Missing Bullets: Bullet Embolization Case Series and Review of the Literature

Abstract

Purpose:

Bullet embolization is a rare but dangerous phenomenon. Based on the location of embolization, migration of bullets can cause limb or intra-abdominal ischemia, pulmonary infarction, cardiac valve injury, or cerebrovascular accident. Bullet emboli can present a diagnostic challenge given the varied nature of complications based on location of embolization, which may not coincide with the site of initial injury. The purpose of this study is to present several cases of bullet embolization from our busy urban trauma center and make recommendations for management.

Methods:

We present 3 cases of bullet embolization seen in injured patients at our Level 1 trauma center. We describe our management of these injuries and make recommendations for management in the context of our institutional experience and comment on the available literature regarding bullet embolization.

Results:

Two of our patients presented in extremis and required operative intervention to achieve stability. The intravascular missile was discovered intraoperatively in one patient and removed in the operating room, while the missile was discovered on postoperative imaging in another patient and again removed operatively after an unsuccessful attempt at minimally invasive retrieval. Our third patient remained hemodynamically stable throughout his hospitalization and had endovascular management of his bullet embolus.

Conclusion:

Bullet emboli present a challenging complication of penetrating trauma. We recommend removal of all arterial bullet emboli and those within the pulmonary venous system. In hemodynamically stable patients, we recommend initial attempts of endovascular retrieval followed by open surgical removal. We recommend open removal in cases of hemodynamic instability.

Introduction

Intravascular embolization of foreign bodies occurs infrequently but can be a devastating complication of ballistic trauma. Patients may be asymptomatic or can experience complications like sepsis, limb-threatening ischemia, cardiac valvular damage, pulmonary embolism, stroke, or death. The first-ever reported case of foreign body embolization was in 1834 and involved a 10-year-old boy with a wooden fragment which embolized to his right ventricle.¹ Later, bullet embolization was seen in .3% of Vietnam War casualties.² There have been less than 200 cases of missile embolization published in the literature since 1900, most of which are arterial.³ In the majority of cases, management has been observation or open surgery, but more recent literature increasingly describes endovascular techniques as a successful alternative.

During a 3-year period (January 2019 to December 2021), approximately 3051 ballistic injuries were treated at Grady Memorial Hospital, a busy urban Adult Level 1 trauma center in Atlanta, Georgia. We present three cases of bullet embolization from our center and recommendations for management.

Case 1

A 22-year-old male presented with a single ballistic wound to the right upper quadrant located 2 cm inferior to the costal margin in the mid-axillary line. Exploratory laparotomy revealed an American Association for the Surgery of Trauma (AAST) grade 1 laceration to the lateral surface of the liver, a nonexpanding right-sided zone 2 hematoma, and a mesenteric injury with a devascularized ascending colon. The patient underwent a right hemicolectomy while also completing a primary closure of the mesenteric defect. The retroperitoneal hematoma was nonexpanding and therefore not explored. No injuries were identified to the diaphragm or left upper quadrant.

A postoperative computed tomography (CT) of the chest, abdomen, and pelvis with intravenous (IV) contrast revealed a bullet fragment located adjacent to the right external iliac vein (Figure 1A) and another in the left pulmonary artery at the lung hilum (Figure 1B). Due to risk of erosion through the pulmonary artery, endovascular retrieval by interventional cardiology was attempted but was unsuccessful. Cardiothoracic surgery subsequently performed an open bullet removal. The patient was discharged home on postoperative day 12 with no further complications. After retrospectively reviewing this case, we believe the bullet most likely gained access to the venous system through the right external iliac vein and traveled up through the inferior vena cava (IVC) and right heart before becoming lodged in the left pulmonary artery, from which the fragment was eventually removed.

Figure 1.

(A) CT demonstrating bullet fragment near right external iliac vein. (B) CT demonstrating bullet fragment in left lung hilum.

