<s>[INST] My son had a ultrasound of the renal tract and the findings where: "Bilateral kidneys are of normal size and echotecture. There is mild fullness of the left pelvicalyceal system noted. This is interittent and therefore may be due to reflux." What does this mean? [/INST] hai,As your son ultrasound indicates some collection of fluid (urine) in the  left kidney (renal pelvic calyx).it is because of the anatomical  positioning of   left kidney and  transferring the fluid  to bladder becomes slow.so stagnation of fluid in the left kidney denotes fullness. it is can be in obstruction of any stone or some  structural defect.thank youhope i answered your query </s>