Atlanto-occipital assimilation with cleft of the posterior arch of C1
Presentation
Head trauma. Incidental finding.
Patient Data
Normal appearance of the posterior cranial fossa and cerebral hemispheres with no parenchymal contusion, extra-or subdural hematoma. No cranial vault or skull base fracture on bone window.
Fusion of the atlas (C1) to the occiput bilaterally, complete on the left and incomplete on the right in keeping with atlanto-occipital assimilation.
A midline defect of the posterior arch of C1 (failure of midline fusion of the two hemiarches), type A according to the Currarino classification.
Case Discussion
CT features of atlanto-occipital assimilation with associated midline defect of the posterior arch of C1 (incidental findings).
Congenital anomalies of the posterior atlas arch are benign anatomical variants and should not be confused with fracture.
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