An Asymptomatic Sigmoid Colonic Fistula Arising from a Large Aneurysm of the Internal Iliac Artery Was Discovered during a Medical Examination.

The rupture of an internal iliac artery aneurysm in the colon is a rare but potentially fatal complication. We report a rectal fistula of an asymptomatic internal iliac artery aneurysm that was discovered incidentally during a medical examination. A 77-year-old man presented at a local hospital for a general medical examination. Although the blood reports revealed severe anemia, the patient did not complain of any associated symptoms including dizziness and hematochezia. Moreover, there was no palpable mass in the patient's abdomen, and there was no evidence of hematochezia, as the patient had been using a bidet. Interestingly, computed tomography (CT) revealed a large right internal iliac artery aneurysm. There was a suspicious finding of a fistula within the colon in the CT, but it was undetected in the preoperative sigmoidoscopy. Furthermore, operative findings showed a protruding retroperitoneal mass adhering to the mesentery of the sigmoid colon. During aneurysm resection, the presence of a fistula was unclear. However, a fistula tract, devoid of any infectious bacteria such as tuberculosis, was found in the specimen after colon resection. After a recovery period of approximately one week, the patient was discharged from the hospital without any unusual findings on the post-operative CT. Sigmoid colonic fistulas arising from iliac artery aneurysms are rare. Also, diagnosis may be delayed in special circumstances wherein a patient routinely uses a bidet.