2-D, 3-D Ultrasonography And MRI For Fetal Tethered Cord Examination

Objective: To compare and analyze the accuracy of 2-D ultrasonography(2D US), 3-D ultrasonography(3D US) and magnetic resonance imaging(MRI) in fetal tethered cord examination, and evaluate the diagnostic value of three methods for tethered cord.Methods: A total of 346 normal fetuses were selected as the normal group, and 11 fetuses with tethered cord were selected as the tethered cord group. All the fetuses with tethered cord were finally confirmed by postnatal autopsy or MRI. The conus distance(CD) of fetuses in normal group and tethered cord group was measured in using 2D US and 3D US, respectively, to establish the normal range of CD in fetuses at different gestational weeks, establish the linear regression equation between CD and gestational weeks, and compare the measurement results in normal group and tethered cord group. Forty cases were randomly selected in the normal group were received MRI and CD measurement. Intraclass correlation coefficient(ICC) was used to test the repeatability of three methods in the same doctor/different doctors. Bland-Altman method was used to test the consistency of three methods in their measurement results. For all the CD values normal group and tethered cord group, Mann-Whitney U test was performed after Z-score conversion, and paired t test was performed for the measurement results of 2D US and MRI in tethered cord group. The measurement results of three methods in tethered cord group were compared and analyzed.Results: 1. The display rate of conus medullaris in 2D US was 96.20% and in 3D US was 95.42%(P>0.05). 2. In 2D and 3D US, the CD values of normal fetuses increased with gestational weeks, and the regression equations were as follows: 2D US: CD(cm) =-0.894 + 0.198 ×gestational weeks, R2=0.922; 3D US:-0.760 + 0.197 ×gestational weeks, R2=0.936; P all<0.05. 3.ALL the CD values of fetuses in tethered cord group were all smaller than in normal group, Z-score of normal group:(0.005±0.973), Z-score of tethered cord group:(-1.532±0.104) (P<0.05). 4. The 2D/3D US and MRI performed by the same doctor/different doctors had good repeatability in the measurement of CD value(0.969-0.987); and the data obtained by the same doctor had the best repeatability(0.982-0.990). 5. Bland-Altman test showed that the measurement results of 2D US and MRI had good consistency, P all<0.05. The measurement results of 2D US and 3D US had good consistency, P all<0.05. 6.The CD values of fetuses in tethered cord group measured by 2D US and MRI were 2.014±0.210 and 2.106±0.154, respectively, t=-1.504, P=0.163.Conclusion: 1. The 2D US, 3D US and MRI were feasible in CD measurement. 2. The CD value increases with gestational weeks; 2D US and 3D US have no difference in the measurement result of CD value. 3. The diagnostic accuracy for tethered cord of 2D US and 3D US have comparable to MRI. 4. The 3D US is superior to 2D US in the diagnosis of tethered cord.