The Role of Interventional Radiology in Trauma

ABSTRACT

Since the development of angiography and transcatheter techniques, interventional radiology has played an important role in the management of trauma patients. The ability to treat life-threatening hemorrhage with transcatheter embolization has spared countless patients the morbidity of surgery. Advances in cross-sectional imaging and increases in understanding of which patients will best benefit from embolization promise to further refine the interventional radiologist's role. As the applications of transcatheter therapy broaden to include embolization of unstable patients with solid organ injuries and endovascular repair of major arterial injuries, the interventional radiologist must be increasingly prepared to provide prompt, efficient, and high-quality service.

Interventional radiologists (IRs) are ideally qualified to play an important role in the management of trauma patients. Aside from their specialized training in the delivery of transcatheter therapies, IRs receive broad-based multimodality imaging training, which renders them highly capable of correlating findings from preprocedural imaging studies to speed diagnosis and treatment of trauma patients in the emergency setting. However, an interventional practice must meet the following criteria to be an effective player in the team management of trauma patients: (1) a skilled IR who is available for consultation on urgent notice; (2) availability of high-quality digital subtraction angiographic equipment, preferably with digital road mapping and/or fade-fluoroscopic capabilities; (3) availability of skilled nursing and equipment needed for monitoring of critically ill patients; and (4) ability to ready these resources within 30 to 60 minutes. Equally important, treatment of trauma patients requires efficient use of resources as well as cooperation and communication among a multidisciplinary team. Patients need to be rapidly and accurately assessed to determine the nature of their injuries with treatments prioritized by injury severity. Angiography and transcatheter therapy can be time-consuming and may delay other important procedures, so it is critical that delays in interventional treatment are minimized.

INTERVENTIONAL TREATMENT MODALITIES

The following interventional treatment methods are commonly utilized in the trauma setting:

1. Balloon occlusion: Inflation of an angioplasty balloon proximal to or at a major arterial injury may temporarily stop or reduce life-threatening hemorrhage and thereby stabilize the patient while definitive surgical or endovascular repair is being arranged.

2. Transarterial embolization (TAE): TAE can stop arterial hemorrhage, thus improving unstable hemodynamics and often avoiding the need for surgery. Prompt, effective, and safe TAE requires skill and knowledge of the available equipment, arterial anatomy, role of collateral arterial flow, and risks. A variety of catheters, including coaxial microcatheters, are available for selective catheterization to virtually all parts of the arterial circulation. Embolic agents vary in their permanency and the anticipated level of arterial occlusion. The choice of embolic agent will vary based on the site and nature of the injury, the desire to preserve collateral flow, and operator preference. Gelfoam, particles (e.g., polyvinyl alcohol), and coils are some of the most commonly selected embolic agents in trauma. Care must be taken to avoid nontarget embolization.

3. Stent-grafts: Stent-grafts are increasingly being applied to the treatment of large vessel injuries and may enable one to avoid complex surgical vascular repairs in areas with trauma-related anatomic distortion and in patients who may be unstable. These considerations must be weighed against the long-term sequelae of device implantation, which are largely unknown.

SOLID VISCERAL INJURIES

The spleen is the most commonly injured solid abdominal organ, closely followed by the liver, with injuries occurring as the result of blunt or penetrating trauma. Less frequently the kidney, mesentery, adrenal gland, small bowel, or pancreas is injured. In the past, surgery was the only treatment for control of hemorrhage. However, TAE quickly earned a role in the nonoperative management (NOM) of these injuries, particularly where organ preservation was important (Fig. 1).

Figure 1.

Active extravasation is well seen on CT (A) in the right hepatic lobe following a gunshot wound to the right upper quadrant. Angiography confirms the extravasation (B), which was successfully treated with TAE using coils superselectively deployed in the bleeding vessel with preservation of surrounding branches (C). (Images courtesy of James Duncan, M.D., Ph.D.)

