S6201 Malignant Peritoneal Mesothelioma Masquerading as Sclerosing Mesenteritis

Introduction: Malignant peritoneal mesothelioma (MPM) is a rare and lethal malignancy that typically present with nonspecific signs or symptoms. MPM can also be discovered incidentally during the workup of another diagnosis. Sclerosing mesenteritis is a rare inflammatory and fibrotic disease of the mesentery that is usually discovered incidentally during the evaluation of nonspecific abdominal or systemic symptoms. We present a case of MPM masqueraded as sclerosing mesenteritis. Our case highlights the diagnostic challenges of primary MPM that mimicked sclerosing mesenteritis. Case Description/Methods: A 61-year-old woman with no history of asbestos exposure presented with abdominal pain and diarrhea. Abdominal and pelvic computed tomography and magnetic resonance imaging showed ascites, significant omental stranding, mesenteric stranding, and slight peritoneal thickening. Paracentesis and fluid analysis indicated peritonitis; cytology was negative for malignant cells. Esophagogastroduodenoscopy and colonoscopy were normal. The patient was then started on prednisone to treat suspected sclerosing mesenteritis. Repeat abdominal and pelvic computed tomography scan after 4 months of taking prednisone showed decreased omental stranding, some improvement of mesenteric stranding and edema, and significant improvement of ascites. Given her positive response to therapy, she was started on azithromycin as maintenance therapy for sclerosing mesenteritis. Repeat abdominal and pelvic computed tomography scan after 5 months of azithromycin showed persistent omental stranding, increased mesenteric stranding, increased ascites, and some peritoneal thickening. Given the recurrence of abdominal ascites and persistent mesenteric stranding, the patient underwent computed tomography-guided core needle biopsy of the mesenteric mass, which showed malignant mesothelioma. Laparoscopic partial omentectomy and parietal peritoneal biopsy were also consistent with mesothelioma. The patient was found to have an extensive disease burden, so it was deemed unresectable. After receiving 4 cycles of pemetrexed and cisplatin with complications, the patient acknowledged that her cancer was incurable and prioritized maintaining her quality of life. Discussion: This case highlights the diagnostic challenges of MPM in its early stage because it can resemble sclerosing mesenteritis in terms of symptoms and imaging findings. Accurate diagnosis with close follow-up to monitor the patient’s symptoms and imaging findings in response to therapy is essential for improved patient outcomes.