Pleural pseudomyxoma secondary to appendiceal mucinous adenocarcinoma: a case report

Introduction: Appendiceal mucinous neoplasms are uncommon gastrointestinal tumors. In some cases, they evolve into pseudomyxoma peritonei (PMP), a condition characterized by mucinous ascites and peritoneal dissemination. Treatment typically requires comprehensive cytoreductive surgery (CRS), commonly combined with hyperthermic intraperitoneal chemotherapy (HIPEC). While PMP usually remains confined to the abdominal cavity, extra-abdominal spread is exceptional. Pleural involvement, often described as pleural pseudomyxoma, has been reported only rarely. Case Presentation: We report the case of a 55-year-old man who was initially diagnosed with PMP arising from a well-differentiated mucin-producing adenocarcinoma of the appendix. He underwent CRS with splenectomy, without HIPEC because of financial and technical limitations. Approximately one year later, he developed progressive dyspnea and cough. Imaging revealed left pleural effusion with nodular pleural thickening and mucinous densities. Video-assisted thoracoscopic surgery (VATS) demonstrated mucinous pleural deposits, and histopathological examination confirmed metastatic well-differentiated mucinous adenocarcinoma involving the pleura. He underwent thoracoscopic pleural debulking followed by systemic chemotherapy, with short-term disease stability. Discussion: No gross diaphragmatic defect was identified during thoracoscopic evaluation. Therefore, direct transdiaphragmatic dissemination was considered less likely, although microscopic transdiaphragmatic spread or iatrogenic seeding cannot be completely excluded. Lymphatic or hematogenous dissemination remains a plausible alternative mechanism. The patient received systemic Capecitabine-Oxaliplatin chemotherapy and remained clinically stable, radiologically disease-controlled, and functionally independent at 12-month follow-up. Conclusion: Pleural pseudomyxoma represents an exceedingly rare thoracic extension of appendiceal PMP. Although CRS-HIPEC remains the preferred treatment strategy for selected patients in specialized centers, individualized thoracoscopic debulking combined with systemic chemotherapy may provide short- to intermediate-term disease control in resource-limited settings.