Imaging plays a large role in the evaluation of trauma patients. FAST (focused assessment with sonography for trauma) can be used to rapidly screen for hemoperitoneum.¹ In skilled hands, FAST can also be used to evaluate for pleural and pericardial fluid and solid organ injury of the spleen, liver, and kidney. FAST is not useful for evaluation of the retroperitoneum, diaphragms, or bones and has only intermediate sensitivity for bowel and mesenteric injuries. Though more costly and time-consuming, computed tomography (CT) is the best imaging study for evaluation of stable trauma patients. Its sensitivity for injury approaches 100%. A prospective multicenter trial using contrast-enhanced helical CT to evaluate stable patients found that 18.4% of patients with visceral injuries had arterial extravasation, and patients with arterial extravasation were significantly more likely to undergo TAE or surgery.² Arterial extravasation is identified as a focus or area of high attenuation that does not conform to a normal vascular structure, is isodense to arterial contrast, and is surrounded by the high-attenuation fluid of a hematoma or is situated within an injured solid organ. This extravasation may be contained, as in the case of a pseudoaneurysm, or uncontained with free spill into the peritoneum. CT angiography (CTA) can also be used to evaluate large-vessel integrity with diagnosis of arterial occlusions, transections, dissections, intimal tears, and more.

Spleen

Patients with hemodynamic instability and evidence of splenic trauma typically undergo immediate surgery. Hemodynamically stable patients with splenic injury are triaged to NOM with observation or TAE. The decision as to who should undergo angiography has changed over time. Early reports advocated mandatory angiography for all patients with imaging evidence of splenic injury who did not undergo immediate surgery.³,⁴ Unfortunately, many patients did not prove to have arterial injuries at angiography and did not require TAE. Subsequently, clinical and imaging parameters were successfully used to stratify patients into those who required angiography and those who could be observed. This division avoided angiography in a majority (74%) of patients.⁵ Currently, the accepted indication for angiography is the presence of active extravasation or pseudoaneurysm formation at CT.⁶ This “contrast blush” is strongly correlated with failure of observation as NOM.⁷,⁸ Stable patients with splenic injuries that do not demonstrate one of these findings can be observed. Most will recover uneventfully, though some will experience delayed hemorrhage requiring intervention. Failure rates for NOM of splenic injuries range from 2 to 52% with most studies reporting rates between 7 and 20%.⁹ These failures can be treated with surgery or delayed TAE.³

Recently, success has been reported with expanded indications for angiography despite the absence of active extravasation or pseudoaneurysm formation by CT. These added indications include significant hemoperitoneum, American Association for the Surgery of Trauma (AAST) grade 3, 4, or 5 splenic injury, declining hematocrit, and persistent tachycardia despite resuscitation.⁵,⁹,¹⁰ Haan et al also reported success in treating a subset of unstable patients with TAE, a group typically treated with surgery.¹⁰

Two methods are available for splenic TAE, proximal and distal embolization, both with proven success. Proximal TAE is performed by deploying coils 2 cm beyond the origin of the dorsal pancreatic artery but proximal to the first pancreatica magna artery. This method reduces pulse pressure to the spleen, promoting native hemostasis, but preserves flow to the spleen through collaterals. Coils should be just larger than the vessel diameter to avoid distal embolization or protrusion into the celiac artery. Distal TAE is typically performed using gelfoam pledgets or slurry distributed by flow. A variant of this is superselective embolization of a single injured vessel, which can be performed using a microcatheter with particles or coils but requires increased time and skill. Combinations of proximal and distal TAE may be useful in some cases. Not surprisingly, postprocedural CT has demonstrated a higher rate and larger size of splenic infarcts following distal “scatter” embolization as compared with proximal TAE.¹¹ Thus, proximal TAE is recommended for organ preservation with distal TAE reserved for refractory hemodynamic instability or control of extraparenchymal extravasation.

