A 69-year-old man with a past medical history of hyperlipidemia presented to the emergency department with severe right flank pain lasting 1-2 days. His vital signs were within normal limits; white count was 8 × 109/L and creatinine was 0.8 mg/dL. Urinalysis shows only red blood cells. His pain is now well controlled with oral analgesics. CT scan is shown below*:
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