A 16 year old girl was thought to be pregnant based on lower abdominal swelling and a positive hCG screening test. Ultrasonography established the presence of a large ovarian tumor. The mass (left photo) weighed 1400 grams. Histological examination revealed variation in the pattern with the less well-differentiated portion in the right portion of the right photo. See next slides also.

One histological pattern was well to moderately differentiated with structures strongly resembling seminiferous tubules. Occasional syncytiotrophoblasts (upper left) were evident with positive immunohistochemical staining for hCG (lower left). In some areas lymphocytes were prominent, a characteristic of this tumor which is the equivalent of the testicular seminoma.

Contributed by Dr. C. James Sung