Fontanelles

The bones of the skull cap ossify in membrane and are mobile at birth, meaning there are soft membranous gaps that are the 6 fontanelles. The fontanelles allow the cranial vault to expand as the brain enlarges during child development and the skull to flex when squeezing through the birth canal during childbirth. These fontanelles include: the diamond-shaped anterior fontanelle (between frontal and parietal bones), the triangular posterior fontanelle (between occipital and parietal bones) as well as paired sphenoid/anterolateral and mastoid/posterolateral fontanelles. These fontanelles close in 2 to 24 months starting with the posterior first and anterior last.

CLINICAL CORNER

Fontanelles are useful for cranial ultrasounds which detect brain abnormalities and haemorrhage (performed on premature babies at the anterior fontanelle due to high risk). Depression or elevation can also indicate dehydration or raised intracranial pressure.

Sutures

The cranial bones later fuse via fibrous joints called sutures in the adult to form a rigid structure. These sutures do not fully ossify until later in life, allowing the cranial vault to grow as a result of intracranial pressure. The main cranial sutures are the:

• Metopic: dividing the frontal bone
• Coronal: between frontal and parietal bones
• Sagittal: between parietal bones
• Lambda: between parietal and occipital bones
• Squamous: between temporal and parietal bones

CLINICAL CORNER

Sutures are involved in many skull growth abnormalities. Raised intracranial pressure (e.g. by hydrocephaly) can result in an abnormally large cranial vault and vice-versa (e.g. by microcephaly). Craniosynostosis is a condition where sutures ossify in early childhood, changing skull growth patterns.