Radiological characteristics of the posterior fossa of the fetal skull and presentation of a rare case of antenatal screening for Dandy-Walker malformation using antenatal fetal ultrasound and MRI.

Dandy-Walker malformation is a rare congenital anomaly of the brain that mainly affects the cerebellum region. It is characterised by abnormal dilatation of the fourth ventricle of the brain and partial or total absence of the cerebellar vermis. This malformation may also be accompanied by other anomalies of the brain. Ante-natal diagnosis is becoming increasingly frequent given the performance of medical imaging, in particular ante-natal ultrasound and MRI. The object of this article is to clarify the possible causes of rare cystic malformations of the posterior cerebral fossa, which are very rare congenital malformations.

Methods: a 30 year old patient, second gesture, mother of a live child by caesarean section, referred to us at 32 weeks of amenorrhoea at the university hospital centre for management of a cystic malformation of the posterior cerebral malformation detected on 2nd trimester ultrasound and confirmed as a Dandy Walker malformation on 3rd trimester fetal MRI. The Dandy-Walker malformation can be described on prenatal MRI as vermian hypoplasia and can be detected as early as the 1st trimester of pregnancy using ultrasound, This cystic malformation poses a problem of differential diagnosis with other pathologies which also result in a cystic image of the posterior cerebral fossa, in particular Black's pouch cyst, arachnoid cyst and mega magna cistern, which requires careful interpretation of cerebral MRI of the foetus.

Conclusions: Imaging techniques play a fundamental role in diagnosis. Prenatal ultrasound and MRI can reveal a Dandy-Walker malformation as early as the 2nd month of pregnancy. MRI is ideal for differentiating differential diagnoses.