Haemodynamic analysis of vessel remodelling in STA-MCA bypass for Moyamoya disease and its impact on bypass patency

The purpose of this study is to estimate the remodelling characteristics of STA-MCA bypass and its influence on patency via the use of computational fluid dynamic (CFD) technology. The reconstructed three-dimensional geometries from MRA were segmented to create computational domains for CFD simulations. Eleven patients, who underwent regular MRA both immediately following surgery and at the six months follow-up, were studied. The flow velocities at STA were measured via the use of quantitative MRA (QMRA) to validate simulation results. STA-MCA bypass patency was confirmed for each patient immediately following surgery. The simulation indicated that the remodelling of the arterial pedicle in nine patients was associated with a reduction in the resistance to flow through the bypass. For these cases, the modelling of a driving pressure of 10 mmHg through the bypass at 6 months post-surgery resulted in a 50% greater blood flow than those found immediately following surgery. However, two patients were found to exhibit contradictory patterns of remodelling, in which a highly curved bending at the bypass immediately post-surgery underwent progression, with increased resistance to flow through the bypass at 6 months follow-up, thereby resulting in a modelled flow rate reduction of 50% and 25%, respectively. This study revealed that STA-MCA bypass has a characteristic remodelling that usually reduces flow resistance. The initial morphology of the bypass may have had a significant effect on the outcome of vessel remodelling.