Schiller' Duval bodies is seen in -

Yolk sac tumors are the most common primary testicular neoplasm in children younger than 3 years of age; in this age group it has a very good prognosis. In adults, yolk sac tumors most often are seen admixed with embryonal carcinoma..A distinctive feature is the presence of structures resembling primitive glomeruli, the so-called Schiller Duvall bodies. ref : Robbins Basic Pathology, 9E,page-661