Positional brachycephaly is a cranial deformity consisting of a more or less symmetrical flattening of the entire back of the head .
It is usually seen in well-lived infants who sleep a lot and almost always face up.
A baby is considered to have brachycephaly when the width (distance from ear to ear) of its skull exceeds 81% of its length (front to back).
The head of these babies is shorter than normal, and to compensate, it can be wider when viewed from the front or taller when viewed from the side.
In some cases the cranial index is very high, between 90 and 100, which gives rise to a practically square head.