Dynamic Model of Communicating Hydrocephalus for Surgery Simulation

We propose a dynamic model of cerebrospinal fluid circulation and intracranial pressure regulation. In this model, we investigate the coupling of biological parameters with a 3D model, to improve the mechanical behavior of the brain in surgical simulators. The model was assessed by comparing the simulated ventricular enlargement evolution with a patient case study of communicating hydrocephalus. In our model, cerebro-spinal fluid production-resorption system is coupled with a 3D representation of the brain parenchyma. We introduce a new bi-phasic model of the brain tissue allowing for fluid exchange between the brain extracellular space and the venous system. The time evolution of ventricular pressure has been recorded on a symptomatic patient after closing the ventricular shunt. A finite element model has been built based on a CT scan of this patient, and quantitative comparisons between measures and simulated data are proposed

Dynamic Model of Communicating Hydrocephalus for Surgery Simulation

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Finite element analysis for normal pressure hydrocephalus: The effects of the integration of sulci.

Finite element analysis (FEA) is increasingly used to investigate the brain under various pathological changes. Although FEA has been used to study hydrocephalus for decades, previous studies have primarily focused on ventriculomegaly. The present study aimed to investigate the pathologic changes regarding sulcal deformation in normal pressure hydrocephalus (NPH). Two finite element (FE) models-an anatomical brain geometric (ABG) model and the conventional simplified brain geometric (SBG) model-of NPH were constructed. The models were constructed with identical boundary conditions but with different geometries. The ABG model contained details of the sulci geometry, whereas these details were omitted from the SBG model. The resulting pathologic changes were assessed via four biomechanical parameters: pore pressure, von Mises stress, pressure, and void ratio. NPH was induced by increasing the transmantle pressure gradient (TPG) from 0 to a maximum of 2.0 mmHg. Both models successfully simulated the major features of NPH (i.e., ventriculomegaly and periventricular lucency). The changes in the biomechanical parameters with increasing TPG were similar between the models. However, the SBG model underestimated the degree of stress across the cerebral mantle by 150% compared with the ABG model. The SBG model also overestimates the degree of ventriculomegaly (increases of 194.5% and 154.1% at TPG = 2.0 mmHg for the SBG and ABG models, respectively). Including the sulci geometry in a FEA for NPH clearly affects the overall results. The conventional SBG model is inferior to the ABG model, which accurately simulated sulcal deformation and the consequent effects on cortical or subcortical structures. The inclusion of sulci in future FEA for the brain is strongly advised, especially for models used to investigate space-occupying lesions.This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2013R1A1A1004827).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.media.2015.05.00

Idiopathic Normal Pressure Hydrocephalus: A Review And A Proposed Role For

Despite nearly five decades of experience treating idiopathic normal pressure hydrocephalus (iNPH), there is still no consensus amongst care providers as to how to reliably identify patients with suspected iNPH who will benefit from shunt surgery, or how to measure post-operative symptom improvement. We performed a selective review of the literature, focusing especially on the role of neuroimaging in aiding in the diagnosis of iNPH, and the various clinical scales that have historically been used to assess outcome. Further, we tested the hypothesis that patient-reported outcomes (PROs) will demonstrate effectiveness of shunt surgery for the relief of iNPH symptoms consistent with that demonstrated through the application of clinical scales. To do this, we performed a retrospective analysis of one provider\u27s experience treating patients with suspected iNPH, scoring outcomes based on patient-reported change in symptom severity. All patients treated for suspected iNPH between January 2012 and January 2014 with at least one month of follow-up and documented responses to direct questioning about pre- versus post-surgical symptom severity were included. Twenty-one patients were included in total. 100% of patients reported improvement in at least one of the three cardinal symptoms of gait disturbance, urinary incontinence, or cognitive impairment following shunt implantation. Gait, urinary, and cognitive symptoms individually improved 95%, 84%, and 89%, respectively. There was a significantly higher rate of improvement in any (i.e. at least one) symptom domain using PROs compared to historical data obtained through evaluation with clinical scales. There was no statistically significant difference between improvements in each individual symptom domain. PROs produce results that are largely consistent with data obtained by clinical scales, and can be used as one metric of patient improvement following shunt surgery for iNPH

Porohyperelastic anatomical models for hydrocephalus and idiopathic intracranial hypertension

