He is afebrile and his cardiac, lung, and abdominal examinations are normal. On visualization of the anus you see no inflammation, masses, or fissures. Digital rectal examination reveals a smooth, enlarged prostate. No discrete masses are felt. There is no blood on the glove or on guaiac testing. An analysis of the urine shows no red blood cells, white blood cells, or bacteria. What disorder of the anus, rectum, or prostate is this most likely to be?