Craniosynostosis consists of premature fusion of 1 or more cranial sutures, often resulting in an abnormal head shape. It may result from a primary defect of ossification (primary craniosynostosis) or, more commonly, from a failure of brain growth (secondary craniosynostosis). Simple craniosynostosis is a term used when only 1 suture fuses prematurely. Complex or compound craniosynostosis is used to describe premature fusion of multiple sutures. When children with craniosynostosis, usually complex, also display other body deformities, this is termed syndromic craniosynostosis.
Also see the Medscape Reference Neurosurgery article Surgery for Craniosynostosis.
Normal skull development
Ossification of the cranial vault starts in the central region of each cranial bone and extends outward toward the cranial sutures.
See the list below:
The coronal suture separates the 2 frontal bones from the parietal bones.
The metopic suture separates the frontal bones.
The sagittal suture separates the 2 parietal bones.
The lambdoid suture separates the occipital bone from the 2 parietal bones.
The primary factor that keeps sutures open is ongoing brain growth.
Normal skull growth occurs perpendicular to each suture.
Primary craniosynostosis 
When 1 or more sutures fuse prematurely, skull growth can be restricted perpendicular to the suture. If multiple sutures fuse while the brain is still increasing in size, intracranial pressure can increase.
Scaphocephaly - Early fusion of the sagittal suture
Anterior plagiocephaly - Early fusion of 1 coronal suture
Brachycephaly - Early bilateral coronal suture fusion
Posterior plagiocephaly - Early closure of 1 lambdoid suture
Trigonocephaly - Early fusion of the metopic sutureFrontal view showing a fused and ridged metopic suture on 3-dimensional CT.
Secondary craniosynostosis 
More frequent than the primary type, secondary craniosynostosis can result from early fusion of sutures due to primary failure of brain growth. Since brain growth drives the bony plates apart at the sutures, a primary lack of brain growth allows premature fusion of all the sutures.
Intracranial pressure is usually normal, and surgery is seldom needed. Typically, failure of brain growth results in microcephaly. Premature suture closure does not compromise brain growth and does not require surgery to open sutures.
Intrauterine space constraints may play a role in the premature fusion of sutures in the fetal skull.  This has been demonstrated in coronal craniosynostosis. Other secondary causes of craniosynostosis include systemic disorders that affect bone metabolism such as rickets and hypercalcemia (see Causes).
Incidence of craniosynostosis is 0.04-0.1%. Of affected individuals, 2-8% have primary craniosynostosis. The remaining cases are secondary craniosynostosis, which frequently is accompanied by microcephaly. The frequencies of the various types of craniosynostosis are as follows: sagittal 50-58%, coronal 20-29%, metopic 4-10%, and lambdoid 2-4%. 
Raised intracranial pressure is rare with fusion of a single suture. It can occur in primary craniosynostosis when multiple sutures fuse.
Primary craniosynostosis: Although the major morbidity is due to the abnormal shape of the skull, intracranial pressure can be elevated. This occurs with a high frequency in multiple suture synostosis and rarely with single suture synostosis.
Craniosynostosis of 1-2 sutures: Cosmetic defect is the primary morbidity.
Craniosynostosis is equally distributed in both boys and girls.
See the list below:
Neonatal period: Craniosynostosis is evident at birth when associated with other craniofacial abnormalities.
Infancy (0-18 mo): Secondary or primary craniosynostosis becomes evident as the child grows.
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