An 81-year-old woman who had been confined to a nursing home for several years with Alzheimer's dementia, type 2 diabetes, and recurrent urinary tract infections, was sent to the hospital with fever, obtundation, and decreased urine output. Physical examination revealed: blood pressure, 110/70 mm Hg; heart rate, 110 beats/min; and oral temperature, 38.4 C. Her mucous membranes were dry; her abdomen was distended, with a palpable, 15 x 15 cm smooth, round mass. An x-ray of the abdomen was ordered (Figure). Use of a Foley catheter resulted in prompt diuresis of 1800 mL of foul-smelling, cloudy urine.