Angiography in Trauma

Angiography in the setting of acute trauma is extremely important, and may be life saving. The following discussions deal with this topic in the separate contexts of thoracic trauma and extremity injuries.

Traumatic Aortic Laceration / Rupture

Traumatic aortic laceration is rapidly lethal. Blunt thoracic trauma with aortic laceration accounts for 16% of all motor vehicle accident fatalities, and 85% to 90% of victims will die prior to reaching a medical facility. The danger of rapid exsanguination in those who survive the initial trauma but remain untreated is 30% within the first 6 hours, and 40% within the first 24 hours following the injury.

The mechanism of injury historically was thought to be rapid deceleration with "whipping" of the aorta at points of attachment (i.e., aortic root, ligamentum arteriosus, diaphragmatic hiatus). More recent evidence suggests that injury at the most common site, the aortic isthmus, is due to compression of the anterior chest wall and pinching of the aorta between structures of the anterior bony thorax and the thoracic spine.

The most common sites of injury are aortic isthmus (88%), right brachiocephalic artery origin (4.5%), left subclavian origin (2.7%), descending thoracic aorta (1.8%), aortocardiac junction (1%), left carotid origin (0.8%), transverse arch (0.6%), and diaphragmatic hiatus (0.4%). Injuries at the aortic root and diaphragmatic hiatus rarely survive the initial trauma. Aortic lacerations most often occur in a transverse or transverse oblique plane. In sixty percent of cases one or more layers of the aortic wall will remain intact and may result in traumatic dissection or traumatic aneurysm.

The natural history of untreated aortic laceration is uncertain. Of the 10-15% of patients who survive the initial trauma, only 60% will survive the next 24 hours. Although subsequent mortality decreases sharply, the risk of rupture of a post-traumatic thoracic aneurysm remains significant. In general, the prognosis for thoracic aneurysms is poorer than that for abdominal aortic aneurysms with 57% one year, 26% three year, and 19% five year survival. Thus, of 100 cases of thoracic aortic laceration, 85 to 90 victims will die immediately, and, left untreated, only 2 to 3 will be alive after five years. Nevertheless, post-traumatic aneurysms occasionally are discovered incidentally 10 to 20 years after the initial injury. In some patients, healing with fibrosis through the site of laceration will result in post-traumatic coarctation of the aorta with the typical features of upper extremity hypertension and lower extremity pulse deficits.

Clinical signs are unreliable in excluding aortic rupture. Clinical findings are present in less than one half of patients, and up to one third of patients have no evidence of external trauma. Reported clinical findings include the following: upper extremity pulse differential (37%), chest pain (26%), dyspnea (25-30%), systolic murmurs (21-30%), back pain (14%), dysphagia (10%), and rarely, paralysis.

There are several radiographic signs of significant mediastinal injury on plane chest films. The most important of these signs are: loss of the aortic knob outline, widening of the mediastinum, rightward shift of the trachea, depression of the left mainstem bronchus, loss of the aorticopulmonary window, displacement of the NGT to the right, and widening of the left paraspinal stripe. However, all these signs lack significant predictive value of aortic injury and, taken alone, none are adequate to dictate therapy.

Based on data from the University of Maryland Shock Trauma Center, a normal chest x-ray (i.e., normal superior mediastinum) has a negative predictive value of 91%, and thus does not entirely exclude aortic injury. Furthermore, the practice of obtaining portable supine films on trauma patients complicates the decision to proceed to aortography, as supine films may result in the false appearance of mediastinal widening and loss of definition of the aortic arch. Consequently, the decision to undergo aortography must be based largely on the mechanism of injury. Positive radiographic signs support this decision, but do not, in themselves, mandate aortography. Conversely, the absence of such signs should not be thought of as negating the need for an aortogram in the patient with a significant history of chest trauma.

