Dandy-Walker malformation at 21+2 weeks of gestation

(A) Median section of the fetal brain showing a large cisterna magna with a small and rotated vermis and elevated tentorium and torcular.
(B) The brainstem-vermis angle is measured by drawing a line tangentially to the dorsal aspect of the brainstem and a second line drawn tangentially to the ventral contour of the vermis.