Skull sutures are fibrous joints that connect the bones forming the human skull. These connections are made of tough, flexible tissue, serving as natural seams where the individual bony plates of the skull meet. They are a fundamental and dynamic component of human anatomy.
Where Skull Sutures Are Found
Skull sutures are located between the flat bones of the cranium. The coronal suture extends from ear to ear, separating the frontal bone from the two parietal bones. The sagittal suture runs along the midline, joining the two parietal bones.
Further back, the lambdoid suture stretches across the rear of the skull, connecting the two parietal bones with the occipital bone. On each side of the skull, above the ear, the squamosal suture connects the temporal bone with the parietal bone. In infants, a metopic suture runs down the middle of the forehead, connecting the two halves of the frontal bone before fusing in early childhood.
Their Essential Roles
Skull sutures play a crucial role during childbirth. Their flexibility allows an infant’s skull bones to slightly overlap and change shape, reducing the head’s size as the baby navigates the birth canal. This temporary compression facilitates a smoother passage and protects the brain from excessive pressure during delivery.
Sutures also accommodate the rapid growth of the brain. During infancy and early childhood, the brain undergoes substantial development and enlargement. The sutures act like expansion joints, allowing the skull to expand as the brain grows, preventing harmful pressure from building inside the cranium. This continuous expansion ensures the developing brain has adequate space for healthy neurological function and development.
How Sutures Change Over Time
In infants, where several sutures intersect, membrane-covered gaps known as fontanelles, commonly referred to as “soft spots,” are present. These fontanelles allow for rapid brain growth. The posterior fontanelle, located at the back of the head, typically closes within one to two months after birth.
The anterior fontanelle, the larger soft spot near the front of the head, usually remains open longer, closing between seven and nineteen months of age. As a child matures, the fibrous tissue of the sutures undergoes a process called ossification, gradually turning into bone. This progressive fusion makes the skull a more rigid and protective structure.
While some sutures, like the metopic suture, may fuse as early as three to nine months, others continue to ossify into adulthood. The sagittal suture might close around age 22, the coronal suture around age 24, and the lambdoid suture around age 26. The squamosal suture can remain open even longer, sometimes closing completely by age 60.
When Sutures Don’t Form Normally
When skull sutures do not develop or fuse as expected, it can affect skull shape and brain development. The primary condition is craniosynostosis, which involves the premature fusion of one or more skull sutures. This early closure restricts growth perpendicular to the affected suture, causing the skull to compensate by growing in other directions, resulting in an abnormal head shape.
Depending on which suture fuses prematurely, the head can take on various distinct shapes. If multiple sutures close too early or if the brain’s compensatory growth is insufficient, craniosynostosis can lead to increased pressure on the developing brain. This elevated pressure can impact brain development, leading to issues like visual problems or developmental delays. Early diagnosis and appropriate intervention are important for managing craniosynostosis and promoting optimal outcomes for affected individuals.