Dynamic CT of the chest is useful in excluding aortic laceration if the mediastinum is normal. However, in the presence of mediastinal hematoma, it is often impossible to define the source of bleeding. Therefore, in the setting of acute trauma with suspected aortic injury, aortography is the appropriate examination and should be undertaken without delay in the stabilized patient. In most cases, patients who cannot be stabilized should be explored immediately without prior angiography. In patients for whom abdominal CT is also indicated, aortography should precede the CT examination, since aortic laceration is immediately life threatening. On the other hand, patients with closed head injuries and suspected aortic laceration should have a cranial CT prior to aortography because both injuries are immediately life threatening and contrast enhancement from the aortogram will potentially interfere with interpretation of the CT study.

The most common angiographic finding in aortic laceration is a traumatic aneurysm. In the majority of patients (60%), the laceration will involve the intima and media only, and hemorrhage is contained by the adventitia. Occasionally, traumatic aneurysm formation may be delayed by several months or years. The acute traumatic aneurysm is recognized by its irregular saccular bulge which usually appears along the anteromedial aspect of the aortic isthmus. Over time the contours of the bulge become smoothed as remodeling occurs. Chronic traumatic aneurysms often have a thin rim of mural calcification. It is important not to confuse the ductus infundibulum with an aortic tear. The ductus infundibulum is usually a focal, smoothly contoured convexity located along the concave margin of the arch, just distal to the left subclavian artery origin.

Isolated intimal tear occurs in 5 to 10% of patients and is identified as a linear lucency in the opacified aorta. This injury may progress to a frank dissection. However, extravasation of contrast through the aortic wall or dissection leading to aortic occlusion is rare.

Post-traumatic dissection may occur following either laceration or intimal tear injuries. The dissection may not be localized and may extend antegrade and/or retrograde from the site of initial injury. Significant dissection occurs in about 10% of patients with aortic laceration and may be either medial or subadventitial. In patients with atherosclerotic disease, the dissection plane is usually in the media. Dissection is recognized by the curvilinear lucency separating the false and true lumina, and by differential filling and emptying of the two channels.

Minimal injuries of the thoracic aorta may result from blunt or penetrating trauma. These injuries are manifested by mural trauma with an intact intima. Since these injuries lack the obvious signs of aneurysm or dissection, it is important to examine the late phase of the arteriogram carefully for intimal displacement or mural thrombus. Patients with minimal injuries are often treated expectantly.

Penetrating trauma to the aorta may be due to high or low velocity objects. In about 80% of cases the injury results in immediate exsanguination. Among the survivors, the injury may result in formation of a false aneurysm, arteriovenous fistula, or thrombotic occlusion of the aorta. Projectiles which come to rest within the aortic lumen will often embolize distally. Therefore, head to toe fluoroscopy may be indicated in cases where there is no exit wound and the projectile is not seen, and in cases of shotgun wounds where it is impossible to account for all of the projectiles.

Peripheral Vascular Trauma

Vascular injuries of the neck, pelvis and extremities are relatively common in emergency practice. These injuries include penetrating trauma due to high or low velocity objects, blunt trauma, crush injuries, degloving injuries, and arterial trauma secondary to skeletal or joint injuries.

Penetrating Injuries

Penetrating wounds may produce vascular injury by either direct penetration or by dissipation of energy in the tissues adjacent to a blood vessel. For vascular injury to occur from a low velocity object, such as a knife, the trajectory of the object must traverse the vessel and the object must penetrate it. As the velocity of the object increases, so does the kinetic energy dissipated as the object decelerates in the soft tissues. This energy dissipation takes the form of cavitation and shock waves which produce local tissue injury. This effect is minor with small caliber low velocity hand guns, but becomes highly significant with large caliber or high velocity projectiles such as from hunting rifles and military weapons. High power weapons such as these may produce significant tissue damage over a radius of 10 cm or more from the trajectory of the bullet. Gunshot wounds resulting in bone fractures may produce secondary blood vessel injury if the bone fragments penetrate or impinge upon adjacent vascular structures

