Transdiaphragmatic extension of a thymoma invading the peritoneum and the spleen.

Thymoma, a rare tumor originating from thymic epithelial cells in the anterior mediastinum, presents various diagnostic and clinical challenges, particularly when exhibiting unusual invasive behaviors. We report a case involving a 66-year-old woman with progressive dyspnea and a dry cough, where a CT scan revealed a large, lobulated mass in the anterior mediastinum that had extended through the diaphragm into the abdominal cavity, infiltrating the pleura, spleen, and adjacent structures. Histopathological examination confirmed a type B2 thymoma, classified as T3N2M0 stage IV B. The case underscores the importance of early and accurate diagnosis, highlighting the need for a multidisciplinary approach involving radiologists, oncologists, and thoracic surgeons to manage such advanced thymoma cases. The unusual transdiaphragmatic extension into the peritoneum and spleen emphasizes the necessity of considering extensive local invasion in the staging and treatment planning of thymomas, which often necessitates a combination of chemotherapy and radiotherapy before potential surgical intervention.