Rupture Of An Abdominal Aortic Aneurysm Following Nonaccidental Blunt Abdominal Trauma

Case Report

A 78-year-old female with a history of schizophrenia presented to our trauma center after allegedly suffering a ground-level fall. On arrival, the patient was hemodynamically stable, and her hemoglobin level was 10 mg/dL. She had extensive ecchymoses over her face, arms, legs, and abdomen (Figure 1). The patient exhibited signs of closed head injury, including confusion and lethargy. The patient's abdominal examination was benign, which, combined with the reported ground-level fall, led to the decision to omit initial imaging of the chest, abdomen, and pelvis by the trauma and emergency department staff. The patient subsequently underwent computed tomography (CT) of the head, which showed an acute and chronic subdural hematoma with midline shift (Figure 2). The patient was taken emergently to the operating room for evacuation of the hematoma by neurosurgery and then was transferred to the intensive care unit.

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Figure 1.

A 78-year-old trauma patient with signs of extensive lower-extremity injuries (photographs taken 2 days after the trauma). Obvious signs of blunt abdominal trauma are present.

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Figure 2.

A computed tomographic scan demonstrating subdural hematoma with midline shift.

Several hours following evacuation of the subdural hematoma, the patient developed hypotension, which required several liters of crystalloid resuscitation. The hemoglobin level dropped to 8 mg/dL, and she was transfused with 4 units of packed red blood cells. The patient was taken for CT of the abdomen and pelvis and was found to have a large retroperitoneal hematoma and radiographic findings of a ruptured 6 cm AAA (Figure 3).

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Figure 3.

A computed tomographic scan demonstrating a 6 cm abdominal aortic aneurysm with retroperitoneal hematoma.

The vascular surgery service was consulted and the patient was taken for emergent repair of the aortic aneurysm. At laparotomy, a small amount of free blood was found in the peritoneum, as well as a large retroperitoneal hematoma. There was no sign of injury to any of the intraperitoneal organs. There was an AAA measuring between 6 and 7 cm in diameter. Proximal control of the infrarenal aorta and distal control of the common iliac arteries were obtained, and the retroperitoneal hematoma was entered. An anterior defect in the aneurysm wall approximately 2 cm in length was found, which represented the site of rupture. The aneurysm was repaired with an 18 mm Dacron tube graft. Postoperatively, the patient had an uncomplicated hospital course and was discharged in good condition.

Later discussions with the patient revealed the true nature of the trauma to be due to assault by the patient's husband. She reported sustaining several blows to the head and abdomen on the date of presentation.

Discussion

Blunt injury to the aorta is a rare entity and accounts for 4 to 6% of trauma deaths in autopsy series. ⁵ Most of these aortic injuries are to the thoracic aorta at points of fixation. Blunt injury is responsible for 95% of injuries to the thoracic aorta. Reports of blunt injury to the abdominal aorta have been primarily due to high-velocity injuries. ² Low-velocity injuries to the abdominal aorta, as in our case, are exceedingly uncommon. Nonaccidental blunt trauma to the abdomen has not been previously described as a cause of rupture of an underlying AAA.

The rarity of aortic injury stems, in part, from its protected position in the retroperitoneum anteriorly by the intestines and posteriorly by the vertebrae and paravertebral musculature. ⁶ The mechanisms of blunt aortic injury cited in the literature include the transmission of blunt forces to the aortic wall and against the relatively incompressible vertebral column. ² Lap seat belts have been reported as a contributing factor in these injuries, known as the “seat-belt aorta,” which carries a 24% mortality rate. Lumbar spine fracture has been associated with up to 35% of blunt aortic injury secondary to seat-belt injuries. ^2,6,7 Although rare, the presence of a seat-belt sign should raise the suspicion of a blunt aortic injury. This type of injury may be more lethal in patients with undiagnosed AAA.

AAA rupture is rare in the setting of blunt abdominal trauma. This leads to a significant potential for delay in diagnosis, which can lead to patient deterioration and poor outcome. At the time of presentation, our patient had an aneurysm between 6 and 7 cm with an estimated 5-year spontaneous rupture risk of 25 to 40%. ¹ The mortality rate associated with ruptured AAA approaches 50% for patients who reach the hospital. Poor prognostic factors include preoperative renal failure and hemodynamic instability. ³ Additional complicating factors include lower limb ischemia and intestinal ischemia. In this case, although initially treated for an alternate life-threatening problem, a timely diagnosis was made, shock was corrected, and the patient did not have signs of organ failure at the time of operation. These factors all likely contributed to the patient's quick recovery.

This patient was thought to have had a ground-level fall; however, it was later discovered that she had also sustained significant blunt abdominal and head trauma during an altercation with her husband. The mechanism of rupture of the aneurysm may have been twofold. First, although spontaneous rupture of AAAs may cause a hypotensive syncopal episode that may lead to a fall, the strong temporal relationship of the trauma with the rupture implicates a direct blow to the abdomen as the etiology of the rupture. This was also suggested by the unusual anterior defect in the AAA found at operation. Anterior ruptures of AAAs usually result in free rupture into the peritoneal cavity with resultant exsanguination; however, in this case, fortunately, the rupture was contained within the retroperitoneum, as indicated by the CT scan. The lack of associated hollow viscus injuries is surprising but attests to the frailty of the aneurysmal aorta. It is unlikely that this aortic rupture would have occurred in the absence of an aneurysm. Second, there is historical evidence that collagenase activity in the aorta increases after major physiologic insults. ⁸ Cohen and colleagues showed that collagenase activity is a local phenomenon related to wound healing at the site of initial injury. ⁹ They found that operative trauma without direct injury to the aorta had no effect on aortic collagenase activity. Since then, other reports have shown an increase in aortic collagenase activity after laparotomy with and without direct mobilization or injury to the aorta. ^10,11 These data suggest that, theoretically, trauma, even remote to the aorta, can lead to a catabolic state that may increase the risk of aneurysm rupture owing to weakening of the collagen fibers that reinforce a nonruptured aneruysm wall. ^8–11 It is unclear which of these two mechanisms ultimately resulted in the rupture of this aneurysm; however, both may be related to the trauma that the patient suffered.

In summary, rupture of an AAA after blunt trauma to the abdomen has been rarely reported and typically involves high-velocity mechanisms such as automobile accidents. This case demonstrates that patients sustaining low-velocity blunt trauma to the abdomen may potentially suffer rupture of an underlying AAA. Careful ongoing evaluation of all trauma patients is of the utmost importance as the presence of the AAA may not be known. In addition, the diagnosis of a ruptured AAA must be entertained in elderly trauma patients who present with hemodynamic compromise after abdominal trauma. To our knowledge, this is the first case reported of a ruptured AAA after nonaccidental trauma and highlights the importance of timely diagnosis and treatment.