Abdominal Aortic Trauma, Iliac and Visceral Vessel Injuries

Introduction

Major vascular injuries may be seen in up to 25% of abdominal trauma and are associated with a high mortality. Following penetrating abdominal trauma, vascular injuries are the most common causes of death. Intra-abdominal hemorrhage can be catastrophic due to the difficulty of rapidly accessing the retroperitoneal vessels. It is for this reason that early recognition of a possible vascular injury is essential and transfer to a center capable of early surgical intervention is vital. The early diagnosis of these injuries has been facilitated with the increasing use of computed tomography (CT) angiography and with its availability close to the resuscitation room.

Civilian vascular injury comprises approximately 1% to 5% of all trauma with data from the PROOVIT (PROspective Observational Vascular Injury Treatment) registry revealing the incidence of abdominal arterial injuries to be 7.8% of all of vascular trauma. The relative rarity therefore makes it difficult for a trauma center and its surgeons to accumulate large caseloads of specific arterial injuries. Although blunt trauma is the most common mechanism of all vascular injury in the PROOVIT registry, there are huge variations in the role of penetrating trauma causing abdominal vascular injury. In urban US trauma centers this is reported to be as high as 88%, whereas in Germany, over a 16-year period, the incidence of penetrating trauma was only 5% in 760 patients with abdominal vascular injury. The incidence of injuries differs between military and civilian trauma. During the Vietnam War and World War II, the incidence of penetrating abdominal vascular injuries was less than 3%, but in the recent conflicts in Iraq and Afghanistan, iliac injuries were found in 3.9% of injuries, and aortic injuries in a further 2.9%. In civilian populations with a high incidence of knife crime, the incidence approaches 10%; and this figure doubles to more than 20% in populations with gun crime. For aortic penetrating injuries, the incidence still remains low, and it is less than 3% for penetrating trauma.

Mechanism of Injury

Anatomy

Vascular injuries in the abdomen are classified according to geographical location ( Fig. 18.1 ). These are usually defined within three zones, albeit a fourth zone is occasionally included.

Zone I begins at the point of entry of the aorta through the diaphragm (i.e., the aortic hiatus) and extends down to the sacrum. The aorta enters the abdomen at the level of the twelfth thoracic vertebra passing behind the median arcuate ligament of the diaphragm. The aorta descends to the level of the fourth lumbar vertebra where it bifurcates into the left and right common iliac arteries. Zone I includes the central retroperitoneal area and the base of the mesentery. The area is further divided into the supramesocolic and inframesocolic areas. The supramesocolic and inframesocolic areas are defined by the levels of the renal arteries. The suprarenal aorta, celiac axis, superior mesenteric artery (SMA), renal arteries, inferior vena cava (IVC), and superior mesenteric vein all lie within this supramesocolic area. The inframesocolic area contains the infrarenal aorta, the inferior mesenteric artery, and the IVC.

Zone II exists either side of zone I and contains the paracolic gutters, kidneys, and renal vessels. It is also referred to as the upper lateral retroperitoneum.

Zone III, containing the iliac vessels, is also known as the pelvic retroperitoneum.

The hepatic artery, portal vein, retrohepatic IVC, and hepatic veins all lie within an area occasionally referred to as zone IV.

Clinical Presentation

The patient should be inspected for signs of penetrating injury. Stab wounds in the abdomen should be obvious but be aware that stab wounds in the chest, back, and gluteal regions can result in injury to abdominal and pelvic vessels. With both penetrating and blunt trauma, examine for bruising in the flanks. This can be a sign of a retroperitoneal bleeding. With gunshot wounds, examine the patient for entry and exit wounds. An attempt to predict the trajectory may provide some idea of the vessels and organs injured. Do not assume that the injury is localized to the missile path. The presentation of arterial injuries may be early or late depending on the artery involved, as well as the type and mechanism of injury.

Early presentation is usually in the form of hemorrhage and hypovolemic shock. Urgent laparotomy will reveal either blood in the peritoneal cavity or a retroperitoneal hematoma. The zone should be defined according to Fig. 18.1 . Some patients may respond to resuscitation but presentation with a distended abdomen should raise the suspicion of a vascular injury. Patients who are stabilized and taken for trauma CT of the abdomen revealing vascular injury may also be included as early presenters. Thrombosis, dissections, and occlusions may present with lower limb ischemia (absent or diminished femoral pulses; cold, pale limbs). This should be considered in the context of blunt injury resulting in pelvic fractures or abdominal crush. Be aware that the presentation may not be immediate with intimal tears, and repeated examinations are mandatory. Injuries to the renal pedicles may present with hematuria. Anuria as a result of bilateral renal artery thrombosis is rare.

