery and how the anatomy changed in the time after treatment based on angiogram follow-ups.

METHODS

A retrospective analysis was performed on patients with angiographic diagnosis of DAVF treated with Gamma Knife radiosurgery (GKRS) between 2013 and 2018. Data collection included demographics, symptoms, grading scores, vascular anatomy, radiation data, treatment strategy, angiographic results, and length of patient follow-up.

RESULTS

Our study reports data on 10 patients with a total of 14 fistulae. On follow-up angiography, 8 (57%) had complete occlusion of the fistula with a median time to follow up of 19.5 months. The remaining 6 (43%) were deemed as near-complete occlusion of fistula with a median time to follow up of 12.0 months. Time from radiosurgery to angiogram revealing incomplete vs. angiogram revealing complete obliteration was significantly different (p=0.045). Nearly all AVFs had decreased feeders over time after treatment with only one AVF developing an additional feeder post-treatment. Arterial feeders, drainage site, sex, Borden type, lesion volume and treatment volume had no predictive value of obliteration outcome.

CONCLUSIONS

This study provides data on the angioarchitecture of fistulae treated with GKRS and also serves as an extension of previous studies reporting the safety and efficacy of GKRS treatment for DAVF in a specific patient population.

Predictors of re-operation in the setting of non-acute subdural hematomas: A 12-year single center retrospective study

Non-acute subdural hematomas (naSDH) may recur after surgical treatment. A second operation affects the quality of life and functional outcome of the patients, and lengthens hospital stay. We aim to identify the predictors of reoperation as the healthcare system in the US is moving towards patient-centered care. This retrospective study included patients treated surgically with burr-holes or mini-craniotomy for non-acute subdural hematoma between February 2006-June 2018. Univariate and multiple logistic regression models were performed. 23 (12.0%) patients had reoperation. Controlling for all the factors, postoperative acute blood in the operative bed was the strongest predictor of recurrence of naSDH (OR = 37.93, 95% CI: 5.35-268.87, p < 0.001). Those undergoing a mini-craniotomy were over six times as likely to experience a recurrent SDH compared to those operated on via burr holes (OR = 6.34, 95% CI: 1.21-33.08, p = 0.029). Finally, patients with a past medical history of thrombocytopenia were nearly six times as likely to experience a recurrence of SDH (OR = 5.80, 95% CI: 1.20-28.10, p = 0.029). Postoperative hematoma thickness showed a trend toward significance such that thicker hematomas were associated with an increased likelihood of experiencing a recurrent SDH. In conclusion, we found that operative technique, thrombocytopenia and the presence of postoperative hemorrhage are significant predictors for reoperation. Given the current interest in endovascular embolization for SDH, understanding these risk factors may aid in determining indications for such adjunctive treatment.

Comprehensive Review of Cranial Chordomas Using National Databases in the USA

AIMS

The management of cranial chordomas is controversial. We provide a comprehensive review of the evolving patterns of care of cranial chordomas in the USA.

MATERIALS AND METHODS

We analysed the National Cancer Database (NCDB) and the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2014 for clinical characteristics and long-term survival, and the National Surgical Quality Improvement Program (NSQIP) dataset between 2005 and 2016 for perioperative characteristics and surgical morbidity.

RESULTS

In total, 936 patients were identified from the NCDB, 405 patients from SEER and 64 patients from the NSQIP. Most patients were men (56.2, 54.8 and 57.8% in NCDB, SEER and NSQIP, respectively) and White (80.9 and 83.2% in NCDB and SEER, respectively). Surgery was the preferred treatment modality (87.3% in NCDB and 86.2% in SEER). Surgery was carried out alone (41.8% in NCDB and 40.7% in SEER) or in combination with radiation (42.1% in NCDB and 45.4% in SEER). Proton therapy was the most common type of radiation (32.2% in NCDB), particularly after 2011. The median operative time, median hospital length and postoperative morbidity were significantly higher in chordoma patients compared with patients who underwent other skull-base procedures. The 5-year survival rate was 79.8% in NCDB and 76.9% in SEER. There was a trend towards longer survival in patients receiving surgery and radiation, which has been increasingly used since 2004. Patients younger than 60 years had a decreased risk of mortality.

CONCLUSIONS

Our analysis reflects patterns of care in the USA. The use of surgery and radiation is increasing, with a trend towards longer survival. Surgery is complicated with long operative time, hospital stay and a higher rate of complications.

Coiling Versus Microsurgical Clipping in the Treatment of Unruptured Middle Cerebral Artery Aneurysms: A Meta-Analysis

BACKGROUND

Open microsurgical clipping of unruptured intracranial aneurysms has long been the gold standard, yet advancements in endovascular coiling techniques have begun to challenge the status quo.

