S1681 Malignant Peritoneal Mesothelioma (PeM) With Rhabdoid Features Masquerading as Idiopathic Necrotizing Pancreatitis With Mucinous Ascites: A Case Report and Literature Review

Abstract

Introduction: Malignant Mesothelioma (MM) is a great masquerader, presenting as infection, metastasis, other cancers or as a paraneoplastic syndrome. Malignant peritoneal mesothelioma (PeM) accounts for about 10-15% of all cases of mesothelioma. MM presenting with malignant gastrointestinal (GI) polyps is also rare, with only 16 reported cases of mesothelioma presenting as metastatic disease in the GI tract. Here, we present the clinicopathologic findings of a case of a malignant peritoneal rhabdoid mesothelioma presenting as a necrotizing pancreatic mass, recurrent deep vein thrombosis (DVT), chylous ascites, and late onset weight loss. Case Description/Methods: A 76-year-old female initially presenting with idiopathic necrotizing pancreatitis. She continued to report persistent vague lower and mid abdominal pain. Six months after her initial admission the patient developed a DVT and pulmonary embolism (PE) requiring thrombectomy and anticoagulation with a recurrent DVT requiring IVC filter placement. She continued to have recurrent ascites and an enlarging peripancreatic fluid collection. Multiple paracenteses were performed with studies negative for infection and cytology negative for malignancy; however, most samples could not be analyzed due to fluid viscosity. An endoscopic retrograde cholangiopancreatography was performed with pancreatic and biliary stents placed. Almost one year after the patient’s initial admission, cross-sectional abdominal imaging showed omental caking with enlargement of the proximal pancreas. An endoscopic ultrasound with fine needle aspiration was performed was non-diagnostic. Lymphangiogram performed chylous nature of ascites. MRI showed a large fluid volume surrounding the pancreas and extended into the pararenal spaces. There was a mass effect leading to displacement of the surrounding structures. Diagnostic laparoscopy showed abdominal wall and peritoneal implants in addition to a large, firm, and highly vascularized epigastric mass. Pathology showed peritoneal mesothelioma. Discussion: We have presented a case of PeM with rhabdoid features present in the peritoneum and in gastric polyps. PeMs are rare tumors with a non-specific clinical presentation. These lesions are also difficult to diagnose and definitive diagnosis of MPM requires surgically obtained tissue. To our knowledge, this is the first case with these features.