A 64-year-old man complains of the absence of urination during the last 12 hours. Objectively, a painful mass is palpable above the pubis, the upper edge of the mass reaches the navel. Rectal examination detects an enlarged prostate. The prostate is painless, lumpy and has a stone-like density. Blood levels of prostate-specific antigen are 24.2 ng/ml. What is the cause of the acute urinary retention in this case?