AB209. SOH25_AB_366. Benign multi-cystic peritoneal mesothelioma—a case report

Background: Benign multi-cystic peritoneal mesothelioma (BMCPM) is an extremely rare pathology with an estimated incidence of 2/1,000,000 per year. Most commonly seen in fertile women can be associated with previous intra-abdominal surgery, pelvic inflammatory disease, and endometriosis but, importantly, is not related to asbestos exposure. It often presents as pain in the abdomen/pelvis or is found incidentally on imaging or intra-operatively. The following describes the case of a patient with a peritoneal mesothelioma.

Case Presentation: We present the case of a 43-year-old Caucasian woman who presented in March 2023 with a 2-day history of abdominal pain with no associated symptoms. A white cell count of 9.1×10³/mL and C-reactive protein (CRP) of 127 mg/L. Computed tomography (CT) reported a 5.8-cm fluid collection at the tip of the appendix keeping with acute complicated appendicitis. On laparoscopy, multiple cystic lesions were seen within the abdomen. These cystic lesions were excised and sent for histopathological analysis. Histology revealed acute gangrenous appendicitis, but a diagnosis of BMCPM was also made. The patient continues to be followed for clinical and radiological surveillance.

Conclusions: Due to the rarity of BMCPM, the aetiology and pathogenesis remain unclear. It is benign in nature; however, malignant transformation has been reported albeit rare. Non-operative approaches such as hormonal therapy, sclerotherapy, or laser ablation have been suggested for the management of asymptomatic patients. Surgical resection is curative, but a risk of local recurrence as high as 50% has been reported. Patients who undergo surgical resection or non-operative management require close clinical and radiological surveillance. Further research is required to determine the optimal management approach and better characterise BMCPM.

Keywords: Mesothelioma; peritoneal; multicystic; benign; appendicitis