The combination of scanning impedance microscopy and conductive atomic force microscopy was applied to single crystals of the perovskite-type oxide CaCu3Ti4O12 (CCTO) in order to provide a local dielectric characterization on ingot sections. Both techniques clearly showed dielectric heterogeneities due to the presence of inclusions within crystals grown in different laboratories. Despite macroscopic characterizations, such as Laue diffraction, gave no indications for the presence of inclusions within the crystals, the discovery of dielectric heterogeneities prompted a careful structural analysis, which revealed the presence of crystalline CaTiO3 (CTO) precipitates. Thus, the scanning probe investigation provided the evidence for the electrical homogeneity within the CCTO crystal and the presence of internal barriers due to the CCTO/CTO interfaces.