Blunt Injuries

Blunt trauma may produce vascular injury directly, as a mural contusion, or through sheer and/or traction forces which may result in intimal/medial disruption or complete transection. Indirect injury may be from extrinsic compression due to hematoma, edema, dislocation, or fracture, with subsequent thrombosis of the vessel. Displaced bone fractures may produce secondary penetrating vascular injuries. Crush injuries produce vascular trauma by similar mechanisms. Degloving is an unusual form of injury where cutaneous and subcutaneous tissues are stripped from an appendage. These injuries may result in avulsion of a blood vessel or traction injury with intimal and medial disruption.

Types of Arterial Injury

Arterial spasm due to trauma is relatively common. Spasm is often associated with some degree of anatomic injury, usually a small intimal tear or mural hematoma. Spasm which is not associated with a discrete injury is usually concentric and relatively smooth, and will often respond to an intraarterial vasodilator such as priscoline.

Extrinsic compression may be either eccentric or concentric, and generally appears smooth in contour. Severe compression or poor distal runoff may result in arterial thrombosis even in the absence of intrinsic arterial injury.

The features of arterial laceration vary with the severity, location and mechanism of the injury. Intimal lacerations occur in the setting of blunt trauma and often cause eccentric spasm with formation of intimal thrombus over the site of the tear. Transmural lacerations result in hemorrhage into the adjacent tissues with formation of a hematoma which will expand until its internal pressure exceeds mean arterial pressure. This is the mechanism that underlies the formation of pseudoaneurysms which result when there is incomplete thrombosis of the hematoma leaving a cavity with persistent communication to the arterial lumen. When a laceration involves both an artery and vein, mounting tension in the hematoma may be relieved as blood flows down the pressure gradient into the vein creating an arteriovenous fistula. Laceration which results in complete transection of an artery often produces profound spasm at both sides of the injury. In these cases there may be surprisingly little hemorrhage despite the severity of the vascular damage.

Intramural hematoma occurs in the setting of blunt trauma, crush injuries, degloving injuries, and in proximity to penetrating wounds from high velocity projectiles. As a result of the hematoma there is inward displacement of the intima/ media forming a smooth, usually eccentric, convex margin. Large intramural hematomas may significantly compromise the lumen and result in thrombosis.

Embolization may occur in a variety of types of injury. In penetrating injuries, a projectile may come to rest within the vessel lumen, and be carried distally with the blood flow. Shotgun wounds and bullets which become fragmented on impact are notorious for both distal arterial and central venous embolization. Injuries described above that result in intraluminal thrombosis may also cause distal (or central) thromboembolism.

Indications for Angiography in Peripheral Vascular Trauma

Indications for angiography following penetrating injury to the extremities can be divided into major and minor categories. Major indications are: (1) diminished or absent pulses, (2) active arterial bleeding or expanding hematoma, (3) bruit over the site of injury, (4) isolated neurological deficit, and (5) hypotension. Minor indications are proximity of the wound to a major vessel and nonexpanding hematoma.

Caution must be exercised when dealing with penetrating wounds near large joints. The rich network of arterial collaterals around large joints may mask the usual clinical findings of a significant arterial injury as distal pulses can be well preserved. It is far better to error on the side of caution in these cases and proceed to angiography.

Proximity wounds are an area of controversy. For low velocity injuries such as knife wounds, proximity alone is not an indication for angiography. In a study of 677 stab wounds at the University of California, Davis, angiograms were performed in 30 patients with proximity as the sole indication. In that series, results were negative in 30 cases and positive in none. Penetrating high velocity wounds do have a potential for arterial injury based on proximity. In a study of 507 gunshot wounds at Parkland General Hospital, there was a true positive yield of 3.6%. In this study there were 31 positive angiograms resulting in 24 explorations and 19 true positive injuries. In the five false positive cases the trauma surgeons disagreed with the radiologist's negative interpretations and proceeded to exploration. There were 13 angiographic complications. Overall, there were a total of 18 complications, 13 from angiography and 5 misinterpretations resulting in unnecessary operations. Thus, there was no statistical difference between the total complication rate and the true positive yield in this study. The guidelines established at Parkland now limit the proximity indication to cases where the patient is examined by a 5th year surgery resident, trauma or vascular fellow, or staff trauma surgeon. The trajectory of the projectile must lie within 10 cm of a major vessel, and the projectile must be of large caliber or from a high velocity weapon.

