Defective development of the calvaria (dome, roof) of the fetal, or unborn child's skull, with areas in which no bone forms: Craniofenestria is a congenital bone diefect of the skull and where bones have not developed.

Incomplete formation of the bones of the vault (shaped like an arch) of the fetal cranium so that there are non-ossified areas in the calvaria (the domelike superior portion of the cranium, consisting of the superior portions of the frontal, parietal, and occipital bones).