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Thrombus Development in Cerebral Aneurysms

Principal Investigator: Malebogo Ngoepe

An aneurysm is a balloon-like dilation of a blood vessel and is caused by the weakening of the vessel wall layers. These are most commonly found on cerebral blood vessels as well as on the aorta. Aneurysms affect 2-6% of the population. While the aneurysm sac is at risk of rupture with subsequent death or disability, most aneurysms remain asymptomatic throughout the life of an individual. Advances in medical imaging technology have led to an increase in the number of aneurysms identified during routine medical scans or scans for other diseases. The current metric used for determining rupture risk makes it difficult to differentiate between aneurysms which are really at risk of rupture and those which are likely to remain asymptomatic.

In most cases, the intervention chosen for cerebral aneurysms results in the formation of a clot in the aneurysm sac. The presence of a clot prevents complex haemodynamics in the sac and redirects flow along the original parent vessel. Clotting is, however, a patient-specific process and in some cases, individuals are prone to too much clotting. In such cases, the clot in the aneurysm sac could break off and travel downstream, causing blockage and subsequent stroke. Clotting has also been observed in aneurysms prior to intervention.

Computational Model of Thrombus Development in Cerebral Aneurysms

MN Ngoepe, Y Ventikos

A computational tool which is able to predict clotting outcome, with and without intervention, prior to treatment is desirable. A combination of computational fluid dynamics, computational biochemistry and level set methods is used to predict clot growth in three-dimensional, image-derived, patient-specific geometries. Based on the haemodynamics and biochemical composition of a specific patient, such a tool would assist in the decision-making process by making clotting outcome an additional metric. The tool could also be used to elucidate some of the features of in vivo clotting in cerebral aneurysms. The clotting process in cerebral aneurysms is a difficult one to anticipate and observe, hence an in silico tool would be of use in framing some of the pertinent questions which need to be answered to further elucidate key features of the process. The primary focus of the study is on clot initiation and propagation.

The diagram on the left represents clot growth without a device while that on the right represents clot growth with a flow diverter in a place. The presence of the device is indicated on certain parts of the vasculature where the wires are clearly visible as a criss-cross pattern. The red surface represents the surface of the growing clot as it propagates away from the surface of the aneurysm sac.