Dandy-Walker syndrome and monochorionic twins: Insight into a possible etiological mechanism

Objective. Dandy-Walker syndrome (DWS) is a developmental malformation of the central nervous system characterized by complete or partial absence of the cerebellar vermis, the presence of a posterior fossa cyst, and ventriculomegaly. Although DWS can be seen with Mendelian and chromosomal disorders, the actual pathophysiologic mechanism responsible for the syndrome is unknown. The incidence of DWS is approximately 1-8/100 000 births. We have noted a higher than expected incidence of DWS in a population of twins referred as complicated monochorionic twins, to include twin-twin transfusion syndrome (TTTS). The purpose of this study was to assess the incidence of DWS in monochorionic twins. Methods. The database of all patients referred with complicated monochorionic twins was queried for the diagnosis of DWS. TTTS was defined sonographically as the combined presence of a maximum vertical pocket (MVP) of ≥8 cm in the recipient and ≤2 cm in the donor twin. Intrauterine growth restriction (IUGR) was defined as ≤10th percentile for gestational age. DWS was diagnosed sonographically as partial or total absence of the cerebellar vermis, the presence of a posterior fossa cyst, and ventriculomegaly. Risk factors for DWS included fetal status (donor/small twin, recipient/large twin), TTTS stage, absent end-diastolic velocity in the umbilical artery (AEDV), and IUGR. Results. The data on 660 patients with monochorionic twin pregnancies were reviewed. DWS was seen in 10 (1.5%) patients (four TTTS, five IUGR, and one monoamniotic twin). The affected fetus was the smaller twin (donor or IUGR) in 8/10 cases (80%, p=0.055, RR 1.64 (1.17-2.19)). DWS fetuses were more likely to be growth-restricted (7/10, 70% vs. 217/650, 33.4%, p=0.03) than the non-DWS counterparts. Conclusion. The incidence of DWS in complicated monochorionic twins is approximately 200 times higher than expected for singletons (p<0.001). DWS is more likely to occur in the smaller twin of a twin pair and more likely to have growth restriction. These findings may assist in our understanding of the pathophysiologic mechanisms responsible for the development of DWS. © 2008 Informa Healthcare USA, Inc.