prominent fetal cisterna magna or more ominous?

This was a 34 week old fetus. No other positive findings were noted.

 

the answer: mega cisterna magna in third trimester fetus. The points favouring this diagnosis:

widened cisterna magna, but normal cerebellar vermis and fourth and lateral ventricles.

For more on this visit:

http://www.ultrasound-images.com/fetal-brain.htm#mega-cisterna-magna