The image below shows a urinary bladder of an adult male opened up to reveal the inside surface. A spherical enlargement of the prostate gland (P) is overhanging and blocking the flow of urine into the urethra (U). The prostate grows around the urethra at the point at which it exits from the bladder and so when the prostate enlarges it tends to squeeze and close off the urethra. More unusually it can grow into a mass in the position seen in this specimen which also blocks off the urine flow. Hyperplasia means increase in the number of cells, which underlies to the increase in size of the prostate. When enlargement occurs the normal egress of urine is blocked, the hydrostatic pressure in the bladder builds up and distends the bladder to a volume which is larger than normal. This increased pressure causes the bladder wall to become thickened and the strips of muscle in the wall to become enlarged – referred to as trabeculae (T). The chronically increased pressure has also caused a ballooning out of one part of the bladder wall to form a diverticulum (D), which by filling with urine lessens the pressure. The opening through the bladder wall into the diverticulum is clearly seen (OD). This is a good example of how one kind of primary pathology, the prostatic enlargement, can drive the development of secondary pathologies – the trabeculae and the diverticulum.
Enlargement of the prostate is an age-related phenomenon with benign prostatic hyperplasia affecting the quality of life in about 40% of men in their fifties and 90% of men in their nineties. The reasons for the increased volume of the prostate in older men is not well understood and regulation of cell growth in the prostate is complex. However, the change in balance of the hormones testosterone and oestrogen in men as they grow older may result in an imbalance between cell death and cell division that results in a preponderance of the latter.
The blockage due to an enlarged prostate can be treated by surgically removing the prostate tissue that is closing off the urethra. This is done by passing instruments up the urethra to cut away the prostatic tissue that is closing it off or by passing a laser up the urethra and burning away the excess tissue. Early urinary symptoms should be reported to a doctor so they can be treated and more serious conditions such as prostate cancer can be ruled out. Early symptoms of benign prostatic hyperplasia can often be treated with medicines that reduce the size of the prostate.