Atlanto-occipital assimilation

Last revised by Ryan Thibodeau on 12 Oct 2023

Atlanto-occipital assimilation is the fusion of the atlas (C1) to the occiput and is one of the transitional vertebrae

Atlanto-occipital assimilation occurs in approximately 0.5% (range 0.08-3%) of the population 2-5. It is thought to affect males and females equally.

Atlanto-occipital assimilation is associated with 2:

It is typically asymptomatic but symptoms from nerve or vascular compression can occur.  

Fusion of C1 to the occiput can be either 3:

  • complete: C1 not identifiable

  • incomplete: C1 partially identifiable

It can also be classified as 

  • posterior arch assimilation

  • anterior arch assimilation

  • assimilation of both the anterior and posterior arches

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