ASCENDING AORTA Incidence Very few patients with ascending aortic injury survive long enough for the diagnosis to be established and repair to be carried out. These injuries are frequently associated with cardiac rupture or severe myocardial contusion, and the aortic tears are multiple in up to 15 to 20 percent. Most victims have been hit by or thrown from moving vehicles or have fallen from great heights.
Diagnosis Since most ascending aortic tears occur within the pericardium, if there is a small complete tear, there is often evidence of both shock and pericardial tamponade. The chest x-ray findings often show a widened superior mediastinum with or without obscuration of the aortic knob. Aortography is generally required for the diagnosis to be established. The aortogram usually shows a pseudoaneurysm with an intimal tear seen as an irregular filling defect within the lumen. If there is an associated valvular injury, aortic insufficiency of varying severity will usually also be seen.
Thoracic aortic injuries distal to the isthmus should be suspected with severe chest trauma in which a lower thoracic vertebra is severely crushed.
DESCENDING AORTA Injuries to the descending aorta are uncommon. The presentations include paraplegia (owing to injuries to vessels supplying the spinal cord), mesenteric ischemia, anuria, or lower extremity ischemia. Angiography is typically required for diagnosis, and cardiopulmonary bypass may be required for surgical management. The more distal the injury, the better the anticipated outcome—assuming that the patient does not exsanguinate prior to surgical repair. Immediate surgery is indicated.
OTHER GREAT VESSEL INJURIES Innominate Artery INCIDENCE In patients reaching the hospital alive, blunt injuries of the innominate artery are second in frequency only to rupture of the aorta at the isthmus. Associated injuries, such as rib fractures, flail chest, hemopneumothorax, fractured extremities, head injuries, facial fractures, and abdominal injuries, are found in more than 75 percent of these patients.
DIAGNOSIS Making a diagnosis of blunt injury to the innominate artery can be very difficult because there are no characteristic physical findings except for some diminution of the right radial or brachial pulse, which occurs in about 50 percent of the patients. Signs and symptoms of distal ischemia are uncommon. Occasionally, a systolic murmur may draw attention to a possible lesion in this area.
The chest x-ray findings are somewhat similar to those seen with TRA, but the mediastinal hematoma tends to be higher and the trachea and esophagus may be pushed to the left. Aortography must generally be performed for the diagnosis to be established. Associated injuries in other brachycephalic vessels or the aorta are found in about 10 percent of patients.
Subclavian Artery ETIOLOGY Although a subclavian artery is occasionally avulsed at its origin because of sudden deceleration, direct trauma to the distal artery with intimal damage and occlusion associated with fractures of the first rib or clavicle are more likely. Shoulder restraints that are loose may be a major factor in causing this injury.
DIAGNOSIS The most important sign of a subclavian occlusion is absence of a radial pulse. In the patient with only a partial laceration and no occlusion, the radial pulse may be preserved. Other physical findings that are highly suggestive of subclavian artery rupture are a pulsatile mass or a bruit in the root of the neck. Occasionally a patient may develop an acute subclavian steal syndrome if the subclavian artery occludes proximal to the origin of the vertebral artery.
Up to 60 percent of patients with blunt injury to the subclavian artery, especially from motor vehicle accidents, will also have some damage to the brachial plexus. Consequently, a complete neurologic examination preoperatively is important in these patients. A Horner's syndrome often indicates avulsion of nerve roots from the spinal cord.
The chest x-ray with subclavian artery injuries may show the presence of a widened superior mediastinum without obscuration of the aortic knob. The angiogram usually shows occlusion, but a pseudoaneurysm is occasionally found. Blunt subclavian artery injuries are associated with other major vascular injuries in about 10 percent of patients.
TREATMENT The treatment of acute subclavian artery injury is usually immediate repair. However, in certain high-risk patients who are doing poorly, occlusion by an interventional radiologist may be the treatment of choice. If the artery is already occluded, observation may be all that is required. The collateral circulation to the distal portions of the vessel is usually very good. However, if there has been severe blunt trauma to the shoulder girdle, many of the collateral vessels may be damaged, resulting in critical ischemia of the hand or upper extremity gangrene in about 30 percent.
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