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

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Case 1
    Drag here to reorder.
  • Case 2
    Drag here to reorder.
  • Case 3: with C2-C3 fusion
    Drag here to reorder.
  • Case 4
    Drag here to reorder.
  • Case 5: with syrinx
    Drag here to reorder.
  • Case 6
    Drag here to reorder.
  • Case 7
    Drag here to reorder.
  • Case 8
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.