In this paper, we propose two solutions to integrate shape prior in a segmentation process based on region growing. Our special region growing algorithm relies upon a variational framework which allows to easily take into account shape prior in the segmentation process. Region growing is described as an optimization process that aims to minimize some special energy combining intensity function and shape information. Two kinds of energy are proposed depending on the existence of a reference model or the possibility to assess some shape features at voxel level. We applied positively these two approaches in the context of life imaging in order to segment mice kidneys from small animal CT-images and lacuno-canicular network from experimental high resolution Synchrotron Radiation X-Ray Computed Tomography (SRμCT) images.