Practice Essentials
An essential feature of mammals and particularly primates is the marked increase in brain volume that occurs following delivery. Head circumference increases from 35 cm at birth to 50 cm by age 3 yrs (average adult head circumference is just 5 cm more). This dramatic postnatal brain volume growth requires that the bones not be fused at birth to facilitate vaginal delivery and that fusion of cranial sutures occurs after age 2 yrs. Accordingly, premature fusion of cranial sutures may have an effect on cranial shape and less frequently on brain growth (primary craniosynostosis).
Abnormalities of head shape are a frequent concern of parents, particularly since the infant head is relatively larger than the adult head. Appropriate recognition and evaluation is important to manage craniosynostosis.
Background
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.
Pathophysiology
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:
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The coronal suture separates the 2 frontal bones from the parietal bones.
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The metopic suture separates the frontal bones.
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The sagittal suture separates the 2 parietal bones.
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The lambdoid suture separates the occipital bone from the 2 parietal bones.
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The primary factor that keeps sutures open is ongoing brain growth.
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Normal skull growth occurs perpendicular to each suture.
Primary craniosynostosis [1]
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.
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Scaphocephaly - Early fusion of the sagittal suture
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Anterior plagiocephaly - Early fusion of 1 coronal suture
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Brachycephaly - Early bilateral coronal suture fusion
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Posterior plagiocephaly - Early closure of 1 lambdoid suture
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Trigonocephaly - Early fusion of the metopic suture
Secondary craniosynostosis [1]
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.
CT image demonstrating features of secondary craniosynostosis with cerebral atrophy. Cerebral atrophy is not present in primary craniosynostosis.
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. [2] 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).
Epidemiology
Frequency
United States
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%. [3]
Mortality/Morbidity
Raised intracranial pressure is rare with fusion of a single suture. It can occur in primary craniosynostosis when multiple sutures fuse.
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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.
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Craniosynostosis of 1-2 sutures: Cosmetic defect is the primary morbidity.
Sex
Craniosynostosis is equally distributed in both boys and girls.
Age
See the list below:
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Neonatal period: Craniosynostosis is evident at birth when associated with other craniofacial abnormalities.
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Infancy (0-18 mo): Secondary or primary craniosynostosis becomes evident as the child grows.
Prognosis
Dependent on cause of craniosynostosis - if secondary then depends on cause of brain injury.
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Diagram of a neonate's skull demonstrating the location of the sutures.
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Frontal view showing a fused and ridged metopic suture on 3-dimensional CT.
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CT image demonstrating features of secondary craniosynostosis with cerebral atrophy. Cerebral atrophy is not present in primary craniosynostosis.
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Positional molding. Note the anterior displacement of the right occiput and of the right frontal region on the same side, which differentiate positional molding from posterior plagiocephaly craniosynostosis.
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Posterior view of 3-dimensional cranial CT demonstrating early fusion of the lambdoid suture.
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Isolated fusion of the metopic suture. Note that the remaining sutures are open.
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Trigonocephaly. Note the triangular shape of the head.
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Infant with primary craniosynostosis. The specific deformity of the skull is Kleeblattschadel or cloverleaf skull.
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Skull deformities associated with single suture synostosis.
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Positional plagiocephaly. Note anterior position of the ear on the side with occipital flattening.
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Sagittal synostosis and the associated scaphocephaly seen on skull radiograph and 3-dimensional craniofacial CT scan.
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Sagittal synostosis before and after cranial vault surgery and the associate improvement of scaphocephaly.
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Unilateral coronal deformity with retrusion of the orbit and harlequin eye deformity. Note the ipsilateral deviation of the nasal radix and the contralateral deviation of the nasal tip.
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Fusion of coronal sutures bilaterally. Note the increase transverse dimension and retrusion of the orbital rim.
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Intraoperative view of bilateral coronal synostosis. Note the decreased anterior-posterior dimension, increased transverse width and retruded orbital rim.
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Pre- and postoperative photos of metopic synostosis. Note the prominent forehead keel corrected after surgical repair.
