Introduction Today’s trend toward patient-specific computational models brings along more complex geometries and larger computational domains. The quality of the corresponding meshes can then become a bottle neck in the image-based analysis, both in computation time as in accuracy of the solution. Therefore, the Treemesh method has been developed to generate high-quality multi-block structured hexahedral meshes [De Santis, 2011]. However, for highly complicated geometries it can still be hard to generate a high-quality Treemesh for the fluid domain. In this work, the extended Treemesh method (XTreemesh) is presented to autogenerate high-quality unstructured hexahedral meshes for both the fluid domain and the structural domain of complex image-based vascular trees.