Relative prevalence and outcome of fetal posterior fossa abnormality

Aim To find out the relative incidence and outcome of posterior fossa abnormality (PFA) in terms of survival at birth until 2 years of age. Methods We conducted a prospective study; all fetuses diagnosed with posterior fossa abnormality were followed-up. The outcome was observed with respect to survival, the presence of associated anomalies, the existence of developmental delay after a telephonic interview. Results Out of 2703 children with congenital anomalies, 921 (34.1%) had a central nervous system defect; 76 cases of PFA were fully followed. Dandy-Walker malformation (DWM) was present in 50% (38/76), mega cisterna magna 18.4% (14/76), Blake pouch cyst 13.2% (10/76), vermian hypoplasia (VH) 13.2% (10/76) and arachnoid cyst 5.2% (4/76). The diagnosis was possible before 20 weeks in only 12 (15.8%) cases. The mean gestational age at delivery was 34.7 +/- 6.7 weeks. Associated anomalies were seen in 35/76 (46.1%) cases. A total of 35/76 (46.1%) survived after 2 years; there was developmental delay in 9.2% of cases. Conclusion There is a large variation in the outcome of PFA depending upon the type of anomaly. Associated anomalies are common in VH and DWM, making their prognosis worse.