Case Report and Minireview of the Literature on Blunt Azygos Injury

Azygos vein injury seems to be an uncommon cause of hemothorax and hemomediastinum; however, this injury is potentially fatal. We report a fatal case of blunt azygos injury and a PubMed search was undertaken to identify English articles from 1989 to 2022 using the key words “azygos”, “injury” and “blunt”. We found 28 articles about blunt azygos injury and 39 patients including the present case (average 41.2 years [range: 18-81 years]; male, n=20; female, n=19). The other variables were as follows: right hemothorax (n=32); unstable circulation on arrival (n=32); and survival (n=19; unknown, n=2). These cases were divided into two groups based on the outcome: the survival group and the fatal group. There were no significant differences with regard to the year of the report, age, sex, rate of right rib fracture, rate of preoperative computed tomography (CT) examination, rate of associated injury, and rate of operation. The rate of shock on arrival in the survival group was significantly lower than that in the fatal group. The rate of azygos arch injury in the survival group was significantly greater than that in the fatal group. The emergency physician must consider azygos vein injury as a possible cause of right hemothorax when a patient with blunt chest trauma presents persistent hypotension.


Introduction
The azygos vein is located on the right side of the vertebral column and penetrates from the retroperitoneum through the diaphragm to join the superior vena cava at the T4 level 1) .Fracturedislocation of the mid-thoracic spine or ribs, as a result of blunt thoracic trauma, can tear the azygos vein 1) .The vein can also be torn, in the absence of skeletal injuries, by horizontal acceleration/deceleration forces 1) .Most reports of blunt trauma to the azygos vein in the relevant literature are related to motor vehicle collisions 1) .Patients frequently present with shock-like symptoms and expanding hemothorax, necessitating prompt surgical repair  . Azygo vein injury seems to be an uncommon cause of hemothorax and hemomedi-astinum; however, this injury is potentially fatal.We herein report a fatal case of blunt azygos injury and a review of the relevant literature.The protocol of this retrospective study was approved by Juntendo Shizuoka Hospital review board (approval number: 298).We obtained oral informed consent from the bereaved.

Case presentation
A 63-year-old man fell from a 2 nd floor veranda while leaning over a banister trying to catch a ladder.When emergency medical technicians checked him, he was in shock state with consciousness disturbance; thus, he was transported to our emergency room (ER) by ambulance within 20 minutes.He had a medical history of diabetes mellitus and colon cancer.On arrival, his vital signs were as follows: Glasgow Coma Scale, E4V3M6; blood pressure, 75/-mmHg; heart rate, 140 beats per minute; respiratory rate, 30 breaths per minute and percutaneous saturation, 98% under 10 L per minute of oxygen.A physical examination revealed a head contusion and weakness of the right respiratory sound.The chest roentgenography showed decreased radiolucency in the right lung field (Figure 1), suggesting right hemothorax.Focus assessment of sonography for trauma also showed fluid collection, which was limited to the right thoracic cavity.Initially, he underwent immediate massive transfusion without cross-matching and tracheal intubation following right thoracostomy, which drained over 1 L of hemorrhaging.As his blood pressure did not respond to massive transfusion, right thoracotomy was tentatively performed by young emergency physicians in order to pack gauze and achieve hemostasis around the pulmonary hilus, where blood was emerging without a hilar clamp, while the patient was in the supine position.However, his unstable circulation deteriorated.After closing the thoracotomy, he was moved to the computed tomography (CT) room and CT revealed hemorrhaging from the inferior azygos vein near a thoracic vertebral fracture (Figure 2) and right subdural hematoma.He experienced cardiac arrest after returning to the ER.A thoracic surgeon standing by at home attended the ER and explored the right thoracic cavity by opening the thoracotomy.The surgeon recognized an azygos arch injury and achieved hemostasis by gauze packing.The surgeon also performed manual compression at the hemorrhaging site of the inferior azygos vein, and transfusion was continued.However, a return of spontaneous circulation was not obtained due to hemorrhaging associated with the trauma itself and the operative incision site due to the patient's bleeding tendency.

