Case Report: Progressive acquired ileal mesenteric venous malformation after right hemicolectomy: serial imaging evolution leading to delayed gastrointestinal bleeding.

Background: Mesenteric venous malformations are rare vascular anomalies. Acquired lesions involving the gastrointestinal mesentery are particularly uncommon and may present years after abdominal surgery with obscure gastrointestinal bleeding, posing a diagnostic challenge. Case presentation: We report a rare case of progressive acquired ileal mesenteric venous malformation developing after right hemicolectomy. A 50-year-old woman underwent curative right hemicolectomy for colon cancer in 2016. Four years later, she presented with recurrent painless hematochezia and anemia, while colonoscopy failed to identify the bleeding source. Contrast-enhanced CT angiography demonstrated clusters of dilated and tortuous veins within the ileal mesentery, forming a caput medusae-like appearance and draining into the superior mesenteric vein, with additional communication to the lumbar vein. Exploratory surgery confirmed a localized venous plexus along the mesenteric border of the terminal ileum. Targeted ligation and suturing of the abnormal vessels resulted in complete resolution of bleeding. Conclusion: Acquired ileal mesenteric venous malformation should be considered in patients with unexplained delayed gastrointestinal bleeding after right hemicolectomy. This case uniquely documents progressive lesion evolution on serial imaging, supporting the hypothesis that postoperative venous outflow alteration and chronic venous remodeling may contribute to lesion development. Recognition of this entity may facilitate timely diagnosis and surgical management.