The primary risk of splenic TAE is infection. Immunizations for encapsulated organisms are recommended. Though scintigraphy has confirmed residual splenic tissue after TAE, there is little data on immunological function of this residual tissue.⁴,¹²

Liver

Hepatic trauma can result in injuries to the hepatic arteries, portal veins, and/or hepatic veins. The mortality rate of surgery for blunt hepatic trauma has been reported to be 33% or greater.¹³ Therefore, NOM is the treatment of choice for stable patients and may increasingly be selected for some unstable patients as well. CT has proven useful in the identification of patients who require angiography.¹⁴ An estimated 50 to 80% of patients with blunt hepatic trauma should be able to undergo NOM with avoidance of surgery in 98.5%.¹⁵ The dual blood supply of the liver makes infarction from TAE unlikely provided the portal vein is patent and flow is antegrade, findings that can be confirmed at angiography. In some cases, superselective catheterization and embolization can be performed to preserve uninjured tissue (Fig. 1). Less selective “scatter” embolization of an entire hepatic lobe or segment may be performed using gelfoam or particles. This method is preferred to treat multiple sites of injury simultaneously and when prompt cessation of hemorrhage is necessary and superselective catheterization is too time-consuming.

Kidney

A recent series of consensus documents on genitourinary trauma highlights the evaluation and management of renal injuries.¹⁶ Similar to hepatic and splenic trauma, the indications for angiography have varied with time but have a basis in CT imaging. Generally, patients with severe injuries or instability are taken to surgery, but one recent report advocated mandatory angiography of high-grade injuries (AAST 4 and 5) whenever the clinical condition allowed it, even in the setting of hypotension.¹⁷ Embolization should be performed as selectively as possible to preserve uninjured renal parenchyma. Superselective TAE preserves renal function, sometimes better than surgery.¹⁸ Both gelfoam and coils are appropriate, though gelfoam may allow for recanalization and tissue preservation. With increasing experience, the role of interventional treatment may expand to include stent-graft insertion for repair of large vessel injury.

AORTA

The aortic injury most concerning in blunt trauma is acute aortic transection, or acute traumatic aortic injury (ATAI), due to its high mortality. Most patients die before transport to the hospital. Of those who reach the hospital, the overall survival rate is 70% with higher mortality associated with delays in treatment.¹⁹ Additional injuries of the aorta and its branches may occur from trauma as well, including intimal tears and dissections. (Fig. 2) Therapy is generally guided by the nature of the injury and the presence or risk of organ compromise.

Figure 2.

Blunt chest trauma resulted in a traumatic injury of the right brachiocephalic artery with pseudoaneurysm formation. The intraluminal filling defect proximal to the vertebral artery origin was felt to preclude safe endovascular treatment and was confirmed to be thrombus at surgery. (Image courtesy of Colin Derdeyn, M.D.)

A high degree of suspicion is needed to diagnose ATAI. Chest radiography is an excellent screening exam with a negative predictive value of 95%. Unfortunately, its specificity is only 25%.¹⁹ Contrast-enhanced CT has proven utility in evaluation of patients with abnormal chest radiographs²⁰ and patients for whom there is a high clinical suspicion.²¹ A normal CT has a negative predictive value of 100% for ATAI.²² In the past, all patients with abnormal chest CT exams underwent catheter angiography. Catheter angiography has generally been considered the gold standard for diagnosis of ATAI, but CTA has shown sensitivity, specificity, and accuracy similar to catheter angiography and is supplanting this procedure in many medical centers.¹⁹,²² Transesophageal echocardiography is also an excellent diagnostic tool for ATAI, particularly in unstable patients.

ATAI is associated with rapid deceleration in motor vehicle collisions, falls from a height, and crush injuries. Several mechanisms have been suggested to explain these injuries.¹⁹ Most injuries involve partial- or full-thickness disruptions of the aortic wall. In patients who reach the hospital alive, ~90% occur at the aortic isthmus, with smaller proportions in the ascending aorta just above the aortic valve (8%) and in the descending aorta at the diaphragmatic hiatus (2%).²² The great vessels are not uncommonly injured as well.

