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Primary basilar invagination

Disease definition

Primary basilar impression (PBI) is a very rare skeletal developmental defect characterized by congenital upward translocation of the upper cervical spine and clivus into the foramen magnum. PBI can be asymptomatic or associated with severe neurological dysfunction.


Classification level: Disorder
  • Synonym(s):
    • Bull-Nixon syndrome
  • Prevalence: Unknown
  • Inheritance: Autosomal dominant 
  • Age of onset: All ages
  • ICD-10: Q75.8
  • OMIM: 109500
  • UMLS: C1862299
  • MeSH: -
  • GARD: 1037
  • MedDRA: -
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