Mediastinal polyembryoma associated with Klinefelter syndrome.

A 4.5-year-old boy presented with isosexual precocious puberty and an anterior mediastinal mass. Surgical resection demonstrated a teratoma with foci of malignant mixed germ cell tumor elements of polyembryoma. On further investigation he was found to have Klinefelter syndrome. Most mediastinal germ cell tumors are treated with adjuvant therapy. He was managed with surgical excision alone and is well at 2 years follow-up. The rationale for this approach is discussed.