  While narrative visualization has been used successfully in various
applications to communicate scientific data in the format of a story to a
general audience, the same has not been true for medical data. There are only a
few exceptions that present tabular medical data to non-experts. However, a key
component of medical visualization is the interactive analysis of 3D data, such
as 3D models of anatomical structures, which were rarely included in narrative
visualizations so far. In this design study, we investigate how neurological
disease data can be communicated through narrative visualization techniques to
a general audience in an understandable way. We designed a narrative
visualization explaining cerebral small vessel disease. Learning about its
avoidable risk factors serves to motivate the audience watching the resulting
visual data story. Using this example, we discuss the adaption of basic
narrative components. This includes the conflict and characters of a story, as
well as the story's structure and content to address and communicate specific
characteristics of medical data. Furthermore, we explore the extent to which
complex medical relationships need to be simplified to be understandable to a
general audience without distorting the underlying data and evidence. In
particular, the data needs to be preprocessed for non-experts and appropriate
forms of interaction must be found. We explore approaches to make the data more
personally relatable, such as including a fictional patient. We evaluated our
approach in a user study with 40 participants in a web-based implementation of
the designed story. We found that the combination of a carefully thought-out
storyline with a clear key message, appealing visualizations combined with
easy-to-use interactions, and credible references are crucial for creating a
narrative visualization about a neurological disease that engages an audience.
