The human skull is composed of several distinct bones. These bones are connected by specialized fibrous joints known as cranial sutures. Sutures are flexible seams that hold the skull bones together, allowing for some movement. This design is particularly important during early development when the brain undergoes significant growth.
Anatomical Position
The coronal suture is a prominent fibrous joint in the skull. It forms a distinct line that separates the frontal bone from the two parietal bones, which make up a large portion of the top and sides of the skull. This suture extends horizontally across the top of the skull, running from one side to the other, resembling where a crown might sit on the head. Its name is derived from the Latin word “corona,” meaning garland or crown. The point where the coronal suture meets the sagittal suture is known as the bregma.
Essential Roles
Cranial sutures, including the coronal suture, serve two primary functions, especially during early life. They allow for the expansion of the skull as the brain grows rapidly during infancy and early childhood. The flexibility of these sutures ensures the skull can accommodate this increasing volume. Without this flexibility, the growing brain would be restricted, potentially leading to developmental issues.
Sutures also play a role during childbirth. The flexible nature of these joints allows the bones of a baby’s skull to slightly overlap and change shape as the head passes through the birth canal. This temporary molding of the skull is important for safe passage during delivery. This flexibility is maintained throughout infancy, protecting the brain as a child learns to move and hold their head.
Developmental Changes and Considerations
Cranial sutures are initially flexible in infants, but they gradually undergo ossification, where fibrous tissue turns into solid bone. The timing of this fusion varies among different sutures. The coronal suture typically begins to fuse around 24 years of age, though some sources indicate it can begin to close earlier or complete ossification later, sometimes between 30 and 40 years of age. This process generally completes by early adulthood when brain growth has largely finished.
When a suture fuses prematurely, before the brain is fully formed, it is a condition known as craniosynostosis. If it affects the coronal suture, it is termed coronal synostosis. This early closure can lead to an abnormal head shape because the skull cannot expand normally in the direction perpendicular to the fused suture.
For example, if one coronal suture closes too early, it can cause the forehead to flatten on that side and bulge on the opposite side, potentially affecting the shape of the eye socket and nose. When both coronal sutures fuse prematurely (bicoronal synostosis), the head may appear short and wide, often with a tall forehead. Severe or untreated cases, especially if multiple sutures are involved, can lead to increased pressure inside the skull, which may be associated with developmental delays.