Imaging of Penetrating Trauma to the Torso and Chest

Mechanism of Injury

Most stab wounds are caused by knives, but they may also result from sharp objects or instruments. Unlike missiles, hand-driven low-energy weapons, such as a knife or ice pick, cause tissue damage only by their sharp cutting edge or point. Only 50% to 75% of victims of stabbing injuries to the anterior abdominal wall will have peritoneal penetration. Only 50% to 75% of these patients will have an injury that requires operative repair.

Unlike stab wounds, GSWs result in peritoneal penetration in 85% of abdominal gunshot wounds, and 80% of these patients will have significant organ injury. Surgeons use a penetrating abdominal trauma index (PATI) score to predict the severity of injury and risk for complications that occur following penetrating injuries. It takes into consideration the severity of the injury (1 minimal to 5 severe) to 14 organs and assigns a risk factor (1 to 5) for each organ. The PATI is obtained by multiplying the severity grade by the risk factor of all the injured organs and summing the individual organ scores. A high PATI score (>25) is typical of gunshot wounding and is associated with a higher likelihood of overtly positive peritoneal signs. Few, if any, further investigations are needed to confirm peritoneal violation.

Anatomic Regions

The torso (defined by the area between the internipple line and upper third of the thigh) is divided into five anatomic regions ( Fig. 12-2 ) to categorize the site of injury, as follows:

• 1.

  The thoracoabdominal area defined by the internipple line superiorly, costal margins extended posteriorly, to the inferior tip of the scapula inferiorly.

• 2.

  The anterior abdomen defined by the costal margins superiorly, anterior axillary lines laterally, inguinal ligaments and symphysis pubis inferiorly.

• 3.

  The flank defined by the anterior and posterior axillary line (tip of the scapula superiorly and iliac crests inferiorly) and from the costal margin to the iliac crest.

• 4.

  The back defined by the tips of the scapula superiorly and iliac crests inferiorly.

• 5.

  The pelvis defined by the iliac crests and inguinal ligaments superiorly and upper thirds of the thighs inferiorly.

Mandatory Laparotomy

Before the mid-1960s it was believed that routine exploration for penetrating torso injuries would reduce mortality by 12% to 27% compared to expectant management. This concept arose from military experience since World War I. However, if such an approach were applied to all civilian penetrating injuries, 15% to 20% of GSWs and 35% to 53% of stab wounds to the torso would lead to an unnecessary (nontherapeutic) laparotomy.

Proponents of mandatory laparotomy based their belief on unproven assertions that intra-abdominal injury cannot be diagnosed short of exploration. They also believed that clinical examination was often unreliable in patients with serious injuries, that delay in diagnosis of these penetrating injuries would result in unacceptably high morbidity and mortality, and that nontherapeutic laparotomies were rarely associated with morbidity.

Indications for urgent laparotomy following penetrating trauma to the torso are shown in Box 12-1 . The standard of care in the United States for patients who are hemodynamically unstable or have overt clinical signs of peritonitis after sustaining gunshot or stab wounds is laparotomy. Other clear indications for immediate laparotomy include aspiration of frank blood via a nasogastric tube, evisceration of bowel, and bleeding from rectum on clinical examination, proctoscopy, or sigmoidoscopy. The availability of new surgical concepts and techniques and sophisticated new radiologic technology, the use of antibiotics, and recognition of the potential morbidity and increased hospital costs associated with laparotomy have challenged the dictum of mandatory exploration of the abdomen in the civilian setting.

Selective Conservative Management

The decision process of deciding which patient can be managed nonoperatively when there are no clear indications for surgery is termed selective conservative management . Over the past 4 decades, evidence of visceral injury has replaced simple peritoneal violation as the main indication for abdominal exploration. In the United States this policy is applied more often to stab wounds than GSWs in stable patients. Ideally a selective conservative approach should reduce the number of negative and nontherapeutic laparotomies without increasing the number, morbidity, or mortality of missed or delayed diagnoses of serious injuries.

The optimal method of ruling out peritoneal violation or significant visceral injury in hemodynamically stable patients with equivocal peritoneal signs following penetrating injury varies among institutions. The basic conservative management strategies, their strengths, and their weaknesses are listed in Table 12-1 . The anatomic location of the entry wound and the local practice at any given trauma center may dictate the management approach selected.

