Endodermal sinus tumor or yolk sac carcinoma occurs with great frequency in both
male and fema1e gonads, but has been described sporadically in extragonadal locations
as well. The histologic features of 15 cases of endodermal sinus tumor arising from
testis (8 cases), ovary (5 cases) and presacrum (2 cases) were presented, and in an
effort to delineate the histogenesis, the light and electron microscopic findings were
compared to that of yolk sac obtained from five normal pregnant rats.
The two Patients with presacral endodermal sinus tumor were female. The mean age
of the patients with endodermal sinus tumor was 13.1 years, 8 being under the age of 5
and only one over 30.
The histologic appearances of the 15 tumors were essentially similar showing loose
mucinous stroma mimicking the magma reticularis and PAS-positive, diastase-resistant
hyaline globules. The pseudo-papillary pattern, in which Schiller-Duval bodies were
abundant, and which was considered as the clue for histological diagnosis in the present
series, was predominant in 5 cases (33.3%). The reticular pattern was predominant in 6
cases (40.0%), whereas no one showed the polyvesicular vitelline structure or solid
pattern as prominent picture. 4 cases (26.7%) of the endodermal sinus tumor showed
mixture of the pseudopapillary and reticular patterns. The light microscopical features of
normal rat yolk sac were similar to that of human endodermal sinus tumor, except the
lack of polyvesicular vitelline structure.
The most prominent ultrastructural feature of the tumors was the presence of volum-
inous basement membrane like material in both intra- and extra-cellular location,
corresponding to the PAS-positive hyaline globules seen in these tumors by light micro-
scopy, and the appearance of skein-like nucleolema. Other ultrastructural findings were
also similar in human endodermal sinus tumor and normal rat yolk sac. These findings
suggest that yolk sac tumor is a peculiar germ cell origin having a property to
differentiate to yolk sac.
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