Causes of small skull size - Microcephalus, chromosomal abnormalities, or fetal injury with inflammation or radiation of high impact such as x-rays or rubella during pregnancy

Small skull size
It is also called microcosmally, a term that refers to mentally disabled small heads. The small size of the skull means that the brain is small, and this condition always includes the levels of severe mental disability.
This small brain may have a family hereditary origin transmitted by an uncontrolled gene, may be related to chromosomal defects, may be caused by fetal infection, and may be caused by some high-impact radiation such as x-rays or rubella during pregnancy.