M Christopher Wallace

Queens University of Charlotte, New York, United States

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Publications (77)261.42 Total impact

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    ABSTRACT: Cerebral cavernous malformations are brain vascular malformations associated with intracranial hemorrhage. It is unclear whether pregnancy is a risk factor for hemorrhage, yet there is speculation that it may be. To compare the risk of clinically significant hemorrhage during pregnancy and nonpregnancy. A total of 186 patients from the University of Toronto Vascular Malformations Study Group were enrolled. The obstetrical history of each patient was collected and matched to their neurological history from the records of the study group. All hemorrhagic events occurring during childbearing years were associated with either a defined pregnancy risk period or nonpregnancy period. Patients were also asked to recall advice that they received from health care professionals regarding risk of hemorrhage in pregnancy. Among our patient population there were 349 pregnancies (283 live births) and 49 hemorrhages during childbearing years, 3 of which were during pregnancy but none during delivery or within 6 weeks post partum. The hemorrhage rate for pregnant women was 1.15% (95% confidence interval: 0.23-3.35) per person-year and 1.01% (95% confidence interval: 0.75-1.36) per person-year for nonpregnant women. Relative risk of pregnancy was 1.13 (95% confidence interval: 0.34-3.75) (P = .84). Neurosurgeons and obstetricians were the source of most hemorrhage risk advice. The majority of neurosurgeons suggested that the risk was unchanged, but the obstetricians were divided. Four patients never conceived, and 2 others began contraception because of the advice that they received. The risk of intracranial hemorrhage from cerebral cavernous malformations is likely not changed during pregnancy, delivery, or post partum.
    Neurosurgery 06/2012; 71(3):626-30; discussion 631. DOI:10.1227/NEU.0b013e31825fd0dc · 3.03 Impact Factor
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    ABSTRACT: Standard endovascular therapy has shown little success in treatment of very large and giant ophthalmic segment aneurysms. We hypothesize that surgical treatment of these aneurysms yields better results in terms of visual function and aneurysm obliteration. The Toronto Brain Vascular Malformation Study Group database was analyzed to retrieve patients treated surgically for very large (>15 mm) and giant aneurysms of the ophthalmic segment of the carotid artery. Preoperative data and postoperative long-term outcomes with specific consideration for visual function and aneurysm obliteration were evaluated. Of the 257 patients with ophthalmic and paraophthalmic aneurysms, 38 patients had very large or giant aneurysms. Twenty-one underwent surgical treatment; 19 had direct clipping; 1 had trapping, and 1 underwent trapping and bypass. Fifteen patients had unruptured and six had ruptured aneurysms. The mean follow-up period was 88 months. Six (28%) aneurysms had a small residual neck remnant. Of the 12 patients with documented preoperative visual deficit, 9 (75%) improved, 2 (16%) remained stable, and 1 (8%) worsened. Two patients had mild to moderate new visual deficit. Thus, the surgery-related visual complications were 14%. Eighteen patients (86%) had a good or excellent outcome (GOS IV and V). Presentation with prior visual deficit and poor neurological function were predictors of worse visual and clinical outcome, respectively (P = 0.02 and 0.01). There is considerable surgery-related risk for optic pathways during treatment of very large and giant ophthalmic segment aneurysms. Surgery, however, seems to be the treatment of choice in terms of overall visual outcome and aneurysm obliteration as compared to the current endovascular results in this subset of patients.
    Acta Neurochirurgica 09/2011; 154(1):43-52. DOI:10.1007/s00701-011-1167-2 · 1.79 Impact Factor
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    ABSTRACT: We report a case of anaplastic ependymoma with extracranial metastases in a 22-year-old female. The patient originally presented with headaches and dysarthria. Neuroimaging revealed a large solid and cystic right fronto-temporal lesion. It was located completely extraventricularly and a glioblastoma was suspected based on the neuroimaging findings. A gross total resection was achieved. Histopathologic examination revealed an anaplastic ependymoma. The patient was treated with radiotherapy. Approximately 1 year after the initial surgery, the patient presented with metastatic disease to the scalp. At 2 years, an intraparotid metastasis was detected. Subsequent neck dissection revealed positive lymph nodes at several levels. It was followed by radiotherapy to the neck. 5 years after the initial surgery, the patient has residual metastatic disease. The case is discussed and the literature on extraventricular ependymal neoplasms is reviewed.
