We report 28 testicular
seminomas with cystic spaces of variable nature, sometimes accompanied by solid and hollow tubular patterns (12 cases). The spaces often suggested reticular or microcystic patterns of
yolk sac tumor, and the solid and hollow tubular patterns often added to the diagnostic
confusion. The
tumors occurred in men 21 to 55 years old and on gross examination had the typical appearance of
seminoma. On microscopic examination, the spaces ranged from small, closely packed and relatively regular to dilated, more dispersed and somewhat irregular. The hollow tubules appeared to result from central discohesion within nests of
tumor. The spaces, particularly when large, often contained occasional
tumor cells or inflammatory cells within pale
edema fluid. The cytologic appearance of the cells lining the spaces, and in the surrounding
tumor, retained the typical features of
seminoma cells. Thirteen
tumors (46%) either lacked (8 cases) or had very scant (5 cases) lymphocytes in the cystic and tubular areas, and hyaline globules were absent. Thirteen of 13
tumors were immunopositive for OCT-3/4 in the nontypical and typical areas; 9 of 10 were
placental alkaline phosphatase positive, and 7 of 10 were c-Kit (CD117) positive. The same 13 cases were negative with
cytokeratin (AE1/AE3) and
alpha-fetoprotein stains. Distinction from
yolk sac tumor is aided by the observation that the spaces of
yolk sac tumor are often more irregular in their individual shapes and frequently form anastomosing channels. Additionally, the spaces of
yolk sac tumor randomly merge with various other
yolk sac tumor patterns. The cells lining spaces in
yolk sac tumor are often flattened with compressed nuclei and lack the typical prominent nucleoli of
seminoma cells. Paucity of lymphocytes and intracystic
edema, however, are not differentially helpful, although basophilic fluid favors
yolk sac tumor. A panel of immunostains (AE1/AE3, OCT-3/4, and
alpha-fetoprotein) is helpful in the differential with
yolk sac tumor in especially problematic cases. The
edema and paucity of lymphocytes may suggest spermatocytic
seminoma, but the varied cell types of that
neoplasm are absent.