Arteriography should include at least two different views of the aortic arch—typically a 45 degree left anterior oblique and an anteroposterior view. Additional views including right anterior oblique and lateral projections can be obtained as needed. Arteriographic findings include an abnormality or outpouching of the aortic contour, an intimal flap or dissection, retention of contrast in a pseudoaneurysm sac, and/or, rarely, the appearance of a coarctation. The proximal segments of the great vessels should be carefully assessed for associated injuries.

Treatment of ATAI has traditionally been operative repair, but increasingly patients are being treated with endovascular stent-grafts. Emergency surgery for treatment of ATAI has mortality rates of 15 to 29% with higher mortality in the elderly.²³

PELVIS

Most patients with pelvic fractures are hemodynamically stable. A small percentage, particularly those with unstable fractures, present with hemodynamic instability. Pelvic fractures alone are associated with mortality rates of 5.6 to 15%, but the addition of hemorrhagic shock raises rates to 36.4 to 54%.²⁴ Death due to hemorrhage frequently occurs in the first 24 hours, and the mortality rate rises with delays in treatment.²⁵,²⁶ Associated organ injuries have been found in 11 to 20.3%,²⁴ injuries that can increase morbidity and mortality. Failure to treat or delay in treatment can result in death due to hemorrhage or abdominal compartment syndrome.

Pelvic hemorrhage most commonly arises from fractured bones or disrupted pelvic veins with only 10 to 20% of severe hemorrhage from arterial injury.²⁷ Once bones are fractured and ligamentous structures disrupted, the pelvis can expand and hold a large volume of blood.

Hemodynamically unstable patients with pelvic fractures require aggressive resuscitation. Treatments for traumatic pelvic hemorrhage include external fixation of unstable fractures, TAE, and pelvic packing. Open surgical procedures like packing are not advised due to the loss of the tamponade effect of the contained hematoma, risking large-volume, uncontrolled venous and/or arterial bleeding.²⁸ Some surgeons advocate prompt stabilization of the bony pelvis, although others prefer immediate TAE.²⁹ External fixation apposes bone surfaces and reduces pelvic volume, enhancing tamponade from the enlarging hematoma. This maneuver may stop bleeding from bone surfaces and veins but is unlikely to stop arterial bleeding³⁰ and delays TAE. Temporary pelvic binders, which can be applied more quickly, may be acceptable alternatives.

Arterial bleeding at angiography has been associated with a lack of response to initial resuscitation, the pelvic fracture pattern, the amount and location of pelvic hematoma, and active extravasation of contrast at CT.²⁹,³¹ CT with contrast diagnoses and localizes arterial extravasation from pelvic trauma with a sensitivity of 60 to 90%, a specificity of 85 to 98%, and an accuracy of 87 to 98%.²⁴,³¹ The internal pudendal artery and superior gluteal arteries are two of the most commonly injured pelvic arteries.²⁵,²⁷ Nevertheless, any pelvic artery can be the source of hemorrhage, and knowledge of pelvic arterial anatomy on cross-sectional imaging can guide the angiographer and save time. It is important to avoid retrograde urethrography or cystography prior to CT or angiography to avoid confusing leakage and arterial extravasation.³²

Most arterial hemorrhage originates from branches of the internal iliac arteries. Nonselective pelvic arteriography can be useful to localize and lateralize a site of hemorrhage. Selective arteriography of the internal iliac arteries should follow. Currently accepted indications for TAE include active extravasation, arterial branch irregularity or truncation, one or more pseudoaneurysms, and arteriovenous fistula formation (Fig. 3). Additional, less uniformly accepted, indications include persistent hemodynamic instability and the presence of a large pelvic hematoma without evidence of active extravasation.³³ These controversial indications also include TAE to treat venous bleeding by reducing arterial inflow.

Figure 3.

