The role of haemodynamic analysis in high flow extracranial to intracranial bypass surgery / Sheau Fung Sia

Use of computational haemodynamics technology is well described for a number of diverse conditions in medicine including predicting flows in the Circle of Willis, risk of rupture of aneurysms,and optimum endovascular stent placement in the management of vascular pathology. Saphenous vein or radial artery interposition grafts are often used for high flow extracranial intracranial bypass procedures. These bypasses have the potential to supply a considerable volume of cerebral blood flow to the brain. However, longterm patency for specific graft types remains unknown. This is a computation haemodynamic analysis of consecutive interposition bypass cases. The bypasses are between the common carotid artery (CCA) and intracranial Internal carotid artery (ICA) or middle cerebral artery (MCA). Emerging evidence supports a pathogenic role of abnormal wall shear stress (WSS) and pressure turbulence flow as important factors in the development of early graft failure at the anastomotic site. This study aimed to develop a com putational fluid dynamics simulator for assessing flow in cerebral high flow revascularisation bypass graftsand to study the impact of variations in the anastomosis angle and pressure gradient across bypass Also the optimum mean arterial pressure required for maintaining the graft flow was investigated

The role of haemodynamic analysis in high flow extracranial to intracranial bypass surgery

"A thesis submitted to fulfil the requirements for the degree of Doctor of Philosophy at the Australian School of Advanced Medicine, Faculty of Human Sciences, Macquarie University, Sydney"."March 2012"Includes bibliographical references.1. High flow extracranial-to-intracranial brain bypass surgery. Review -- 2. Comparative patency between intracranial arterial pedicle and vein bypass surgery -- 3. Measuring competence development for performing high flow extracranial-to-intracranial bypass -- 4. Computational haemodynamic fluid analysis in high flow extracranial to intracranial bypass surgery -- 5. Evaluation of brain extracranial-to-intracranial (EC-IC) bypass treatments by using computational haemodynamic technology -- 6. Haemodynamic effects resulting from a common carotid to middle cerebral bypass with varying degrees of proximal internal carotid stenosis -- 7. Mean arterial pressure required for maintaining patency of high flow extracranial to intracranial bypass grafts: an investigation with computational haemodynamic models. Case series -- 8. Flow resistance analysis of high flow extracranial-to-intracranial bypass -- 9. Thesis discussion and conclusion -- Appendices."Use of computational haemodynamics technology is well described for a number of diverse conditions in medicine including predicting flows in the Circle of Willis, risk of rupture of aneurysms, and optimum endovascular stent placement in the management of vascular pathology. Saphenous vein or radial artery interposition grafts are often used for high-flow extracranial-intracranial bypass procedures. These bypasses have the potential to supply a considerable volume of cerebral blood flow to the brain. However, long-term patency for specific graft types remains unknown. This is a computation haemodynamic analysis of consecutive interposition bypass cases. The bypasses are between the common carotid artery (CCA) and intracranial Internal carotid artery (ICA) or middle cerebral artery (MCA). Emerging evidence supports a pathogenic role of abnormal wall shear stress (WSS) and pressure turbulence flow as important factors in the development of early graft failure at the anastomotic site. This study aimed to develop a computational fluid dynamics simulator for assessing flow in cerebral high flow revascularisation bypass grafts and to study the impact of variations in the anastomosis angle and pressure gradient across bypass. Also the optimum mean arterial pressure required for maintaining the graft flow was investigated.Mode of access: World Wide Web.1 online resource (xxii, 222 pages) illustrations, portrait

High flow extracranial-to-intracranial brain bypass surgery

High flow extracranial to intracranial (HF EC-IC) cerebral revascularisation may be necessary in the management of complex skull base tumours and intracranial aneurysms. Vascular reconstruction techniques, in addition to direct clip reconstruction, have been described since the first successful bypass more than 50 years ago. Bypass grafting can be considered high flow when a radial artery or the saphenous vein is interposed between the extracranial carotids arteries and intracranial vessels. The decision as to whether to use a low flow or high flow bypass is determined by the anticipated cerebral blood flow needed and the availability of a supply source. In this review, we consider the indications, diagnostic evaluation strategies and long-term graft patency of HF EC-IC bypass surgery.5 page(s

Measuring competence development for performing high flow extracranial-to-intracranial bypass

We report our experience with competence development in the performance of high flow extracranial-to-intracranial (HF EC-IC) bypass surgery because of the infrequency of, and hence potential exposure to, this challenging surgery. We reviewed the National Hospital Morbidity Database for the incidence of EC-IC bypass surgery as well as a prospectively collected database (institutional experience). The following were recorded from the institutional experience: graft occlusion, stenosis, disruption, distal ischaemia, surgical complications of the bypass leading to a modified Rankin Scale (mRS) score >2, and intraoperative cross-clamping time. The cross-clamping time was considered the total time that circulation may have been impaired, which included both the distal and proximal cross-clamping periods. The Australian national EC-IC bypass rate (of all bypass types) averaged 1.9 cases per 1,000,000 head of population annually. The institutional experience (170 cases) of high flow EC-IC bypass in this series was associated with 14.7% (95% confidence interval [CI] 10.1-20.9) of graft complications. Graft-specific complications leading to a mRS score >2 were 5.9% (95% CI 3.1-10.6). For the 83 patients where the cross-clamping time was known, the time of cross-clamping was 44 ± 14 min. We concluded that HF EC-IC bypasses are rarely performed procedures that challenge the development of surgical competence. Novel ways of developing and maintaining surgical skills are necessary, including simulation and laboratory experience.6 page(s

A New expandable cannula system for endoscopic evacuation of intraparenchymal hemorrhages