Observation

Thirty-four percent to 72% of all patients with penetrating injury to the anterior abdomen or back are hemodynamically stable without overt signs of peritonitis and may be candidates for observation. The practice of observation with serial physical examination (ideally performed by the same examiner) can be accomplished safely, thereby reducing the number of nontherapeutic laparotomies. This technique could easily be performed on abdominal stab wounds. In the appropriate clinical setting this practice may also be applied to GSWs. The majority of patients with a reliable clinical examination who have minimal or no abdominal tenderness can be discharged after 24 hours of observation. Missed injuries requiring subsequent surgical exploration may occur in 4% to 6% of patients in the observation group, with an average delay in treatment ranging from 3 hours to 5 days. Compared to mandatory laparotomy, this management approach reduces the nontherapeutic laparotomy rate from 53% to 3% to 8%.

One disadvantage of observation with serial examination is the need for admission to the hospital for up to 72 hours because a significant amount of time may be needed for clinical signs of peritonitis to develop after perforation, especially if the injury involves the retroperitoneal colon or duodenum. In a busy trauma center or in a small community hospital, staff may not be available to perform frequent examinations. This limits the number of patients that can be regularly observed. Physical examination may be unreliable, and it may be difficult to elucidate signs of peritonitis in patients with associated severe head or spinal cord injuries, intoxication with alcohol or drugs, or other distracting injury.

Local Wound Exploration and Diagnostic Peritoneal Lavage

Local wound exploration and diagnostic peritoneal lavage (DPL) have been used to evaluate hemodynamically stable patients without peritonitis who are at risk for penetration of the peritoneum. A positive tap in blunt trauma is aspiration of 10 mL of blood. In penetrating trauma the definition of a positive tap is less clear. A tap is considered positive if feces, bile, or food material is aspirated through a catheter placed in the peritoneal cavity. A negative peritoneal tap is followed by a peritoneal lavage performed through the same catheter using 1 L of normal saline. The lavage effluent is sent for analysis. Local wound exploration is generally performed in the admission area under local anesthesia and sterile conditions. Local wound exploration is appropriate only for anterior abdominal stab wounds. It should not be used for gunshot wounds or stab wounds to the back or flank. If the peritoneum has not been violated, the exploration site is closed and the patient can be discharged following wound care. If there is penetration of the peritoneum or if wound exploration is equivocal for peritoneal violation, DPL may then be performed to assess for intraperitoneal injuries.

There is no uniform agreement among surgeons on the peritoneal lavage red blood cell (RBC) count that is an appropriate trigger for exploration. Currently the number of RBCs per cubic millimeter sufficient to perform surgical exploration ranges from 1000 to 100,000/mm ³ ; it varies among trauma centers and is based on the injury mechanism ( Table 12-2 ). The lavage technique is highly sensitive when based on low RBC counts and highly specific using high RBC counts.

Significant injuries to the diaphragm and small bowel may occur with minimal hemorrhage and can be associated with false-negative DPL results. The inability to define the anatomic source of hemorrhage or severity of injury by DPL may increase the rate of nontherapeutic laparotomies in nonbleeding solid visceral injuries. Because DPL does not survey the retroperitoneum, it is unreliable in evaluating retroperitoneal organ injury and should not be used as the sole technique in the evaluation of patients with penetrating injuries to the flank and back. Local wound exploration may be difficult in obese patients, patients with thick back muscles, penetration in the thoracoabdominal region, or the presence of a large actively bleeding abdominal wall hematoma.

To improve patient flow, busy trauma centers prefer local wound exploration and DPL to observation with serial physical examination in order to triage asymptomatic patients with penetrating torso injury. Patients that have a DPL should be admitted for 24 hours to screen for any DPL complication and/or missed gastrointestinal injury. Unlike serial physical examination that warrants admission of a large number of patients for up to 3 days, these techniques can immediately eliminate patients who need not be observed. Intraperitoneal injuries in asymptomatic patients are also more likely to be detected acutely. This approach eliminates the risk for potential morbidity and mortality associated with a delay in injury diagnosis.

