IMA originates from the subclavian artery and comprises the anterior intercostal, perforating,
musculophrenic, superior epigastric, and pericardiophrenic branches. Injury to the IMA and/or its branches is rare in chest trauma, but the anatomical proximity to the heart could result in significant and life-threatening bleeding. In addition, bleeding confined to the mediastinum may result in extracardiac tamponade or the accumulation of blood in the thoracic cavity, resulting in tension hemothorax; both of these conditions could further compromise hemodynamic stability. Early detection is challenging but is very important in clinical practice.
Most chest trauma patients receive a plain chest film first. However, for IMA injury, an unacceptably high proportion of patients would be missed since there are no significant findings. Before multidetector CT was prevalent, angiography was arranged for patients with a high suspicion of mediastinal vessel injury. In our review, eight patients underwent angiography without CT, all of whom were from studies before 2000 (3, 6, 15, 17, 19, 30, 34, 37). After 2000, although diagnosis and treatment could be performed simultaneously by angiography, most physicians chose contrast-enhanced chest CT as the diagnostic tool because of its easy accessibility and ability to provide more comprehensive information. For blunt chest trauma, the National Emergency X-Radiography Utilization Study chest algorithm (NEXUS-chest) has already provided well-validated and practical recommendations for the implementation of chest imaging (39). For penetrating chest trauma, if an IMA injury is suspected according to the depth and route of injury, a contrast-enhanced chest CT scan is the reasonable first choice as long as the patient’s condition is suitable for the exam.
The treatments for IMA injury include observation, TAE, and surgery. Four patients in our review recovered after observation, and all were from the same series (36). In the series from Whigham et al., angiography was performed in all of their 18 patients, but four of them did not receive embolization since no active bleeding was identified. According to our review, TAE for IMA bleeding was first described in 1982 (15). Since the technique and image quality have made large progress in recent decades, TAE has become the mainstay choice in the literature for managing IMA bleeding due to its less invasive nature and equivalent success rate for hemostasis compared to surgery.
Shock remained the most important reason for surgery. Five patients in our review were operated on directly without CT or angiography (2, 4, 14, 17). Four patients were in shock status before the operation, and the other patient was sent back to the operating room due to massive hemothorax after receiving laparotomy for intra-abdominal bleeding. Fourteen patients underwent surgery after the initial CT scan, including 4 patients for shock(1, 12, 28), three for extracardiac tamponade(10, 16, 23), two for massive hemothorax(1), two for both extracardiac tamponade and hemothorax(1, 24), one for a large aneurysm(25), one for a foreign body (5), and one for persistent bleeding after pericardiotomy (11). Seven patients underwent surgery after angiography. Three were for AVF (3, 6, 19), two for shock (17, 22), one for combined subclavian and vertebral artery injury (27), and one for diagnosis only (37).
The outcome of IMA injury is good. Although the overall mortality rate seems high in our review, only one death was caused by uncontrolled exsanguination due to IMA, while the others were caused by severe associated injuries or organ failure. Most patients had an uneventful course after hemostasis was achieved. In fact, no patients with isolated IMA injury had complications. All reported complications were related to the respiratory system and occurred in those with associated injuries.
Notably, not all IMA injuries were identified at the beginning. Nearly 10% (7 patients) had a delayed presentation (6, 8, 19, 20, 25, 30, 37), especially those with AVF (4 in 5 patients). The duration from the trauma to the delayed diagnosis ranged from 1 week to 10 months. Little is known about these injuries were not identified at first presentation, but we believe that sometimes subtle vessel injuries such as AV shunting do need time to become symptomatic and evident.
Figure 2 is an integrative algorithm for IMA injury that we created after reviewing all of the literature. After performing the initial assessment and resuscitation according to the principles of Advanced Trauma Life Support 10 ed., extremely unstable patients should undergo surgical treatment promptly. For those who could be stabilized, the NEXUS CT-major or NEXUS CT-all criteria should be applied to decide the next step for blunt injuries, and CT is recommended for penetrating injuries if an IMA injury is suspected. If there is no evidence of active bleeding, conservative treatment could be considered, but these patients need close observation. If there is evidence of active bleeding, i.e., contrast extravasation or aneurysm/pseudoaneurysm, TAE could be considered first if the patient is clinically stable. If the following indications exist, surgical exploration is preferred prior to nonsurgical treatment: massive hemothorax, extracardiac tamponade, foreign bodies that need to be removed, difficult approach for TAE (e.g., AVF or large aneurysm), or concomitant injuries that need surgery immediately (e.g., cardiac rupture).