    Journal of Neuro-Oncology 09/2011; 104(2):599-604. DOI:10.1007/s11060-010-0525-x · 2.79 Impact Factor
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    ABSTRACT: Brainstem arteriovenous malformations are challenging lesions, and benefits of treatment are uncertain. To study the clinical course of Brainstem arteriovenous malformations and the influence of treatments on outcome. We reviewed a prospective series of 31 brainstem arteriovenous malformations. Demographic, morphological, and clinical characteristics were recorded. Factors determining initial and final outcomes (modified Rankin Scale), results of treatments (cure rates, complications), and disease course were analyzed. Brainstem arteriovenous malformations were symptomatic and bled in 93% and 61% of cases, respectively. Examination was abnormal and initial modified Rankin Scale score was < 3 in 71% and 86% of patients, respectively. The average follow-up time was 6.2 years, and 26% of patients rebled (5.9 %/y). Treatment modalities included conservative, radiosurgical, endovascular, surgical, and multimodality treatment in 13%, 58%, 35%, 16%, and 26% of cases, respectively. The obliteration rate was 60% overall and 39% after radiosurgery, 40% after embolization, and 75% after microsurgery, with respective complication-free cure rates of 71%, 50%, and 0%. Overall procedural mortality and morbidity were 2.3% and 18.6%, respectively. Final modified Rankin Scale score was < 3 in 77% of cases. Neurological deterioration (35%) was related to treatment complications in 74% of cases with a negative impact of surgery (P = .04), palliative embolization (odds ratio = 16), and multimodality treatments (odds ratio = 24). Radiosurgery was inversely associated with worsening (odds ratio = 0.06). Brainstem arteriovenous malformations require individualized treatment decisions. Single-modality treatments with a reasonable chance of complete cure and low complication rate (such as radiosurgery) should be favored.
    Neurosurgery 05/2011; 70(1):155-61; discussion 161. DOI:10.1227/NEU.0b013e31822670ac · 3.03 Impact Factor
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    ABSTRACT: Type A intradural arteriovenous fistulae of the sacral filum terminale are rare lesions fed primarily by the distal anterior spinal artery. The artery is frequently too narrow or tortuous for endovascular obliteration, and direct surgical resection of the fistula requires an invasive sacrectomy. We present a less invasive indirect surgical approach through an L4 laminectomy and transection of the filum terminale rostral to the fistula. A 62-year-old man presented with a 6-month history of progressive bilateral lower extremity paresthesias and weakness and associated incontinence and impotence. Spinal magnetic resonance imaging demonstrated perimedullary flow voids. Selective spinal angiography revealed a fistula at S2-3 between the distal anterior spinal artery and an early draining vein returning cranially along the filum terminale, diagnostic of an intradural arteriovenous fistula. An L4 laminectomy and transection of the filum terminale rostral to the lesion were performed to disrupt the medullary arterial supply to the intradural fistula and outflow to the medullary venous plexus of the spinal cord. At 10-month clinical follow, up the patient had regained bowel and bladder continence, was able to ambulate with a cane, and reported subjective improvement of lower extremity paresthesias. Selective spinal angiography at 1 year demonstrated no residual arteriovenous shunt. Pathological venous hypertension of a type A intradural arteriovenous fistula of the sacral filum terminale can be treated by transection of the filum terminale at L4. This avoids posterior partial sacrectomy required for direct resection; however, subsequent clinical follow-up is necessary to monitor for reconstitution.
