Morphological and topological quantification of complex pore networks is of great relevance for environmental engineering, earth science and industry. Recent developments of 3D imaging techniques such as X-ray microtomography or X-ray microscopy provide an opportunity to perform a comprehensive analysis of the pore network topology. Such an analysis is crucial to understand how transport or mechanical properties evolve during the growth and/or the aging of a pore network, especially near a percolation threshold. In the first part of this work, we present some properties related to the graph of retraction of a 3D pore network, a powerful way to characterize the topological evolution. In the second part, we analyze the topology of an evolving 3D pore network in the vicinity of a percolation transition. Two distinct scenarii of evolution are presented. The last part is dedicated to an experimental example of evolving pore network: the setting of an ordinary cement paste probed in its early age by synchrotron X-ray microcomputerized tomography.