Atlanto-occipital assimilation
Atlanto-occipital assimilation is the fusion of the atlas (C1) to the occiput and is one of the transitional vertebrae.
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Epidemiology
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.
Clinical presentation
It is typically asymptomatic but symptoms from nerve or vascular compression can occur.
Gross anatomy
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 or
- assimilation of both the anterior and posterior arches
Associations
Atlanto-occipital assimilation is associated with 2:
- fusion of C2 and C3 (occurs in 50% of cases)
- basilar invagination: type 1
- cleft palate
- cervical ribs
- urinary tract anomalies
- cranio-cervical instability 5
Related Radiopaedia articles
Anatomy: Spine
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osteology
- vertebrae
- spinal canal
- cervical spine
- thoracic spine
- lumbar spine
- sacrum
- coccyx
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anatomical variants
- vertebral body
- neural arch
- transitional vertebrae
- ossicles
- ossification centers
- intervertebral disc
- articulations
- ligaments
- musculature of the vertebral column
- muscles of the neck
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suboccipital muscle group
- rectus capitis posterior major muscle
- rectus capitis posterior minor muscle
- obliquus capitis superior muscle
- obliquus capitis inferior muscle
- splenius capitis muscle
- splenius cervicis muscle
- erector spinae group
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- quadratus lumborum muscle
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suboccipital muscle group
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spinal cord
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white matter tracts (white matter)
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dorsal columns
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