Background: Atlanto-occipital assimilation (AOA) and congenital posterior arch defects of the atlas share an embryologic origin and may coexist. Such variants can mimic acute fractures in trauma evaluations and can be associated with retro-odontoid pseudotumor (ROPT) that regresses after stabilization. Case Description: Case 1- A 60-year-old man presented after a head impact while surfing. High-resolution computed tomography revealed a C1 posterior arch midline cleft with smooth corticated margins and unilateral AOA. Although the axial plane suggested a transverse fracture line, multiplanar reconstructions confirmed occiput–C1 continuity, and short tau inversion recovery magnetic resonance imaging showed no marrow edema. The patient improved with conservative management. Case 2: An 80-year-old woman presented with neck pain and hand clumsiness. Imaging demonstrated AOA and a ROPT compressing the cord. Occipitocervical fixation without direct decompression led to radiological regression of the mass and clinical improvement. Conclusion: Coexisting AOA and Currarino Type A posterior arch defect have practical implications for neurosurgical decision-making: Accurate fracture differentiation in trauma settings and recognition that ROPT may regress following stabilization.
Kawanishi et al. (Fri,) studied this question.
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