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Circumportal pancreas: rarely seen often missed

Axial contrast-enhanced computed tomography (CT) section through the upper abdomen of a 40-year-old lady revealed an incidental, relatively rare and often under-recognized congenital variant of pancreas. An annulus of pancreatic parenchyma was completely encasing the main portal vein in keeping with circumportal pancreas (Fig. 1). Circumportal pancreas or portal annular pancreas represents an uncommon and frequently overlooked congenital pancreatic variant with a reported detection rate of 1.14–2.5% on CT. Circumportal pancreas, as the name suggests, refers to complete encasement of the portal or mesenteric vein by an annulus of pancreatic tissue (Fig. 2). Although contentious, it is presumably a sequel of anomalous fusion of the ventral and dorsal pancreatic buds occurring cranial and to the left of the portal/mesenteric vein which results in aberrant encasement of the portal vein by the uncinate process of the pancreas. The main pancreatic duct in patients with circumportal pancreas traverses either in a normal fashion anterior to the portal vein or at times can course posterior to the portal vein (i.e. retroportal pancreatic duct). Joseph et al. classified circumportal pancreas into three types: type I with a retroportal pancreatic duct; type II with concomitant pancreas divisum and a retroportal pancreatic duct; and type III characterized by an anteportal pancreatic duct (Fig. 3). Each type can be further sub-classified into suprasplenic, infrasplenic and mixed variety based upon the level of the annulus in relation to the splenic vein. Type III is the commonest morphology as per the literature review by Joseph et al. accounting for 60% of reported cases. The retroportal pancreatic ductal anatomy (types I and II) accounts for approximately 40% of the cases.