OBJECTIVE

To compare endovascular coiling with microsurgical clipping among adults with unruptured middle cerebral artery aneurysms (MCAA) by conducting a meta-analysis.

METHODS

A systematic search was conducted from January 2011 to October 2015 to update a previous meta-analysis. All studies that reported unruptured MCAA in adults treated by microsurgical clipping or endovascular coiling were included and cumulatively analyzed.

RESULTS

Thirty-seven studies including 3352 patients were included. Using the random-effects model, pooled analysis of 11 studies of microsurgical clipping (626 aneurysms) revealed complete aneurysmal obliteration in 94.2% of cases (95% confidence interval [CI] 87.6%-97.4%). The analysis of 18 studies of endovascular coiling (759 aneurysms) revealed complete obliteration in 53.2% of cases (95% CI: 45.0%-61.1%). Among clipping studies, 22 assessed neurological outcomes (2404 aneurysms), with favorable outcomes in 97.9% (95% CI: 96.8%-98.6%). Among coiling studies, 22 examined neurological outcomes (826 aneurysms), with favorable outcomes in 95.1% (95% CI: 93.1%-96.5%). Results using the fixed-effect models were not materially different.

CONCLUSION

This updated meta-analysis demonstrates that surgical clipping for unruptured MCAA remains highly safe and efficacious. Endovascular treatment for unruptured MCAAs continues to improve in efficacy and safety; yet, it results in lower rates of occlusion.

Pediatric Clival Chordoma: A Curable Disease that Conforms to Collins' Law

BACKGROUND

Skull base chordomas in children are extremely rare. Their course, management, and outcome have not been defined.

OBJECTIVE

To describe the preeminent clinical and radiological features in a series of pediatric patients with skull base chordomas and analyze the outcome of a cohort who underwent uniform treatment. We emphasize predictors of overall survival and progression-free survival, which aligns with Collins’ law for embryonal tumors.

METHODS

Thirty-one patients with a mean age of 10.7 yr (range 0.8-22) harboring skull base chordomas were evaluated. We retrospectively analyzed the outcomes and prognostic factors for 18 patients treated by the senior author, with uniform management of surgery with the aim of gross total resection and adjuvant proton-beam radiotherapy. Mean follow-up was 119.2 mo (range 8-263).

RESULTS

Abducens nerve palsy was the most common presenting symptom. Imaging disclosed large tumors that often involve multiple anatomical compartments. Patients undergoing gross total resection had significantly increased progression-free survival (P = .02) and overall survival (P = .05) compared with those having subtotal resection. Those who lived through the period of risk for recurrence without disease progression had a higher probability of living entirely free of progression (P = .03; odds ratio = 16.0). Age, sex, and histopathological variant did not yield statistical significance in survival.

CONCLUSION

Long-term overall and progression-free survival in children harboring skull base chordomas can be achieved with gross surgical resection and proton-beam radiotherapy, despite an advanced stage at presentation. Collins’ law does apply to pediatric skull base chordomas, and children with this disease have a high hope for cure.

Defensive medicine in neurosurgery: the Canadian experience

OBJECT

Recent studies have examined the impact of perceived medicolegal risk and compared how this perception impacts defensive practices within the US. To date, there have been no published data on the practice of defensive medicine among neurosurgeons in Canada.

METHODS

An online survey containing 44 questions was sent to 170 Canadian neurosurgeons and used to measure Canadian neurosurgeons’ perception of liability risk and their practice of defensive medicine. The survey included questions on the following domains: surgeon demographics, patient characteristics, type of physician practice, surgeon liability profile, policy coverage, defensive behaviors, and perception of the liability environment. Survey responses were analyzed and summarized using counts and percentages.

RESULTS

A total of 75 neurosurgeons completed the survey, achieving an overall response rate of 44.1%. Over one-third (36.5%) of Canadian neurosurgeons paid less than $5000 for insurance annually. The majority (87%) of Canadian neurosurgeons felt confident with their insurance coverage, and 60% reported that they rarely felt the need to practice defensive medicine. The majority of the respondents reported that the perceived medicolegal risk environment has no bearing on their preferred practice location. Only 1 in 5 respondent Canadian neurosurgeons (21.8%) reported viewing patients as a potential lawsuit. Only 4.9% of respondents would have selected a different career based on current medicolegal risk factors, and only 4.1% view the cost of annual malpractice insurance as a major burden.

CONCLUSIONS

Canadian neurosurgeons perceive their medicolegal risk environment as more favorable and their patients as less likely to sue than their counterparts in the US do. Overall, Canadian neurosurgeons engage in fewer defensive medical behaviors than previously reported in the US.

Transsphenoidal surgery for Rathke’s cleft cyst can reduce headache severity and frequency

PURPOSE

The purpose of this study was to determine the effect of transsphenoidal surgery for Rathke’s cleft cyst(RCC) on headache frequency, severity, and duration.

