[Histological and ultrastructural characteristics of yolk sac tumors of gonadal and extragonadal localization in children].

30 yolk sac tumours of a gonadal and extragonadal localization in children (19 testis tumours, 5 ovarian tumours, 6 tumours of extragonadal sites: presacral, sacralcoccygens, gluteal, retroperitoneal regions, vagina, liver) are studied histologically, in 8 cases electron-microscopically as well. The description of main histological and ultrastructural features that either may be used for differential diagnosis or may indicate the degree of tumour cells differentiation is presented.