Discussion
This review of cases of blunt azygos injury is the first report to suggest that shock on arrival and the location of azygos vein injury may have an influence on final outcome of the patient.
Shock on arrival in patients with blunt trauma suggests massive bleeding from injured sites and/ or spinal cord injury, and previous reports have also demonstrated that shock on arrival is a poor prognostic factor 30,31) .Accordingly, ER physicians must consider azygos vein injury as a possible cause of right hemothorax in patients with blunt chest trauma who show persistent hypotension.
The reason for the favorable outcome of azygos arch injury in comparison to other sites might be that it is easier to visually recognize the injured site.Usually, trauma patients are managed in supine position in the ER and tentative thoracotomy is also performed in the same position because subsequent tentative laparotomy might be required to explore abdominal injuries 32) .The azygos arch was easily visually recognized in the supine position, however, other sites might be hidden by the pulmonary hilus, lung or diaphragm 33) .
In the present hemostasis at the site of the azygos arch injury was obtained by direct gauze packing; however, the packing at the inferior injury site of the azygos vein was insufficient.This review of cases of blunt azygos injury failed to show that recent medical development has resulted in favorable outcomes.Recent surgeons are familiar with using preoperative radiological studies to perform a planned operation precisely, safely and less invasively.In contrast, experienced trauma surgeons can perform urgent surgical operations without radiological studies, with manual intraoperative exploration to identify the site of bleeding and apply hemostasis 34) .Advanced Trauma Life Support ® (ATLS ® ) does not recommend that trauma patients with unstable circulation be moved to a CT room or for CT examination to be used to identify sites of bleeding 35) .However, it is important for hemostasis to be immediately achieved at hemorrhaging sites in patients with unstable circulation.The number of patients with severe trauma has been decreasing year by year, and the number of experienced trauma surgeons in Japan has declined 36) .The fact that the diagnostic studies included as part of the initial ATLS ® trauma survey are not well equipped to diagnose such a fatal vascular injury 37) .In addition, recent studies showed the efficacy of evaluation using whole CT during resuscitation in the hybrid ER, for even trauma patients with unstable circulation, in order to detect sites of hemorrhaging and facilitate the immediate performance procedures to obtain hemostasis [38][39][40][41] . Acordingly, to increase the survival rate of patients with fatal vascular injuries, such as blunt azygos injury, the early recognition of the site of hemorrhaging using CT and the immediate execution of surgical hemostasis in an appropriate position for modern surgeons (less experienced in the management of severe trauma) may be required, even when initial fluid resuscitation fails and unstable circulation remains.
Regarding what measures should be taken by young physicians in a standard hospital without a hybrid ER to obtain a survival outcome in patients with fatal azygos injury and unstable circulation until veteran surgeons arrive.Aside from the ATLS® protocol, a 1:1:1 ratio of packed red blood cells, fresh plasma, and platelets with minimal crystalloids is the preferred resuscitative strategy to avoid diluted coagulopathy by crystalloid fluid resuscitation 42) .Recently, in patients experiencing hemorrhagic shock, whole-blood transfusion was reported to be associated with both an improved survival and decreased overall blood utilization 43) .If a patient does not obtain stable circulation even after massive transfusion, they should be intubated to secure the airway 35) .After definitively securing the airway, a CT examination should be considered, although the proper timing of CT remains controversial 44) .A chest drain is usually inserted to drain the hemothorax and evaluate the volume in order to decide the timing of radical operation.Tentative drain clamping may be effective for achieving hemostasis at the bleeding source or reducing the total hemorrhaging volume by the hematoma tamponade effect, based on our personal experience and evidence from total knee arthroplasty 45) .However, it should be noted that drain clamping may result in hemorrhagic death or fatal tension hemothorax.Intensive hypotensive resuscitation is recommended, as it is safe and has a lower mortality rate than normotensive resuscitation in hemorrhagic shock patients.There is also less blood loss, hemodilution, ischemia, and hypoxia in tissues with such an approach 46) .If young physicians aggressively attempt damage control intervention using right thoracotomy but fail to identify the bleeding source, hilar clamping or twisting may be attempted to detect the bleeding source 47,48) .If the bleeding cannot be stopped with these procedures, the bleeding source likely lies outside of the pulmonary artery and venous system.In addition, in cases with an unknown bleeding source, a large amount of gauze should be packed blindly in order to achieve hemostasis 49) .Alternatively, clam-shell thoracotomy may be useful for identifying the bleeding source, even in the supine position 50) .

Conclusion
We presented a fatal case of blunt azygos injury and the results of an analysis of the relevant literature.ER physicians must consider azygos vein injury as a possible cause of right hemothorax in patients with blunt chest trauma if the individual shows persistent hypotension.In addition, the early recognition of the site of hemorrhaging using CT may be required, even if the patient's circulation remains unstable after initial fluid resuscitation.

Figure 1
Figure 1 Chest X-ray on arrivalThe X-ray suggested right hemothorax.

Figure 2
Figure 2 Enhanced chest computed tomography after tentative thoracotomy Bleeding from the azygos arch was controlled (upper arrow) but hemorrhaging from the inferior azygos vein near the thoracic vertebral fracture remained (lower arrow).

Table 1
Summary of case of blunt azygos injury

Table 2 .
There were no statistically significant differences with regard to the year of the report, age, sex, rate of right rib fracture, rate of preoperative CT examination, rate of associated injury and rate of operation.The rate of shock on arrival in the survival group was significantly lower than that in the fatal group, and the rate of azygos arch injury in the survival group was significantly greater than that in the fatal group.

Table 2
Comparison between the survival and fatal groups