Pleural and transdiaphragmatic retroperitoneal metastasis developing two and half years after resection of invasive thymoma.

We report transdiaphragmatic pleural and retroperitoneal metastasis developing two and half years after resection of invasive thymoma (Masaoka stage III; WHO type B1, lymphocyte-rich) in a 34-year-old man. Post-surgery, he received radiotherapy and chemotherapy. Follow-up computed tomography (CT) one year post-surgery did not reveal any local recurrence or metastasis. He remained asymptomatic throughout. A follow-up CT done two and half years later revealed an enhancing retrocrural-retroperitoneal (posterior pararenal space) soft tissue mass measuring 12 cm x 10 cm x 6 cm. Another enhancing deposit was found in the left pleural space. This lesion was found infiltrating into the subjacent lung. Both these deposits were resected along with wedge resection of the affected subsegment of the lung. Histopathology confirmed these lesions to be metastases from the lymphocyte-rich thymoma.