Endodermal sinus tumor stained for alpha fetoprotein. Scattered tumor cells show cytoplasmic positivity. Most testicular endodermal sinus tumors of the pure type occur in infants and children under the age of 3.
Tumors are usually well demarcated from surrounding tissues.
On cut section the tumors are tan to yellow, usually solid with a mucinous quality. Microcysts and areas of hemorrhage may be present. Histologically the tumor tends to show a network arrangement of tumor cells with glandular and papillary structures. Scattered isolated or clustered groups of globular hyaline droplets are present which contain alpha fetoprotein and alpha 1 antitrypsin. Most testicular endodermal sinus tumors of the pure type occur in infants and children under the age of 3.