The cisterna magna size in normal second-trimester fetuses

Objective: The purpose of this study was to evaluate cisterna magna size of the fetuses between 16 and 24 weeks of gestation, and to establish a normogram for cisterna magna measurements during gestation. Methods: A prospective study of normal singleton pregnancies was established. Measurement of the fetal cisterna magna was performed by transabdominal ultrasonography between 16 and 24 weeks of gestation in 194 fetuses. Results: A linear correlation was obtained between gestational age (GA) and cisterna magna (R-2 =0.75, P < 0.0001). A linear correlation was also found between biparietal diameter and cisterna magna (R-2 =0.74, P < 0.0001). The normal mean ( +/- SD) for each gestational week was defined. Conclusion: The present data offer the normal range of the cisterna magna. Cisterna magna measurement may provide normative data for fetal growth and development. Abnormal measurement of cisterna magna may be a clue for posterior fossa pathologies or a chromosomal disorder.