Objective: To investigate the imaging features of patients with developmental stenosis of atlas (small atlas) complicated with degenerative cervical myelopathy and to explore the diagnostic criteria of small atlas. Methods: The clinical data of patients with degenerative cervical myelopathy treated by posterior cervical laminoplasty and resection of posterior arch of atlas from 2006 to 2020 in the Department of Orthopedics, Peking University Third Hospital were retrospectively analyzed. Sixteen cases had spinal cord compression at C1 level after the exclusion of ossification of cervical posterior longitudinal ligament (OPLL) and other pathology. These cases were suspected small atlas (small atlas group). Forty-six cases without posterior arch resection in the same period were selected as control group. The middle sagittal diameter of atlas and the vertical distance from posterior tubercle of atlas to occipitoaxial line under CT in both groups were compared. The sagittal diameter of the spinal canal at the atlas level under MRI, the Japanese Orthopaedic Association (JOA) score for functional state of cervical spine before operation and at last follow-up were also measured. Results: There were 9 males and 7 females in the small atlas group, aged (63±12) years. There were 21 males and 25 females in the control group, aged (57±10) years. The patients in both group were followed-up for at least one year. The sagittal diameter of atlas in the small atlas group was (26.4±3.1) mm, which was significantly smaller than that in the control group [(29.6±2.2) mm, P=0.010]. The vertical distance from the posterior tubercle of atlas to the occipitoaxial line in the small atlas group was larger than that in the control group[(6.79±1.17) mm vs (5.57±1.29) mm, P=0.001]. The diameter of atlas canal in the small atlas group was (8.25±1.44) mm which was significantly smaller than that in the control group [(13.00±1.66) mm, P<0.001]. The JOA score of the small atlas group before operation and at the last follow-up were both slightly lower than that in the control group (both P<0.05), but there was no significant difference in the recovery rate of JOA score between the two groups (61.9% vs 66.0%, P=0.066). Among the 16 cases in the small atlas group, 5 cases of occipital-axial connection were located at the posterior 1/3 of the posterior arch of atlas, and 11 cases of occipital-axial connection were completely located at the posterior arch of atlas. Conclusions: The effective sagittal diameter of atlas is smaller in small atlas group which can lead to more severe cervical myelopathy. The presence of a small atlas should be highly suspected when the sagittal diameter of atlas canal is less than 26 mm under CT. The existence of the small atlas should be alert when the occipitalaxial line is located at the dorsal 1/3 or behind of the posterior arch of atlas.
目的： 研究寰椎发育性椎管狭窄（小寰椎）合并退变性颈脊髓病患者的病例的影像学特点，探索小寰椎的诊断依据。 方法： 回顾性分析2006年至2020年北京大学第三医院骨科通过颈后路手术+寰椎后弓切除术治疗的退变性颈脊髓病的病例资料，除外后纵韧带骨化等因素，16例存在寰椎水平脊髓受压，高度怀疑存在小寰椎，命名为小寰椎组。匹配同时期颈后路手术未行寰椎后弓切除的病例46例作为对照组。比较两组CT下寰椎椎管中矢状径、寰椎后结节至枕枢连线垂直距离以及MRI下寰椎椎管有效径的大小，以及术前及末次随访时的日本骨科学会（JOA）颈椎功能状态评分，比较其特点。 结果： 小寰椎组男9例，女7例，年龄（63±12）岁。对照组男21例，女25例，年龄（57±10）岁。两组患者均获得至少1年的随访。小寰椎组的寰椎椎管中矢状径为（26.4±3.1）mm，小于对照组的（29.6±2.2）mm（P=0.010）。小寰椎组寰椎后结节至枕枢连线垂直距离大于对照组［（6.79±1.17）mm比（5.57±1.29）mm，P=0.001］。MRI下小寰椎组的寰椎椎管有效径明显小于对照组［（8.25±1.44）mm比（13.00±1.66）mm，P<0.001］。小寰椎组的术前及末次随访时JOA评分均低于对照组（均P<0.05），但是二者JOA评分末次随访与术前改善率差异无统计学意义（61.9%比66.0%，P=0.066）。小寰椎组的16例中，有5例枕枢连线位于寰椎后弓的后1/3处，有11例枕枢连线完全位于寰椎后弓的后方。 结论： 小寰椎导致寰椎水平的椎管有效径明显减小，可以导致更加严重的颈脊髓损害。CT下寰椎椎管中矢状径<26 mm时，应高度怀疑存在小寰椎。当枕枢连线位于寰椎后弓的后1/3或者以远时，应当警惕小寰椎的存在。.