PLE-5685

A 49-year-old woman is admitted to the hospital because of renal failure. She has had episodes of flank pain over the past 20 years, and she has also had nocturia 2 to 3 times nightly for 10 years. Her blood pressure is 160/100 mm Hg. Examination shows pale mucous membranes, and a mass is palpated in the right flank. What is the most likely diagnosis?