WP Chung O T in Craniofacial Surgery 9781496348265

1 C H A P T E R

Section I: Craniosynostosis

Fronto-Orbital Advancement

Rajendra Sawh-Martinez and John A. Persing

DEFINITION

■■ Retrusion of the supraorbital rims bilaterally and flaring of the parietal bones as a form of compensation for con- tinuing brain growth bilaterally ■■ The orbits are symmetrical in appearance. ■■ The squamous temporal bones are not convex, but flat- tened in profile and retrusive. ■■ Hypotelorism PATHOGENESIS ■■ Craniosynostosis occurs as nonsyndromic forms and as part of a varied number of syndromic patterns. ■■ Metopic and coronal synostoses are believed to have a positive family history in approximately 10% of cases. ■■ Ephrin-A4 has been implicated in nonsyndromic cranio- synostosis, whereas FGFR3 and TWIST gene mutations may be linked to familial inheritance of craniosynostosis. 5 ■■ Syndromic craniosynostosis cases are linked to var- ied genetic mutations corresponding to the underlying syndrome. ■■ Multiple environmental factors have been suggested as pro- moters or risk factors for synostosis, including abnormal intrauterine position, multiple gestation, antenatal head compression, and infants large for their gestational age. ■■ Additionally, maternal smoking, advanced maternal age, gestation at high altitude, fertility treatments, and endocrine abnormalities have also been associated with the develop- ment of craniosynostosis. ■■ The natural history of all forms of craniosynostosis is that they are, at the very least, stable, if not progressive during early childhood due to the expanding brain. Compensatory abnormalities increase the discrepancy between the fused bones and the remainder of the skull. ■■ The main theories of pathogenesis of premature fusion relate to timing of the fusion as either a primary event or a second- ary occurrence as the effect of a yet undetermined cause. ■■ Despite ongoing research on the underlying mechanisms, general principles dominate the resultant morphology. 1,6,7 ■■ Prematurely fused bones act as a single bone plate with lim- ited growth potential. ■■ Asymmetrical, increased bone deposition occurs at perim- eter sutures directed away from the affected bone plate. ■■ Unaffected, adjacent perimeter sutures compensate more in growth than do distant unaffected sutures. PATIENT HISTORY AND PHYSICAL FINDINGS Metopic craniosynostosis 4,6,8

■■ Fronto-orbital advancement is a series of adjustments to modifications of anatomy in coronal and metopic synostosis. ■■ Fronto-orbital advancement strives to approximate normal- ity of deficient supraorbital rim and adjacent frontal and temporal bone deformities. ■■ Unilateral coronal synostosis (UCS), bilateral coronal syn- ostosis, and metopic synostosis have unique fronto-orbital deformities, which require individualized treatment for optimal results. Periorbital deformities are characterized by flattening of the frontal bone ipsilateral to the fused half of the coronal suture. 1,2 ■■ Recession of the ipsilateral supraorbital rim ■■ Overprojection anteriorly of the ipsilateral zygoma ■■ Convex deformity of the squamous temporal bone ■■ Diminished mediolateral dimension of the orbit com- pared to normal ■■ Increased vertical height of the ipsilateral orbit ■■ Enlarged and more superiorly positioned ipsilateral orbital roof and accompanying greater wing of the sphe- noid (harlequin deformity) ■■ Depression of contralateral orbital roof/supraorbital rim ■■ Ipsilateral nasal radix deviation ■■ Contralateral chin point deviation ■■ Bilateral coronal synostosis ■■ Characterized by premature fusion of the coronal sutures bilaterally and brachycephaly (shortening) of the antero- posterior dimension of the skull, to include the anterior cranial fossa with compensatory widening of the skull 3 ■■ The frontal bones bilaterally, and the supraorbital rim adjacent to them, are hypoplastic and retrusive, relative to normal frontal bone development. ■■ Squamous temporal bone is more convex in form than normal. ■■ The zygomas are deficient in the anteroposterior projection. ■■ The malar area, as well as the midface, may be more sig- nificantly retruded in patients with syndromic forms of bilateral coronal synostosis. ■■ Metopic synostosis ■■ Fusion of the metopic suture, associated with ridging of the midline frontal bone structure, and symmetric retru- sion of the lateral frontal bones bilaterally 4 ■■ Unilateral coronal synostosis ■■

ANATOMY

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■■ Premature fusion of the metopic suture.

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