Expanding Porencephalic Cysts: Prenatal Imaging and Differential Diagnosis

Objectives: The aim of this study was to report the prenatal imaging findings of expanding porencephalic cyst, which have not been previously described in the prenatal period, and to underline that these lesions can involve the cerebellum and not exclusively the supratentorial structures. Materials and Methods: This is a retrospective observational study of five cases with a prenatal diagnosis of expanding porencephalic cyst. Results: The cystic lesion was located in the supra- and infratentorial space in 2 cases, respectively, or in both in one case. The lesion expanded into the pericerebral space or communicated with the ventricular system in 4 and 1 cases, respectively. Differential diagnosis included tumoural lesion in 2 cases because of internal echogenic components related to haemorrhagic changes, which were identified using foetal MRI, and arachnoid cyst in 2 cases because of expansion into the pericerebral space. In the last case, communication within the ventricular system mimicked a unilateral ventriculomegaly. Conclusion: Differential diagnosis of any cystic lesion with extra-axial component should include expanding porencephalic cyst. Foetal MRI is helpful to differentiate this entity from extra-axial lesions such as arachnoid cysts but also from rare tumours.