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Congenital C1 arch deficiency: unilateral cleft

Case contributed by Bruno Di Muzio
Diagnosis certain



Patient Data

Age: 30-year-old
Gender: Male

CT Cervical spine


The cranio-cervical junction is intact. Normal spinal alignment preserved. Partial agenesis of the left portion of the C1 posterior arch (anatomical variant), with only a small non-fused ossification center positioned further caudally than the normal location. There is no soft tissue edema or other indication to suggest this is a traumatic finding. No vertebral body fractures or facet joint dislocations. No regions of high grade cervical canal or neural foramen stenosis. Pre and paravertebral soft tissues are unremarkable.

Case Discussion

This case illustrates a congenital deficiency of the posterior arch of C1 (Atlas): unilateral cleft, where one of the two arms of the posterior arch is incompletely or totally not formed. There is a classification of the C1 arch deficiencies according to the publication of Currarino et al in 1994. 

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