What Is the Sagittal Suture?

The sagittal suture, or interparietal suture, is a fibrous and immovable interlocking joint between the right and left parietal bones of the skull. An anatomical plane called the sagittal plane is based on the sagittal suture, and is parallel to it. To allow for the growth of the brain, the sagittal suture is open from birth and gradually ossifies or becomes bony over time like other cranial sutures. When there is premature ossification of this suture, problems such as sagittal suture craniosynostosis, scaphocephaly, and plagiocephaly occur, leading to brain development problems, deformities, and the need for surgical correction. The Latin name of the sagittal suture is sutura sagittalis, which means arrow joint, a name derived from its posterior notching relative to another suture in the skull called the lambdoid suture.

Two parietal bones are located on the posterior portion of the skull just above the occipital bone. The sagittal suture connects the right and left parietal bones, and intersects with both the lambdoid suture, which unites the parietal bones with the occipital bone, and the coronal suture, which interlocks the frontal bones and the parietal bones. While the point of intersection between the sagittal and lambdoid sutures is called the lambda, the point of intersection between the sagittal and frontal sutures is called the bregma. Both the lambda and the bregma are used when measuring the skull.

The sutures of fetuses and infants still consist of large fibrous areas called fontanelles or fonticuli. The most prominent among these are the anterior fontanelle, formed by the sagittal and frontal sutures, and the posterior fontanelle, formed by the sagittal and lambdoid sutures. The softness of the bones of the skull and the presence of these fontanelles allow the head to undergo molding when it passes through the birth canal during delivery.

Sagittal suture craniosynostosis is a condition that occurs when the parietal bones become totally fused prematurely, and this premature fusion is called sagittal synostosis. It usually occurs when there is asymmetry between the mother’s pelvic size and the fetal head size, thereby leading to synostosis prior to birth. It has been noted that male fetuses are at higher risk because their heads are usually larger than the heads of female fetuses. Although the risk of sagittal craniosynostosis cannot be reduced prenatally, it can still be treated after birth. The common procedure done to treat craniosynostosis is called craniectomy, a reconstructive surgery for the skull that helps correct the early fusion of the sagittal suture and restores normal brain development.