The arrow points to the culprit in this case of hydronephrosis--a ureteral calculus caught at the ureteropelvic junction. This kidney demonstrates marked hydronephrosis with nearly complete loss of cortex. Such a kidney would be non-functional. If the other kidney had sufficient function, then renal failure will not ensue. There is sufficient renal reserve capacity that it is possible to survive with half of a normal kidney.

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