Introduction: Prenatal investigations make it possible to follow up malformative intracranial cysts from their detection in utero through the postnatal period. By including those that will remain silent postnatally, precious information can be provided about their real natural history.
Diagnosis: Contrary to common belief, the vast majority of these lesions, if not associated with other fetal anomalies, are benign in nature, remain clinically silent, do not evolve or even frequently regress spontaneously. They are compatible with a strictly normal life, whether requiring postnatal treatment or not.
Treatment: Surgery is rarely needed for the treatment of an evolving hydrocephalus or an expanding cyst.
Prognosis: Clinical outcome is not correlated with cyst volume or location. Prognosis, therefore, does not rely upon brain deformation or translation but rather more upon brain integrity. To establish a correct prognosis all efforts must therefore aim to precisely analyze the brain anatomy. In this respect, fetal MRI is mandatory. Although chromosomal anomalies are rarely associated with isolated intracranial cysts, karyotype study is necessary.
Conclusion: The accuracy of diagnosis and prognosis depends mainly upon our ability to correctly interpret images, which in turn depends on the resolution of prenatal imaging and on experience. Median retrocerebellar fluid collections remain the most difficult to prognosticate, retrocerebellar cysts often being difficult to differentiate from mega cisterna magna and Dandy-Walker complex. In our hands, prenatal prognostication was correct in approximately 90% of the cases.