Both penetrating and blunt trauma can result in vascular injuries that present late. With the increasing use of CT angiography, arterial injuries are being detected early, reducing the incidence of late presentation. Pseudoaneurysms frequently present late. They may each present as a pulsatile mass compressing adjacent structures. Compression of the duodenum may present as bowel obstruction. The false aneurysm may erode into the bowel resulting in massive gastrointestinal hemorrhage. Similarly, internal iliac pseudoaneurysms have presented with rectal bleeding. Pseudoaneurysm of the renal artery can present with hematuria. Arterial fistulas have been seen with hepatic artery injuries and penetrating liver injuries. These fistulas may present with hemobilia, right upper quadrant pain, and upper gastrointestinal hemorrhage. Injuries involving both arteries and veins can cause arteriovenous fistulas. The clinical manifestation may be obvious or subtle. Aortocaval fistulas are associated with lower limb edema and an abdominal bruit. Other arteriovenous fistulas may present later with high-output cardiac failure and lower limb chronic venous skin changes.

Investigations

The choice of investigation will depend on the patient's physiologic status and the available local facilities. CT has become the gold standard investigation. Availability close to the resuscitation room is an important factor in the planning of a major trauma center. Catheter angiography still maintains an important role in trauma and has the advantage of being coupled with therapeutic options such as stenting and embolotherapy. Early availability of experienced interventional radiologists and the location of the radiology suite often limit use to the hemodynamically stable patient. The use of ultrasound in trauma has increased in the form of focused assessment with sonography for trauma (FAST) scans. Bedside ultrasonography is able to detect intraabdominal free fluid, facilitating the decision for early exploratory laparotomy. The exploratory trauma laparotomy remains an important diagnostic tool and is coupled with the techniques of damage control surgery. Duplex scanning is less useful in the acute trauma presentation. It has a role in assessing neck trauma and can be used for surveillance to detect late pseudoaneurysms and arteriovenous fistulas. In the context of abdominal vascular injuries, its use is limited.

Surgical Techniques

The operative approach will be dependent on the location of the hematoma and the degree of urgency. The latter is dictated by the degree of hemodynamic shock.

When a decision is made to proceed to surgery, the patient should be prepared with sterile drape application allowing exposure of the abdomen, chest, and groins. This allows for incisions to be extended into the chest; and, if deemed necessary, a left anterolateral thoracotomy can be utilized to gain control of the descending aorta prior to entry to the abdomen. To facilitate distal control, exposure of the common femoral arteries may be required. The initial incision is a long midline laparotomy from the xiphisternum to the pubis. If further access is required, the incision may be extended in the midline to include a median sternotomy or through the sixth or seventh intercostal spaces for a lateral thoracotomy.

On initiating the laparotomy the surgeon may be presented with an abdominal cavity containing free blood. At this stage it may be difficult to establish the source of bleeding and the principles of damage control surgery should be applied. In order to identify the source of bleeding, the surgeon should proceed with small bowel evisceration and packing of the abdominal cavity, using large packs to either stop or slow the bleeding. These packs are then removed from each compartment until the source of bleeding is identified. The four-quadrant packing technique requires packs to be placed in the right upper quadrant over the right lobe of the liver, the left upper quadrant, the infracolic compartment (elevate the greater omentum and pack either side of the small bowel mesentery), and the pelvis. Pelvic packing is performed by lifting the small bowel out of the pelvis before applying the packs into the pelvis.

Exposure of the aorta and its branches is best achieved using the technique of a medial visceral rotation. This can be performed from either the left or right side; the decision will be dependent on which vessels need to be exposed. The medial visceral rotation can be a time-consuming technique, even in experienced hands, and temporary control may be required, especially if active hemorrhage is occurring from the supramesocolic aorta. Direct manual compression of the aorta against the spine may control the bleeding but frequently restricts exposure of the aorta and therefore subsequent repair. It can be a useful technique to control the inflow, but the ultimate aim should be to apply a clamp.

Division or creation of a window within the lesser omentum enables exposure of the supraceliac aorta. This technique is aided by retracting the stomach and the esophagus to the left. The liver is retracted in a cephalad direction. Division of the diaphragmatic crura further aids exposure, and then a supra celiac aortic clamp can be applied. This is the quickest way to apply a supraceliac clamp and to gain control of the bleeding abdominal aorta. Although inflow will be controlled, back-bleeding from the visceral vessels and lumbar arteries may be significant. The presence of visceral branches can make distal control challenging.

In order to perform a left-sided medial visceral rotation, the peritoneal attachments of the sigmoid and the descending colon are divided. The incision is started in the lateral avascular peritoneal reflection of the sigmoid colon and is continued proximally along the left paracolic gutter. The plane is developed by mobilizing the sigmoid colon and the descending colon to the midline. The retroperitoneal attachments of the left kidney, pancreatic tail, and spleen can be divided, mobilizing these organs to the midline and hence facilitating complete exposure of the abdominal aorta from its origin at the diaphragm to its bifurcation at the level of the fourth lumbar vertebra ( Figs. 18.2 and 18.3 ). This technique carries a significant risk of damage to the spleen, left kidney, and left renal vessels. Developing a dissection plane anterior to the left kidney can reduce the risk of intraoperative renal injury.

If rapid proximal control of the abdominal aorta is required before the medial visceral rotation, a clamp can be applied to the distal descending thoracic aorta. This is especially useful with an expanding zone I hematoma. The aorta is exposed by division of the left crus of the diaphragmatic aortic hiatus. Incision is made at the 2 o'clock position exposing the descending thoracic aorta and hiatal aorta. This is the quickest way to achieve proximal control during a medial visceral rotation. The presence of celiac nerves and lymphatic tissue around the aorta, together with dense diaphragmatic muscle fibers, makes careful dissection of the most proximal abdominal aorta difficult, time consuming, and hence unsuitable for the severely hypotensive patient.

