Heterogeneous media constitute random disordered environments where transport is drastically hindered. Employing extensive molecular dynamics simulations, we investigate the spatio-temporal dynamics of tracer particles in the Lorentz model in the vicinity of the localization transition. There transport becomes anomalous and non-gaussian due to the presence of self-similar spatial structures, and dynamic scaling behavior is anticipated. The interplay of different time and length scales is revealed by the intermediate scattering functions, which are sensitive both to the underlying spatial fractal as well as the anomalous transport. We compare our numerical results in the transition regime to a mode-coupling approach, and find that certain aspects are surprisingly well predicted.