Craniosynostosis is the premature partial or complete ossification of one or more of the sutures separating the membranous bones of the skull. The incidence of craniosynostosis has been estimated to be 1 in 2,500 live births.

Primary, or simple, craniosynostosis is ‘single- or multiple/compound’ suture synostosis in children who are otherwise neurologically normal, and almost always present prenatally except in some with cranio facial syndromes of Crouzan's, Apert's and Carpenter's type in whom progressive postnatal closure may occur. Synostosis that occurs as part of a syndrome of complex congenital malformations is frequently called complex, or syndromic, craniosynostosis.

Secondary stenosis may occur in children with metabolic disorders, and hematological disorders. Rickets, Hyperthyroidism, Thalassaemia, or Mucopolysaccharidosis may be associated. It can also occur as the consequence of lack of growth at the suture lines because of microcephaly, encephalocele, or shunted hydrocephalus.

PATHOGENESIS:

The cranial vault develops intramembranous bone formation between the periosteum and the dura. This process begins during the 6th week of embryonic development. The posterior fontanel closes at 3 mths of age and the anterior one, at 8mths of age. The bones ossify by the end of first year. The skull growth ceases by 10-12 yrs of age. The ossification of the cranial sutures occurs by the 4th-5th decade. The base develops from a series of primordial cartilages that undergo ossification. The growth of the base proceeds at a slower rate.

The skull contains two types of sutures- syndesmoses and synchondroses.

Syndesmoses occur in the vault and consist of fibrous tissue interposed between bone surfaces. Synchondroses occur in the skull base from a bar of cartilage. The role of sutures is unclear.

The normal infant's skull is oval shaped and widest posteriorly. The growth occurs in the direction perpendicular to the suture lines, the direction of least resistance.

In craniosynostosis the deformity is related to the suture involved and the effects of increasing growth of the brain upon the unfused skull plates. The craniosynostoses comprise a heterogeneous group of disorders of multifactorial origin.

Most cases of simple craniosynostosis,  are sporadic. The cause is unknown. Many theories exist.

Genetic determinants play a part in some coronal and pansynostosis, particularly where there is an associated craniofacial abnormality. Some cases are inherited. Affected families may have members with involvement of different sutures, and, in the case of familial coronal synostosis, family members may have unilateral or bilateral involvement. Mendelian disorders may cause simple or complex craniosynostosis, but craniosynostosis associated with chromosomal aberrations is usually part of a syndrome.² Approximately 27 different chromosomal aberrations have been reported for craniosynostosis, and more continue to be described each year. Dominant inheritance is more common than recessive inheritance. Most cases of simple craniosynostosis, however, are sporadic.

Abnormal tensile forces along the dural tracts running from the cranial base to the vault induce premature suture fusion. These dural tracts consist of tentorium cerebelli, the falx and dural bands from the lesser wing to the vault.

Some blame the fetal head constraint in utero. The periosteum overlying the suture may be involved.

Scaphocephaly: (Boat Skull)

ASSOCIATED DISORDERS:

The sagittal synostosis is rarely associated with other abnormalities.

About 30% of the unilateral coronal synostosis and 60% of those with bicoronal synostosis have other congenital abnormalities, such as syndactyly and cardiac anomalies.

The patients with craniofacial syndromes of the Crouzon’s, Apert’s or Carpenter’s variety almost invariably have associated craniosynostosis.

Apert's syndrome: There is brachycephaly with midface hypoplasia. There is a unique hand malformation. Both hands are affected equally, as are the feet. This unusual variation of syndactyly can be used to identify Apert's from other similar syndromes. Usually, cases are sporadic, but the syndrome may be inherited in an autosomal dominant fashion.

Apert's  Apert's feet syndactyly   Apert's hands syndactyly

Crouzon’s syndrome: It is commoner. There is brachycephaly with midface hypoplasia and shallow orbits with proptosis. The skull base is implicated, and sphenofrontal synostosis is a factor involved in producing exophthalmos. Maxillary hypoplasia, the characteristic facial deformity, is a more important cause of exophthalmos. In 5 per cent of cases, the calvaria is normal. Hydrocephalus is more common in Crouzon's syndrome than in simple craniosynostoses.

