Down syndrome, also known as trisomy 21, is associated with congenital cervical spine abnormalities, including atlantoaxial instability with or without os odontoideum, atlanto-occipital instability, and hypoplasia of the atlas. Herein, we report a case of Down syndrome complicated by congenital atlanto-occipital dislocation. The patient presented with severe cervical myelopathy at 13 years of age after a 10-year follow-up. Radiography and computed tomography revealed os odontoideum protruding into the foramen magnum and congenital anterior atlanto-occipital dislocation. Additionally, a bifurcated internal occipital crest with a thinned central portion of the occipital bone was noted. Magnetic resonance imaging revealed kyphotic alignment of the spinal cord with severe compression at the foramen magnum level. As the neurological impairment was partially improved by halo vest immobilization, we performed in situ O-C2 fusion with an iliac autograft and decompression of the foramen magnum and posterior arch of C1. An improvement was observed immediately after surgery. Two years after surgery, radiography and computed tomography showed solid O-C2 segment fusion. The accumulation of similar cases is essential for determining the prognosis or optimal treatment for this rare congenital condition.

唐氏综合症，也称为 21 三体，与先天性颈椎异常有关，包括伴或不伴齿状骨的寰枢椎不稳定、寰枕不稳定和寰椎发育不全。本文报道一例唐氏综合症并发先天性寰枕脱位的病例。10 年随访后，该患者在 13 岁时出现严重脊髓型颈椎病。X 光检查和计算机断层扫描显示齿状骨突出到枕骨大孔中，并且存在先天性寰枕前脱位。此外，还发现枕骨内嵴分叉，枕骨中央部分变薄。磁共振成像显示脊髓后凸排列，枕骨大孔水平严重受压。由于 Halo 背心固定可部分改善神经损伤，因此我们采用自体髂骨进行原位 O-C2 融合，并对枕骨大孔和 C1 后弓进行减压。手术后立即观察到改善。手术两年后，X 光检查和计算机断层扫描显示 O-C2 节段确实融合。类似病例的积累对于确定这种罕见先天性疾病的预后或最佳治疗至关重要。