Giant ossifying malignant thymoma in a child.

We present the first reported case of an ossifying pediatric thymoma. Our patient was diagnosed with a massive thymoma replacing the whole of the left thoracic cavity. Percutaneous biopsy was attempted 3 times followed by an open incisional biopsy and adjuvant chemotherapy. Complete resection required a median sternotomy and a "trap door" thoracotomy after the tumor failed to respond to chemotherapy. Histology confirmed World Health Organization type B1 lymphocyte-rich thymoma, Masaoka stage I, with extensive osseous metaplasia.