This can be due to a kidney infection, or an anatomical variant.
I agree with the antibiotic treatment. Repeating the ultrasound after the treatment course can be considered to see if the dilation resolves.
If there continues to be blood in the urine after antibiotics, a cystoscopy can be done to evaluate the bladder for any signs of cancer.
These options can be discussed with your urologist.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_