The natural history and pathogenesis of the cranial coronal ring articulations: implications in understanding the pathogenesis of the Crouzon craniostenotic defects.

The craniostenotic birth defects seen in patients with Crouzon syndrome have prompted this developmental study on the system of articulations between the human frontal, sphenoid, and ethmoid bones. The Crouzon facies, including midfacial hypoplasia and exorbitism, have been linked to the premature synostosis of calvarial sutures. However, considerable evidence shows that midfacial positioning is linked to increasing length of the midline cranial base. Thirty-seven typical-for-age (8 to 29 weeks) embryos were histologically prepared, read serially, and three-dimensionally reconstructed to map the so-called coronal ring articulations that continuously join the frontal, sphenoid, and ethmoid bones. A morphologic staging plan was used to show the progressive development of bones and intervening joints. Data show that a coronal ring exists beginning at 8 weeks. Those portions of the ring separating the frontal and sphenoid bones (within the orbit and laterally along the coronal suture) show the typical structure of a five-layered suture. This sutural component of the ring is C-shaped with a cartilaginous bridge between the optic foramina completing the ring. This is the sphenoethmoidal (S-E) synchondrosis of the midline cranial base. It is suggested that this deeply located cartilage joint is the primary site of pathogenesis in the craniostenotic facies and not the coronal sutures which are operated upon. Even though the S-E cartilage would be difficult and potentially morbid to approach surgically, this study would suggest that preoperative computed tomography (CT) of the skull base with special emphasis on the S-E region may provide a better prognosis regarding midface growth effects after surgery. It appears to be the fused S-E synchondrosis and not necessarily the premature closure of the coronal sutures that may tether the midface posteriorly.