Notice how this kidney demonstrates a large number of cysts of variable size (from a few mm to many cm), which are filled with fluid of variable colour - from clear or straw coloured to altered blood or chocolate coloured to purulent when infected. In Polycystic kidney disease, the clusters of fluid-filled sacs, or cysts, interfere the kidneys ability to filter waste products from the blood. The growth of cysts causes the kidneys to become enlarged and can lead to kidney failure. Photo by @claudia_ricciardi_