LAUSR

diameter is greater than 10 mm. Pancreatic resection is usually recommended as the changes are often multifocal. Fistula formation is a recognized but rare complication of IPMN and is associated with intestinal-type IPMN. Pathogenesis of fistula formation is related to either mechanical penetration from increased ductal pressures or, less commonly, direct invasion of an IPMN into surrounding organs. Common sites for fistula include, in order of decreasing frequency, duodenum, stomach and common bile duct. Our case is due to mechanical penetration, given the lack of high-grade dysplasia seen around the fistula margin, with splenic vein obstruction constituting a sequela of increased ductal pressure. This was also described in a case report by Goto et al. which highlighted that splenic vein occlusion does not necessarily indicate invasive disease or a worse prognosis. Obstruction of pancreatic ducts by secretion of thick mucin leads to increased ductal pressure, a precursor to mechanical fistula formation, and progressive parenchymal atrophy resulting in pancreatic insufficiency. Fistula formation enables release of enzymes; however, in our case, this occurred in an acidic stomach resulting in denaturation and development of malabsorptive symptoms. While exocrine (enzyme) insufficiency does not correlate with the degree of dysplasia, endocrine insufficiency, detected by increased glycated haemoglobin, is associated with more invasive disease. Improvement in symptoms following Creon treatment in our case suggests that pancreatic enzyme insufficiency secondary to IPMN was responsible for his bowel symptoms rather than the colorectal tumour as initially thought. As such, the colorectal cancer was the incidental finding. Between 20% and 30% of patients with IPMN are diagnosed with a synchronous or metachronous extra-pancreatic malignancy. Pathogenesis of extra-pancreatic malignancy development is not fully understood and may be independent of IPMN or may be possibly associated with certain subtypes. We have presented, with accompanying images, a rare case of a patient who has presented with pancreatic enzyme insufficiency and subsequent diagnosis of a main duct IPMN that has spontaneously formed a fistula into the posterior wall of the stomach. While the diameter of the pancreatic duct suggests a high risk of present or future invasive change, histology of the fistula shows mechanical not invasive aetiology. While the images are dramatic, this finding does not worsen the prognosis. Total pancreatectomy and resection of the fistula opening in the stomach is the recommended treatment. Patient consent was obtained for publication of this case report.