What Causes Bilateral Pelvicaliectasis In A Child?

Hello, My 7 year old had an ultrasound yesterday and his urologist said from the ultrasound it looks like he has grade 2 bilateral pelvicaliectasis. She said it is concerning and she wanted to do further testing. She is on vacation for the next week and she is going to schedule another appointment for ultrasound or xray with contrast to see what is causing it. My son had a bonemarrow transplant about a year back and he has been exposed to large amounts of chemotherapy and radiation. Is it wise to wait another couple of weeks , what could be the cause ? what is the prognosis ? Can we wait another couple of weeks till she comes back or call someone else and get things moving ? Thanks, Mini