Wormian bone

Last revised by Mostafa Elfeky on 26 Mar 2023

Wormian bones (also known as intrasutural bones) is the name given to the additional small bones sometimes found between the cranial sutures of the bones of the skull vault, most commonly in relation to the lambdoid suture. Some reserve the term Wormian bones to just the intrasutural bones proximate to 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) ref. In general, males are more frequently affected than females ref.

Their associations are various, and include:

Wormian bones can also be idiopathic (anatomical variant). 

A useful mnemonic is PORKCHOPS.

Wormian bones are named after the Danish physician, theologian and antiquary Ole Worm (Olaus Wormius) (1588-1654) 4, who first described them.

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