Dandy Walker variant with agenesis of corpus callosum diagnosed late prenatally by foetal ultrasound: a case report.

Introduction and importance: Dandy Walker variant is an intracranial disorder involving variable hypoplasia of cerebellar vermis without posterior fossa enlargement. An anomaly scan performed at mid second trimester has good sensitivity and specificity for detecting foetal congenital anomalies. Despite that, some cases like the authors' might go undiagnosed due to normal biometric parameters for that gestational age and may be detected later in intrauterine life. Case presentation: A primi-gravid mother underwent sonographic evaluation at 20+4 weeks of gestation that revealed all foetal parameters within normal limits. Only at 31+2 weeks of gestation, a posterior fossa cyst communicating with forth ventricle was detected. Foetal MRI done at 8 days of life (DOL), confirmed these findings and diagnosis of Dandy Walker variant with agenesis of corpus callosum was made. Clinical discussion: Although the chances of a CNS anomaly is exceedingly low when foetal metrics like head circumference, atrial width and Cisterna Magna are within normal limits, some cases like the authors' may develop anomalies later in the intrauterine life which may lead to delayed diagnosis of the cases. Thorough performance of anomaly scan involving a multiplanar approach may help in prompt diagnosis of foetal anomalies. Conclusion: The risks of development of posterior fossa anomalies can exist even after second trimester scan, Clinicians should be aware of this possibility and assess the posterior fossa at repeat scans done later in intrauterine life. Early diagnosis can provide an option to couples of the termination of pregnancy which is complicated when detected later in the intrauterine life.