Reflux is basically of 2 types i.e. Primary and Secondary.
Primary reflux is one in which there is no abnormality in the rest of the urinary tract, except an abnormal junction of the ureter and the bladder. Usually, the ureter does not join the bladder thru a hole - but, a part of the ureter has a submucosal tunnel thru which is passes before opening in the cavity of the bladder. This means after entering the bladder on the outer side, it goes between the muscle and mucosal(innermost layer) of the bladder. The length of the tunnel is about 3 - 4 times the diameter of the ureter. This submucosal tunnel acts as flap valve that gets compressed as the bladder fills up with urine and prevents the urine from the bladder going up into the ureter, at the same time it allows the urine from the ureter to enter the bladder. In some children, if the submucosal tunnel length is too short or the bladder muscle support is inadequate, the valve action cannot occur efficiently and reflux can occur.


Secondary reflux occurs in those children where the junction of the ureter and the bladder is normal, but, there are high pressures in the bladder and the back pressure can allow the reflux of urine into the ureter(s). The high pressures in the bladder may be due to an obstruction at the neck of the bladder, or in the urethra from where the urine is ultimately expelled out of the body. The high pressure in the bladder is transmitted backwards and can cause the reflux. In a few children, there may be damage to the nerves supplying the bladder and even less quantity of urine may generate very high pressures and lead to reflux. Therefore it is important to know the cause of the reflux and then traet the cause after a proper investigation.