Several years ago, the authors treated an infant with sagittal and bilateral parietomastoid suture fusion. This made them curious about the normal course of fusion of “minor” lateral sutures (sphenoparietal, squamosal, parietomastoid). Accordingly, they investigated fusion of these sutures on 3D volume-rendered head CT reconstructions in a series of pediatric trauma patients.
The authors reviewed all volume-rendered head CT reconstructions obtained from 2010 through mid-2012 at Children’s Hospital Colorado in trauma patients aged 0–21 years. Each sphenoparietal, squamosal, and parietomastoid suture was graded as open, partially fused, or fused. In several individuals, one or more lateral sutures were fused atypically. In these patients, the cephalic index (CI) and cranial vault asymmetry index (CVAI) were calculated. In a separately reported study utilizing the same reconstructions, 21 subjects had fusion of the sagittal suture. Minor lateral sutures were assessed, including these 21 individuals, excluding them, and considering them as a separate subgroup.
After exclusions, 331 scans were reviewed. Typically, the earliest length of the minor lateral sutures to begin fusion was the anterior squamosal suture, often by 2 years of age. The next suture to begin fusion—and first to complete it—was the sphenoparietal. The last suture to begin and complete fusion was the parietomastoid. Six subjects (1.8%) had posterior (without anterior) fusion of one or more squamosal sutures. Six subjects (1.8%) had fusion or near-complete fusion of one squamosal and/or parietomastoid suture when the corresponding opposite suture was open or nearly open. The mean CI and CVAI values in these subjects and in age- and sex-matched controls were normal and not significantly different. No individuals had a fused parietomastoid suture with open squamosal and/or sphenoparietal sutures.
Fusion and partial fusion of the sphenoparietal, squamosal, and parietomastoid sutures is common in children and adolescents. It usually does not represent craniosynostosis and does not require cranial surgery. The anterior squamosal suture is often the earliest length of these sutures to fuse. Fusion then spreads anteriorly to the sphenoparietal suture and posteriorly to the parietomastoid. The sphenoparietal suture is generally the earliest minor lateral suture to complete fusion, and the parietomastoid is the last. Atypical patterns of fusion include posterior (without anterior) squamosal suture fusion and asymmetrical squamosal and/or parietomastoid suture fusion. However, these atypical fusion patterns may not lead to atypical head shapes or a need for surgery.