Blunt trauma to the pelvis resulted in injury of the left internal iliac artery with a contrast blush in the left pelvis (A) confirmed as a pseudoaneurysm of the proximal anterior division branch (B). Marked irregularity of the posterior division branch was not appreciated on CT. Both injuries were treated with coil embolization.

The chosen embolic agent and technique should provide hemostasis while preserving normal vessels and collateral flow where possible. Gelfoam in pledgets or slurry has been the agent of choice due to its temporary nature. Coils, however, may be appropriate for single arterial abnormalities and for distal-to-proximal embolization across the neck of a large-vessel pseudoaneurysm. Distal gelfoam embolization from a proximal catheter position may be necessary if the patient is unstable, selective catheterization is overly time-consuming, or there are multiple arterial injuries in the supplied region (Fig. 4). Proximal embolization with coils to decreased pulse pressure to a site of bleeding is not generally successful due to the robust pelvic collateral network. It is important to evaluate the contralateral internal iliac artery to exclude continued hemorrhage from collaterals or additional sites of bleeding. Success rates for TAE range from 85 to 100% with mortality rates of 17.6 to 47% despite successful embolization.²⁴ Lower mortality rates have been associated with early TAE.²⁵ Higher mortality has been seen in older patients and patients with greater hemodynamic compromise.²⁵,²⁹

Figure 4.

Multiple small pseudoaneurysms of the right internal iliac branches are present on this pelvic angiogram. The diffuse nature of the injury makes gelfoam “scatter” TAE optimal.

Tissue necrosis, paresis, impotence, abscess formation, and sepsis have all been attributed to pelvic TAE.³⁴ Unfortunately, it is difficult to separate the complications of TAE from the sequelae of pelvic fractures and their treatment. A recent study noted the rate of sexual dysfunction to be similar in patients with pelvic fractures regardless of whether they had TAE.³³ Nevertheless, based on the potential complications, empiric embolization cannot be recommended, and bilateral embolization should be carefully elected.

EXTREMITIES

The extremities are frequently injured in trauma, particularly penetrating trauma from gunshot and stab wounds, but arterial injuries can also occur in blunt trauma, typically due to crush injuries, tissue disruption (e.g., degloving,) joint dislocation, and laceration from broken bones or penetration by external objects.

The physical exam is key in evaluating extremity trauma. The results can triage patients to surgery, arteriography, or observation. The extremity should be evaluated for the presence of a penetration wound as well as the trajectory and location of that injury. Arterial injury may often be excluded based on this evaluation alone. Next, evaluation should center on the neurovascular exam. The “hard signs” of an extremity arterial injury include loss of distal pulses, an expanding or pulsatile hematoma, a thrill or bruit, pulsatile bleeding, and limb ischemia. “Soft signs” include pallor or a change in color, coolness to the touch, a stable hematoma, a neurological deficit in an anatomically adjacent nerve, unexplained hypotension, and nonpulsatile bleeding. Proximity injuries are injuries in which penetration occurred near an artery but without hard signs of arterial injury. These are of most concern in gunshot wounds where the pressure changes associated with the projectile course through the tissues can cause trauma to tissues distant from the missile's path. Serious arterial injury is rare in these cases, however.³⁵

In the past, all patients with suspected vascular injury underwent operative exploration, but this resulted in unnecessary surgeries with the risks of anesthesia and infection. Currently, most patients with hard signs of vascular injury or evidence of compartment syndrome undergo immediate surgery. Delays in treatment of major arterial injuries have been associated with the need for amputation. Early recognition with vascular repair has improved limb salvage.³⁶ Preoperative angiography may or may not be performed depending on the degree of ischemia and surgeon preference.

