Parasitic cysts of spleen also called hydatid cysts. These cysts are cause by a parasite called Echinococcus granulosus. This parasite is present in dogs and other carnivores. The eggs of this parasites are released in to feces of dog and then are ingested to other animals including human. In the human the eggs are hatched and release small hooked worms which can grow in liver, spleen, lungs and kidney. There, they develop a cyst in which tapeworm larvae can grow. These cysts are treated with metronidazole and surgery. For more details, visit Splenic parasitic cysts.