The authors describe a newly developed expandable cannula to enable a more efficient use of an endoscope in removing intraparenchymal spontaneous hypertensive intracerebral hematomas. The cannula is introduced like a conventional brain cannula, using neuronavigation techniques to reach the targeted hematoma accurately, and, once deployed, conventional microsurgical techniques are used under direct endoscopic visualization. This method was used in 6 patients, and, based on the results of intraoperative intracranial pressure monitoring and postoperative CT scanning, the authors were able to achieve good hematoma removal. They found that by using the expandable cannula, efficient endoscopic surgery in the brain parenchyma was possible.4 page(s

Multiphase particle-in-cell simulation in severe internal carotid artery stenosis

Internal carotid artery (ICA) stenosis, usually caused by atherosclerosis plaque, restricts the blood supply to the brain and causes cerebral ischemia. The plaque can be stable and asymptomatic, or it can cause embolization. An emboli can break from the plaque and travel to the blood vessels in the brain, causing a transient ischemic attack (TIA) or thromboembolic stroke. To reduce the risk of a stroke, estimation of the blood flow and stress distribution at the ICA stenosis is important. Common diagnostic methods, such as computed tomography (CT) and magnetic resonance imaging (MRI) are only able to provide a stenotic configuration. In addition, conventional image-based computational fluid dynamics (CFD) assumes the blood is a single-phase fluid, ignoring the circulating blood cell particles. This may result in an unreliable estimation of the blood flow and stress distribution at the ICA stenosis. Therefore, a multiphase particle-in-cell (MP-PIC) model was introduced to calculate the plasma flow and blood cell motion separately. The MP-PIC simulation showed a reverse flow, flow stagnation, and flow swigging at the stenosis that was not demonstrated by the single-phase model simulation. Thus, the blood cell motion caused significant temporal and spatial flow oscillation variations at the stenosis and must be considered in a hemodynamic simulation. © 2018 Elsevier B.V

Flow resistance analysis of extracranial-to-intracranial (EC-IC) vein bypass

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Cerebral nocardiosis in an immunocompetent patient : a diagnostic dilemma

Nocardia are aerobic, partially acid-fast, branching filamentous Gram-positive bacilli, found in soil and decaying vegetables which are acquired by direct inoculation or inhalation. Nocardiosis generally affects the immunocompromised patients and has become a significant opportunistic infection as the number of immunocompromised individuals has grown worldwide. Nocardial cerebral abscesses are rare and account for about 1–2% of all cerebral abscesses. The insidious manifestations and paucity of clinical and laboratory signs of bacterial inflammation often prompt the diagnosis of neoplasia. Early biopsy of the lesion to achieve specific identification, anti-microbial sensitivity profiles and institution of appropriate treatment are important for positive outcome of nocardial infections. This is a case of a nocardial brain abscess in an immunocompetent patient which has posed a diagnostic dilemma as the causative agent was only managed to be isolated after multiple biopsies.5 page(s

Malignant Transformation of a Rosette-Forming Glioneuronal Tumor with IDH1 Mutation: A Case Report and Literature Review

Background: Rosette-forming glioneuronal tumor (World Health Organization grade I) is considered as a benign tumor with very low potential for progression. The potential for malignant transformation of this tumor is not known and has never been reported before in literature. Case Description: We report a 42-year-old man, diagnosed with rosette-forming glioneuronal tumor of the fourth ventricle with a positive isocitrate dehydrogenase 1 mutation, progressed to glioblastoma after 6 years from diagnosis. We discuss the clinical history, radiological findings, and histopathological characteristic with immunohistochemistry findings observed in this unique case. Conclusions: Despite being acceptable as benign, based on our observations in this case, there is a potential for malignant transformation of rosette-forming glioneuronal tumor. The role of isocitrate dehydrogenase 1 mutation leading to malignant transformation could not be established as our finding is novel and further prospective studies are required to prove this association. Key words: Glioblastoma IDH mutant, IDH 1 mutation, Malignant transformation, RGN

Evaluation of brain extracranial-to-intracranial (EC-IC) bypass treatments by using computational hemodynamic technology

TComputational fluid dynamics(CFD) techniques were used to investigate the hemodynamic effect on EC-IC brain bypass. Local hemodynamic factors at the vascular anastomosis sites have long been thought to play an important role in the platelet activation, growth of intimal hyperplasia and thrombosis of brain bypass anastomosis and hence, affecting graft longevity. In this study, the medical imaging data computed tomography (CT) angiography were collected in DICOM format and processed by using commercial visualization and mesh generation software, which allowed extraction of the luminal surface of the vascular anastomosis in brain bypass surgery. 3-D geometries were reconstructed for the purpose of numerical analysis. With the real-time velocities derived from doppler ultrasound measurements as boundary conditions, the results of blood flow pattern across the patient-specific brain bypass was evaluated. On the computational simulation, we observed there was almost a constant blood flow rate in the graft and internal carotid artery (ICA), and energy loss between proximal and distal also appeared constantly up to 60 % ICA stenosis. Beyond this point with further narrowing of the ICA, the blood flow shunting started to occur. There was also a significant energy loss and pressure gradient different at the bypass segment. We found there was no significant wall shear stress (WSS) different at the border-zone of middle cerebral artery (MCA) against the different angle of distal bypass anastomosis. The results indicated that hemodynamic characteristics were not sensitive to the anastomosis angle. Image-based patient-specific computational models can be used in an efficient manner that allows clinical studies of brain bypass hemodynamics. This modeling not only help us to quantify the WSS, velocity and pressure gradient in brain bypass surgery, it may also help guide future therapeutic strategies to reduce graft failure and preserve the perfusion at the border-zone area.4 page(s