AF are defined as a communication between the aortic lumen and adjacent organs,such as cardiovascular structures, airway, and digestive tract.It is an uncommon pathology and its main cause is secondary to vascular procedures,both surgical and endovascular, or trauma. Primary fistulas are rarer, withatherosclerosis being the main etiology. Other less frequent ones are infections,neoplasms, collagen diseases, etc. Incidence of AF is rising due to the increase ofendovascular procedures and the prevalence of arteriosclerotic disease.AF can debut with massive bleeding, hypovolemic shock and even death. However,they can also present slightly more clinical such as with intermittent and moderatebleeding. The clinical picture will depend on the structure affected. Diagnostic imagingis of great importance here because it can be difficult to clinically diagnose the AF,especially if there is no known history of vascular interventions.Radiologic modalities available:- CT: initial examination of choice, enables quick acquisition of images with highspatial resolution.- Angiography: allows better definition of the vascular anatomy and is mainlyused in interventional procedures.- MRI: has important limitations in emergencies including less availability andincreased image acquisition times. Endovascular prostheses may produceartefacts in the image. It is particularly useful in cases where an underlyinginfection is suspected.- Nuclear medicine: may be useful in suspected underlying infection and inintermittent and very limited bleeding.- Ultrasound (US): has limited assessment of the aorta though it may be useful inunstable patients allergic to iodinated contrast media. The use of US contrastmedia may help visualise the passage of blood into the fistulised structure.

Transesophageal echocardiography (TEE) is useful in the evaluation of flowthrough fistulae in the aortic arch, aortic root, and proximal descending aorta.