What causes a cyst on kidney and is it dangeeous?

Very common: Renal cysts can be genetic in origin or the result of one of multiple diseases. Simple renal cysts are very common and account for 65-70% of masses discovered on imaging. Most of these are benign, usually produce no symptoms and no further studies are indicated. However if the cyst has calcifications, septae or occur in a cluster of cysts studies are needed to be certain renal cancer isn't present