‘Retro-uncinate Superior Mesenteric Vein’ – first report of a rare congenital anomaly and possible embryological explanation

We evaluated a 61-year-old female for a periampullary cancer. The preoperative contrast enhanced CT scan demonstrated an abnormal course of superior mesenteric vein (SMV). The vein was absent from its normal location in the groove behind neck of the pancreas and anterior to the superior mesenteric artery. It was found to be coursing anomalously, posterior to the uncinate process of pancreas and on the right of superior mesenteric artery. This is probably the first report of this anomaly. We had to coin the term ‘retro- uncinate SMV’ to describe this anatomical variation. Rest of the porta structures and pancreas were found to be anatomically normal in this patient. This is a rare anomaly, probably does not have a pathological consequence and remained unreported. Congenital variations in porta structures are relatively common. Careful and thorough preoperative assessment of radiology is essential to have a roadmap to avoid injuries to such anomalous structures during surgery. Preoperative identification of this anomaly resulted in a safe pancreaticoduodenectomy in this patient. Development of portal venous system and pancreas are closely related due to their anatomical proximity. Normally, the left part of ventral pancreatic anlage regresses and right part rotates posterior to the developing SMV. Malrotation of this right ventral pancreatic anlage anterior to the developing SMV or Regression of right ventral pancreatic anlage and persistence and development of left ventral pancreatic analge anterior to the developing SMV is the only logical explanation for development of this anomaly.