Sonographic measurement of the size of fetal cisterna magna in low risk population of pregnant women at 16-38 weeks of gestation

Abstract

Introduction: The purpose of this study was to determine the normal size values of fetal cistern magna (CM) and to evaluate its changes in normal fetuses in low risk population of pregnant women in the second and third trimesters of pregnancy using transabdominal ultrasonography.

Methods: This was a prospective cross-sectional study involving 290 women with uncomplicated singleton gestation between 16-38 weeks. CM was visualized in 264 cases. Gestational age was calculated by measuring fetal biparietal diameter (BPD). CM was measured from the posterior aspect of the cerebellar vermis to the inner edge of occipital bone. Nomogram of the sizes of CM was prepared.

Results: CM was visualized in 91% of the fetuses. The ages of the patients ranged from 17-30 years (mean 24.29, SD 2.78). The maximum numbers of case were at 23 and 27 weeks of gestation and the minimum number of cases were at 37 weeks of gestation. The mean size of the CM was 6.32mm (SD1.09; range 3- 9 mm).

Conclusion: The size of fetal CM showed continuous increment and showed significant positive correlation with the gestational age ( r2 value of 0.48; p<0.001). The findings were consistent with the previous studies done by various authors. The percentile fitted values and nomograms will be valuable for the serial measurement of the CM for complicated pregnancies.