Penetrating abdominal trauma mandates laparotomy and abdominal angiography in such cases is rarely indicated. However, both penetrating and blunt pelvic trauma can result in hemorrhage that is extremely difficult to locate and control by surgical means. Hypotension and/or expanding pelvic hematoma mandate immediate angiography with embolization to control bleeding. Isolated pelvic trauma with massive hemorrhage carries a 30 day surgical mortality of about 60%, while angiographic management of such cases has a 30 day survival of 95%.

Posterior dislocations of the knee joint and anterior dislocations at the elbow usually require angiography to rule out a significant vascular injury that may be masked by the extensive collateral blood supply in these areas.

Angiographic Technique in Suspected Vascular Injuries

In the angiographic work-up of vascular trauma, the critical importance of a thorough examination cannot be overemphasized. In an extremity injury it is necessary to study the arterial inflow to at least the level of the proximal major joint. In older individuals, the inflow should be examined proximally to the aorta. Furthermore, arterial outflow must be studied to the most distal part of the extremity to rule out embolization. In the case of shotgun wounds or fragmented bullets, a fluoroscopic examination from the distal end of the extremity to the chest should be done to search for embolized pellets or fragments. A minimum of two angiographic views centered on the area of injury should be done, with additional views as required. Either conventional or high resolution digital imaging can be used. It is important to examine all phases of the angiogram. Therefore, angiographic study using a multistation runoff technique is inappropriate.

Interpretation of Angiographic Signs of Arterial Injury

In many cases the angiographic signs of arterial injury are nonspecific as to the exact nature of the injury. Arterial occlusion may be due to transection, thrombosis secondary to mural hematoma, or extrinsic compression, etc. The important finding is arterial occlusion indicating a significant vascular injury. Definitive diagnosis may be possible in cases of intimal tear. Mural hematoma, spasm and extrinsic compression may have identical appearances at angiography. Spasm which is relieved by intraarterial vasodilators most likely represents irritation due to adjacent injury, but does not entirely rule out injury intrinsic to the vessel.

Pseudoaneurysms and arteriovenous fistulae have characteristic features and easily recognizable angiographic signs. Pseudoaneurysms usually are saccular or tear-drop in shape, and have prolonged retention of contrast media. However, a pseudoaneurysm may fill slowly, or it may be obscured by superimposed opacified vessels on early films. This emphasizes the importance of examining the late films in the angiographic sequence. Prolonged retention of contrast in a pseudoaneurysm indicates active bleeding while rapid wash out is usually a sign of a stable injury. In acute traumatic arteriovenous fistulae there may be an associated pseudoaneurysm visible on the angiogram. However, the important finding is early and dense opacification of an adjacent vein. Many of these injuries can be managed by transcatheter embolization of the involved artery adjacent to the site of injury.

Final Comment Regarding Angiography in Trauma

Arterial injuries pose a significant risk to life and limb. While it is true that many of these injuries present at the most inconvenient of times, quick and accurate diagnosis is essential. A large percentage of these angiograms are expected to be normal. If this is not the case, then the indications being applied are too stringent, and it is probable that significant injuries are being overlooked. Angiography is an invasive procedure that does carry some small risk to the patient. However, that risk is minor in comparison to the potential risk imposed by an undiagnosed vascular injury. Therefore, even in cases where the indications are "soft", it is almost always better to error on the side of caution and do the arteriogram.