The sutures between the bones of the skull sometimes close or fuse prematurely. When this occurs it results in a deformity in the shape of the skull, which may get worse as the skull grows during the first two years of life. This is termed synostosis (or craniosynostosis). Normally the two frontal bones are separated by the metopic suture, the two parietal bones by the sagittal suture. The coronal suture lies between the frontal and parietal bones, and the lambdoid suture between the occipital and parietal bones.
The particular deformity and resultant shape of the head is determined by which suture has prematurely fused. If the metopic suture fuses between the frontal bones, the forehead develops a triangular shape with a prominent ‘keel’. There is a recession of the region lateral to the eyes (temples) with a decreased distance between the eyes (hypotelorism). The resultant head shape is termed trigonocephaly.
If one of the coronal sutures between the frontal and parietal bones fuse then the resultant head shape is called plagiocephaly and consists of a flattening of the forehead on that side, a bulge posteriorly, a widening of the bony orbit, and malposition to the nose and chin. As mentioned above this needs to be carefully distinguished from deformational plagiocephaly.
If the sagittal suture between the two parietal bones becomes fused, growth is restricted from side to side and the growing brain pushes forward and backwards, producing an elongated head shape known as scaphocephaly.
If both coronal sutures are fused, the length of the skull from front to back is reduced and there is a compensatory widening to give a short, squarish head which is termed brachycephaly.
If one of the lambdoid sutures is fused, the changes are similar to plagiocephaly but more pronounced at the back of the skull.
More than one suture may be fused, although this usually occurs within the setting of one of the craniofacial syndromes described later. When multiple sutures are fused, the shape of the head often resembles a cloverleaf and this has been termed cloverleaf skull or Kleeblattschadel deformity. This is very serious because brain growth will be restricted.