High-energy gamma rays of interstellar origin are produced by the interaction of cosmic-ray (CR) particles with the diffuse gas and radiation fields in the Galaxy. The main features of this emission are well understood and are reproduced by existing CR propagation models employing a 2D galactocentric cylindrically symmetric geometry. However, the high-quality data from instruments like the Fermi Large Area Telescope reveal significant deviations from the 2D model predictions on few to tens of degree scales, indicating that the details of the Galactic spiral structure should be included and thus require 3D spatial modelling. In this contribution the high-energy interstellar emissions from the Galaxy are calculated using the latest release of the GALPROP code for the first time employing full 3D spatial models for the CR source, interstellar gas, and interstellar radiation field (ISRF) densities. The interstellar emission models that include arms and bulges for the CR source and ISRF densities provide plausible physical interpretations for features found in the residual maps from high-energy gamma-ray data analysis. The 3D models provide a more realistic basis for interpreting the non-thermal interstellar emissions toward the inner Galaxy and about the Galactic centre.