Coronal Craniosynostosis

Early closure of the coronal suture on one side (unilateral) is also known as frontal plagiocephaly (see Fig. 1). Plagiocephaly from Greek "plagios", slanting, refers to the "twisted" shape of the skull when viewed from the top. The fused coronal suture becomes an apparent, palpable ridge.

Coronal synostosis can occur either on the right or left side (unicoronal), or both (bicoronal.) It frequently occurs prenatally, and appears to occur more commeonly in males. Restriction of normal cranial growth at one suture between the frontal and parietal bones produces a characteristic flattening of the forehead on the fused side, and a bulging of the forehead on the non-fused side.
    This bulging, or bossing, is a result of compensatory growth of the contralateral (opposite side) coronal suture. Secondary bulging of the temporal region on the ipsilateral (same) side can also occur. The placement of the eyes within the orbit is also typically affected: the superior margin of the orbit on the synostosed side is raised, a feature known as Harlequin eye deformity.

Figure 2 is an example of unicoronal synostosis in a one year old male, compared with a normal, unaffected two year old dried skull specimen. Compare the left coronal sutures. Also notice that the metopic suture has fused in the normal specimen, one of the first sutures to fuse by 2 years of age.

Unicoronal synostosis is associated with marked change in the symmetry of the face. Fusion of the coronal suture indirectly creates lower facial deformities, in which the midline of the face is shifted or twisted. Structures that normally exist within the midline, e.g. the nasal septum, are deviated towards the affected side. The maxilla is fairly normal in size, but displays some degree of asymmetry, being shorter in (anterior to posterior) on the side with the synostosis. The mandible is normally developed, but can exhibit secondary asymmetry. (Cohen, 1986) This may result from the mandible adjusting its growth to an affected maxilla in order to assure functional occlusion of the mandible and maxilla. In individuals with unicoronal synostosis there is a tendency toward hypertelorism, and the ipsilateral ear is usually situated more anterior and inferior than usual.

A specific gene mutation has been found in some, but not all cases of coronal synostosis indicating that some forms of non-syndromic craniosynostosis may have a genetic basis (Bellus et al 1996, Moloney et al 1997). For more in-depth genetic info, check out the genetic-related links of the Related Links page.

Most clinicians agree that unilateral coronal synostosis requires cosmetic repair; the type of surgical technique varies depending on the amount of bossing and deformity in the orbital rim. Common procedure involves craniectomy, dural plication, reshaping of the frontal bone in a mosaic manner, and replacement or reconstruction of the upper margin of the orbit (Cohen, 1986) For more information check out the clinical section of the Related Links page.