Enlarged bladder in your age can be due to a enlargement of the prostate. The big prostate causes blockage of the urinary passage. To overcome this blockage, bladder muscles have to overwork. The overworked muscles give the bladder enlarged look and this is termed as hypertrophy of the bladder. The other reason of the enlargement of the bladder muscles is continuous retention of the urine in bladder. This also contributes for the increase in size of the bladder.
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