Right ventricle of baby's brain measuring 10 mm

Hello - I just had my 20 week ultrasound.  My doctor said everything looked perfect except for one "minor" concern.  The right ventricle in the baby's brain is measuring 10 mm, which is still within the "normal" range, but since it's at the top end of the normal range, my OB wants me to get a level 2 u/s and talk to a high-risk OB.  She said they are just being careful and want to make sure the width of the ventricle does not increase, as anything over 10 mm could be a sign of fluid building up on the brain.  We are trying to remain calm and remind ourselves that our baby's ventricle is still normal, but thinking about what it could be is terrifying.  I should also tell you that we have had genetic testing (for Downs Syndrome and other chromosomal abnormalities) performed already, and everything was normal.  Nothing else out of the ordinary was found on the u/s, either.  Has anyone had a similar experience?  I'd appreciate any advice/thoughts.  Thank you!!
Reported

[Yao Sun, MD, PhD]

As you noted, a measurement of 10 mm by itself is still within normal limits.  Your Obstetrician is giving you good advice in terms of having a level II ultrasound and a referral to a Perinatologist, but these referrals do not mean that your baby will necessarily have any problems.  The fact that your prenatal genetic testing was normal is also reassuring.  

Although it is always difficult not to worry, there is nothing at this point in time to indicate that your baby will not have a normal outcome.  If anything concerning turns up during your further evaluations, your Obstetrician and Perinatologist will discuss that with you and answer any questions you might have.

[AMS04]

I didn't realize doctors answered these questions - my question is:  Is a measurement of 10 mm concerning on it's own?  I'm terrified of things I see online such as hydrocephalus.  Thank you!