Morphology of the Occipital Bones and Foramen Magnum resulting from Premature Minor Suture Fusion in Crouzon Syndrome

Background: Nearly all skull sutures fuse prematurely in Crouzon syndrome, resulting in foramen magnum dysmorphology. Although previously suggested, no direct evidence demonstrates minor suture fusion causes occipital bone and foramen magnum dysmorphology. 

Hypothesis: We hypothesize minor suture fusion directly restricts occipital bone development in the Crouzon skull base.

Methods: 60 pre-operative patients with Crouzon syndrome younger than 12 (years) were selected from the Wake Forest Craniofacial Imaging Database (WFCID) and retrospectively studied. Each patient was age- and sex-matched to obtain a 60-patient normal control group. No participant had prior craniofacial surgery. Skull-base suture closure degree and cephalometric measurements were obtained using preoperative CT scans. Multiple linear regression models were used to evaluate whether premature minor suture fusion in Crouzon syndrome correlates with occipital bone and foramen magnum cephalometric outcomes.

Results: A causal relationship between minor suture fusion and linear skull base cephalometric measures was not established using regression analysis. However, 3D volumetric evaluation of the basioccipital, exo-occipital, and supra-occipital bones revealed decreased growth in Crouzon patients which could be attributed solely to premature minor suture fusion. Spheno-occipital and petrous-occipital suture fusion reduced growth of the basiocciput; lambdoid arch, occipitomastoid and posterior intraoccipital synchondrosis fusion reduced growth of the supra-occiput; and petrous-occipital suture and anterior intraoccipital synchondrosis fusion reduced growth of the exo-occiput. Foramen magnum morphology is restricted in Crouzon patients, relating to premature fusion of the posterior intraoccipital synchondrosis.

Conclusions: Premature minor fusion directly restricts the volume of the developing occipital bone in Crouzon patients, mediating foramen magnum morphology.