PurposeTo obtain three-dimensional ultrasonic (3D US) structural details and biometrics of the fetal cerebellar vermis and evaluate the value of developmental and malformation identification.MethodsThe 3D US minute structure of the fetal cerebellar vermis in mid-sagittal view was detected in normal fetuses (n=438; 16-41weeks). Biometric sizes were measured to establish the stage-specific norms and reproducibility analysis. Additionally, 28 fetuses with suspected abnormal posterior fossa contents were assessed to analyze the clinical value.ResultsThe minute structure of normal fetuses, including cerebellar vermis contours and the fastigial recess of the fourth ventricle, were visible around Week 19. The main lobules and fissures were apparent around Week 22, and all nine lobules, fissures, and the fourth ventricle were clearly displayed by Week 28. Cerebellar vermis biometric sizes (anterior-posterior length, cranio-caudal length, circumference, and surface area (SA)) grew in a linear fashion with high reliability, especially SA measurements (for intraclass, ICC 0.989, 95% CI (0.980-0.994); for interclass, ICC 0.992, 95% CI (0.984-0.996)). On the middle sagittal section of 3D US, the SA reduced at least 50% in the Dandy-Walker group with no recognizable cerebellar vermis structures showing. The SA in vermian hypoplasia malformation reduced during (x) over bar -2SD to 50% with the primary/secondary fissures absent or partly absent and arborization of the lobules reduced. That would be an important diagnosis and antidiastole clue. Combined with minute structural observation, sonographic diagnoses were accurate in 88% of cases.ConclusionMinute structures obtained by 3D US were clinically useful in the evaluation of cerebellar vermis development and cerebellar vermis malformations.