Wormian bones are small bones that are often found within the sutures and fontanelles of the skull. When a child presents an unexplained fracture or fracture(s), osteogenesis imperfecta is usually suggested when an “abnormally high number” of fractures are seen.

To assess the frequency, number, and topography of wormian bones in a “normal” paediatric population.

In a population aged from 0 to 3 years, we retrospectively analysed 605 CT brain scans carried out for a range of indications, excluding cases in which there was a suspicion of constitutional bone disease.

In our population, wormian bones were found in 53% of children (n=320): 43% of the children had between one and three (n=260), 10% had four or more (n=60), and 6% had five or more (n=40). There was no significant relationship between the number of wormian bones and the various indications that had led to the CT scan being carried out. Wormian bones in the lambdoid suture were found in by far the greatest numbers.

Wormian bones are common and can sometimes be numerous without necessarily pointing to osteogenesis imperfecta, since 10% of the children in our study had at least four.