Iliac Artery Aneurysm with Primary Arteriocolic Fistula: An Unusual Cause of Lower Gastrointestinal Hemorrhage

Arteriocolic fistula is a rare but life-threatening condition. We report the case of a 70-year-old man who presented with passage of bloody stools and intolerable abdominal pain. Esophagogastroduodenoscopy and colonoscopy failed to identify the source of the bleeding. Contrast-enhanced abdominal computed tomographic scans showed an aneurysm arising from the left common iliac artery with close adhesion between the aneurysm and adjacent sigmoid colon, but no extravasation was detected. After an episode of severe abdominal pain with massive bleeding, emergency laparotomy revealed that the aneurysmal wall was closely adhered to the sigmoid colon with fistula formation. Iliac arterial aneurysm with arteriocolic fistula was diagnosed. The aneurysm was excised, and femoral-femoral bypass grafting was done. No bleeding recurred during 6 months of follow-up. Although bleeding from a primary iliac arteriocolic fistula is rare, it should be considered in the differential diagnosis of lower gastrointestinal bleeding, especially in patients with severe abdominal pain.