Misdiagnosis of Primary Iliac Aneurysmo-Colonic Fistula as a Submucosal Tumor Leading to Delayed Treatment: A Case Report.

An aortoenteric fistula (AEF) is an uncommon cause of gastrointestinal bleeding that requires prompt diagnosis and intervention owing to its high mortality rate. Moreover, iliac aneurysmo-colonic fistula is an exceptionally infrequent presentation. We report a unique case of a 71-year-old male presenting with hematochezia, later diagnosed with a primary fistula between a common iliac artery aneurysm and the sigmoid colon. Initially, the patient was misdiagnosed as having a gastrointestinal stromal tumor, leading to delayed and emergent surgical intervention due to massive bleeding 2 days later. This case is particularly notable for its rarity, misinterpretation of the initial diagnosis, complicated surgical procedures, and development of complications including ischemic myopathy. This case highlights the criticality of accurate diagnosis with a high index of suspicion, significance of consultation with a vascular surgeon for vascular abnormalities, and importance of considering ischemic time in the sequence of surgical treatments to ensure timely and appropriate management.