Craniosynostosis (or craniostenosis) is the early fusion of skull sutures. Sutures allow growth of the skull bone at right angles to their axis. Skull X-rays show narrow, straight, or obliterated sutures and thickened bone, with increased convolutional markings close to the suture. The metopic suture closes antenatally and the rest have fibrous union by 6 months and bony union by 8 years.
Diagrammatic illustration of the various skull sutures, premature fusion of any of which may lead to craniosynostosis.
Craniostenosis. Lateral skull x-ray showing copper-beating reflecting the identation of growing gyri within the skull. A ventriculoperitoneal shunt is in situ. (Courtesy of Dr P. Anslow.)
Early union of the metopic suture causes a narrow, pointed frontal region with a ridge in the line of the suture and is of little clinical significance. Early closure of the sagittal suture is the most common type of craniosynostosis (Hunter and Rudd 1976).
It is more common in boys. It causes a long, narrow head which is recognizable at birth. Although not associated with symptomatic raised intracranial pressure, it is usually treated surgically for cosmetic reasons. Early closure of the coronal suture is more common in girls (Hunter and Rudd 1977).
Unilateral closure causes an asymmetric skull deformity, which should be treated surgically for cosmetic reasons but is not usually associated with raised intracranial pressure. Bilateral synostosis may cause raised intracranial pressure and primary or secondary optic atrophy. Although cognitive impairment may occur, this is not purely related to raised pressure. The skull is short and wide. There may be mainly a skull-vault abnormality or this may be combined with basal suture synostosis in the coronal plane, in which case a characteristic facial deformity occurs, with widely spaced eyes, shallow orbits with proptosis, and hypoplasia of the maxillae. This is the appearance seen in Crouzon syndrome, one of the many syndromes that include craniosynostosis. Early surgical treatment of the skull vault is used, but for the facial deformities much more extensive reconstruction procedures are now used.
CT reconstruction of a skull may be showing right unicoronal synostosis with a ridge (arrowheads) indicating premature fusion of the right coronal suture, and the early development of a Harlequin eye.
Unilateral lambdoid synostosis is very uncommon and produces a characteristic deformity if not surgically treated. It is important that the very uncommon unilateral coronal and lambdoid synotosis are separated from the common problem of postural plagiocephaly. In this situation the baby has a right or left head turn preference, probably from intrauterine life, and this is associated with flattening of the skull, eg. left posterior and right anterior flattening for a left preferred head turner, so that the head has developed a predictable postural deformity (Jones et al. 1997).
In unilateral coronal or lambdoid synostosis, the skull flattening would be on the same side anteriorly and posteriorly. Postural plagiocephaly is more common in relatively inactive babies, in whom a similar deformity of the chest may also occur. Postural plagiocephaly does not require surgical treatment. Total craniosynostosis is rare and causes a small head with very marked convolutional markings on skull X-ray, which distinguish it from primary microcephaly secondary to lack of brain growth in which convolutional markings are diminished or absent. Total craniostenosis requires early surgery. Surgical details of all such procedures are available in specialist texts (Sun and Persing 1999).
There is a strong genetic background to craniosynotosis and several discrete syndromes in which multiple additional impairments occur. It is important to recognize that such neurological impairments are not usually caused by raised intracranial pressure but appear to be primary. The gene locations of several of these are known (Aicardi 1998).