    Neurosurgery 04/2011; 69(3):E780-4; discussion E784. DOI:10.1227/NEU.0b013e31821bc64c · 3.03 Impact Factor
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    ABSTRACT: Epileptic seizures are a common presentation in patients with newly diagnosed brain arteriovenous malformations, but the pathophysiological mechanisms causing the seizures remain poorly understood. We used magnetic resonance imaging-based quantitative cerebrovascular reactivity mapping and conventional angiography to determine whether seizure-prone patients with brain arteriovenous malformations exhibit impaired cerebrovascular reserve or morphological angiographic features predictive of seizures. Twenty consecutive patients with untreated brain arteriovenous malformations were recruited (10 with and 10 without epileptic seizures) along with 12 age-matched healthy controls. Blood oxygen level-dependent MRI was performed while applying iso-oxic step changes in end-tidal partial pressure of CO(2) to obtain quantitative cerebrovascular reactivity measurements. The brain arteriovenous malformation morphology was evaluated by angiography, to determine to what extent limitations of arterial blood supply or the presence of restricted venous outflow and tissue congestion correlated with seizure susceptibility. Only patients with seizures exhibited impaired peri-nidal cerebrovascular reactivity by magnetic resonance imaging (0.11 ± 0.10 versus 0.25 ± 0.07, respectively; P < 0.001) and venous drainage patterns suggestive of tissue congestion on angiography. However, cerebrovascular reactivity changes were not of a magnitude suggestive of arterial steal, and were probably compatible with venous congestion in aetiology. Our findings demonstrate a strong association between impaired peri-nidal cerebrovascular reserve and epileptic seizure presentation in patients with brain arteriovenous malformation. The impaired cerebrovascular reserve may be associated with venous congestion. Quantitative measurements of cerebrovascular reactivity using blood oxygen level-dependent MRI appear to correlate with seizure susceptibility in patients with brain arteriovenous malformation.
    Brain 01/2011; 134(Pt 1):100-9. DOI:10.1093/brain/awq286 · 10.23 Impact Factor
  • Cian J O'Kelly, Julian Spears, David Urbach, M Christopher Wallace
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    ABSTRACT: In the management of subarachnoid hemorrhage (SAH), the potential for early complications and the centralization of limited resources often challenge the delivery of timely neurosurgical care. We sought to determine the impact of proximity to the accepting neurosurgical centre on outcomes following aneurysmal SAH. Using administrative data, we analyzed patients undergoing treatment for aneurysmal subarachnoid hemorrhage at neurosurgical centres in Ontario between 1995 and 2004. We compared mortality for patients receiving treatment at a centre in their county (in-county) versus those treated from outside counties (out-of-county). We also examined the impact of distance from the patient's residence to the treating centre. The mortality rates were significantly lower for in-county versus out-of-county patients (23.5% vs. 27.6%, p=0.009). This advantage remained significant after adjusting for potential confounders (HR=0.84, p=0.01). The relationship between distance from the treating centre and mortality was biphasic. Under 300 km, mortality increased with increasing distance. Over 300 km, a survival benefit was observed. Proximity to the treating neurosurgical centre impacts survival after aneurysmal SAH. These results have significant implications for the triage of these critically ill patients.
    The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 01/2011; 38(1):36-40. · 1.60 Impact Factor
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    ABSTRACT: Surgical activity is probably the most important component of surgical training. During the first year of surgical residency, there is an early opportunity for the development of surgical skills, before disparities between the skill sets of residents increase in future years. It is likely that surgical skill is related to operative volumes. There are no published guidelines that quantify the number of surgical cases required to achieve surgical competency. The aim of this study was to describe the current trends in surgical activity in a recent cohort of first-year Canadian neurosurgical trainees. This study utilized retrospective database review and survey methodology to describe the current state of surgical training for first-year neurosurgical trainees. A committee of five residents designed this survey in an effort to capture factors that may influence the operative activity of trainees. Nine out of a cohort of 20 first-year Canadian neurosurgical trainees that began training in July of 2008 participated in the study. The median number of cases completed by a resident during the initial three month neurosurgical rotation was 66, within which the trainee was identified as the primary surgeon in 12 cases. Intracranial hemorrhage and cerebrospinal fluid diversion procedures were the most common operations to have the trainee as primary surgeon. Based on this pilot study, it appears that the operative activity of Canadian first-year residents is at least equivalent to the residents of other studied training systems with respect to volume and diversity of surgical activity.