Case 2

A 15-year-old male presented with a single ballistic wound to the right anterior chest. Plain radiographs of the chest and pelvis demonstrated a ballistic projectile in the right midabdomen raising concerns for a transdiaphragmatic trajectory with intra-abdominal pathology. The transthoracic focused assessment with sonography in trauma (FAST) view of the heart revealed a large pericardial effusion. The patient was taken emergently to the operating room due to concerns for progressive tamponade and multisystem injury.

The patient first underwent a sub-xiphoid pericardial window, which revealed hemopericardium. A sternotomy was then performed, where a ballistic wound on the right side of the pericardium was found with an accompanying injury to the superior vena cava-right atrial (SVC-RA) junction. After ensuring hemostatic control following operative repair, the patient underwent an exploratory laparotomy. Although there were no intra-abdominal injuries, a bullet was palpated within the right common iliac artery. A transverse arteriotomy of the right common iliac artery was performed to extract the bullet followed by Fogarty embolectomy of residual thrombus and standard closure of the arteriotomy. On further inspection of the heart, there were no other traumatic injuries. The patient was subsequently discharged home after a prolonged postoperative recovery. It was evident that the bullet had embolized to the right common iliac artery from the heart.

Case 3

A 43 year-old man sustained an isolated ballistic injury to the left hip. Initial radiographic imaging demonstrated a bullet in the right chest at the atriocaval junction (Figure 2A). The patient remained hemodynamically stable, the FAST exam was negative, and no additional findings were observed on secondary survey. A CT scan was completed with evidence of the bullet in the pelvis with no hemoperitoneum and no hollow viscous or solid organ injuries (Figure 2B). The CT demonstrated a left iliac crest ballistic fracture with tract tracking through the left iliopsoas into the left common iliac and distal IVC with a ballistic fragment that was now situated in the right iliac vein. Additional serial imaging studies showed the ballistic fragment oscillating between these two locations.

Figure 2.

(A) Chest radiograph demonstrating bullet at atriocaval junction. (B) CT demonstrating a ballistic fracture of the left iliac crest and injury to the left common iliac vein (arrow pointing to the left iliac vessels). (C) Bullet trapped via stenting across ostia of right internal iliac vein.

Vascular surgery attempted endovascular retrieval which was unsuccessful. At the time of the procedure, intravascular ultrasound revealed that the bullet lodged in the right internal iliac vein. Therefore, a self-expanding stent was placed across the ostia of the internal iliac vein to trap the missile in place and prevent further embolization (Figure. 2C).

Discussion

Missile embolization is a rare complication of traumatic injury. The overall annual incidence of bullet embolization at our institution over this study period was .03%. Bullet embolization should be suspected in three scenarios: when discordant radiographic evidence of bullets is present that cannot be explained by trajectory, when there is an odd number of ballistic wounds, and if there is radiographic evidence of a “wandering bullet.” Embolization occurs when a bullet has lost enough kinetic energy that it penetrates only a single wall of a vessel and stops inside the lumen, which is most commonly seen with small-caliber, low velocity bullets.⁴ Once within a vessel, the direction of migration of the foreign body depends on hydrostatic pressure, gravity, body position, and anatomic factors.⁵ Thicker-walled arterial vessels are most commonly affected, comprising 80% of bullet emboli cases.⁶ However, bullet embolization can be arterial, venous, or paradoxical. Arterial emboli generally lodge in peripheral vessels and lead to limb- or organ-threatening ischemia; they are therefore routinely removed.⁵ Venous emboli tend to migrate to the right heart (48%, of which 58% get caught in the right ventricle), lodge in the pulmonary circulation (36%), or go to the peripheral/central veins (16%).⁷ Most patients with venous bullet emboli are asymptomatic (70%-90%), but symptoms can be present at the time of injury or several years after injury.⁷ Complications after centrally migrated bullet emboli include valve dysfunction, endocarditis, bullet erosion through cardiac or vascular tissue, abscess formation, myocardial irritability, or anxiety related to having a bullet in the heart; these complications are seen in 25% of cases of initially asymptomatic patients with venous bullet emboli.⁸ Paradoxical bullet embolization describes cases where a bullet enters the venous circulation but migrates into the arterial circulation, generally through a patent foramen ovale or other cardiac defect or through a traumatic fistula. Given that these impact the arterial circulation, they tend to require removal.