Multidetector Computed Tomography

Currently, triple-contrast multidetector computed tomography (MDCT) has become a valuable imaging modality to evaluate penetrating trauma to the torso considered for nonoperative management immaterial of the entry site or the number of gunshot or stab wounds. In this group of patients, MDCT can be very helpful and accurate in facilitating management decisions. Oral and intravenous contrast is also used routinely to optimize the detection of injuries to the intraperitoneal bowel, solid organs, mesentery, retroperitoneal genitourinary system, and duodenum. Penetrating trauma to the flank and back in asymptomatic patients is rarely associated with injury to critical retroperitoneal viscera because these organs are well protected by ribs, the spine, and the large back and paraspinal muscles. Patients with isolated retroperitoneal injuries resulting from these two anatomic locations may not present with overt clinical signs or symptoms and are not evaluated by DPL. It is important to routinely use rectal contrast material to opacify the entire colon to demonstrate contrast extravasation or focal colonic wall thickening, which enhances the ability to diagnose subtle colonic injuries that require surgical repair. Fifty-eight percent of patients with penetrating trauma to the back or flank incur intraperitoneal injuries. Combined intraperitoneal and retroperitoneal injuries may occur in about 16% of these patients.

Triple-contrast MDCT is highly sensitive and accurate in excluding peritoneal violation in patients with penetrating torso trauma. Among patients with peritoneal violation, MDCT has a high specificity, positive predictive value, and accuracy in predicting the need for laparotomy. It also helps to diagnose isolated liver injury, allowing nonoperative management for patients with penetration limited to the right upper quadrant.

Typically triple-contrast MDCT results are classified into negative, minor, or low risk for injuries and major or high risk for injuries. Patients with minor or low-risk injuries (small retroperitoneal hematoma or minor renal injury) are generally managed conservatively. Patients with major injuries are managed with surgery or angiography. In a busy trauma center, triple-contrast spiral MDCT is a safe and reliable technique to triage stable patients with penetrating injuries to the torso with no clinical or radiographic signs of peritoneal violation.

Diagnostic Laparoscopy

Laparoscopy enables direct visualization of the peritoneum and the intraperitoneal viscera to diagnose peritoneal violation and evaluate potential organ injury. Typically the diagnostic laparoscopy is converted to a laparotomy in the presence of peritoneal violation, major organ injury, or significant hematoma. Patients with no peritoneal penetration or with nonbleeding solid organ injuries may be observed or discharged. Laparoscopy still carries a 17% to 20% rate of nontherapeutic laparotomy and 17% negative laparotomy rate. Laparoscopy can prevent unnecessary laparotomies in 34% to 60% of patients with a concurrent reduction in hospitalization duration and costs.

The strength of diagnostic laparoscopy appears to be in the evaluation of patients with penetrating injuries to the left thoracoabdominal area with potential for small diaphragmatic rents. Local wound exploration is unreliable and associated with the risk for creating a pneumothorax. Laparoscopy reduces the number of nontherapeutic laparotomies, as compared to DPL, that may be performed among the subset of patients with minor splenic and liver injuries that have stopped bleeding by the time of surgery. Laparoscopy has also been shown to be optimally suited to evaluate the diaphragm for injuries in asymptomatic patients with less than 10,000 RBCs/mm ³ in the DPL effluent.

The limitations of laparoscopy include the need for general anesthesia and inadequate visualization of the retroperitoneum. Laparoscopy may also miss gastrointestinal injuries. The sensitivity can be as low as 18% for diagnosing bowel injury following penetrating trauma to the abdomen.

Tension pneumothorax may develop during laparoscopy in patients with diaphragm injury, and special precautions should be taken to avoid this complication. One major contraindication for laparoscopy includes prior history of multiple adhesions and patients with elevated intracranial pressure, who may suffer adverse effects from the insufflation of carbon dioxide. A significant cost savings will be gained only if laparoscopy is performed under local anesthesia.

Ultrasonography

There has been little enthusiasm to embrace ultrasonography as an initial screening study to evaluate patients with penetrating trauma to the torso. Though ultrasound can demonstrate free intraperitoneal fluid in blunt trauma patients, these results have not been reproduced in patients suffering penetrating injuries to the abdomen. The overall sensitivity of focused assessment sonography for trauma (FAST) to detect free fluid in the peritoneal cavity (in the perisplenic, perihepatic, pelvic, and pericardial spaces) is 47%. Ultrasonography is typically used only to detect free fluid. A significant number of patients with negative FAST study results have serious abdominal injuries requiring surgical repair. Positive FAST results are a strong predictor of intra-abdominal injury (specificity of 94%, positive predictive value of 90%). Thus positive FAST results should prompt immediate exploration.