胎儿脊髓圆锥位置的超声定量指标研究

Ultrasonography quantitative indicator for position of fetal conus medullaris

目的探讨脊髓圆锥末端至骶骨末端距离的正常值及临床应用价值。方法2013年6月1日至2014年9月30日，在福建医科大学附属第二医院就诊的孕妇中，纳入超声孕龄与实际孕龄相符、排除胎儿畸形、分娩后随访新生儿无异常的单胎妊娠孕妇550例。产前超声测量胎儿双顶径、股骨长、头围、腹围，并测量脊髓圆锥末端至骶骨末端距离。根据孕周分组，计算各孕周的平均值。抽取50例孕妇进行质量控制，比较甲、乙2名医师测量结果的-致性，以及甲医师间隔半小时对同-例孕妇测量结果的-致性。计算胎儿脊髓圆锥末端至骶骨末端距离与孕周、双顶径、股骨长、头围、腹围的回归方程。采用组内相关系数（intraclasscorrelationcoefficient，ICC）和Bland-Altman分析图分析重复性。结果550例胎儿中，518例（94．2％）成功测量到脊髓圆锥末端至骶骨末端距离。随孕周增加，胎儿脊髓圆锥末端至骶骨末端的距离逐渐增加，妊娠〉14～≤15周（n=17）为（10．0±3．3）mm，妊娠〉20～≤21周（n=18）为（27．7±3．8）mm，妊娠〉26～≤27周（n=8）为（41．5±2．4）mm，妊娠〉32～≤33周（，z=17）为（54．7±3．0）mm，妊娠〉41～≤42周（n=6）为（71．9±2．7）mm。胎儿脊髓圆锥末端至骶骨末端距离（mm）的回归方程分别为：股骨长（mm）×1．04-8．71、腹围（mm）X0．23—10．11、头围（mm）×0．28-18．10、双顶径（mm）X0．90-17．65、孕周（周）×2．34-20．94（相关系数分别为0．990、0．985、0．978、0．974和0．973，P值均〈0．01）。甲、乙医师测量数据的ICC和甲医师测量2组数据的ICC分别为0．984（95％CI：0．972~0．991）和0．992（95％CI：0．985-0．995），95％-致性界限分别为：-1．8-3．5mm和-4．3～2．1mm。Bland—Altman分析图可见大部分测量值位于95％-致性界限内，提示-致性较好。结论超声测量的胎儿脊髓圆锥末端至骶骨末端距离与股骨长等因素呈正相关，可作为评估脊髓圆锥末端位置的定量指标。

Objective To determine the normal position of the fetal conus medullaris and assess its clinical significance. Methods A total of 550 singleton pregnant women who were examined by fetal ultrasonography in the Department of Ultrasound at the Second Hospital of Fujian Medical University from June 1, 2013 to September 31, 2014 were included. Inclusion criteria were pregnancies with regular menstruation cycle and known last menstrual period, gestational age （GA） confirmed by ultrasonographic examinations, and neonate abnormality excluded by pediatrician after born. Routine obstetric ultrasound examinations were performed to measure the biparietal diameter （BPD）, femur length （FL）, head circumference （HC） and abdominal circumference （AC）. The conus distance （CD） was determined by measuring the distance between the distal end of the conus medullaris and the caudal end of the last vertebra. The average value was calculated for each group according to GA. Fifty normal fetuses were randomly selected for quality control. For inter-observerreliability assessment, the same data were collected and analyzed by two different operators. For intra-observer reliability assessment, the data were collected and analyzed twice by the same operator with an interval of half an hour. Linear regression correlation analysis was performed to analyze the relationship between CD and GA, BPD, FL, HC and AC. Intraclass correlation coefficient （ICC） and Bland-Altman analysis were used to analyze the repeatability of the analysis. Results In 518 （94.2%） of 550 fetuses, the CD was successfully measured. Positively correlations between the conus distance and the gestational age was observed. The CD was （10.0_ 3.3） mm at 〉 14- ≤ 15 weeks （n=17）, （27.7±3.8） mm at 〉 20- ≤ 21 weeks of gestation （n=18）, （41.5±2.4） mm at 〉 26- ≤ 27 weeks （n=8）, （54.7±3.0） mm at 〉 32- ≤ 33 weeks （n=17）, and （71.9±2.7） mm at 〉 41- ≤ 42 weeks （n=6）. Linear regression correlations between CD （mm） and FL, AC, HC, BPD and GA were： CD=1.04× FL （mm） - 8.71, CD=0.23× AC （mm） - 10.11, CD=0.28× HC （mm） - 18.10, CD=0.90× BPD （mm） - 17.65, CD=2.34× GA （weeks） - 20.94 （r=0.990, 0.985, 0.978, 0.974 and 0.973, respectively, all P 〈 0.01）. The measurement of the conus distance exhibited good reproducibility between different operators （ICC=0.984, 95%CI; 0.972-0.991） and for the same operator （ICC= 0.992, 95%CI： 0.985-0.995） with the 95% limits of agreement of - 1.8 to 3.5 mm and - 4.3 to 2.1 mm. Bland-Altman analysis showed that most of the measured values were within 95% confidence interval suggesting good consistency. Conclusions The distance, between the end of the conus medullaris and the end of the last vertebral body under ultrasound scan, is positively correlated with FL and other ultrasonographic indicators, which implies that it could be used as a new index for position of fetal conus medullaris.