3rd ventricle enlargement

I just had my 20 week ultrasound and the 3rd ventricle was slightly enlarged at 3.8mm. The lateral ventricles, the 4th ventricle and the rest of the brain was normal. There was no hydrocephalus. What does this mean? Im going for a more detailed scan this week. The only info I can find is developmental problems and association with Downs Sydrome and some psychiatric conditions but thats usually in association with enlarged lateral ventricles. I have some medical background and if you have reference to any studies I could read that would be appreciated.
Many thanks for your help.

[Yao Sun, MD, PhD]

There is not much literature on isolated 3rd ventricle enlargement, and I am not an expert in this particular area.  I suggest discussing this more with the perinatologist after your detailed scan.  The risk of underlying genetic conditions or problems with neurodevelopment go up if other anomalies are found.  On the other hand, the overall risk goes down if no other problems are found and the enlargement is stable.