In our first case, we saw a bullet entering the venous system with central embolization, where it lodged in the pulmonary vasculature. Conversely, in our second case, we observed a bullet injury to the SVC-RA junction with bullet fragment embolization to the right common iliac artery, implying paradoxical embolization. In our first two cases, the bullet was removed with no further complications. In our third case, an interesting phenomenon occurred as both anterograde and retrograde bullet embolization was observed. As seen through temporal radiography, the bullet was observed oscillating from the atriocaval junction to the right pelvis. Removal of the bullet in this case was unsuccessful, so the bullet fragment was trapped with an endovascular stent. In our first case, the location of the bullet seemed too dangerous to simply observe, and in our third case, the bullet oscillation seemed too unstable to not attempt removal.

Although arterial bullet emboli are typically removed due to risk of distal ischemia, management of venous bullet emboli is somewhat more controversial. Due to the rare occurrence of bullet embolization, no clear clinical guidelines have been established. Management tends to be based on surgeon and institution preference and experience. A recent article by Yoon et al.⁷ provides guidelines for management of venous bullet emboli with the recommendation that any venous embolus located in the central veins or right heart be retrieved with an initial attempt of percutaneous intervention. If this fails, hybrid or open approaches are recommended. Observation is suggested if the following criteria are met: bullet less than 5 mm in diameter, smooth appearance of bullet, bullet being firmly lodged, lack of contamination, hemodynamic stability. In the case of bullet emboli to the pulmonary arterial vasculature, they recommend serial imaging in asymptomatic patients and open removal if symptoms develop.⁷ Based on our institutional experience, “jailing” or trapping venous bullet emboli is also a potential option, as seen in our third case. In a hemodynamically stable patient, we believe endovascular retrieval should be attempted first due to its less invasive nature compared to a sternotomy. In a hemodynamically unstable patient, or those emboli unable to be retrieved by endovascular snare, median sternotomy or other open surgery should be performed. We agree with Yoon et al.⁷ in opting for observation if the above criteria are met.

There is very limited evidence to guide decisions regarding anticoagulation after bullet embolization. Schroeder et al.⁹ describe a case of a 19 year-old man who sustained a ballistic injury to the anterior chest with subsequent bullet migration to the left internal iliac vein which required endovascular retrieval. Postoperatively, this patient was maintained on enoxaparin 40 mg daily for 3 weeks, with discontinuation after lower extremity ultrasound revealed no evidence of thrombosis. Aidinian et al.¹⁰ present four cases of military vascular trauma involving explosive or bullet wounds where fragment embolism was noted. In the 2 cases where metallic fragments were seen in the lungs, 12 months of oral anticoagulation was administered to prevent thrombus formation or propagation, as these intrapulmonary fragments were not retrieved. Mattox et al.¹ report on 28 patients between 1965 and 1977 with intravascular bullet emboli. Of the seven cases with embolism to the pulmonary artery, fragments were left in place in five cases due to their small size; these cases did not receive anticoagulation and were asymptomatic on follow up. The variability in management surrounding thrombosis after missile embolization is apparent, and it is difficult to make strong recommendations regarding anticoagulation in the absence of more evidence.

Bullet emboli present a challenging complication of penetrating trauma. They can be difficult to diagnose, and a high index of suspicion needs to be maintained in order to discover them. They can present with various and sometimes life-threatening pathologies. We recommend removal of all arterial bullet emboli and those within the pulmonary venous system. In hemodynamically stable patients, we recommend initial attempts of endovascular retrieval followed by open surgical removal. We recommend open removal in cases of hemodynamic instability.