Atlantooccipital assimilation with basilar invagination

Case contributed by Utkarsh Kabra
Diagnosis almost certain


Weakness in bilateral upper limbs

Patient Data

Age: 55 years
Gender: Male

Partial fusion of anterior arch of atlas with clivus. Posterior arch of atlas is not visualized separately and is likely fused with occiput.
Atlantoaxial subluxation is seen with atlantodental interval being approx 9 mm.
Basilar invagination is also seen with superior migration of dens of C2, projecting above foramen of magnum causing severe compression of cervicomedullary junction and upper cervical cord.
​Hyperintensities are seen in cervicomedullary junction and upper cervical cord at C2 level.
​Erosion/cystic change seen in dens of C2 with tiny calcifications at anterior aspect of dens and heterogeneous soft tissue in atlantodental interval - likely degenerative changes. Possibility of inflammatory arthritis, example rheumatoid appears less likely.
C2-C3 block vertebra seen.

CT confirming the above findings on MRI.

Case Discussion

Overall above findings are suggestive of atlantooccipital assimilation with atlantoaxial subluxation, basilar invagination causing compressive myelopathy at cervicomedullary junction and upper cervical cord.

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