Medical image analysis has to support the clinicians ability to identify, manipulate and quantify anatomical structures. On scalar 2-D image data, a human observer is often superior to computer assisted analysis, but the interpretation of vector-valued data or data combined from different modalities, especially in 3-D, can benefit from computer assistance. The problem of how to convey the complex information to the clinician is often tackled by providing colored multimodality renderings. We propose to go a step beyond by supplying a suitable modelling of anatomical and functional structures encoding important shape features and physical properties. The multiple attributes regarding geometry, topology and function are carried by the symbolic description and can be interactively queried and edited. Integrated 3-D rendering of object surfaces and symbolic representation acts as a visual interface to allow interactive communication between the observer and the complex data, providing new possiblities for quantification and therapy planning. The discussion is guided by the prototypical example of investigating the cerebral vasculature in MRA volume data. Geometric, topological and flow-related information can be assessed by interactive analysis on a computer workstation, providing otherwise hidden qualitative and quantitative information. Several case studies demonstrate the potential usage for structure identification, definition of landmarks, assessment of topology for catheterization, and local simulation of blood flow.