Claudia,
This is from the front page of the Bladder Cancer Web Cafe... I learned a lot about hydronephrosis while I was googling around for some background on BCG and hydronephrosis. I'm not sure how to answer your question about it. This was not a reaction that I had, but it sounds like (from my googles) that it is not unheard of....
From my googles, its seems that "hydronephrosis" is also the correct term for kidney swelling....
hydronephrosis - Swelling of the top of the ureter, usually because something is blocking the urine from flowing into or out of the bladder; a condition that occurs as a result of urine accumulation in the upper urinary tract
It is interesting to me that a lot of tumors appear outside of the ureter orifice. That's also where my Doctor found my tumor....
Good luck. I hope someone has some more information for you. This is the first that I have heard of this BCG reaction since I began reading posts here over 2 years ago....
Sorry I'm not more help...
Rosemary