Blake pouch cyst and its differential diagnoses in pre- and postnatal MR imaging: a pictorial review

Kurzzusammenfassung PURPOSE: The clinical variability of Blake pouch cyst (BPC) may range from asymptomatic via ataxia to sequelae of decompensated hydrocephalus. On the other hand, Dandy Walker malformation (DWM) and cerebellar vermis hypoplasia generally correlate with less favorable neurologic development. We aim to illustrate the potential of pre- and postnatal neuroimaging to distinguish a BPC or persistent BP, respectively, from other posterior fossa malformations (PFM). METHODS: This pictorial review addresses the inconsistent nomenclature, clinical features, and magnetic resonance imaging (MRI) patterns of BPC and five differential diagnoses. The MRI findings of eleven patients, acquired at up to 3 Tesla in three institutions, are demonstrated. Further, the literature has been searched for recent increase in genetic and embryological background knowledge. RESULTS: Posterior fossa malformations often resemble each other and may even be imitated by sequelae of hemorrhagic, ischemic, or infectious disruptions. Hydrocephalus is a typical, albeit not always congenital finding in BPC. It is frequently associated with cerebellar disruptions and DWM, however, a rare complication of posterior fossa arachnoid cysts. A moderately elevated vermis needs follow-up to confirm persistent BP versus vermian hypoplasia or DWM. The fetal „cerebellar tail“ –previously supposed to be specific for DWM– may be imitated in cases of persistent BP. CONCLUSION: The accurate diagnosis of isolated BPC is not always straightforward, which is especially critical in the context of fetomaternal medicine. A detailed description of posterior fossa malformations is to be preferred over unspecific terminology.

Lernziele We aim to illustrate the potential of pre- and postnatal neuroimaging to distinguish a BPC or persistent BP from other PFM. Narrowing the differential diagnoses in an early stage could help determine the clinical proceedings as the eligible diagnoses differ in their impact on developmental outcomes.