Which condition is characterized by the backward flow of urine from the bladder to the kidneys, potentially leading to urinary tract infections?

The condition that is characterized by the backward flow of urine from the bladder to the kidneys is vesicoureteral reflux (VUR). This occurs when the ureter enters the bladder at an abnormal angle, which can lead to the flow of urine going in the reverse direction rather than just from the kidneys to the bladder. This backward flow can cause urine to stagnate in the kidneys, which increases the risk of urinary tract infections (UTIs) as bacteria can proliferate in the stagnant urine. Persistent infections can subsequently lead to renal scarring and damage over time.

In contrast, nephrotic syndrome involves a group of symptoms related to kidney damage, including proteinuria and edema, but does not cause the backward flow of urine. Cryptorchidism refers to undescended testicles and has no direct association with urinary reflux. Cystitis is an inflammation of the bladder, typically due to an infection, but it does not specifically refer to the backflow of urine to the kidneys. Therefore, vesicoureteral reflux is the condition that directly corresponds to the description in the question, linking it to the risk of urinary tract infections effectively.