Answer by
wyeth (435)
Cysts are fluid filled spaces.Many kidneys have a few but in Polycystic Kidney Disease they can largely replace and destroy the normal tissue. Tumors are solid growths of abnormal tissue and can be benign and fairly harmless, or malignant such as Renal Cell Carcinoma or Cancer. Wilm's Tumor is a kidney cancer mainly of children under 10 years of age.