Which of the following is a common cause of obstructive urinary retention?

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Obstructive urinary retention happens when urine flow is blocked at the bladder outlet. In men, the most common cause is benign prostatic hyperplasia, where the prostate enlarges and presses on the urethra. This narrowing makes it hard to start or maintain a stream, leading to incomplete emptying and, in some cases, a sudden inability to void. Clinically, you’d see a weak or interrupted stream, straining to void, a sense of incomplete emptying, and possibly nocturia or acute retention with a distended bladder. While hyperthyroidism can affect urinary patterns in other ways, and dehydration or hyponatremia affect fluid balance, none of these create a mechanical blockage of the urethra. Therefore, the familiar culprit behind obstructive retention in men is the enlargement of the prostate.