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Start free with EleplanPrimary basilar invagination
ORPHA:2285Morphological anomaly
Also called Bull-Nixon syndrome
What it is
A rare skeletal developmental defect characterized by congenital upward translocation of the upper cervical spine and clivus into the foramen magnum. It can be asymptomatic or associated with severe neurological dysfunction.
Key facts
- Age of onset
- All ages
- Inheritance
- Autosomal dominant
- Classified as
- Morphological anomaly
Signs and symptoms
Very common80–99%
5These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.
ICD-10 codes
ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.
Related health topics
Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.
Cross-references
Orphadata Science: Free access data from Orphanet. © INSERM 1999. Data version 2026-06-23. Available under CC BY 4.0. This is a reference, not medical advice.
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