This is the accepted manuscript of a paper published in the Journal of Neurosurgery, Published online February 6, 2015; DOI: 10.3171/2014.12.JNS14516.OBJECT Brain deformation can be seen in hydrocephalus and idiopathic intracranial hypertension (IIH) via medical images. The phenomenology of local effects, brain shift, and raised intracranial pressure and herniation are textbook concepts. However, there are still uncertainties regarding the specific processes that occur when brain tissue is subject to the mechanical stress of different temporal and spatial profiles of the 2 neurological disorders. Moreover, recent studies suggest that IIH and hydrocephalus may be diseases with opposite pathogenesis. Nevertheless, the similarities and differences between the 2 subjects have not been thoroughly investigated. METHODS An anatomical porohyperelastic finite element model was used to assess the brain tissue responses associated with hydrocephalus and IIH. The same set of boundary conditions, with the exception of brain loading for development of the transmantle pressure gradient, was applied for the 2 models. The distribution of stress and strain during tissue distortion is described by the mechanical parameters. RESULTS The results of both the hydrocephalus and IIH models correlated with pathological characteristics. For the hydrocephalus model, periventricular edema was associated with the presence of positive volumetric strain and void ratio in the lateral ventricle horns. By contrast, the IIH model revealed edema across the cerebral mantle, including the centrum semiovale, with a positive void ratio and volumetric strain. CONCLUSIONS The model simulates all the clinical features in correlation with the MR images obtained in patients with hydrocephalus and IIH, thus providing support for the role of the transmantle pressure gradient and capillary CSF absorption in CSF-related brain deformation. The finite element methods can be used for a better understanding of the pathophysiological mechanisms of neurological disorders associated with parenchymal volumetric fluctuation.Dr. M. Czosnyka is a consultant for J&J (Codman), and has received payment for lectures from Integra Lifescience. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRFK) funded by the Ministry of Science, ICT, & Future Planning (2013R1A1A1004827); and the International Research & Development Program of the NRFK funded by the Ministry of Education, Science, and Technology of Korea (Grant No. 2014K1A3A1A21001366)

Priorities for hydrocephalus research: report from a National Institutes of Health-sponsored workshop

Journal ArticleObject. Treatment for hydrocephalus has not advanced appreciably since the advent of cerebrospinal fluid (CSF) shunts more than 50 years ago. Many questions remain that clinical and basic research could address, which in turn could improve therapeutic options. To clarify the main issues facing hydrocephalus research and to identify critical advances necessary to improve outcomes for patients with hydrocephalus, the National Institutes of Health (NIH) sponsored a workshop titled "Hydrocephalus: Myths, New Facts, and Clear Directions." The purpose of this paper is to report on the recommendations that resulted from that workshop. Methods. The workshop convened from September 29 to October 1, 2005, in Bethesda, Maryland. Among the 150 attendees was an international group of participants, including experts in pediatric and adult hydrocephalus as well as scientists working in related fields, neurosurgeons, laboratory-based neuroscientists, neurologists, patient advocates, individuals with hydrocephalus, parents, and NIH program and intramural staff. Plenary and breakout sessions covered injury and recovery mechanisms, modeling, biomechanics, diagnosis, current treatment and outcomes, complications, quality of life, future treatments, medical devices, development of research networks and information sharing, and education and career development. Results. The conclusions were as follows: 1) current methods of diagnosis, treatment, and outcomes monitoring need improvement; 2) frequent complications, poor rate of shunt survival, and poor quality of life for patients lead to unsatisfactory outcomes; 3) investigators and caregivers need additional methods to monitor neurocognitive function and control of CSF variables such as pressure, flow, or pulsatility; 4) research warrants novel interdisciplinary approaches; 5) understanding of the pathophysiological and recovery mechanisms of neuronal function in hydrocephalus is poor, warranting further investigation; and 6) both basic and clinical aspects warrant expanded and innovative training programs. Conclusions. The research priorities of this workshop provide critical guidance for future research in hydrocephalus, which should result in advances in knowledge, and ultimately in the treatment for this important disorder and improved outcomes in patients of all ages

CSF Dynamics for Shunt Prognostication and Revision in Normal Pressure Hydrocephalus.

