>My 8 month old jill has just had her right kidney removed. I posted >here yesterday, but had little response. I am trying to find any info on >cystic kidneys in ferrets. What is the most common cause likely to be in >such a young ferret? Dear Carol: In an 8-month-old ferret with cysts only on one side, there are two possible causes. The first, and most common, is a congenital defect. These are extremely common in ferrets, and we see cysts 25% or so of ferrets at necropsy (for other reasons.) Perhaps someone one day will do a study - this would be relatively easy to quantitate with ultrasound - they are usually of a size that they would jump out at you. The second reason, and the more likely reason for a kidney to be removed is that we are not dealing with a true cystic kidney, but a case of unilateral hydronephrosis. Hydronephrosis occurs when the outflow of urine is blocked from one of the kidneys. In the ferret, the most common cause is a urinary tract infection which ascends from the bladder up the ureter (the pipe that connects the kidney to the bladder.) If inflammatory debris blocks the outflow of urine, the pressure will build up in the ureter and back up into the kidney. That kidney is going to continue to make urine - it doesn't know that the plumbing is blocked. As the pressure builds up in the kidney, the kidney tissue eventually withers away under it, and eventually, you are left with a large bag full of urine. The third possibility which is very remote would be true polycystic kidney disease, a rare genetic defect of ferrets in which all of the plumbing is malformed, and many large cysts develop, eventually resulting in renal failure. But that is extremely rare in this species. With kindest regards, Bruce Williams, DVM [Posted in FML issue 3711]