Recurrent Hematochezia Due to a Rectal Fistula Caused by a Left Internal Iliac Artery Aneurysm.

Arterio-enteric fistulas (AEFs) are a rare cause of gastrointestinal bleeding involving direct communication between an artery and the intestinal tract. The duodenum is the most common fistula site for AEFs, but none of the rectal cases are known. We present the case of an elderly man with hematochezia due to a rectal fistula caused by a left internal iliac artery aneurysm, which was detected on contrast-enhanced computed tomography (CT), showing typical fistula formation and ectopic gas images. This case highlights the importance of considering the occurrence of rare but potentially fatal AEFs in elderly patients with hematochezia and that the timely performance of contrast-enhanced CT is critical for an accurate diagnosis.