Yolk sac tumors with pure and mixed polyvesicular vitelline patterns.

Four cases of polyvesicular vitelline tumor are presented; two were of a previously unreported pure type, and the other two were mixed with endodermal sinus tumor. The morphologic features of the vesicles favor an endodermal origin, as originally proposed by Teilum. Marked specialization of the vesicular lining cells, seen ultrastructurally, suggests a differentiation toward gut structures and mature yolk sac. One case of pure polyvesicular vitelline tumor showed massive erythropoiesis. We propose that the pure tumor reflects an intermediate degree of differentiation within the selectively endodermal yolk sac tumor group, that is, a further stage of organization than the endodermal sinus tumor. In our cases of pure polyvesicular vitelline tumor, the marked degree of differentiaiton was correlated with an improved prognosis, as in the case of the possible homologue of this tumor, the yolk sac tumor of the infant testis. In contrast, the two cases of the tumor admixed with endodermal sinus tumor illustrated the low survival rate expected in the pure endodermal sinus tumor; in these cases the metastases had no polyvesicular component. Because of the significance of such a difference in prognosis we emphasize the importance of an accurate diagnosis, suggesting that a large number of sections be taken in order to demonstrate any endodermal sinus tumor component that may be present, and that the possibility of pure polyvesicular vitelline tumor always be considered in the differential diagnosis of multicystic ovarian tumors.