A Case of Well-differentiated Papillary Mesothelioma Developing Malignant Mesothelioma with Seeding Mass on the Trocar Insertion Site of Diagnostic Laparoscopy and Malignant Change

Although well-differentiated papillary mesothelioma (WDPM) is usually classified as benign, the natural history of this lesion has not been clearly established. We present a case of WDPM in 60-year old woman developing malignant mesothelioma with seeding mass on the trocar insertion site over a period of 2 years. The initial symptom exhibited by the patient was abdominal distension from massive ascitic fluid. With an impression of peritoneal carcinomatosis, we performed a diagnostic laparoscopy. On the laparoscopic finding, a small whitish nodule was found on the liver surface and the pathologic result revealed reactive mesothelial hyperplasia. At exploro-laparotomy, multiple small nodules were found on the omentum and a biopsy revealed well-differentiated papillary mesothelioma of the peritoneum. The patient underwent pelvic lymphadenectomy and omentectomy of the colon and was followed for 2 years without any further treatment. Subsequently, she presented with abdominal distention with massive ascites and palpable abdominal wall mass at the previous trocar insertion site. Malignant mesothelioma was confirmed histologically via re- exploration. The rare transformation of well-differentiated papillary mesothelioma into a typically malignant diffuse mesothelioma and the unusual seeding on trocar insertion site prompted us to report this case.