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Age: 14

Sex: Male

Indication: Trauma

Congenital Anomalies of C1

Mimicking a Fracture or Acute Trauma

Findings Relating to the Mimic

  • Failure of C1 anterior and posterior arch fusion, anatomic variant.  No acute fracture or malalignment.


  • Congenital anomalies of C1 are relatively common and almost always benign and incidental. Failure of posterior arch fusion/ossification is most common and occurs in approximately 4% of the population.
  • These anomalies can be classified according to a system created by Currarino.  While it’s not necessary to memorize this scheme, it’s worth being familiar with to avoid misdiagnosing a benign process as something pathologic.
    • Currarino’s Classification Scheme
      • A Failure of posterior midline fusion of the two hemiarches
      • B Unilateral posterior arch defect
      • C Bilateral posterior arch defects
      • D Absence of posterior arch, with persistent posterior tubercle
      • E Absence of the entire arch, including the tubercle
  • Usually these anomalies are easy to differentiate from fracture or acute trauma given the margins of the defects are well-corticated and smooth.


Faiilure of posterior midline and right posterior arch fusion as well as anterior arch fusion (red arrows). Notice the well corticated/smooth margins of the defects.

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