Severe hemorrhage is a life-threatening condition. Fractured trabecular bones and ruptured pelvic veins constitute the majority of bleeding sources, while arterial bleeding is reported in about 20% of cases [8]. Different fracture types, including lateral compression, anteroposterior compression, vertical shear, and combined mechanisms, can cause varying degrees of bleeding. Usually, the last three cause the most severe damage and require angiography in 20% of cases [1]. For unstable patients, early fracture stabilization is crucial to stabilize the pelvic ring and reduce hemorrhage [5]. The type of fracture underlying the bleeding has a large impact on hemorrhage control: in cases of lateral compression injury, bleeding stops in 99% of cases, whereas the intrinsic instability of posterior compression, vertical shear, and combined mechanism fractures results in ineffective bleeding control after compressive maneuvers in 18% to 22% of cases, especially if arterial involvement is present [1]. Another critical factor to consider is trauma-induced coagulopathy (TIC), which is caused mostly by hypothermia and repeated transfusions. Wherever possible, the presence of coagulopathy should guide the interventional radiologist in choosing the embolic material. In fact, it is widely known that because their methods of action are essentially dependent on clot formation, coagulopathy limits the effectiveness of embolization performed with gelatin sponges and coils [9–12]. Many authors have advocated for the use of non-adhesive liquid embolic agents (NALEA) and n-butyl cyanoacrylate (NBCA) in patients with coagulopathy because their embolization mechanisms are based on mechanical actions of polymerization (NBCA) and solidification (NALEA) rather than thrombus formation [9,13].

Before performing vascular embolization, it is imperative to have a comprehensive understanding of the vascular anatomy of the pelvis and any potential variations. The primary arterial vascular supply of the pelvis is given by the dividing branches of the internal iliac arteries and, to a lesser extent, by the branches of the external iliac artery [14]. The internal iliac arteries are typically divided into anterior and posterior branches. The anterior trunk serves the majority of the pelvis organs through the obturator, umbilical, inferior vesical, gonadal, internal pudendal, and inferior gluteal branches. The posterior trunk serves the posterior abdominal wall and pelvis through the iliolumbar, lateral sacral, and superior rectal branches [4].

About 30% of patients also have middle rectal arteries. These arteries usually originate together with prostatic arteries in the prostate-rectal trunk [14]. Both non-targeted embolization and recurrent hemorrhage can result from anastomoses with the superior and inferior rectal arteries, which are frequently seen [15].

A relatively high risk of hemodynamically significant bleeding, death, and morbidity is also associated with injuries to the external iliac artery, which have been reported to occur in 3.5–17% of cases of PT [16,17]. For effective endovascular therapy, a complete evaluation of the external iliac arteries is therefore mandatory. One particularly significant anatomic variant is the Corona Mortis, which is a vascular anastomosis between the external iliac artery and the obturatory artery. It is reported to be present in a third of patients on routine CT examination [18].

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The undisputed indications for performing angiography are active extravasation of contrast medium on CT, the presence of pseudoaneurysms, and the presence of arteriovenous fistulas [1]. Nevertheless, the sensitivity of a CT scan in detecting active bleeding after trauma is known to be between 60 and 90% [24,25]. There are several cases in which angiography may be necessary even in the absence of evidence of arterial injury on CT examination, such as, for example, in patients with persistent hemodynamic instability after PPP or in the presence of a large (>500 cm³) pelvic hematoma even in the absence of active blush on CT examination [26].

The common femoral artery is punctured at the level of the femoral head, generally on the opposite side to the hematoma, to facilitate pelvic vessel catheterization. Two femoral accesses could be obtained in some elderly individuals or in patients with especially convoluted arteries to shorten the amount of time needed for the procedure. Puncture on palpatory guidance is not always possible given the hypotension these patients might have. In addition, pelvic binders may hide the artery. In these cases, the use of ultrasound guidance for a puncture may help.

