Fetal Cavum Septum Pellucidum–Tentorium Angle Measured with Three-Dimensional Ultrasonography and Its Clinical Value

Abstract

To establish the ranges of normal reference values of fetal cavum septum pellucidum- tentorium angle(CTA) in normal fetuses at different gestational weeks, and evaluate their clinical values in the diagnosis of mega cisterna magna and Dandy-Walker malformation. Totally 350 normal singleton fetuses between 21 and 32 weeks of gestation during September 2016 to December 2016 were enrolled in this study. Their average weeks of gestation was 26.0±3.2. Fourteen fetuses with mega cisterna magna contemporarily and twelve fetuses with Dandy-Walker malformation previously were control group A and B respectively, their average weeks of gestation were 27.6±3.1 and 28.5±2.9. Three-dimensional ultrasound (3D US) with volume contrast imaging (VCI) of GE Voluson Expert E8 was used to measure their CTA. CTA is an angle of two single line, one is a line joined from the front edge and the posterior border of the cavum septum pellucidum, the other is a tangent line of the tentorium. The correlations of CTA with gestational age were analyzed by Pearson correlation. The consistency and repeatability was investigated by Bland-Altman plot analysis and intraclass correlation coefficient. CTA of 14 fetuses with mega cisterna magna and 12 fetuses with Dandy-Walker malformation were compared with those of the normal fetuses by t-test. There were significant differences if P< 0.05. In these normal fetuses, CTA showed no correlations with gestational age (r =0.014, P＞0.05).CTA of 14 fetuses with mega cisterna magna were not significantly different from those of normal fetuses (56.66±4.18°vs 55.82±5.32°,t=0.56,P＞0.05), while CTA of 12 fetuses with Dandy-Walker malformation were significantly smaller than those of normal fetuses and the fetuses with mega cisterna magna (32.76±6.23°vs 55.82±5.32°,t=25.12,P＜0.05;32.76±6.23°vs 56.66±4.18°,t=26.04,P＜0.05). The repeatability of the same physician and the consistency between two different physicians were good, their intraclass correlation coefficient and 95% confidential interval were 0.95 (0.88-0.97) and 0.88 (0.76-0.94) respectively. 3D US with VCI is feasible for measuring CTA of fetuses and the measured values can be used as the reference standards for CTA measurement. The ranges of normal reference values of fetal CTA is 43.79°～68.88°(55.82±5.32°). The measuring of CTA can help differentiate mega cisterna magna from Dandy-Walker malformation.