Left Internal Iliac Artery Aneurysm Presenting With Nephrostomy-Site and Rectal Bleeding From an Arterio-Ureteral Fistula in a Patient With Rectovesical Fistula After Colorectal Cancer Therapy: A Report of a Rare Case.

Internal iliac artery aneurysms (IIAAs) are rare vascular abnormalities, while arterio-ureteral fistulas (AUFs) are uncommon but potentially fatal causes of hematuria. Both conditions are typically associated with prior pelvic surgery, radiotherapy, or long-term ureteric stenting. We describe the case of a 75-year-old man with a history of colorectal carcinoma managed with surgery and adjuvant pelvic radiotherapy, complicated by a rectovesical fistula and bilateral nephrostomies for obstructive uropathy. The patient presented with intermittent bleeding from the left nephrostomy and per rectum. A CT angiography demonstrated a left internal iliac artery aneurysm arising from the anterior division, in proximity to the distal left ureteric stent, raising suspicion of an arterio‑ureteral fistula. Endovascular coil embolization of the aneurysm was performed, resulting in complete resolution of bleeding. Follow-up CT angiography performed one month after the procedure confirmed complete exclusion of the aneurysm and absence of recurrent bleeding. This case illustrates a rare presentation of an internal iliac artery aneurysm with an arterio-ureteral fistula in the setting of a rectovesical fistula after colorectal cancer treatment, emphasizing the importance of early recognition and prompt endovascular management in complex post-oncologic pelvic bleeding.