They are specialized joints located between the bones of the skull.
Sutures allow the individual bones of the skull to move relative to each other.
These joints are made of muscular fibrous tissue, which holds the bones of a baby’s skull together until the bones fuse, usually around two years of age.
Until the fusion time, the sutures intersect at the fontanelles, which are the soft spots on the baby’s head.
The largest of the four fontanelles is in the front of the skull (anterior). The anterior fontanelle is the soft spot you feel just behind your baby’s forehead. The next largest is at the back. Each side of the skull has a small fontanelle.
The space between the bones is filled with highly specialized ligaments called Sharpey Fibers. These fibers allow the joints to move and “float” without completely separating, allowing the skull some elasticity.
The bones of the skull and the skull base ossify separately and gradually coalesce at the skull sutures.
The skull comprises the following bones, two of which are paired.
- Frontal bone.
- Parietal bones (paired).
- Occipital bone.
- Temporal bones (paired).
- Sphenoid bone.
- Ethmoid bone.
Morphology of the cranial sutures
Cranial sutures can be considered as a complex consisting of four main components:
- Osteogenic fronts of approximate bone plates.
- The suture mesenchyme spans the osteogenic fronts.
- The overlying pericranium or cranial periosteum.
- The underlying dura is a tough, fibrous membrane that makes up the outer meningeal layer that surrounds the brain and forms the inner lining of the cranial bones and sutures.
Types of sutures
Cranial sutures include the metopic or interfrontal suture, the sagittal suture, the coronal suture, and the lambdoid sutures. The metopic suture or frontal suture is variably present in adults.
The large cranial sutures are as follows:
The coronal suture joins the frontal bone with the parietal bones.
The sagittal suture joins the two parietal bones in the midline.
The lamboid suture joins the parietal bones with the occipital bone.
The squamous suture joins the squamous portion of the temporal bone with the parietal bones.
When the metopic suture is present, it joins the two frontal bones.
The other small cranial sutures are:
This small suture separates the parietal bone from the sphenoid bone.
It separates the squamous part of the temporal bone from the sphenoid bone.
Separates the parietal bone from the mastoid area of the temporal bone.
Separate the occipital bone from the mastoid process.
Effects of premature closure of sutures
Cranial sutures are essential components in the development of the skull.
Non-functional sutures during the cranial vault and skull base evolution lead to evolving deformities that can end in neurologic sequelae.
Premature closure may affect a single suture, but multiple sutures may be involved, and severe deformities may develop, including the orbits and anterior fossa.
This premature closure is called craniosynostosis.
Although the term craniosynostosis was used for the first time, referring to the premature closure of a cranial suture, it was Sommerring who described the anatomy of the suture in 1791 and postulated not only its role in the average growth of the skull but also the effects of the closure.
During the 19th century, it was stated that premature closure of sutures (craniostenosis) prevented growth perpendicular to the suture and was accompanied by compensatory growth in others.
Since this first identification of craniosynostosis as a distinct clinical entity, several theories have been proposed to explain the pathogenesis of premature suture fusion and the resulting aberrations in calvarial growth resulting in a dysmorphic skull.
Recent advances in clinical genetics have identified genetic mutations in the significant craniosynostosis syndromes.