A rare variant in the confluence of the inferior mesenteric vein: a report on a formalin-embalmed cadaver

Introduction: The inferior mesenteric vein (IMV) typically joins either the splenic vein or the superior mesenteric vein to form the portal venous system. Several international imaging studies have reported that the frequency of IMV drainage variations ranges from 10% to 20% depending on the population; however, detailed descriptions of these drainage patterns remain inconsistent. Such variations can significantly affect colorectal, pancreatic, and hepatic surgeries, yet they have been rarely reported in Vietnam. Objective: To document and describe in detail a rare variant of the inferior mesenteric vein observed in a formalin-embalmed cadaver, thereby contributing additional data on the anatomical diversity of the mesenteric–portal venous system in the Vietnamese population. Methods: Dissection was performed on a 65-year-old male cadaver preserved in formalin. The mesenteric venous system and its related vascular structures were exposed, photographed, and diagrammatically illustrated in comparison with the typical anatomical pattern. Both qualitative and quantitative observations were recorded. Results: The inferior mesenteric vein did not drain directly into either the splenic vein or the superior mesenteric vein, but instead joined a branch of the middle colic vein before entering the superior mesenteric vein, forming an indirect drainage pattern. This configuration altered the anatomical relationship between the inferior mesenteric vein and the left colic artery, potentially increasing the risk of vascular injury during colorectal and pancreatic surgeries. No associated pathological abnormalities were found. Conclusion: This case provides additional descriptive evidence of the anatomical diversity of the inferior mesenteric vein in the Vietnamese population. Early recognition of such variants using CT angiography and three-dimensional reconstruction may help surgeons adjust their operative approach, reduce intraoperative complications, and improve surgical safety. However, as this is a single cadaveric case report, further studies on larger sample sizes are needed to confirm these observations.