BACKGROUND: Despite the quantitative information derived from testing of the CSF circulation, there is still no consensus on what the best approach could be in defining criteria for shunting and predicting response to CSF diversion in normal pressure hydrocephalus (NPH). OBJECTIVE: We aimed to review the lessons learned from assessment of CSF dynamics in our center and summarize our findings to date. We have focused on reporting the objective perspective of CSF dynamics testing, without further inferences to individual patient management. DISCUSSION: No single parameter from the CSF infusion study has so far been able to serve as an unquestionable outcome predictor. Resistance to CSF outflow (Rout) is an important biological marker of CSF circulation. It should not, however, be used as a single predictor for improvement after shunting. Testing of CSF dynamics provides information on hydrodynamic properties of the cerebrospinal compartment: the system which is being modified by a shunt. Our experience of nearly 30 years of studying CSF dynamics in patients requiring shunting and/or shunt revision, combined with all the recent progress made in producing evidence on the clinical utility of CSF dynamics, has led to reconsidering the relationship between CSF circulation testing and clinical improvement. CONCLUSIONS: Despite many open questions and limitations, testing of CSF dynamics provides unique perspectives for the clinician. We have found value in understanding shunt function and potentially shunt response through shunt testing in vivo. In the absence of infusion tests, further methods that provide a clear description of the pre and post-shunting CSF circulation, and potentially cerebral blood flow, should be developed and adapted to the bed-space

Development of an alternative ventricular catheter and an in vitro model of its obstruction

This thesis was previously held under moratorium from 5th November 2014 until 2nd June 2020.Intracranial pressure and volume varies considerably between hydrocephalic patients, and with age, health and haemodynamic status; if left untreated intracranial pressure rises and the ventricular system expands to accommodate the excess cerebrospinal fluid (CSF), with significant morbidity and mortality. Although considerable improvements in design have been made since their introduction all CSF shunts in use today have a high incidence of failure with shunt obstruction being the most serious. Conventional proximal shunt catheters are made from poly (di-methyl) siloxane (PDMS), the walls of which are perforated with holes for the CSF to pass through. The limited range of catheters, in terms of material selection and flow distribution, is responsible in large part for their poor performance.;The aim of the study is to design and fabricate an alternative design of proximal catheter with permeable walls, and to evaluate its performance in the presence of glial cells, which are responsible for blockage. Electrospun Poly-ether Urethane (EPU) samples were fabricated from solvent, by means of an electrospinning technique, to yield microfibrous polymer conduits. The hydrodynamic properties of EPU and conventional shunt were studied using a purpose-built shunt testing system.;The viability and growth of cells on candidate catheter materials such as PDMS and polyurethane in the form of cast films, microfibrous mats and porous sponges were studied in presence of proteins present in CSF after 48h and 96h in culture. The number of viable cells was significantly less on EPU samples compared to the other substrates, which suggests that the fibrous form of the material from which the catheter is made has a bearing on the cell growth. A cell culture model of shunt obstruction was developed in which the cells were subjected to flow during culture in vitro, and the degree of obstruction quantified in terms of hydraulic permeability post static and perfusion culture. The results indicate that a catheter made of EPU would be able to maintain CSF flow even with the presence of cells for the time period chosen for this study. These findings have implications for the design and deployment of micro porous shunt catheter systems for the treatment of hydrocephalus.Intracranial pressure and volume varies considerably between hydrocephalic patients, and with age, health and haemodynamic status; if left untreated intracranial pressure rises and the ventricular system expands to accommodate the excess cerebrospinal fluid (CSF), with significant morbidity and mortality. Although considerable improvements in design have been made since their introduction all CSF shunts in use today have a high incidence of failure with shunt obstruction being the most serious. Conventional proximal shunt catheters are made from poly (di-methyl) siloxane (PDMS), the walls of which are perforated with holes for the CSF to pass through. The limited range of catheters, in terms of material selection and flow distribution, is responsible in large part for their poor performance.;The aim of the study is to design and fabricate an alternative design of proximal catheter with permeable walls, and to evaluate its performance in the presence of glial cells, which are responsible for blockage. Electrospun Poly-ether Urethane (EPU) samples were fabricated from solvent, by means of an electrospinning technique, to yield microfibrous polymer conduits. The hydrodynamic properties of EPU and conventional shunt were studied using a purpose-built shunt testing system.;The viability and growth of cells on candidate catheter materials such as PDMS and polyurethane in the form of cast films, microfibrous mats and porous sponges were studied in presence of proteins present in CSF after 48h and 96h in culture. The number of viable cells was significantly less on EPU samples compared to the other substrates, which suggests that the fibrous form of the material from which the catheter is made has a bearing on the cell growth. A cell culture model of shunt obstruction was developed in which the cells were subjected to flow during culture in vitro, and the degree of obstruction quantified in terms of hydraulic permeability post static and perfusion culture. The results indicate that a catheter made of EPU would be able to maintain CSF flow even with the presence of cells for the time period chosen for this study. These findings have implications for the design and deployment of micro porous shunt catheter systems for the treatment of hydrocephalus

