Three-dimensional understanding of the morphological complexity of the human uterine endometrium

The histological basis of the human uterine endometrium has been established by 2D observation. However, the fundamental morphology of endometrial glands is not sufficiently understood because these glands have complicated winding and branching patterns. To construct a big picture of endometrial gland structure, we performed tissue-clearing-based 3D imaging of human uterine endometrial tissue. Our 3D immunohistochemistry and 3D layer analyses revealed that endometrial glands formed a plexus network in the stratum basalis, similar to the rhizome of grass. We then extended our method to assess the 3D morphology of adenomyosis, a representative 9endometrium-related disease9, and observed 3D morphological features including direct invasion of endometrial glands into the myometrium and an ant colony-like network of ectopic endometrial glands within the myometrium. Thus, 3D analysis of the human endometrium and endometrium-related diseases will be a promising approach to better understand the pathologic physiology of the human endometrium.