Purpose: The shape and size of the foramen magnum (FM) can be altered in craniosynostoses. However, few studies have investigated these changes. In this paper, we investigate the morphology of the foramen magnum in syndromic and non-syndromic brachycephaly.
Methods: Surface area, anteroposterior (AP) diameter, and transverse diameters of the FM were measured on high-resolution CT scans in children with Crouzon (25), Pfeiffer (21), Apert (26), Saethre-Chotzen (7) syndromes, and isolated bicoronal synostosis (9) and compared to an age-matched control group (30).
Results: A significantly smaller FM surface area was observed in Crouzon (6.3 ± 1.7 cm(2)) and Pfeiffer (6.4 ± 2.3 cm(2)) syndromes as compared to the control group (7.4 ± 1.3 cm(2), p = 0.006 and p = .017, respectively). In comparison to the control group, no statistically significant alteration in FM surface area was noted in patients with Apert, Saethre-Chotzen, or isolated bicoronal synostosis (p = 0.37, p = 0.71, p = 0.40 respectively). The transverse diameter of FM was significantly smaller in Crouzon, Pfeiffer, and Apert syndromes compared to the control group (p = 0.005, p = 0.002, p = 0.03 respectively). In Saethre-Chotzen and isolated bicoronal synostosis, no difference in transverse diameter was demonstrated. Among all groups, only Crouzon syndrome showed reduced anteroposterior diameter as compared to controls (p = 0.005). In Pfeiffer and Apert syndromes, there was elongation of the shape of the FM with a relatively narrowed width as demonstrated in a significantly increased AP to transverse diameter ratio (p = 0.002 and p = 0.019, respectively).
Discussion and conclusions: The FM shape and area is significantly altered in fibroblast growth factor receptor (FGFR)-related brachycephaly syndromes (Crouzon, Pfeiffer, and Apert), whereas in patients with Saethre-Chotzen syndrome (TWIST-1 mutation) and isolated non-syndromic bicoronal synostosis, the shape and mean FM area was not statistically different from that of normals. This study brings to light the important role of FGFRs on FM growth and shape. TWIST-1 mutation (Saethre-Chotzen syndrome) does not appear to have an important effect in shaping the FM.