IMPROVING VENTRICULAR CATHETER DESIGN THROUGH COMPUTATIONAL FLUID DYNAMICS

Cerebrospinal fluid (CSF) shunts are fully implantable medical devices that are used to treat patients suffering from conditions characterized by elevated intracranial pressure, such as hydrocephalus. In cases of shunt failure or malfunction, patients are often required to endure one or more revision surgeries to replace all or part of the shunt. One of the primary causes of CSF shunt failure is obstruction of the ventricular catheter, a component of the shunt system implanted directly into the brain\u27s ventricular system. This work aims to improve the design of ventricular catheters in order to reduce the incidence of catheter obstruction and thereby reduce overall shunt failure rates. Modern CSF shunts are the result of six decades of neurosurgical progress; however, in spite of revolutionary advances in engineering, the ventricular catheter remains largely unchanged in its functionality and performance from its original design. A thorough review of the history of ventricular catheter design, and the contemporary efforts to improve it, have given valuable insight into the challenges still remaining. One of the challenges is to better understand shunt flow in order to improve the flow performance of ventricular catheters. To characterize CSF flow through catheters, this work integrated computational fluid dynamics (CFD) modelling with experimental validation. A fully-parametrized, 3-dimensional CFD catheter model was developed that allowed for exploration of the geometric design features key to the catheter’s fluid dynamics. The model was validated using bench tests and advanced fluid imaging techniques, including positron emission particle tracking (PEPT). Once validated, the model served as a basis for automated, iterative parametric studies to be conducted. This involved creating a coupled framework between the CFD simulations and a parametric analysis toolkit. Sensitivity analyses and optimization studies were performed with the objective of improving catheter flow patterns. By simulating thousands of possible geometric catheter designs, much insight was gathered that can provide practical guidelines for producing optimal flow through ventricular catheters. Ultimately, those insights can lead to better quality of life for patients who require shunts, by reducing ventricular catheter obstruction rates and the need for revision surgeries

Pathophysiology of normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH), a CSF circulation disorder, is important as a reversible cause of gait and cognitive disturbance in an aging population. The inconsistent response to CSF shunting is usually attributed to difficulties in differential diagnosis or co-morbidity. Improving outcome depends on an increased understanding of the pathophysiology of NPH. Specifically, this thesis examines the contribution of, and inter-relationship between, the brain parenchyma and CSF circulation in the pathophysiology of NPH. Of the four core studies of the thesis, the first quantifies the characteristics of the CSF circulation and parenchyma in NPH using CSF infusion studies to measure the resistance to CSF absorption and brain compliance. The second study assesses cerebral blood flow (CBF) was using O15-labelled positron emission tomography (PET) with MR co-registration. By performing CSF infusion studies in the PET scanner, CBF at baseline CSF pressure and at a higher equilibrium pressure is measured. Regional changes and autoregulatory capacity are assessed. The final study examines the microstructural integrity of the parenchyma using MR diffusion tensor imaging. These studies confirm the importance of the inter-relationship of the brain parenchyma and CSF circulation. NPH symptomatology and its relationship to the observed regional CBF reductions in the basal ganglia and thalamus are discussed. Regional CBF reductions with increased CSF pressure and the implications for autoregulatory capacity in NPH are considered. The reduction in CBF when CSF was increased was most striking in the periventricular regions. In addition, periventricular structures demonstrated increased diffusivity and decreased anisotropy. The relationship between these changes and mechanisms such as transependymal CSF passage are reviewed. The findings of this thesis support a role of both the CSF circulation and the brain parenchyma in the pathophysiology of NPH. The results have implications for the approach to the management of patients with NPH