First-trimester cystic posterior fossa: reference ranges, associated findings, and pregnancy outcomes

AbstractObjective: To report reference ranges for fetal cerebral posterior fossa measurements and to describe the sonographic findings, karyotype results, and pregnancy outcomes in fetuses presenting with cystic posterior fossa (CPF) in the first trimester of pregnancy.Methods: Two groups of patients undergoing first-trimester sonographic screening at 11–13 weeks’ gestation were studied. The first (control group) consisted of 253 consecutive fetuses with normal posterior fossa, in which the brainstem (BS), fourth ventricle, cisterna magna, and BS-occipital bone (BS−OB) diameter were prospectively measured and the BS/BS−OB diameter ratio was calculated. The second (study group) consisted of 14 fetuses in which a CPF was detected. Information on sonographic findings, prenatal karyotype results, and pregnancy outcomes was obtained by reviewing ultrasound reports and medical records. The results from the two groups were then compared.Results: In the control group, the size of all posterior fossa structures in...