Mycotic aortic aneurysm is a rare entity, manifesting with nonspecific symptoms of abdominal pain, fever, general malaise. We present a case of an 83-years-old-man, with hematemesis, generalized abdominal pain, and a six-month history of constipation, anorexia, and involuntary weight loss. Upper endoscopy revealed an erosion with oozing hemorrhage and hemostasis was performed. Later he developed a hemorrhagic shock. Abdominal computed tomography disclosed a 3,7×2,5x- 2,5cm aneurysm of the abdominal aorta with an aortoduodenal fistula, inducing an inflammatory plastron that encompassed the descending colon and duodenum. The inflammatory plastron prompted partial duodenal and colonic obstruction and led to an atypical presentation of an aortic aneurysm. Mycotic aneurysms complicated with aorto-enteric fistulas are potentially life-threatening conditions. We highlight the rarity of this case, as the clinical manifestations were prolonged and atypical. The goal is to drive awareness to maintain a high clinical suspicion, as early detection is critical to avoid a tragic outcome.