METHODS

The medical records of 43 consecutive patients who underwent transsphenoidal resection of a pathologically-proven RCC at our institution by the senior author (E.R.L.) between April 2008 and April 2014 were reviewed. Patients were called by telephone and asked to answer questions about the severity, location, type, duration,and quality of their headaches, both pre- and postoperatively.This information was joined with detailed data collected directly from each patient’s medical record regarding headaches upon presentation and at 1-week,6-week, 3-month, and annual post-operative appointments.

RESULTS

Twenty-three patients (53 %) responded to our telephone survey after repeated attempts at contact. Median follow-up was 64 months (range 6–83 months). Of these patients, 19 (82.6 %) reported pre-operative headaches,compared to 12 (52.2 %) who reported post-operative headaches (OR = 1.75, p = 0.02). Average headache severity on a 1–10 scale decreased from 6.4 (SD = 2.0)pre-operatively to 3.4 (SD = 1.9) post-operatively (p = 0.006), while average maximum severity decreased from 8.6 (SD = 2.2) pre-operatively to 4.0 (SD = 3.3)post-operatively (p<0.001). The frequency of headaches also decreased, from 18.1 (SD = 12.6) per month pre-operatively to 3.7 (SD = 8.4) per month post-operatively(p<0.001). Overall, 14 patients (60.9 %) reported improvement in their headaches, and three patients(13.0 %) reported that their headaches had completely resolved.

CONCLUSIONS

In a carefully selected patient population,transsphenoidal surgery for RCC can reduce headache monthly frequency, average typical severity, and average maximum severity with minimal risk of morbidity or mortality.

Experimental therapies: gene therapies and oncolytic viruses

Glioblastoma is the most common and aggressive primary brain tumor in adults. Over the past three decades, the overall survival time has only improved by a few months, therefore novel alternative treatment modalities are needed to improve clinical management strategies. Such strategies should ultimately extend patient survival. At present, the extensive insight into the molecular biology of gliomas, as well as into genetic engineering techniques, has led to better decision processes when it comes to modifying the genome to accommodate suicide genes, cytokine genes, and tumor suppressor genes that may kill cancer cells, and boost the host defensive immune system against neoantigenic cytoplasmic and nuclear targets. Both nonreplicative viral vectors and replicating oncolytic viruses have been developed for brain cancer treatment. Stem cells, microRNAs, nanoparticles, and viruses have also been designed. These have been armed with transgenes or peptides, and have been used both in laboratory-based experiments as well as in clinical trials, with the aim of improving selective killing of malignant glioma cells while sparing normal brain tissue. This chapter reviews the current status of gene therapies for malignant gliomas and highlights the most promising viral and cell-based strategies under development.

Intraoperative real-time MRI-guided stereotactic biopsy followed by laser thermal ablation for progressive brain metastases after radiosurgery

Stereotactic radiosurgery is one of the treatment options for brain metastases. However, there are patients who will progress after radiosurgery. One of the potential treatments for this subset of patients is laser ablation. Image-guided stereotactic biopsy is important to determine the histopathological nature of the lesion. However, this is usually based on preoperative, static images, which may affect the target accuracy during the actual procedure as a result of brain shift. We therefore performed real-time intraoperative MRI-guided stereotactic aspiration and biopsies on two patients with symptomatic, progressive lesions after radiosurgery followed immediately by laser ablation. The patients tolerated the procedure well with no new neurologic deficits. Intraoperative MRI-guided stereotactic biopsy followed by laser ablation is safe and accurate, providing real-time updates and feedback during the procedure.

Complications after transsphenoidal surgery for patients with Cushing's disease and silent corticotroph adenomas