    The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 11/2010; 37(6):855-60. · 1.60 Impact Factor
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    ABSTRACT: In this study, the authors evaluated how an appropriate allocation of patients with occipital arteriovenous malformations (AVMs) who were treated according to different strategies would affect nonhemorrhagic headache, visual function, and hemorrhage risk levels. Of the 712 patients with brain AVMs in the Toronto Western Hospital prospective database, 135 had occipital AVMs. The treatment decision was based on patients' characteristics, presentation, and morphology of the AVM. The management modalities were correlated with their outcomes. The mean follow-up period was 6.78 years. Nonhemorrhagic headache was the most frequent symptom (82 [61%] of 135 patients). Ninety-four patients underwent treatment with one or a combination of embolization, surgery, or radiosurgery, and 41 were simply observed. Of the 40 nontreated patients with nonhemorrhagic headache, only 12 (30%) showed improvement. In the observation group 2 patients (22%) had worsening of visual symptoms, and 2 experienced hemorrhage, for an annual hemorrhage rate of 0.7% per year; 1 patient died. In the treatment group, the improvement in nonhemorrhagic headache in 35 patients (83%) was significant (p < 0.0001). Visual deficit at presentation worsened in 2 (8%), and there were 8 new visual field deficits (9%). The visual worsening was not significantly different. There were 2 other neurological deficits (2%) and 2 deaths (2%) related to the AVM treatment. One AVM hemorrhaged. The annual hemorrhage rate was 0.1% per year. The hemorrhage risk in the observation and treatment groups was lower than the observed hemorrhage risk of all patients with AVMs (4.6%) at the authors' institution. Appropriate selection of patients with occipital AVMs for one or a combination of treatment modalities yields a significant decrease in nonhemorrhagic headache without significant visual worsening. The multidisciplinary care of occipital AVMs can aim for an apparent decrease in hemorrhage risk.
    Journal of Neurosurgery 10/2010; 113(4):742-8. DOI:10.3171/2009.11.JNS09884 · 3.15 Impact Factor
  • The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 09/2010; 37(5):681-3. · 1.60 Impact Factor
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    ABSTRACT: Multidetector computerized tomography angiography (MDCTA) is now a widely accepted technique for the management of intracranial aneurysms. To evaluate its accuracy for the postoperative assessment of clipped intracranial aneurysms. We analyzed a consecutive series of 31 patients that underwent direct surgical clipping procedures of 38 aneurysms. A 64 slice MDCT scanner (Aquilion 64, Toshiba) was used and results were compared with digital subtraction angiographies (DSA). Two independent neuroradiologists analyzed the following data: examination quality, artifacts, aneurysm remnant, and patency of collateral branches. Interobserver agreement, sensitivity, and specificity were calculated. Seventy-nine percent of the aneurysms were located in the anterior circulation. Significant artifacts were found with multiple and cobalt-alloy clips. According to DSA, remnants >2 mm were found in 21% of the cases, and 2 patients had one collateral branch occluded. Sensitivity and specificity of 64-MDCTA for the detection of aneurysm remnants were 50% and 100%, respectively. Sensitivity and specificity of 64-MDCTA for the detection of a significant remnant (>2 mm) and the detection of the occlusion of a collateral branch were, respectively, 67% and 100% and 50% and 100%. No relationship was found with the location, type, shape, size, or number of clips, but missed remnants tended to be larger with cobalt-alloy clips. 64-MDCTA is a valuable technique to assess the presence of a significant postoperative remnant in single titanium clip application cases and might be useful for long-term follow-up. DSA remains the most accurate postoperative radiological examination.
