Effusion cytology of endodermal sinus tumor of the colon. Report of a case.

A three-year-old boy presented with a peritoneal effusion due to an occult endodermal sinus tumor in the ascending colon. Cytologic examination of the ascitic fluid revealed clusters of round plump cells that had large hyperchromatic nuclei, finely stippled chromatin, multiple prominent nucleoli and vacuolated or mucin-containing cytoplasm, features suggesting an adenocarcinoma. The colonic primary was discovered during emergency laparotomy performed due to suspected acute hemoperitoneum. Endodermal sinus tumor should be included in the differential diagnosis when cytologic features reminiscent of adenocarcinoma are encountered in a fluid specimen from a child, especially if there is a history of a gonadal or extragonadal childhood neoplasm.