A case of Klinefelter syndrome with retroperitoneal teratoma

Klinefelter syndrome (ICS) is often associated with various neoplasms, espe cially germ cell tumors. Mediastinum is the most favored site of extragonad al germ cell tumors with KS, which is somewhat different from those without KS. The retroperitoneal germ cell tumor in KS is very rare. A five-month-o ld boy with an abdominal mass was found to have a retroperitoneal tumor. Af ter surgical removal, he was diagnosed to have mature cystic teratoma. Cyto genetic study of his peripheral lymphocytes revealed that his karyotype was consistent with KS. This case suggests that patients with KS might be at r isk of having germ cell rumors in sites other than mediastinum. It also sug gests that all cases with these tumors should be screened for the presence of karyotypic abnormalities, and it might help to assess the exact correlat ion between germ cell rumors and KS, and to treat them accordingly.