    Neurosurgery 09/2010; 67(3):844-53; discussion 853-4. DOI:10.1227/01.NEU.0000374684.10920.A2 · 3.03 Impact Factor
  • The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques 07/2010; 37(4):532-4. DOI:10.1017/S0317167100010611 · 1.60 Impact Factor
  • André A le Roux, M Christopher Wallace
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    ABSTRACT: Aneurysmal subarachnoid hemorrhage (aSAH) is a neurosurgical catastrophe. It affects 33,000 patients in the United States annually and has a mortality rate of 50% to 60% at 30 days. Half of the survivors are dependent. Outcome is closely related to the level of consciousness at the time of presentation, global cerebral edema, subarachnoid blood load as seen on CT, and rehemorrhage. Age, hyperglycemia, and medical complications are associated with worse outcomes. The cost impact factor of this condition is high from a financial perspective as well as from a patient perspective. Care givers show increased morbidity when compared with the nonaffected community. Early aggressive treatment of good grade patients seems to provide the best outcome for this serious condition.
    Neurosurgery clinics of North America 04/2010; 21(2):235-46. DOI:10.1016/j.nec.2009.10.014 · 1.54 Impact Factor
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    ABSTRACT: Enrolling a selected sample of ruptured intracranial aneurysms, the International Subarachnoid Aneurysm Trial (ISAT) found endovascular coiling to be superior to microsurgical clipping. The performance of coiling in a more general population of ruptured aneurysms has not been adequately studied. Using provincial administrative data from Ontario, the authors conducted a retrospective cohort study of adult patients with subarachnoid hemorrhage (SAH) who underwent aneurysm repair. The exposure was defined as endovascular versus surgical aneurysm repair. The prespecified primary outcome was time to death or readmission for SAH. Data from the entire cohort were analyzed using a multivariable adjusted Cox proportional hazards model. Propensity scores were used to compare a matched subgroup of patients with aneurysms who had similar baseline characteristics. The potential impact of unmeasured confounding was assessed using sensitivity analysis. Between 1995 and 2004, 2342 aneurysms were clipped and 778 were coiled in Ontario. The proportion of aneurysms treated by coiling increased steadily over time. In the adjusted analysis of the entire cohort, endovascular coiling was associated with a significantly increased hazard of death or SAH readmission (hazard ratio 1.25 [95% CI 1.00–1.55], p = 0.04). Similar results were obtained from the propensity score matched analysis (hazard ratio 1.25 [95% CI 1.04–1.50], p = 0.02). Measures of procedural morbidity and mortality were not significantly different between groups. The results of the current analysis call into question the generalizability of the ISAT to all ruptured aneurysms. Given the limitations inherent in this form of analysis, further clinical studies—rigorously assessing the performance of endovascular therapy in patients with non-ISAT-like aneurysms—are indicated.
    Journal of Neurosurgery 10/2009; 113(4):795-801. DOI:10.3171/2009.9.JNS081645 · 3.15 Impact Factor
  • Stroke 05/2009; 40(5):e412; author reply e413-4. DOI:10.1161/STROKEAHA.108.545327 · 6.02 Impact Factor
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    ABSTRACT: Chronic shunt-dependent hydrocephalus is a recognized complication of aneurysmal subarachnoid hemorrhage. While its incidence and risk factors have been well described, the long-term performance of shunts in this setting has not been not widely reported. Using administrative databases, the authors derived a retrospective cohort of patients undergoing treatment of a ruptured aneurysm in Ontario, Canada, between 1995 and 2005. The authors determined the incidence of shunt-dependent hydrocephalus and analyzed putative risk factors. Mortality rates and indicators of morbidity were recorded. Patients were followed up for the occurrence of shunt failure over time. Of 3120 patients in the cohort, 585 (18.75%) developed shunt-dependent hydrocephalus. On multivariate analysis, age, acute hydrocephalus, ventilation on admission, aneurysms in the posterior circulation and giant aneurysms were all significant predictors of shunt-dependent hydrocephalus. The mortality rate was not increased in patients with chronic hydrocephalus (hazard ratio 1.04, p = 0.63); however, indicators of morbidity were increased in these patients. Of the 585 patients with shunt-dependent hydrocephalus, only 173 (29.6%) underwent a subsequent revision procedure. Ninety-eight percent of these revisions were completed within 6 months. Subsequent revisions occurred more frequently. On multivariate analysis, significant predictors of shunt revision included aneurysm location in the posterior circulation and endovascular treatment of the initial ruptured aneurysm. Shunt-dependent hydrocephalus affects a significant proportion of subarachnoid hemorrhage survivors, contributing to additional morbidity among these patients. Shunt failures occur less frequently in patients who underwent treatment for a ruptured aneurysm than with other forms of hydrocephalus. Most failures occur within 6 months, suggesting that shunt dependency may be transient in the majority of patients.
