Accumulation of urine in the pelvis is abnormal and usually occurs if there is an obstruction to the flow from the pelvis into the ureter and bladder, or, to put it another way if the volume of urine exceeds the volume that can normally be accommodated in the pelvis - the latter will stretch and expand to allow the urine build up within. This dilatation of the pelvis is called Hydronephrosis. The commonest cause of hydronephrosis in children is due to obstruction to the flow of urine from the kidney pelvis to the ureter and bladder. The urine accumulates in the pelvis; more urine is formed every minute and this accumulation continues to cause the pelvis to stretch like a balloon filled with water. If the obstruction is very severe gradually this will cause back pressure on the substance or parenchyma of the kidney that produces the urine. If the obstruction is not relieved, the function of the kidney will progressively decrease. The recoverability of the kidney function after relief of the obstruction depends on how long and how severe it was. The commonest site of obstruction is at the junction of the pelvis and the ureter, and this is usually present since birth. The narrowing is at the junction which may be adequate to allow minimal quantities of urine to pass in the newborn and infant stage - if it is not severe; as the child grows, the kidney and the volume of urine produced per minute will also increase but the junction may not increase by the same proportion and hence accumulation of urine will now cause a dilatation of the pelvis. When the limit of stretching of the pelvis is reached, the pressure will now fall on the renal substance and with time this will begin to thin out due to pressure of the urine. This then affects the function of that kidney. Other reasons for pelvic dilatation could be a stone in the kidney that may obstruct the flow of urine.

How does one suspect and diagnose this condition? This may be very easy if the child presents with a mass in the abdomen that can be seen and felt. This will lead to investigations and diagnosis. However, some children may present with recurrent abdominal pain, or episodes of urinary infection. This child must be shown to a doctor who may suspect a renal problem and ask for some basic investigations after a detailed examination of the child.