Acute aortic syndrome (AAS) (aortic dissection, intramural aortic haematoma, or penetrating atherosclerotic ulcer) is a surgical emergency. Computed tomography (CT) is the reference technique for the diagnosis of this critical situation. However, a few reports of false-positive images leading to unnecessary interventions have been published. It is important to recognize and understand the pitfalls in the CT diagnosis of AAS. We describe the case of a 76-year-old man with clinical signs of AAS and a CT-scan compatible with a diagnosis of aortic intra-mural haematoma, leading to emergency surgery. The peroperative findings revealed a normal aortic wall with the presence of an unusual pericardial recess at the right side of the aorta.