Thymic carcinoma with a large cystic lesion

A 59-year-old man presented with a large anterior mediastinal mass. A computed tomography (CT) and magnetic resonance imaging showed a well-circumscribed cystic mass, 12 cm in size adjacent to the heart border and superior vena cava (SVC). A CT guided needle biopsy was performed, and instead of detecting malignant tissues but finding that gray muddy fluid was suctioned, suggesting cystic teratoma. At surgery, the tumor was confirmed advanced thymic carcinoma with pleural dissemination, then the tumor was extirpated with resection of SVC, followed by 2 cycles of chemotherapy. Histologically, the cystic wall was lined with malignant cells. We herein present a diagnostic pitfall case of thymic carcinoma having a large cystic component with which rare association should be recognized.