Primary mucinous cystic neoplasm of the retroperitoneum

A 40-year-old healthy female presented with mild epigastric pain, fatigue and a mass in the left abdomen. Blood tests revealed mild thrombocytopenia with all other laboratory values unremarkable, including no eosinophilia. Serum tumour markers were within normal range. Ultrasound, computed tomography, and subsequent magnetic resonance imaging, demonstrated a complex 10 cm retroperitoneal cystic lesion. The splenic vein was compressed with resultant splenomegaly and variceal enlargement of the gastroepiploic vein (Fig. 1). The patient grew up in rural Australia with possible hydatid exposure. In Australia, the sylvatic and domestic cycle both contribute to the prevalence of echinococcus granulosus.1 The patient noted contact with kangaroos, however denied exposure to sheep, cattle, pigs, dingoes or wild dogs. Given the cystic nature on imaging, location of the lesion and social history, hydatid disease was considered. However, the patient's standard hydatid serology (HA) and hydatid-specific western blot were negative. Despite this, infectious disease consultation recommended 6 weeks of albendazole. The patient suffered no side effects or liver function abnormalities from the albendazole and underwent laparoscopic resection after repeat imaging showed no change in lesion size. The descending colon was mobilized medially to expose the tumour. An attempt was made to aspirate the cyst, sealing the puncture with a purse string, however yellowish fluid leaked from the suture holes. Intra-operatively splenic vein compression and splenomegaly was confirmed. The pancreas and splenic vein were unable to be separated from the tumour, and a distal pancreatectomy with ligation of the splenic vessels and 95% splenectomy was performed, with more spleen unable to be preserved, unlike in our recently described technique.2 Blood loss was 400 mls and the patient recovered well and was discharged on day six. Follow up imaging at six and 12 months did not show recurrence. Macroscopic examination of the specimen reported a multiloculated cyst with smooth inner lining. Histopathology revealed a mucinous cystic neoplasm containing ovarian (-like) stroma with focal high-grade dysplasia (<10%) without invasive malignancy. On immunohistochemistry, the stroma was positive for oestrogen and progesterone receptors (Fig. 2). Mucinous cystic neoplasms (MCNs) are cystic tumours with mucin-producing epithelium surrounded by ovarian-like stroma. Although MCNs are more commonly found in the pancreas and ovaries, they have also been reported in extra-pancreatic sites. Primary retroperitoneal mucinous cystic neoplasms (PRMCNs) are very rare neoplasms and have been described almost exclusively as case reports or small series.3-5 To our knowledge, less than 90 cases have been reported in the world literature3-5 These tumours occur almost exclusively in middle-aged women. Unfortunately, a definitive diagnosis can only be made through histological examination of the specimen. Mucinous cystic neoplasms are classified into three categories as per the WHO classification; MCN with low grade dysplasia (adenoma), MCN with high grade dysplasia (carcinoma in situ) and MCN with invasive carcinoma.6 The European guidelines recommend resection of pancreatic MCN which are greater than 40 mm in size, have high risk features (ie, mural nodule) or are symptomatic.7 The American College of Gastroenterology (ACG) guidelines similarly recommend resection of MCN greater than 30 mm or with high risk features.8 These recommendations are intended for pancreatic MCN in which the rate of malignancy at resection is estimated to be 4%.9 By contrast, retroperitoneal MCN has high rates of malignancy reported at time of resection between 26% and 51%.4, 10 PRMCN is a rare tumour with high malignant potential that should be resected. Surgical technique selection depends on the surgeon's expertise and tumour factors for safe resection. The patient was consented for her presentation to be written up anonymously as a case report for educational purposes. Open access publishing facilitated by The University of Queensland, as part of the Wiley - The University of Queensland agreement via the Council of Australian University Librarians. Adam McNamara: Writing – original draft. Naduni Wijesekera: Writing – original draft. Nicholas O'Rourke: Supervision; validation; visualization; writing – review and editing.