Fronto-Orbital Advancement



Fronto-Orbital Advancement


Rajendra Sawh-Martinez

John A. Persing





DEFINITION



  • Fronto-orbital advancement is a series of adjustments to modifications of anatomy in coronal and metopic synostosis.


  • Fronto-orbital advancement strives to approximate normality of deficient supraorbital rim and adjacent frontal and temporal bone deformities.


  • Unilateral coronal synostosis (UCS), bilateral coronal synostosis, and metopic synostosis have unique fronto-orbital deformities, which require individualized treatment for optimal results.


ANATOMY



  • Unilateral coronal synostosis



    • 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 compared to normal


    • Increased vertical height of the ipsilateral orbit


    • Enlarged and more superiorly positioned ipsilateral orbital roof and accompanying greater wing of the sphenoid (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 anteroposterior dimension of the skull, to include the anterior cranial fossa with compensatory widening of the skull3


    • 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 significantly 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 retrusion of the lateral frontal bones bilaterally4


    • Retrusion of the supraorbital rims bilaterally and flaring of the parietal bones as a form of compensation for continuing brain growth bilaterally


    • The orbits are symmetrical in appearance.


    • The squamous temporal bones are not convex, but flattened 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 craniosynostosis, whereas FGFR3 and TWIST gene mutations may be linked to familial inheritance of craniosynostosis.5


    • Syndromic craniosynostosis cases are linked to varied genetic mutations corresponding to the underlying syndrome.


  • Multiple environmental factors have been suggested as promoters 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 development 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 secondary 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 limited growth potential.


  • Asymmetrical, increased bone deposition occurs at perimeter 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 craniosynostosis4,6,8



  • Premature fusion of the metopic suture.



  • Key relevant anatomic features include the following:



    • Central ridging/bulged metopic suture


    • Characteristic triangular-shaped forehead (bilateral fronto-orbital hypoplasia) occurs to varying degrees, with classification schemes related to the severity of angulation


    • Hypotelorism


    • Lateral orbital rim posteriorly displaced and hypoplastic


    • Flattened profile of the squamosal bone


    • Biparietal widening of the skull


Unilateral coronal craniosynostosis6,9,10



  • Premature bony bridging of the coronal suture, typically in the approximate midpoint of the course of the coronal suture


  • Patent sagittal suture is displaced away from the fused suture posteriorly and toward it anteriorly.


  • Key features:



    • Flattened ipsilateral forehead


    • Contralateral forehead bossing


    • Intrinsic orbital changes (pathognomonic harlequin deformity)



      • Ipsilateral flattened supraorbital rim and vertically taller/narrower orbit with steep superior orbital fissure and greater/lesser sphenoid wings


      • Depression (inferior displacement) of contralateral supraorbital rim


    • Squamosal-temporal bone convexity


    • Depression of the free border of the superolateral orbital rim


    • Protrusive zygoma, ipsilateral to the coronal fusion


    • Raised eyebrow and widened palpebral opening ipsilateral to the fused suture


    • Root of nose deviation toward the affected (fused) side and nasal tip towards the contralateral (open) side


    • Ear displacement anteriorly/superiorly, ipsilateral to fused suture


    • Contralateral chin point deviation


    • Base of skull deformity



      • Severity can be determined by evaluating the sphenopetrosal angle and the degree of angulation from midline structures (cribriform plate) ipsilateral to fusion2,6,9


Bilateral coronal craniosynostosis2



  • Bilateral premature fusion of the coronal suture with symmetric foreshortened anterior cranial base


  • Key features:



    • Bilateral retrusion of frontal bone and supraorbital rims


    • Bilateral lateral bulge of squamous temporal bones


    • Increased biparietal diameter


    • Syndromic vs nonsyndromic features include midface hypoplasia and mandibular deformity in syndromic cases


  • Frontosphenoidal synostosis11,12,13


  • Rare case of anterior plagiocephaly


  • Often misdiagnosed


  • Requires 3D CT reconstruction to identify in isolated cases


  • Angulation of the anterior cranial base


  • Deflection of the anterior cranial fossa opposite to fused suture


  • Altered relationship between cranial vault and facial skeleton, resulting in a phenotype similar to UCS


  • Contralateral bossing and ipsilateral brow depression


  • Nasal tip deviation reported in 50% of cases


  • Harlequin deformity may not be present or be minimally evident.


  • Key orbital/ophthalmologic evaluation


  • Orbital size/shape


  • Globe position/prominence


  • Corneal inflammation (exposure)


  • Distinct structural differences between ipsilateral and contralateral orbits


  • Extraocular movement (strabismus), particularly superior oblique dysfunction


  • Visual acuity


  • Lid margin and levator function (anterior plagiocephaly)


  • Supratarsal crease reduction (anterior plagiocephaly)


  • Hypertelorism (brachycephaly) in some syndromic cases


  • Malar recession in syndromic cases


IMAGING



  • The definitive diagnostic study for craniosynostosis is a CT scan demonstrating fusion of a cranial vault suture.


  • However, imaging of cranial anatomy has been used less frequently, as the typical clinical structure in the individual forms of craniosynostosis is more recognized.



    • This has been highlighted by concerns related to exposure of infants to ionizing radiation by CT scan and for sedation and anesthetics often required to obtain MR scans.


    • Ultrasound examinations, except in the very young, are not accurate enough to serve as a definitive diagnostic source and therefore used infrequently.


  • Occasional cases of craniosynostosis are best examined using CT scan, with 3D reconstruction, which may help in certain forms of craniosynostosis for planning of surgery (FIG 1).


SURGICAL MANAGEMENT

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Nov 24, 2019 | Posted by in Craniofacial surgery | Comments Off on Fronto-Orbital Advancement

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