A usually rapidly growing malignant germ cell tumor arising from the ovary. It usually occurs in children and adolescents. Signs and symptoms include abdominal pain and a large abdominal or pelvic mass. The serum alpha-fetoprotein is almost always elevated preoperatively. Morphologically, there is marked heterogeneity due to numerous patterns of differentiation coexisting in the same tumor. The most common pattern is reticular. The disease is ovarian yolk sac tumor (Monarch Disease Ontology term MONDO_0006344). Also known as: endodermal sinus neoplasm of ovary, endodermal sinus neoplasm of the ovary, endodermal sinus tumor of ovary, endodermal sinus tumor of the ovary, endodermal sinus tumour of ovary, endodermal sinus tumour of the ovary, germ cell endodermal sinus neoplasm of ovary, germ cell endodermal sinus neoplasm of the ovary.