The problem of fluid accumulation in the bladder indicates that the body is unable to completely expel the urine from the bladder after urination, so some of the urine remains in the bladder. Under normal physiological conditions, there is no fluid in the bladder after urination, so this is a case of residual urine in the bladder, which can be detected through urological ultrasound. In addition, the increase of residual urine in the bladder is mainly due to obstructive diseases of the urinary system, such as urinary stones embedded in the urethra or urethral strictures caused by urinary tract infections, as well as male prostatic hyperplasia or elevated bladder neck and weak contraction of the bladder forcing muscles, such as neurogenic bladder, which can cause residual urine in the bladder. The specific causes of increased residual urine in the bladder.