Haemodynamic simulations of the brain arterial system are becoming a popular tool for better understanding vascular pathologies, such as Intracranial Aneurysms (IA). However, due to a lack of measurements, some of the physical aspects of these simulations have to be described through heuristics, as often is the case for distal ends of the simulation domain. In particular, the outflow split is frequently modelled through Murray's Law, relating outgoing volumes with the respective vessel cross-section area. This approach, while being regarded as one of the most suited in the absence of measurement data, remains challenging for the communicating arteries found in the Circle of Willis (CoW). To assess the influence of Murray's Law on communicating vessels, patient-specific geometries featuring IA at the ICA-PCom bifurcation are studied. For each geometry different domain extensions of varying complexity are simulated, covering widely applied modelling choices in the scientific community. In the present work, Full CoW simulations are used as a baseline to assess the relevance of these modelling assumptions on haemodynamic indicators. The focus is hereby directed onto IA growth and rupture-associated quantities, such as the Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI).
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