OBJECT The purpose of this study was to describe complications associated with the endonasal, transsphenoidal approach for the treatment of adrenocorticotropic hormone (ACTH)-positive staining tumors (Cushing's disease [CD] and silent corticotroph adenomas [SCAs]) performed by 1 surgeon at a high-volume academic medical center. METHODS Medical records from Brigham and Women's Hospital were retrospectively reviewed. Selected for study were 82 patients with CD who during April 2008-April 2014 had consecutively undergone transsphenoidal resection or who had subsequent pathological confirmation of ACTH-positive tumor staining. In addition to demographic, patient, tumor, and surgery characteristics, complications were evaluated. Complications of interest included syndrome of inappropriate antidiuretic hormone secretion, diabetes insipidus (DI), CSF leakage, carotid artery injury, epistaxis, meningitis, and vision changes. RESULTS Of the 82 patients, 68 (82.9%) had CD and 14 (17.1%) had SCAs; 55 patients were female and 27 were male. Most common (n = 62 patients, 82.7%) were microadenomas, followed by macroadenomas (n = 13, 14.7%). A total of 31 (37.8%) patients underwent reoperation. Median follow-up time was 12.0 months (range 3-69 months). The most common diagnosis was ACTH-secreting (n = 68, 82.9%), followed by silent tumors/adenomas (n = 14, 17.1%). ACTH hyperplasia was found in 8 patients (9.8%). Of the 74 patients who had verified tumors, 12 (16.2%) had tumors with atypical features. The overall (CD and SCA) rate of minor complications was 35.4%; the rate of major complications was 8.5% (n = 7). All permanent morbidity was associated with DI (n = 5, 6.1%). In 16 CD patients (23.5%), transient DI developed. Transient DI was more likely to develop in CD patients who had undergone a second operation (37.9%) than in those who had undergone a first operation only (12.8%, p < 0.05). Permanent DI developed in 4 CD patients (5.9%) and 1 SCA patient (7.1%). For 1 CD patient, intraoperative carotid artery injury required endovascular sacrifice of the injured artery, but the patient remained neurologically intact. For another CD patient, aseptic meningitis developed and was treated effectively with corticosteroids. One CD patient experienced major postoperative epistaxis requiring another operative procedure to achieve hemostasis. For 2 CD patients, development of sinus mucoceles was managed conservatively. For 1 SCA patient, an abdominal wound dehisced at the fat graft site. No patients experienced postoperative CSF leakage, visual impairment, or deep vein thrombosis. CONCLUSIONS Transsphenoidal surgery is the treatment of choice for patients with CD and other ACTH-positive staining tumors. Recent advances in endoscopic technology and increasing surgeon comfort with this technology are making transsphenoidal procedures safer, faster, and more effective. Serious complications are uncommon and can be managed successfully.

Awake right hemisphere brain surgery

We report the indications and outcomes of awake right hemispheric brain surgery, as well as a rare patient with crossed aphasia. Awake craniotomies are often performed to protect eloquent cortex. We reviewed the medical records for 35 of 96 patients, in detail, who had awake right hemisphere brain operations. Intraoperative cortical mapping of motor and/or language function was performed in 29 of the 35 patients. A preoperative speech impairment and left hand dominance were the main indicators for awake right-sided craniotomies in patients with right hemisphere lesions. Four patients with lesion proximity to eloquent areas underwent awake craniotomies without cortical mapping. In addition, one patient had a broncho-pulmonary fistula, and another had a recent major cardiac procedure that precluded awake surgery. An eloquent cortex representation was identified in 14 patients (48.3%). Postoperatively, seven of 17 patients (41.1%) who presented with weakness, experienced improvements in their motor functions, 11 of 16 (68.7%) with seizures became seizure-free, and seven of nine (77.7%) with moderate to severe headaches and one of two with a visual field deficit improved significantly. There were also improvements in speech and language functions in all patients who presented with speech difficulties. A right sided awake craniotomy is an excellent option for left handed patients, or those with right sided cortical lesions that result in preoperative speech impairments. When combined with intraoperative cortical mapping, both speech and motor function can be well preserved.

Use of preoperative FLAIR MRI and ependymal proximity of tumor enhancement as surrogate markers of brain tumor origin

Neural stem cells proliferate in the subventricular zone and give rise to progeny that differentiate and migrate throughout the brain. We aimed to test the hypothesis that glioma behavior and grade may correlate with the identity of the tumor cell of origin. We evaluated three preoperative radiographic features (fluid attenuated inversion recovery [FLAIR] MRI characteristics, tumor proximity to ventricular ependyma, and subependymal representation) as surrogate markers of tumor origin using a retrospective cohort design. The medical records of 228 patients who underwent surgical resection of a glioma from January 2004 to August 2008 were reviewed. Average patient age was 54.5 years (standard deviation [SD] 15.3) with a male predominance (62.9%). World Health Organization glioma grades amongst the cohort were Grade IV (71.6%), Grade III (21.3%) and Grade II (7.1%). Mean survival was 11.2 months (SD 10.5) with a mean follow up of 12.8 months (SD 11.3). Glioma tumor grade was significantly correlated to FLAIR signal proximity to the ependymal surface (p<0.01) and inversely with proximity of tumor mass to the ependyma (p<0.01). The mean distance of tumor-associated FLAIR signal from the ependymal surface for glioblastoma multiforme (GBM) was 1.2mm (SD 3.3) compared to 4.8 (SD 6.5) for anaplastic astrocytomas and 6.6mm (SD 6.7; p<0.01) for low grade gliomas. Conversely, the mean distance of the enhancing tumor mass from the ependyma for GBM was 7.3mm (SD 9.4), Grade III glioma 2.3mm (SD 4.9), and Grade II glioma 3.8mm (SD 6.8; p<0.05). These findings suggest that higher grade gliomas might arise from less differentiated neuroepithelial cells in the subventricular zone that possess greater migratory potential.