    Journal of Neurosurgery 05/2009; 111(5):1029-35. DOI:10.3171/2008.9.JNS08881 · 3.15 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate the authors' initial experience with the integration of high-resolution rotational and biplanar angiography during neurovascular operative procedures. Eight patients with intracerebral arteriovenous malformations (AVMs) and aneurysms underwent surgical treatment of their lesions in a combined endovascular surgical suite. After initial head positioning, preoperative biplane and rotational angiography was performed. Resection of the AVM or clipping of the aneurysm was then performed. Further biplane and rotational 3D angiograms were obtained intraoperatively to confirm satisfactory treatment. One small residual AVM identified intraoperatively necessitated further resection. One aneurysm was clipped during endovascular inflation of an intracarotid balloon for temporary proximal control. The completeness of treatment was confirmed on intraoperative 3D rotational angiography in all cases, and there were no procedure-related complications. Intraoperative rotational angiography performed in an integrated biplane angiography/surgery suite is a safe and useful adjunct to surgery and may enable combining endovascular and surgical procedures for the treatment of complex vascular lesions.
    Journal of Neurosurgery 04/2009; 111(1):188-92. DOI:10.3171/2008.12.JNS081018 · 3.23 Impact Factor
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    ABSTRACT: Extracranial-intracranial (EC/IC) bypass is a useful procedure for the treatment of cerebral vascular insufficiency or complex aneurysms. We explored the role of multidetector computed tomography angiography (MDCTA), instead of digital subtraction angiography (DSA), for the postoperative assessment of EC/IC bypass patency. We retrospectively analyzed a consecutive series of 21 MDCTAs from 17 patients that underwent 25 direct or indirect EC/IC bypass procedures between April 2003 and November 2007. Conventional DSA was available for comparison in 13 cases. MDCTA used a 64-slice MDCT scanner (Aquilion 64, Toshiba). The proximal and distal patencies were analyzed independently on MDCTA and DSA by a neuroradiologist and a neurosurgeon. The bypass was considered patent when the entire donor vessel was opacified without discontinuity from proximal to distal ends and was visibly in contact with the recipient vessel. MDCTA depicted the patency status in every patient. Bypasses were patent in 22 cases, stenosed in one, and occluded in two. DSA always confirmed the results of the MDCTA (sensitivity = 100%, 95% CI = 0.655-1.0; specificity 100%, 95% CI = 0.05-1.0). MDCTA is a non-invasive and accurate exam to assess the postoperative EC/IC bypass patency and is a promising technique in routine follow-up.
    Neuroradiology 04/2009; 51(8):505-15. DOI:10.1007/s00234-009-0522-y · 2.37 Impact Factor

Publication Stats

3k Citations
261.42 Total Impact Points


  • 2012
    • Queens University of Charlotte
      • Department of Surgery
      New York, United States
  • 2011
    • University of Alberta
      • Division of Neurosurgery
      Edmonton, Alberta, Canada
  • 1996–2011
    • Toronto Western Hospital
      Toronto, Ontario, Canada
  • 1994–2011
    • University of Toronto
      • • Department of Surgery
      • • Division of Neurosurgery
      Toronto, Ontario, Canada
    • The University of Chicago Medical Center
      • Section of Neurosurgery
      Chicago, Illinois, United States