The skull of an infant or young child is made up of bony plates that allow for growth. The borders at which these plates come together are called sutures or suture lines.
In an infant only a few minutes old, the pressure from delivery may compress the head, making the bony plates overlap at the sutures and creating a small ridge. This is normal in newborns. In the next few days the head expands, the overlapping disappears, and the edges of the bony plates meet edge to edge. This is the normal position.
Diseases or conditions that cause an abnormal increase in the pressure within the head can cause the sutures to spread apart. These separated sutures can be a sign of pressure within the skull (increased intracranial pressure).
Separated sutures may be associated with bulging fontanelles. If intracranial pressure is increased a lot, there may be large veins over the scalp.