Posterior fossa malformation in fetuses: a report of 56 further cases and a review of the literature.

OBJECTIVE

The purposes of this study were to determine the outcome of fetuses diagnosed as having a posterior fossa abnormality (PFA) and to find out if there are associated features helpful in determining the prognosis.

METHODS

This is a retrospective study of all posterior fossa abnormalities detected prenatally in our Units within the last 10 years. Fifty six patients were selected. Outcome data was collected from the Clinical Genetics Department records and the attending obstetrician or pediatrician.

RESULTS

An enlarged cisterna magna (ECM, diameter greater than 10 mm at 18-23 gw) was detected in 22 fetuses, which was isolated in 14 cases. All the patients followed-up (n = 11) with isolated ECM were normal at birth (100%). Non-isolated ECM was present in 8 cases. Further information was available in 7, 5 (71%) of whom had a poor outcome. A Dandy Walker complex abnormality (DWC) was detected in 34 patients. The majority of them had a poor prognosis, 54% if isolated and 84% if non-isolated.

CONCLUSIONS

Isolated ECM detected on prenatal scans has a favourable outcome, while DWC is associated with a very high chance of a poor prognosis.