Any of several types of kidneys .
Some are present at birth; others are caused by tubular obstruction. Large cysts can cause backaches and a dragging sensation. Multiple cysts occur as a result of various disorders, including kidney vascular diseases, lymphatic vessel blockage, congenital diseases, and tapeworm infestation. The most serious is medullary cystic disease, which has no warning symptoms but causes {{link=anemia">anemia , low blood sodium levels, and uremia . The kidneys become shrunken, grainy, and scarred. Cysts should usually be checked surgically to rule out cancer. See also urogenital malformation .