Objective: To discuss the clinical significance of accumulated fluid in fetal posterior fossa.
Methods: Prenatal ultrasonography examination was performed on 5 400 woman at more than 20 weeks gestation, 110 women with fetus accumulated fluid in the posterior fossa more than 5mm were included in this study. The changes of accumulated fluid in fetal posterior fossa and the associated intracranial and extracranial anomalies were observed regularly every 2 or 3 weeks until delivery. The infants were also followed up.
Results: The incidence of the fetal posterior fossa fluid was 2.0%. Generally, the accumulated fluid in fetal posterior fossa was diagnosed at first time at 22 approximately 41 gestation weeks, median was (31 +/- 4) weeks. Most of them were be found between 29 approximately 32 weeks (42 cases, 38.2%), and the maximum amount of accumulated fluid in fetal posterior fossa was also in 29 approximately 32 gestation weeks (39 cases, 35.5%). The amount of accumulated fluid was from 6 mm to 26 mm, mean (11 +/- 3) mm, mostly between 10 approximately 14 mm (79 cases, 71.8%). The incidence of defected infants was 4.0%, 7.6% and 83.3% respectively, when the posterior fossa fluid was less than 10 mm, 10 approximately 14 mm and more than 15 mm.
Conclusion: Most of cases could be diagnosed between 29 approximately 32 weeks gestation. The more fluid in the posterior fossa found, the more defected fetal or infant would be observed. In cases of more than 10 mm, especially more than 15 mm, anomales should be observed carefully.