What is bladder outlet obstruction (BOO)?

Bladder outlet obstruction (BOO) occurs when there is a blockage at the base or neck of the bladder. Such a blockage reduces or stops the flow of urine into the urethra, which carries urine from the body. BOO is most common in older men and often is linked to prostate problems. More men than women have BOO.

What causes bladder outlet obstruction (BOO)?

The causes of bladder outlet obstruction include:

  • Scar tissue in the urethra.
  • Bladder stones.
  • An enlarged prostate gland.
  • Prostate cancer.
  • Tumors in the rectum, uterus or cervix.

What are the symptoms of bladder outlet obstruction (BOO)?

You may have BOO if you:

  • Have pain when passing urine.
  • Have trouble starting your urine stream.
  • Feel like you have a full bladder but cannot empty completely.
  • Feel like some urine remains in your bladder after voiding.
  • Pass urine frequently during sleeping hours.
  • Have pain in your abdomen.
  • Have urine flow that starts and stops.
  • Have a urinary stream that is slow.
  • Void often with small urine volume.

Last reviewed by a Cleveland Clinic medical professional on 02/21/2017.


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