Revision with unchanged content. Visual navigation of hierarchically structured graphs is a technique for interactively exploring large graphs with an additional hierarchical structure such as call graphs of telephone networks. In order to reduce the complexity of the graph, only the interesting subgraphs are shown in detail, while the others are collapsed. As the areas of interest change over time, clusters are expanded or contracted, for which an efficient data structure is needed. In this work a new variant of this problem is introduced, which supports insertion and deletion of graph nodes. So far efficient data structures were known only for more static variants. The proposed data structure builds on a novel technique of superimposing a search tree over an ordered list main-tenance structure. For visualizing the expanding and contracting a local update scheme for the well-known algorithm of Sugiyama and Misue is presented, which has applications ranging from UML diagrams to bio-chemical pathways. Experimental results show that this update scheme is more efficient than redrawing, yet the performance gain is not at the expense of quality as regards the area of the drawing and the number of crossings.