Wormian bones are a subset of the small intrasutural bones that lie between the cranial sutures formed by the bones of the skull vault. The title Wormian bones is reserved for abnormal intrasutural bones that are typically found around the lambdoid suture.
Some consider them abnormal only if greater than 10 in number.
The reported incidence is variable, ranging from around 10% (in Caucasian skulls) and 40% (in Indian skulls) to 80% (in Chinese skulls). In general, males are more frequently affected than females.
Their associations are various, and inclusive of:
- osteogenesis imperfecta
- kinky hair syndrome
- cleidocranial dysostosis
- otopalatodigital syndrome
- primary acroosteolysis (Hajdu-Cheney syndrome)
- Down syndrome
Wormian bones can also be idiopathic (anatomical variant).
A useful mnemonic is PORKCHOPS.
- lambdoid suture: most common
- lambda (also known as the pre-interparietal or inca bone)
- pterion: up to 12%; former anterolateral fontanelle (also known as the epipteric bone or pterion ossicle)
- sagittal and coronal sutural bones: uncommon
History and etymology
Erroneously, these bones are named after the person who supposedly first described them:
- Ole Worm (1624-1639), professor of Anatomy, Copenhagen, Denmark
- anatomic position
- regional anatomy
- systems anatomy
- macroscopic structure
- microscopic structure
- bone growth
- bones types
- blood vessels
- 1. S.B. Nayak "Multiple Wormian bones at the lambdoid suture in an Indian skull" Neuroanatomy (2008) 7: 52–53
- 2. S.B. Nayak and K.V. Soumya "Unusual sutural bones at pterion" International Journal of Anatomical Variations (2008) 1: 19–20
- 3. Jones KL, Smith DW. Smith's recognizable patterns of human malformation. W.B. Saunders Company. (1997) ISBN:0721661157. Read it at Google Books - Find it at Amazon