Broadly speaking, neoplastic cysts are usually complex, meaning that they're larger than 10 centimeters, have irregular borders, and have internal septations creating a multilocular appearance.
Some originate from surface ovarian epithelium, such as serous cystadenomas, which are often bilateral and filled with a watery fluid, and mucinous cystadenomas, which tend to be multilocular and contain a mucus-like fluid.