Purpose: Complete mesocolic excision requires central mesenteric dissection near the middle colic vein (MCV) confluence, where anatomic variability may increase operative risk. However, MCV multiplicity, confluence patterns, and relationships to the middle colic artery (MCA) are not sufficiently defined.

Methods: We performed a retrospective secondary analysis of 300 consecutive three-dimensional vascular reconstructions from a prospectively maintained database of patients undergoing surgery for right-sided colon cancer (age 65 ± 9 years; 59% female) between November 2017 and December 2022. We classified transverse mesocolic venous trunks operationally as MCV1, MCV2, and MCV3 according to their right-to-left position to standardize the description of multiple venous drainage patterns. MCV trunks (MCV1-3), their confluence patterns, and their spatial relationships to the MCA were analyzed using descriptive statistics. The reconstruction method had been previously validated intraoperatively and was performed by a single investigator.

Results: The MCV was identified in all cases (397 veins total). There was one trunk in 68.7%, two in 30.3%, and three in 1.0% of patients. Confluences were most often into the superior mesenteric vein (65.7%), followed by the inferior mesenteric vein (12.6%) and gastrocolic trunk (9.8%). MCV1 drained mainly into the SMV (72.7%). MCV2 showed variable drainage into the SMV (45.7%), IMV (31.9%), jejunal vein (9.6%), left SMV (3.2%), and left colic angular vein (2.1%). MCV3 drained into the IMV in 66.7% and the left SMV in 33.3%. The MCV and MCA were separate in 67.0% of cases, with anterior crossing in 17.7% and posterior crossing in 15.3%. Left-sided drainage patterns were seen in 20-50% of patients with 2 trunks and 3.

Conclusions: MCV anatomy is highly variable, with multiplicity in 31.3% and frequent alternative confluence pattern. Preoperative 3DCT can identify alternative variants and may support safer, tailored vascular ligation during lymphadenectomy.