Two Cases of Rectal Cancer with Retzius Shunt Treated with Robot-Assisted Surgery.

The retroperitoneal intestinal vein-general circulation anastomotic pathway is referred to as a Retzius shunt; however, it is not a well-recognized condition. Here, we describe two patients with a Retzius shunt who underwent robot-assisted surgery for rectal cancer. The first case was an 81-year-old woman who had tested positive for fecal occult blood. A type 0-Is tumor was found in the middle rectum, and we used robot-assisted surgery for resection. Intraoperative findings included a dilated vein between the inferior mesenteric artery (IMA) and inferior mesenteric vein (IMV); further, computed tomography (CT) revealed flow into the inferior vena cava (IVC). We clipped the vein without major bleeding and the tumor-specific mesorectal excision was completed. Thereafter, we reviewed relevant literature and identified the structure to be a Retzius shunt. The second case was 77-year-old man with type 1 advanced cancer in the middle rectum who underwent robot-assisted surgery. In this case, we recognized the Retzius shunt on preoperative CT due to our experience with the first case and surgery was completed without any problems. Preoperative recognition of vascular malformations, such as the Retzius shunt by CT is critical to ensure the safety of robot-assisted surgery.