Type IV: Rupture In addition to the 4 grades of aortic injury, the risk of rupture can also be categorized. If both the inner layer and the muscle layer of the aortic wall are both involved in the injury then the injury is categorized as significant aortic injury. If just the inner layer and a portion of the muscle layer are involved in the injury then the injury is characterized as minimal aortic injury. Radiographically this would be seen as an intimal flap less than 1 cm in size. Between the mobile ascending aorta and the relatively fixed descending thoracic aorta is the aortic isthmus. When there is a sudden deceleration the mobile ascending aorta pushes forward creating a whiplash effect on the aortic isthmus. However, a different mechanism is involved when the ascending aorta proximal to the isthmus is torn. When there is a rapid deceleration the heart is pushed to the left posterior chest. This causes a sudden increase in intra-aortic pressure and can cause aortic rupture. This is known as the water hammer effect. Based on the location of the injury in the thorax subsequent injuries can take place. If the injury is in the descending thoracic aorta this could lead to a hemothorax. Where as an injury to the ascending aorta could lead to hemoperricardium and subsequent tamponade or could compress the SVC. Symptoms It is difficult to rely on symptoms to diagnose a thoracic aortic injury. However some symptoms do include severe chest pain, cough, shortness of breath, difficulty swallowing due to compression of the esophagus, back pain, and hoarseness due to involvement of the recurrent laryngeal nerve. There might be external signs such as bruising on the anterior chest wall due to a traumatic injury. Clinical signs are uncommon and nonspecific but can include generalized hypertension due to the injury involving the sympathetic afferent nerves in the aortic isthmus. A murmur can also be audible as turbulent blood flow goes over the tear. Diagnosis Classification There are inconsistencies in the terminology of aortic injury. There are several terms which are interchangeably used to describe injury to the aorta such as tear, laceration, transection, and rupture. Laceration is used as a term for the consequence of a tear, whereas a transection is a section across an axis or cross section. For all intents and purposes, the latter is used when a tear occurs across all