Position of the choroid plexus of the fourth ventricle in first‐ and second‐trimester fetuses: a novel approach to early diagnosis of cystic posterior fossa anomalies

Abstract

The aim of this study was to describe the sonographic appearance and position of the choroid plexus of the fourth ventricle (4thVCP) between 12 and 21 weeks' gestation in normal fetuses and in fetuses with posterior fossa anomalies. Two-dimensional ultrasound (US) images of the midsagittal and coronal views of the brain through the posterior fontanelle and three-dimensional volumes datasets were obtained between 12 and 21 weeks prospectively from 90 normal singletons and retrospectively from 41 fetuses identified as having an abnormal posterior brain on first-trimester ultrasound examination. In all cases the diagnosis was confirmed at MRI, prenatally and/or postnatally, and/or at postmortem examination. During the study period, 41 fetuses, with apparently isolated cystic posterior fossa anomaly based on first trimester ultrasound assessment of intracranial spaces, were reviewed in the second trimester and were found to have Dandy Walker Malformation (DWM) in 8 cases, Blake's Pouch Cyst (BPC) in 29 and they were normal in 4 patients. The position of 4thVCP was different in DWM, BPC and normal cases either at first and at second trimester examination. In particular, in normal fetuses no cyst was present, and on median and coronal planes of posterior fossa the choroid plexus appeared as an echogenic and oval shaped structure located inside the 4th ventricle apparently attached to the cerebellar vermis. In fetuses with DWM, on median view of posterior fossa, it was not possible to visualize the CP. It was infero-laterally dislocated due to the presence of a cyst which displaced the 4thVCP and could be visualized only on a coronal plane of the posterior brain. In all DWM cases the CP was positioned outside the cyst. In BPC, the 4VthCP was always located inside the cyst, on its superior part, near the vermis and was visualized on median and coronal planes. Our study demonstrated that a longitudinal ultrasound assessment of 4thVCP and its temporal changes from 12 to 21 weeks is feasible. The ability to define the position of the 4thVCP as inside or outside the cyst is a novel finding which can be assessed in the first trimester of pregnancy and it is useful to differentiate DWM from BPC, consistently with the pathophysiology of the two conditions. This article is protected by copyright. All rights reserved.