Patients with a normal neurovascular exam do not require angiography or surgical exploration as the negative predictive value of a normal exam approaches 100%.³⁶,³⁷ This has been demonstrated for blunt as well as penetrating trauma.³⁸,³⁹ Further, there are long-term data to support observation of patients with a normal neurovascular exam as well as patients with occult abnormalities seen at angiography including small pseudoaneurysms and nonocclusive intimal defects with intact and patent distal vessels.³⁷ A small percentage of patients may ultimately require surgery, but, in one report, all came to attention within 6 to 12 months with onset of hard signs of vascular injury, and none suffered limb morbidity or loss. Patients with soft signs of injury or concern for occult injury can undergo assessment of Doppler pressure indices. Patients with penetrating trauma who do not have hard signs but have abnormal Doppler pressure indices (< 1.0) should probably undergo angiography with intervention as deemed necessary.⁴⁰

Angiography should begin with a nonselective injection of the thoracic arch for upper extremity evaluation and the abdominal aorta or ipsilateral iliac system for lower extremity evaluation. A complete evaluation will often require selective and possibly subselective catheterization of the affected extremity. Imaging at the injury site should be performed in at least two projections as subtle injuries and intimal tears may be visible only on one view.

It is important to differentiate limb-threatening angiographic abnormalities in critical arteries from non–limb-threatening injuries in these arteries and abnormalities in noncritical arteries. Major angiographic findings include active extravasation, large pseudoaneurysms, and arterial occlusion or transection (Fig. 5). Minor angiographic findings include vessel narrowing or displacement by hematoma, spasm, obstruction of or thrombus in minor noncritical branches, nonocclusive intimal tears, small pseudoaneurysms, and small arteriovenous fistulas.

Figure 5.

Multiple injuries of the extremities are possible from trauma including probable dissection with intramural hematoma (A), transection with pseudoaneurysm formation (B), and active extravasation (C) treated with TAE (D). (Images A, C, and D courtesy of Michael Darcy, M.D. Image B courtesy of James Duncan, M.D., Ph.D.)

Transcatheter treatments include balloon occlusion, TAE, and endovascular repair with insertion of stent-grafts. Injuries of the aorta or large proximal extremity vessels like the subclavian artery or superficial femoral artery are particularly life-threatening because it is difficult to apply direct pressure to these sites. These patients not infrequently present in extremis, and balloon occlusion can be particularly helpful.⁴¹ Coils are often the best agent for embolization of small vessel injuries as particles can reflux, causing nontarget embolization. An appreciation of the collateral circulation to the distal extremity is necessary to determine the safety of and method of embolization.

Though arterial transactions, dissections, and occlusions have traditionally been repaired surgically, there has been increasing interest in endovascular repair using insertion of stent-grafts.⁴² Reports are available on endovascular treatment of the aorta,²³ the carotid artery,⁴³ the subclavian artery,⁴⁴ the brachial artery,⁴² and the iliac arteries.⁴⁵,⁴⁶ Many of the reported repairs using stent-grafts occurred when operative repair was associated with a greater than normal difficulty or there was an immediate need for cessation of hemorrhage.⁴⁴ There are little data on long-term utility and safety of this treatment. In particular, areas of mobility such as the thoracic outlet may be associated with stent fatigue or fracture, and the decision to proceed with stent-graft insertion should be considered carefully. The choice of stent-graft should also take into consideration the location of the injury and the potential for external compression, which could crush or deform a stent-graft.

CTA is increasingly useful in the evaluation of extremity arterial injury and is replacing catheter angiography in some settings.⁴⁷ CTA has a sensitivity of 90 to 95.1% and a specificity of 98.7 to 100% for detection of extremity arterial injury.³⁵ Signs of injury are similar to those at catheter angiography. CTA may be limited due to poor arterial opacification, motion artifact, streak artifact from adjacent metallic fragments, or slowing of flow beyond injured sites. Fortunately, catheter angiography can typically be performed if additional information is needed.

CONCLUSION

Interventional radiology has much to offer in the evaluation and treatment of traumatic injuries. Current literature suggests that this role may expand in time due to desire for organ preservation and avoidance of surgery as well as due to improvements in transcatheter equipment. A solid understanding of the benefits and risks of the different transcatheter therapies is required to provide patients with the best care possible.