Worried from today's 4D ultrasound?

Hello everyone, today I got my 4D ultrasound, I'm aprox 17.4 weeks and we found out we're having a boy :) Anyway, what got us a bit worried is we saw a little bump on the fetus's belly (it wasn't the umbilical chord, it was around where the liver is) and I'm just wondering if this is normal to see since maybe it could be a shadow, etc. The Ultrasound specialist wrote some info down and that it should be observed in the coming weeks... that wasn't very reuring...I'm gonna talk to my OB about this, but I was just wondering if anybody had a 4D ultrasound at around this time and saw something similar and turned out to be nothing, thanks.