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Why can posterior urethral valves damage the kidneys?

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Posterior urethral valves can damage the kidneys because they act as an obstruction in the urinary tract, impeding the normal flow of urine and causing it to back up into the bladder and kidneys.1

This backup of fluid, known as hydronephrosis, causes the renal pelvis and calyces to become grossly distended. The resulting pressure on the kidney structures interferes with blood flow to the organ, which accelerates the degeneration of functioning kidney tissue. Over time, the structures responsible for producing urine are replaced by fibrous scar tissue, and the accumulation of nitrogenous wastes in the blood can lead to uremia and renal failure. Furthermore, the stagnant urine in the obstructed tract increases the risk of infections, which can cause additional inflammation and further damage to the urinary system.1