Unlike in Apert’s there is no syndactyly.

This condition is inherited in an autosomal dominant fashion, but there is an equal incidence of sporadic cases, which probably represent new mutations. Penetrance is high, although severity is variable. Within the same family, members tend to have similar facial deformities but variable calvarial deformities. This phenotypic heterogeneity makes genetic counseling difficult.

Variations of this type of craniofacial dysostosis are seen.

In Carpenter's syndrome, the calvarial deformity is variable and is less striking than the facial and digital anomalies. Mental retardation, cardiac anomalies, and hypogonadism are also common.

Saethre-Chotzen syndrome is a relatively benign condition. The features of this condition include brachycephaly or plagiocephaly, facial asymmetry with hypertelorism and orbital dystopia, low frontal hairline, ptosis, and mild maxillary hypoplasia. Syndactyly is usually mild, and mental retardation is much less common.

Pfeiffer's syndrome is characterized by tall, broad skull, hypertelorism, slanted palpebral fissures, and broad thumbs and toes; mentation is usually normal.

CLINICAL FEATURES:

1) The skull deformity is obvious, so also are the associated facial deformities.

2) Mental retardation can occur due to associated brain malformations, or increased ICT. It is unknown in single suture synostosis.

3) Hydrocephalus is infrequent. The mechanism is not known.

4) Increased ICT is rare in single synostosis. It is more frequent in the first 2 yrs.The pressure tends to normalize at six years of age. The pressure may take months to come down after decompressive surgery.

DIAGNOSIS:

The plain x-rays and CT scan in axial and coronal planes, with bone windows, will give adequate information and also reveal brain malformations and the presence of increased ICT, if any.

X- ray(AP)-brachycephaly	X- ray(lat)-brachycephaly	X-Ray(AP)  scapocephaly	X-Ray(lat)  scapocephaly	X-ray-Harlequin orbit-Plagiocephaly

3D CT adds to the clarity. MRI shows any associated cerebral malformations better. Positional deformity, due to birth molding, may be diagnosed by the presence of patent sutures and absence of any orbital deformity. In microcephaly, the brain fails to grow and the head remains small. The fontanels close early. The x-rays reveal a thick vault, and the frontal vault is disproportionally small. X-rays do not show any silver beaten appearance or sellar changes.

Apert's -3D CT   3D CT- craniolacunae

MANAGEMENT:

The management is by a multidisciplinary team comprising of the neurosurgeon, the plastic surgeon, the pediatrician, the ophthalmologist, dental surgeon, anesthetist and the social worker.

 The aim of surgery is

                     1) to allow normal brain growth.

                     2) to correct increased ICT.

                     3) to achieve cosmetically acceptable head.

                     4) to protect the eyes.

The ideal time for surgery in the absence of increased ICT, is 3 - 6mths of age to give the growing brain the ideal surroundings and also to facilitate normal shape to the skull. Surgery for cosmetic reasons, especially in coronal synostosis, can be performed at a later age.

A generous craniectomy with extension to adjacent sutures is the basic procedure. Frontal and orbital advancement techniques are needed in coronal synostosis. Dural-pericranial stitches or use of tantalium foils at the site of craniectomy is advised to prevent reossification.

The associated facial deformities can wait until about 5 yrs of age to allow the roots of the teeth to descend and permit safe correction of the maxilla.

Frontal bones exposed	Excised supraorbital ridge	supra orbital ridge advanced	frontal bones repositioned

In metopic synostosis, the surgery is for cosmetic reasons and involves remodeling of the frontal bone and supralateral orbital advancement. The triangular forehead is removed and recontoured to the appropriate shape or bone may be taken from another area of the skull to replace this bone. The entire bony supraorbital bar is removed and reshaped with supralateral orbital advancement to restore the normal brow contour. Wires or micro-plates are used to secure the frontal bar to the facial bones and maintain the normal contour.

In bicoronal synostosis, both frontal bones are reconstructed. The supraorbital bar is completely removed, reshaped, and straightened. The supraorbital bar is advanced and lowered as necessary on the affected side and rigidly fixed in position to the face. The reconstructed forehead is then secured to the supraorbital bar. In unicoronal synostosis, the surgery is for cosmetic reasons and restricted to the involved side.