The advantage of this technique is that, after mobilizing the spleen and the tail of the pancreas, the anterior midline visceral branches of the aorta are well exposed and can be controlled, repaired, or ligated.

A right-sided medial visceral rotation is performed by dividing the peritoneal reflection lateral to the ascending colon ( Fig. 18.4 ). A dissection plane is developed anterior to the kidney, facilitating mobilization of the colon and terminal ileum to the midline. This allows exposure of the duodenum, which can then be kocherized. The duodenum and the pancreatic head are mobilized to the left, and the retroperitoneal tissue left of the IVC is divided to expose the suprarenal aorta, the celiac axis, and the SMA. If exposure of the diaphragmatic hiatal aorta is required, this technique should be avoided.

If injury is isolated to the infrarenal aorta, exposure to this part of the aorta can be achieved via an anterior approach that resembles that for an infrarenal abdominal aortic aneurysm. Peritoneal incision is made left of the duodenojejunal flexure, the peritoneum dissected off the aorta, and an infrarenal aortic clamp applied. More proximal application of an infrarenal aortic clamp can be facilitated by ligation and division of the left renal vein, preferably preserving its adrenal and gonadal tributaries.

Surgical exposure of the celiac artery is either via a medial visceral rotation or via a direct dissection through the lesser sack. Fullen's anatomical classification can be used for the purpose of describing injuries to the SMA. Exposure of the proximal SMA (Fullen's zone I) is via a left medial visceral rotation. If severe bleeding dictates very rapid exposure, this part of the SMA can be exposed by dividing the neck of the pancreas. The easiest and quickest way of doing this is by using a stapling device, but, if this is not available, intestinal clamps should be applied before the division of the pancreatic neck to control any bleeding. The proximal infrapancreatic SMA can be exposed through root of the small bowel mesentery, and this may be facilitated further by mobilization of the duodenum and retraction of the pancreas. The more distal SMA may be exposed directly in the bowel mesentery.

The inferior mesenteric artery origin is easily exposed via an infrarenal approach to the aorta. The renal arteries can be exposed through respective medial visceral rotation techniques. In the presence of a large retroperitoneal hematoma, the application of a supraceliac aortic clamp should be used for proximal control. If the renal artery is bleeding from a more distal point (e.g., renal hilum), the renal artery can be exposed at its origin without the need for a visceral rotation. The small bowel is eviscerated to the right, and the aorta is approached anteriorly. The duodenojejunal flexure is mobilized as previously described. The left renal vein can be either divided as previously described or retracted proximally. The latter can be facilitated by division of the left gonadal and adrenal veins. This will allow exposure of the origin of the renal arteries.

The left renal artery can be seen following dissection of the surrounding peritoneal tissue. The right renal artery may require lateral retraction of the IVC to identify its origin. Additionally, medial rotation of the duodenum and then of the pancreas may be required to visualize the right renal vein, which will need to be looped and retracted before the remaining right renal artery can be exposed. The presence of a large retroperitoneal hematoma around the right kidney and juxtarenal IVC can make this a challenging dissection. Identifying the IVC distally and then dissecting in a proximal direction along the course of the IVC through the hematoma is an alternative approach.

Although the focus of this chapter is on arterial injuries due to their close proximity, the veins may be injured with the artery in the patient with multiple injuries. Achieving hemostasis during combined venous and arterial bleeding can be challenging. The application of clamps to a large vein can further tear the vein and therefore should be avoided or used with extreme caution. Using mounted sponges or swabs to apply pressure above and below the injury can achieve hemorrhage control and is less likely to damage the vein. With the aid of an experienced assistant, the surgeon can repair or ligate the vein. An alternative technique is using Foley catheters within large veins to control the inflow and back-bleeding.

Aortic Injuries

The majority of injuries to the aorta are consequences of penetrating traumas. Blunt injuries are rare and may be associated with seatbelt injuries and thoracolumbar fractures of the spine. The majority of patients who experience a rupture do not survive transport to hospital.

The complex forces that are associated with blunt trauma can damage the aortic intima resulting in aortic dissection, thrombosis, and consequently end-organ ischemia or limb ischemia. This may not be apparent at the initial presentation, and a high index of clinical suspicion is vital. Less commonly, patients may have delayed presentation with a pseudoaneurysm or arteriovenous fistula.

An aortic branch may be avulsed and present as a large retroperitoneal hematoma during the trauma laparotomy. Gunshot wounds appear to be associated with a higher incidence of aortic injuries than knife wounds. The clinical presentation will be dependent on a number of factors. If the injury results in bleeding into the peritoneal cavity, the patient presents in severe shock with peritonitis and a distended abdomen. Frequently these patients do not survive transfer to the hospital. If the injury is to the lateral wall and bleeding is confined to the retroperitoneum, hemorrhage may tamponade temporarily within the retroperitoneum.