The worst outcome of a widened fetal posterior cranial fossa is fetal hydrocephalus or combined chromosomal abnormalities. During prenatal ultrasound, the width of the posterior cranial fossa pool is observed, which ranges from 2 to 10 mm. In mid- to late-term pregnancies, the fetal posterior cranial fossa pool needs to be followed closely if it is measured to be greater than or equal to 10 mm. If the width of the posterior cranial fossa increases with the number of weeks of gestation, the incidence of fetal anomalies increases when it is greater than 15 mm, and amniocentesis, cordocentesis or chromosomal examination is needed to observe the fetus for chromosomal abnormalities. MRI is also needed to observe the abnormalities of the cerebellar structure of the fetus. If the cerebellar structure is abnormal or combined with chromosomal abnormalities, the pregnancy needs to be terminated by induction of labor, while simple widening of the posterior cranial fossa can continue to be observed. The causes of the widening of the posterior cranial fossa may include maternal diabetes, hypertension, infectious diseases, fetal chromosomal abnormalities, infections, metabolic diseases, etc.