Hi Starrysky, your SIL is right, you won't know the entire extent of the problem until her baby is delivered. The placenta does the function of the kidney's in utero so it is difficult to determine if and how well a compromised kidney will function before birth.

Firstly, the fact that the right kidney is of normal structure and has a normal blood supply and fluid flow is an excellent sign. Depending on what study you read, between 1 in 500 and 1 in 2500 live births are of a baby with a single kidney. If that single kidney functions normally, the patient should go on to have a normal life.

The PUJ refers to the (renal) pelvis-ureter junction. The bottom of the kidney is where the urine pools once it has been formed by filtration of the glomerulus (say that fast 10 times!!), this area is known as the renal pelvis. The urine then drains by the ureter (a tube) to the bladder where it waits to be passed by the urethra (another tube!). In normal anatomy, each person has two kidneys, two ureters, one bladder and one urethra. From the information you have, your niece/nephew has an obstruction in the left kidney at that point where the renal pelvis meets the ureter. This obstruction may caused by the cyst itself or it may be an obstruction due to a separate cause, the urologist will be able to tell your SIL. S/he will also be able to tell your sister whether the obstruction is complete or partial, meaning whether any fluid at all is able to pass through the ureter on the left side.

It is my understanding that if the kidney were to be reabsorbed by the baby, this would have occurred in the first trimester. I don't think that the kidney can be reabsorbed at 30 weeks gestation, but again your SIL should check with the urologist!

There are several treatments for a PUJ obstruction; if the obstruction is very minor (it sounds like this might not be the case) it may simply be monitored and the kidney function may improve with growth, the surgeon can try to dilate the ureter to increase the lumen (the internal size of the tube), the blockage can be cut out and the ureter reattached, or sometimes the kidney function is too compromised and the kidney is damaged so it must be removed.

Life with one functioning kidney is not much different to that of someone with two - we are very careful of infection (my DS has complications of his existing kidney which make infection far more likely) and my DS was circumcised on the very strong advice of his urologist as UTI's are much, much less common in a male infant who has been circumcised. Contact sports are another area we are very careful. I am happy for my DS to kick a footy around with his mates and have a play wrestle, but I encourage him to play non contact sports for recreation. There are quite a few professional AFL players who have lost a kidney due to on field incidents! Lowering the risk of diabetes is an ongoing concern, so we encourage a healthy diet and one which is low in sodium. As he gets older, my DS will have to be careful not to develop hypertension (high blood pressure) as the hypertension itself may damage the kidney and may also be a sign that his kidney is failing. DS will need to be a careful alcohol consumer when the time comes. We are very conscious of the fact that DS only has a single kidney, but it really doesn't affect his day to day life. He is almost 8 now, and he is pretty aware of making good choices.

Feel free to ask any more questions, and I'll answer them if I can. Of course, the best person for your SIL to speak to is a paediatric urologist. I know a fantastic one if she happens to be in Melbourne!

Hugs to both of you.