胸椎椎弓根置钉安全区与禁区的影像学研究

A CT and MRI-based location of projection of thoracic pedicle medial wall,dural sac and spinal cord on lamina

目的采用CT和MRI技术对胸椎椎弓根内侧壁、硬膜囊和脊髓在椎板上投影区与椎板解剖标志点相对位置研究,确定椎弓根钉置入安全区和禁区。方法收集自2009-06—2012-07的56例青少年特发性脊柱侧凸(AIS)和54例正常青少年胸椎CT资料,以及31例AIS和30例正常青少年胸椎MRI资料。CT测量椎弓根最狭窄处内侧壁在椎板上的投影点与"原点"的距离(DPO)。MRI测量双侧椎弓根最狭窄处对应的硬膜外间隙(EDS)、硬膜下间隙(SDS)、脊髓外间隙(SES),并对AIS患者顶椎区各间隙凹凸侧进行分组对比。结果 AIS患者与正常人椎体CT轴切面上椎弓根最狭窄处内侧壁投影点与"原点"位置基本重合,二者T_(1~12)椎体DPO差异均无统计学意义(P<0.05)。正常人硬膜囊在椎板上投影区(椎弓根钉置入相对禁区)为双侧椎板上原点向内1.43~1.98 mm的区域,脊髓在椎板上的投影区(椎弓根钉置入绝对禁区)为双侧椎板上原点向内4.64~6.35 mm的区域。AIS患者顶椎区硬膜囊略向侧弯凹侧移位,但两侧EDS差异无统计学意义(P>0.05);顶椎区凹侧SDS、SES明显小于凸侧,差异有统计学意义(P<0.05)。结论胸椎椎弓根内侧壁在椎板上投影点与椎板标志点位置重合,结合MRI对硬膜囊和脊髓在椎板投影位置的确定,可帮助临床医师在置入椎弓根钉时更好地判断椎弓根、硬膜囊和脊髓的位置,确定椎板上的置钉禁区,避免螺钉置入椎管造成硬膜囊或脊髓损伤。

Objective To locate the projections of the medial wall of the thoracic pedicle, dural sac and spinal cord on the lamina, and identify a ＂forbidden zone＂ of pedicle screw placement. Methods CT images of 56 AIS（Adolescent idiopathic scoliosis） and 54 normal adolescent, 61 MRI images of 31 AIS and 30 normal adolescent from June 2009 to July 2012 were collected. The most concave point at the junction of the transverse process and the upper edge of the lamina was used as landmark. The projection point of the transverse medial pedicle wall and the landmark on the lamina were measured using CT.The distances between the transverse medial pedicle wall and the dural sac and spinal cord were measured using MRI.Distances between the projections of the dural sac and spinal cord on the lamina and landmark were studied. Comparisons were made between normal patients and AIS. Results The projection of the medial pedicle wall on the lamina was coincident with the landmark. The projection of the dural sac on the lamina（relative forbidden zone） was an area of 1.43-1.98 mm medial to the landmark respectively in the lamina. The projection of the spinal cord on the lamina（the forbidden zone） was an area of 4.64-6.35 mm medial to the landmark in the lamina. SDS and SES was smaller in the concavity in apical region(P〈 0.05）, EDS showed no difference between concavity and convexity, while spinal cord shifted toward the concavity of the scoliosis in the apical vertebral region of AIS patients. Conclusion The measurements may help surgeons determine the locations of the pedicle, dural sac and spinal cord accurately and identify the forbidden zone on the lamina during the pedicle screw placement to avoid neurological injuries.