A 35-year-old woman presents with low back pain, frequency of urination, and dysuria for 3 days, with recurrent similar episodes over the past 3 years. Urinalysis (UA): WBC 30-40/HP, RBC 20-30/HP; midstream urine culture shows bacterial growth; renal ultrasound: bilateral kidneys show hyperechoic masses distributed along the renal pyramids in a radial pattern, with multiple small stones; IVP 1 year ago revealed multiple cysts and dilated tubules in both kidneys, with contrast filling the renal pyramids forming irregular shadows in a 'bouquet' pattern. The most likely diagnosis is: