Hindbrain morphometry and choroid plexus position in the differential diagnosis of posterior fossa cystic malformations.

OBJECTIVE: To assess the differential diagnostic significance of a series of quantitative and qualitative variables of the cerebellar vermis in 67 cases of posterior fossa cystic malformations including Dandy-Walker Malformation (DWM), Vermian Hypoplasia (VH), and Blake's Pouch Cyst (BPC), with particular attention at the differential diagnosis of the last two entities.

METHODS: This is a retrospective study including all cases of DWM, VH and BPC diagnosed in the period 2005-2017, with good quality three-dimensional volume datasets of the posterior fossa acquired transvaginally, through the posterior fontanelle. The midìsagittal view of the posterior fossa was the reference view for the study. The following variables were assessed: brainstem-tentorium angle (BTA), brainstem-vermis angle (BVA), cranio-caudal and antero-posterior diameters and area of the vermis. The last 3 parameters were normalised by BPD, to take advancing gestational age into account (CCVD/BPD*100, APVD/BPD*100, VA/BPD*100). Finally, the position of the 4th ventricular choroid plexus (4VCP) was defined as normal ("UP") or abnormal ("DOWN"), in relation to its position in relation to the 4th ventricle roof/cyst inlet).

RESULTS: Sixty-seven cases of posterior fossa malformations were analysed (DWM 24 cases, VH, 13 cases, BPC, 30 cases). Mean gestational age at acquisition was 23.6 completed weeks. All variables were significantly different in the three categories, but the best Area Under the Curve was shown by the VA/BPD ratio, both on the whole series and in cases < 23 gestational weeks (p < 0.05 and p < 0.001, respectively). As for the 4VCP position, it was DOWN in all cases of DWM and VH, while it was UP in all cases of BPC.

CONCLUSIONS: Our data seem to support the concept that, to differentiate between DWM, VH and BPC in the fetus, the VA/BPD ratio and the 4VCP position should be used. The latter has shown in our series the highest accuracy, but we feel that a larger number of VH cases should be evaluated to state without doubts that an UP position of the 4VCP identifies BPC while a DOWN position is univocally found in DWM or VH. This article is protected by copyright. All rights reserved.