As regards the upper limb arteries approach, these arteries have historically been punctured in situations of significant pelvic soft-tissue injury or when pelvic devices prevent transfemoral access. Nevertheless, radial artery access is becoming more and more popular in trauma patients, with technical success rates comparable to those of femoral access [27,28].

If there are no obvious sources of bleeding on the CT scan, non-selective as well as selective angiographies in various projections should be performed to search for sources of bleeding.

Selective angiographies should always be performed and are of the utmost importance to rule out or confirm bleeding spots [29].

The primary goal of embolization is to quickly stop blood flow to the injured vessels to restore hemodynamic stability. Whenever feasible, super-selective embolization is preferable; however, it should be considered that the time required to manipulate a microcatheter into smaller pelvic visceral arteries might cause the treatment to take longer than necessary.

If, for instance, the patient is hemodynamically unstable or has deteriorating vital parameters, a quick embolization of the entire anterior or posterior division branch of the internal iliac artery is preferable to a time-consuming super-selective embolization of the single vessel responsible for the bleeding. Moreover, the increased risk of ischemia given by non-selective embolization is mitigated by the rich collateral network present in this anatomical region [1]. Other authors, however, assert that selective embolization may be carried out as quickly as proximal embolization without reducing the survival rate of trauma patients [30].

The hemodynamic status of the patient should also guide the IR to choose between multiple embolic agents and devices that can be used in the management of PT. The choice of the embolic agent depends on the physician’s experience and the vascular injuries on a case-by-case basis. Generally, temporary embolic agents such as gel foam should be used in the case of large territory embolization or empiric embolization, while definitive embolic material, liquids or solids, should be preferred for super-selective embolization. In addition, as previously mentioned, it is important to access the coagulation profile of the patient prior to embolization. If coagulation is altered, as is frequently seen in trauma patients, some embolic materials (i.e. coils, gel foam) will not achieve hemostasis easily.

A borderline case is when there are no signs of bleeding on angiography in a hemodynamically unstable patient who has not had a CT scan and there is free fluid in the abdomen on FAST ultrasound. In these cases, prophylactic embolization with resorbable material (i.e. gel foam) is recommended for temporary occlusion [31,32]. In addition, no significant differences in survival, complications, and days of hospitalization are reported in patients who underwent this procedure.

Complications related to embolization are not frequent and are mostly related to access site points, including bleeding, hematoma, pseudoaneurysms, and arteriovenous fistulae. Other complications associated with arterial embolization itself arise either accidentally from non-target embolization or as an inevitable consequence of big vessel or bilateral embolization. The femoral head, lower leg, pelvic viscera, and gluteal muscles can all be affected by ischemia or necrosis [33].

REBOA is a relatively new temporary measure to control hemodynamically unstable trauma patients in the early resuscitative phase. It consists of the inflation of an endovascular aortic balloon through a femoral introducer sheath.

In short, REBOA is an alternative to emergent resuscitative thoracotomy (RT) in hemodynamically unstable trauma patients [34,35], whose only requirement is a femoral arterial access. It enables the reestablishment of a systolic blood pressure >90 mmHg, which allows for further diagnostic investigations (CT scan with contrast medium injection) or interventions such as pelvic packing or embolization.

Due to the potential for visceral organ ischemia, REBOA should ideally not be positioned in Zone 2 (para-renal), but rather in Zone 1 (supra-celiac or descending aorta) or Zone 3 (infra-renal).

Zone 3 REBOA may be the best option for pelvic bleeding since it allows for a prolonged occlusion period of 4–6 hours and prevents ischemic/reperfusion injury to visceral organs [36].

REBOA complications can be severe and bring the resuscitative effort to a premature end due to arterial disruption or dissection [37,38].

International registries on the use of REBOA in trauma have yielded positive results, but there are still open questions regarding its application, such as the best location and timing for access, the best zone for inflation, and which medical specialist should oversee the procedure [5].