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Differential Closure of the Spheno-Occipital Synchondrosis: Insight Into Midface Hypoplasia?
Jennifer McGrath, BS1, Christopher Derderian, MD1, Scott P. Bartlett, MD1, Hyun-Duck Nah, DMD PhD1, Jesse A. Taylor, MD2.
1Children's Hospital of Philadelphia, Philadelphia, PA, USA, 2Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, PA, USA.
BACKGROUND: The spheno-occipital synchondrosis (SOS) is a key driver of cranial base, and consequently facial, growth. It is known to remain open until approximately age 12 to 14 in females and males respectively, and its premature fusion has been shown in animal models to be associated with cranial base and midface hypoplasia. The degree of midface hypoplasia seen clinically is variable among craniosynostosis syndromes. The purpose of this study was to review CT scans of Apert syndrome and Muenke syndrome patients to determine whether they had premature fusion of the SOS when compared to subjects without craniosynostosis syndromes.
METHODS: Thirty-eight fine-cut head CT-scans of Apert syndrome patients and 20 of Muenke syndrome patients were assessed by two reviewers. An equal number of CT scans for age- and sex-matched controls were reviewed for both the Apert and Muenke syndrome groups. Axial images were analyzed for SOS fusion and were graded as either not fused, partially fused, or completely fused. Special attention was focused on the subset of patients age 7 years to 14 years as no normal patient fused prior to age 7 or had failed to fuse after age 14. The Fisher exact test was used to compare groups.
RESULTS: Thirty-eight of 38 Apert syndrome patients had some degree of closure of the SOS, compared to 29 of 38 age- and gender-matched controls (p=0.0023). Seventeen of 20 Muenke syndrome patients showed evidence of SOS closure, compared to 14 of 20 matched controls (p=0.4506). Nineteen of 38 Apert patients exhibited complete closure by age 14 compared to only 3 of 20 Muenke patients (p=0.0110). Patients began to demonstrate partial SOS fusion as early as age 2 in Apert syndrome and age 6 in Muenke syndrome patients; the earliest sign of fusion was seen at age 7 in the control group.
CONCLUSIONS: The spheno-occipital synchondrosis closes significantly earlier in patients with Apert syndrome than age-and sex-matched controls. The bulk of this difference is distributed in the age range of 8 to 12 years of age. Muenke syndrome patients did not show a significant difference in closure time of the spheno-occipital synchondrosis when compared to controls. Apert syndrome is clinically observed to have a higher degree of midface hypoplasia, which is supported by premature fusion of the spheno-occipital synchondrosis in the cranial base. While causality cannot be concluded from this study, there exists an association between phenotype of the midface and degree of closure of the spheno-occipital synchondrosis.
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