Answer:
Premature fusion of one of the coronal sutures results in plagiocephaly (a Greek term meaning oblique skull). This is an uncommon disorder, occurring in 1 of 10,000 live births. In unilateral coronal synostosis, fusion at the coronal suture results in a single frontoparietal bone plate ipsilateral to the fused suture, with an apparent reduced growth potential. This impairment prevents the ventral expansion of the anterior cranial fossa, resulting in a shortened anterior cranial fossa ipsilateral to the fused suture. Growth superiorly results in elongation of the forehead, while inferiorly directed growth produces deformity of the middle cranial fossa with ventral bowing of the greater wing of the sphenoid. The deformity of the sphenoid results in effacement of the temporal fossa, which, combined with shortening of the lateral wall of the orbit, produces proptosis of the globe. The “harlequin” orbit seen on AP radiographs is pathognomonic for unilateral coronal synostosis and is secondary to the lack of descent of the greater wing of the sphenoid during development. Compensatory overgrowth of bone occurs asymmetrically at all perimeter sutures that border the now fused single frontoparietal bone plate that incorporates the coronal suture. This accounts for the bulge in the ipsilateral squamous portion of the temporal bone, contralateral frontal and parietal bones, and, to a much lesser degree, contralaterally in the occipital bone. The fused coronal suture may demonstrate prominent ridging, and the ipsilateral frontal and parietal bones are flattened.
Clinical facial features include widening of the ipsilateral palpebral fissure, superior and posterior displacement of the ipsilateral orbital rim and eyebrow, elevation and anterior displacement of the ipsilateral ear, and deviation of the nasal root toward the flattened side of the frontal bone. The chin point deviates to the contralateral side, and the malar eminence is frequently anterior on the same side as the flattened side forehead (and fused coronal suture) when compared to the contralateral malar eminence.
Operative Procedure:
The greater wing of the sphenoid, which is thickened and displaced superiorly, is rongeured to the level of the lateral supraorbital fissure. A supraorbital rim osteotomy is performed bilaterally and the orbital rims are contoured to symmetry, then advanced. Where the prominence of the brain and dura is increased, dural plication can be performed gently with the bipolar cautery or with suture. In unilateral coronal synostosis, the dura is plicated in the frontal bone region contralateral to the fused coronal suture to achieve frontal region projection symmetry. A temporalis myo-osseous flap is developed and used to support the advanced supraorbital rim. The frontal bone is remodeled using radially oriented osteotomies, and selective fractures are performed to achieve the desired form. The frontal bone plate is attached to the orbital rims superiorly and laterally but not posteriorly so as to allow further growth of skull at the “neo” coronal suture.