Pediatric Skull Deformities
Skull deformities are the single most common reason for referral of new patients to the pediatric neurosurgeon. The great majority of deformities are managed non-surgically. A basic understanding of the causes and treatments of infantile skull deformities enables the primary physician not only to make an appropriate referral in a timely fashion but also to shape parental expectations appropriately.
The infant skull is composed of 7 flat membranous bones joined along their borders by condensations of dura and pericranium called "sutures." The sagittal suture forms the border between the paired parietal bones. The metopic suture lies between the frontal bones. The coronal suture occurs between the frontal and the parietal bone on each side. The lambdoid sutures separate the parietal bones from the occipital bone. A squamosal suture separates the parietal bone from the temporal bone on each side. Sutures also join the bones of the skull vault with the cartilage-derived bones of the skull base. At the intersection of sutures are larger membranous areas called fontanels. The largest 2 fontanels occur at the intersection of the sagittal, coronal, and metopic sutures – the anterior fontanel – and at the intersection of the sagittal and lambdoid sutures – the posterior fontanel.
The membranous bones of the calvarium grow and take shape in response to pressure from the growing brain and cerebrospinal fluid spaces. Pressure from the growing brain causes tension in the overlying calvarium that results in the deposition of new bone along the sutures and over the external surface of the skull. Furthermore, pulsations of the growing brain cause resorption of bone along the internal surface of the skull. Brain growth thus determines the size and shape of the calvarium.
In the absence of pathological constraints, such as cranial synostosis or positional head deformity, the calvarium expands smoothly in a normal ellipsoidal shape. On the other hand, if the growth of the calvarium is restricted in a certain direction, the brain will push outward in an alternative direction of least resistance and result in skull deformity. Because these deformities almost always occur in distinctive patterns, they are fairly easy for an experienced practitioner to recognize, even without imaging studies.
