Surgical case report: The rare case of incidental retroperitoneal mesothelioma.

Introduction And Importance: This is a first reported case of isolated retroperitoneal mesothelioma. Most patients present with symptoms of abdominal pain, distension and weight loss. However, a minority of cases are asymptomatic and are found incidentally on imaging. It is important to provide an early histological diagnosis to help with management and prognostication.

Case Presentation: We present a male patient who was referred to our surgical clinic with an incidental finding of an indeterminate retroperitoneal lesion. The patient underwent numerous investigations without further clarity of the lesion. A 5 cm lobulated cystic lesion was excised in the retroperitoneum and found to be loosely adherent but separate to the duodenum, inferior vena cava and right adrenal gland. Histopathology revealed a localised multinodular epithelioid mesothelioma. The patient was referred to a specialist cancer centre and has remained well on subsequent follow-up.

Clinical Discussion: Although multiple reports of lung, liver and kidney mesotheliomas are described, to our knowledge this is the first report of isolated retroperitoneal mesothelioma. Diagnosis of peritoneal mesothelioma is diagnostically challenging as there are no features on imaging characteristic for peritoneal mesothelioma. Hence, tumour markers and magnetic resonance imaging should be used in conjunction. The prognosis of mesothelioma is dependent on the patients' histopathology, where diffuse mesothelioma poses a worse prognosis than localised mesothelioma. Modern therapies for diffuse mesothelioma now include cytoreduction surgery (CRS) and hyperthermic intraoperative peritoneal perfusion with chemotherapy (HIPEC).

Conclusion: An excisional biopsy may be warranted for indeterminate lesions with a high degree of suspicion for malignancy.