Carcinoma arising from an oesophageal duplication cyst in an adult cat

A 17-year-old female Siamese cat was referred for a history of progressive dyspnoea, depression and anorexia. The cat was tachypnoeic, dyspnoeic and the thoracic auscultation revealed muffled cardiac and respiratory sounds. Radiographs of the thorax demonstrated pleural effusion and a well-circumscribed soft tissue mass in the caudodorsal aspect of the mediastinum, most likely consistent with an oesophageal mass. CT findings demonstrated a cystic-like mass in the caudal mediastinum, which was located in the right wall of the oesophagus, pleural effusion and subpleural nodules. Microscopic examination revealed that the wall of the cystic-like mass had an inner mucosal layer lined by squamous epithelium and contained two muscle layers, consistent with an oesophageal duplication cyst (ODC). A carcinoma was found in the ODC as well as pleural carcinomatosis. To the authors' knowledge, this is the first case of a neoplastic ODC.