My daughter just had a renal ultrasound as a remedial due to surgery she had on her kidney as a baby. She had a clean bill of health at 11 months and has not needed any follow-up since then. The ultrasound showed hydronephrosis on her right kidney even though she has ZERO symptoms. The doctor reading her scans casually mentioned that it is most likely caused by scarring from the previous surgery. Other than saying he would have to report the hydronephrosis, the doctor didn't seem concerned...
Current hydronephrosis
Current hydronephrosis