Primary malignant thymoma in a 6-year-old boy.

Although not uncommon in adults, thymomas are the least common mediastinal tumors in children. The behavior of these tumors in children is partially distinct with a much more rapid course and a poor prognosis. A symptom-free 6-year-old boy was treated for malignant thymoma detected incidentally on a chest X-ray in a school mass examination. At operation, the tumor was found to have already invaded the surrounding tissue. Complete removal at the base of the invasive tumor is the treatment of choice.