Findings
- Failure of C1 anterior and posterior arch fusion, anatomic variant. No acute fracture or malalignment.
Diagnosis
Congenital Anomalies of C1 (Mimic)
Discussion
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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.
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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.
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Currarino’s Classification Scheme
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A Failure of posterior midline fusion of the two hemiarches
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B Unilateral posterior arch defect
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C Bilateral posterior arch defects
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D Absence of posterior arch, with persistent posterior tubercle
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E Absence of the entire arch, including the tubercle
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Usually these anomalies are easy to differentiate from fracture or acute trauma given the margins of the defects are well-corticated and smooth.
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Annotated Images & Illustrations
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