A 40-year old male complains of a vague dragging sensation in his abdomen for the last 6 months. There was no history of fever, renal colic or dysuria. Physical examination reveals a blood pressure at 150/96 mm Hg. Renal ultraound : Bilaterally enlarged kidneys with multiple cysts. Urinary analysis: Mild Proteinuria WBCs 4/HPF (Normal: < 5/HPF) RBCs 10/HPF (Normal :< 5/HPF) The renal pathology was a result of -