Computational modelling for cerebral aneurysms: risk evaluation and interventional planning

Abstract

ABSTRACT. Advanced computational techniques offer a new array of capabilities in the healthcare provision for cerebral aneurysms. In this paper information is provided on specific simulation methodologies that address some of the unanswered questions about intracranial aneurysm and their treatment. These include the evaluation of rupture risk, the thrombogenic characteristics of specific lesions and the efficacy assessment of particular interventional techniques and devices (e.g. endovascular coil embolisation and flow diversion using stents). The issues connected with ease-of-use and interactivity of computed simulations is discussed, and it is concluded, that the potential of these techniques to optimise planning of complex and multifaceted interventions is very significant, in spite of the fact that most of the methodologies described are still being developed and perfected. As a result of increasing numbers of diagnostic brain scans, more intracranial aneurysms are being incidentally detected. Their diagnosis and the potentially dire consequences of rupture create a dilemma for patients and doctors, a dilemma centred on the risk of aneurysms growing or bleeding and amplified by the availability of minimally invasive endovascular treatments. Estimates of the incidence of aneurysmal subarachnoid haemorrhage range from 9 to 20 per 100 000 [1], considerably lower than aneurysm prevalence (3.6% at autopsy, 6.0% via angiography [2]). Thus, the majority of aneurysms do not rupture, a consistent finding in observation studies [3,4]. For the individual diagnosed with an unruptured aneurysm the uncertainty remains and, despite the statistical reassurance, substantial numbers request prophylactic (and potentially unnecessary) surgical clipping or coiling.Computational studies are now being applied to this problem in order to understand the mechanisms that cause aneurysm formation, growth and rupture. There have been many previous attempts to explain why the particular arteries forming the circle of Willis are liable to develop aneurysms and it is generally agreed that anatomical, genetic, haemodynamic and pathological factors are involved [5]. Understanding their relative contributions and applying this knowledge to the individual seeking advice after diagnosis can be considered a mechanical as well as a biological challenge. Patient-specific computational simulations offer a solution to evaluate the risk of rupture objectively and are equally pertinent to treatment planning and follow-up assessments.Aneurysm rupture occurs when stress exceeds the strength of the wall tissue. Accurate mechanical models, which can predict the stress distributions in an aneurysm, have the potential to assist diagnostic decisions [6]. However, the micro-structure, material properties, thickness and the strength of the aneurysm tissue are difficult to determine non-invasively. Consequently, there is uncertainty in the advantages of using a stress-based criterion for rupture; statistical trials are required to see if they are more effective...

Intracranial Venous Hemodynamics and Rupture of Cerebral Aneurysm

“…The management of unruptured cerebral aneurysms remains somewhat dissimilar and debatable giving rise to controversy on many occasions. Wide and varied factors are frequently placed in the evaluation for treatment of unruptured cerebral aneurysms, yet decisions may be very inconsistent and perhaps inconclusive 1,3,5,7,[10][11][12][13][14][15][16][17][18][19][20][21] . Asymmetry of the dural sinus may be considered a potential risk factor for aneurysm rupture as reported previously 8,11 .…”

“…The variable etiologies of cerebral aneurysm rupture have been extensively published including age, gender, genetics, smoking, size, site, configuration, flow profile and wall stress and other factors 1,[4][5][6][10][11][12] . However, the implication of those factors in clinical practice may be very inconsistent 8,[10][11][12][13][14][15][16][17][18] . In the past, we have observed interesting data of cerebral aneurysm rupture likely relating to asymmetry of the dural sinus especially in female populations 9,12 and recently encountered one patient with aneurysm rupture related to venous pressure gradient 20 .…”

Personalizing flow‐diverter intervention for cerebral aneurysms: from computational hemodynamics to biochemical modeling

“…Reynolds Number (6) and Womersley Number (7) are measures of the ratio of inertial forces to viscous forces and the ratio of vessel diameter to laminar boundary layer growth over a single pulsatile period (T) respectively. Both are defined below:…”

Computational Fluid Dynamics of a Fatal Ruptured Anterior Communicating Artery Aneurysm

“…It may be useful for indicating interventions and planning the types of interventions, such as flow diverter implantation or selective therapeutic inflow artery occlusion. 2 Using CFD to model the hemodynamics in ruptured aneurysms may provide better insight into the rupture risk described by the hemodynamic parameters in light of the real rupture situation. Several studies have assessed the hemodynamic parameters in ruptured aneurysms, such as wall shear stress (WSS), flow velocity, or flow characteristics.…”