Background: The spheno-occipital synchondrosis is a driver of cranial base and facial growth. Its premature fusion has been associated with midface hypoplasia in animal models. The authors reviewed computed tomographic scans of patients with Apert and Muenke syndrome, craniosynostosis syndromes with midface hypoplasia, to assess premature fusion of the spheno-occipital synchondrosis when compared with normal controls. Methods: Ninety head computed tomographic scans of Apert syndrome patients and 31 head scans of Muenke syndrome patients were assessed, in addition to an equal number of control scans. Spheno-occipital synchondrosis fusion on axial images was graded as open, partially closed, or closed. Analysis focused on ages 7 to 14 years, as no control patient fused before age 7 or had failed to fuse after age 14. Results: All 38 Apert syndrome patients aged 7 to 14 had some degree of spheno-occipital synchondrosis closure, compared with 29 of 38 matched controls (p = 0.0023). Seventeen of 20 Muenke syndrome patients showed closure, compared with 14 of 20 matched controls (p = 0.4506). Partial fusion was seen as early as age 2 in Apert syndrome and age 6 inMuenke syndrome patients; the earliest fusion was seen at age 7 in the control group. Conclusions: Compared with matched controls, the spheno-occipital synchondrosis closes significantly earlier in patients with Apert syndrome but not Muenke syndrome. This correlates well to reported incidences of midface hypoplasia in these syndromes. Although causality cannot be concluded from this study, an association exists between midface phenotype and degree of sphenooccipital synchondrosis closure.
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