A 38-year-old man visited our hospital complaining of anterior chest pain. He had no significant medical or family history, and the vital signs were stable. Ischemic events were not observed in electrocardiography, but chest X-ray and computed tomography (CT) showed a cystic lesion (6.0 × 7.0 × 10.0 cm) in the anterior mediastinum (Fig. 1a). Although the cystic capsule demonstrated contrast enhancement, its fluid component had low radiation absorbance. Based on these findings, we suspected the mass to be a thymic cyst. Blood tests indicated the presence of inflammation (white blood cell count 11,200/μL and C-reactive protein 3.38 mg/dL).
Two days after hospitalization, the patient developed dyspnea and his chest pain worsened. Subsequent chest CT showed that the cystic lesion had become inhomogeneous and the radiation absorbance of the cyst’s fluid component had increased (Fig. 1b). The cyst wall became thickened, and bilateral effusion was observed. Blood tests indicated that hemoglobin levels had decreased from 15.8 to 12.8 g/dL, and levels of inflammatory markers had increased, with the fever exceeding 38.5 °C. Needle aspiration biopsy and tumor wall biopsy with a small skin incision were performed; however, we could not obtain a diagnosis. One week after admission, general condition and laboratory data of the patient gradually improved. A chest CT on day 13 showed that the tumor had become small in size with a thickened wall (Fig. 1c). The effusion on the right side had decreased and that on the left side had disappeared.
The patient had recovered enough to undergo surgery; the tumor was resected by sternotomy on day 18. The tumor was found to be encased in a smooth, yellow, and elastic coat. The tumor was densely adhered to the junction of the left brachiocephalic vein and superior vena cava, and it was required to detach the tumor from the dense adhesion site carefully. The right phrenic nerve was preserved, and the right pleural effusion was serous. The tumor and thymic tissue were resected en bloc. The operative time was 288 min, and the estimated blood loss was 521 mL. The resected tumor was covered with a thick, fibrous capsule, and the lumen was filled with necrotic tissue and hemorrhagic material (Fig. 2a, b). The postoperative course was uneventful, and he was discharged on day 26.
The pathological findings showed a fibrotic cyst wall; the cyst was filled with necrotic tissue. The slight proliferation of lymphocytes was confirmed in the necrotic tissue and around the cyst wall (Fig. 3a, b). The tumor was diagnosed as type B1 cystic thymoma (Fig. 3c). As the tumor did not appear to have spread beyond the capsule, it was determined to be at Masaoka stage I. Nevertheless, the dense adherence of the tumor to its surrounding tissue indicated the possibility of invasion, and postoperative radiotherapy (50 Gy) was administered.
Two years after the surgery, recurrent metastasis of the tumor was found on the right pleura and the left upper lobe of the lung. The patient was treated with chemotherapy, radiotherapy, and local resection. The patient remains alive 12 years after the first surgery. Following an analysis of the tissue obtained from the resected recurrent tumor, the pathological diagnosis was changed to type B3 thymoma.