寰椎侧块螺钉钉道与颈内动脉位置关系的三维CT血管成像分析

背景：植入寰椎侧块的双皮质螺钉存在损伤位于寰椎侧块前方的颈内动脉的风险。目的：通过对颈部三维CT血管成像多平面重建测量，研究寰椎侧块螺钉钉道与颈内动脉的位置关系，以避免寰椎侧块螺钉植入造成颈内动脉的损伤。方法：从2012年9月至2012年11月行头颈CT血管造影扫描的患者中选取寰枢椎及头颈部血管无明确病变者126例，利用其图像数据进行三维多平面重建成像，在寰椎侧块螺钉进钉平面上测量颈内动脉与寰椎前皮质的最短距离，寰椎侧块的宽度，颈内动脉内侧缘分别至寰椎正中线、过横突孔内侧缘的矢状线、过进钉点的矢状线的距离，并测量进钉点与颈内动脉内侧缘切线的外偏角，同时在进钉平面上根据寰椎侧块进行区域划分，根据颈内动脉内侧缘所在区域分析颈内动脉与寰椎侧块的位置关系。结果：在寰椎侧块螺钉进钉平面上，颈内动脉与寰椎前皮质的最短距离为（3．32±1．07）mm，有35侧（13．9％）小于2mm，最小值为1．49mm；颈内动脉内侧缘至寰椎正中线的距离为（22．99±2．86）mm；颈内动脉内侧缘与过横突孔内侧缘的矢状线距离为（1．08±1．50）mm，其中182侧（72．2％）颈内动脉内侧缘位于横突孔内侧；颈内动脉内侧缘与过进钉点的矢状线距离为（3．99±1．84）mm；进钉点与颈内动脉内侧缘切线的外偏角为（9．90±5．57）°，最小值为-4．6°，其中有17侧（6．7％）小于0°。各项测量指标左、右侧差异均无统计学意义（P〉0．05）。颈内动脉内侧缘位于侧块外侧有95侧（37．7％），位于侧块前方有157侧（62．3％），其中位于侧块前方区域外1／3有136侧（54．O％），位于侧块前方区域中1／3有21侧（8．3％），未发现有位于侧块前方内1／3及侧块内侧者。结论：颈内动脉位于寰椎侧块的前外侧方，采用5°的内偏钉道有利于避免寰椎双皮质侧块螺钉对颈内动脉的损伤，术前通过颈部三维CT血管成像可以清楚地显示两者的解剖位置关系，为寰椎侧块螺钉的安全植入提供帮助。

Study on anatomic structural relationship between trajectory of C1 lateral mass screw and internal carotid artery by three dimensional CT angiography

Background： Injury to the internal carotid artery （ICA） is a risk from placement of bicortical C1 lateral mass screw. Objective： To study anatomic structural relationships between trajectory of C1 lateral mass screw and ICA by three-dimensional CT angiograph multi-planar reconstruction from the perspective of avoiding ICA injury. Methods： A total of 126 patients without any pathological changes of craniocervical junction were enrolled in this study, in whom CT angiography was performed in head and neck from September 2012 to November 2012. Their axial images were used to reconstruct the images by CT multi-planar reconstruction techniques. The parameters were measured including shortest distance between C1 anterior cortical surface and the ICA, width of massa lateralis atlantis, distance from C1 midsagittal line to medial edge of ICA, distance from the medial edge of the iCA to perpendicular lines drawn in the sagittal plane along the medial border of the foramen transversarium and through C1 lateral mass screw entry point, and the angle made be- tween sagittal axis and trajectory of the ICA medial wall according to the ideal entry point of the C1 lateral mass screw. To analyze anatomic relationships between the ICA and C1 lateral mass, we categorized location of the ICA into 3 areas on the plane for ideal screw trajectory. Results： The mean distance between C1 anterior cortical surface and the ICA was （3.32±1.07）mm, and was less than 2 mm in 35 cases （13.9%）; the minimum was 1.49mm. The mean distance from C1 midsagittal line to medial edge of ICA was （22.99±2.86）mm. The distance from the medial edge of the ICA to perpendicular lines drawn in the sagittal plane along the medial border of the foramen transversarium was （1.08±l,50）mm. The medial edge of the ICA was medial to the foramen transversarium in 182 patients （72.2%）. The mean distance from the medial edge of the ICA to perpendicular lines drawn in the sagittal plane through C1 lateral mass screw entry point was （3.99±1.84）mm. The angle made between sagittal axis and trajectory of the ICA medial wall was （9.90±5.57）°, and was less than 0° in 17 cases （6.7%）; the minimum was -4.6°. There were no significant differences in the above parameters between left and right side （P〉0.05）. The medial edge of the ICA was lateral to the C1 lateral mass in 95 cases （37.7%） and located in front of the lateral mass in 157 cases （62.3%）, with 136 cases （54.0%） in front of the lateral one third of the lateral mass and 21 cases （8.3%） in front of the middle one third of the lateral mass. No medial edge of the/CA faced the medial one third of the lateral mass and was located in front of the spinal canal. Conclusions： The ICA trajectory is anterolateral to C1 lateral mass. The possibility of ICA injury can be excluded by correct insertion of the screw 5° inward. The preoperative three-dimensional CT angiography can clearly show the anatomical structures and improves the security of the operation.