Dr. Shanmuganathan is an Associate Professor and Dr. Mirvis is a Professor of Radiology, Department of Diagnostic Radiology and Maryland Shock-Trauma Center, University of Maryland School of Medicine, Baltimore, MD. Dr. Mirvis is also the Editor-in-Chief of this journal.

Firearm-related injuries have become a public health problem with a devastating impact on American society. ¹ There are substantial emotional, physical, and financial costs associated with firearm injuries, which are common in our society and often lethal. For every firearm death, it is estimated that 3 to 5 other nonfatal firearm injuries occur. ² During the last decade, computed tomography (CT) has been used to evaluate patients with penetrating injuries to the back and flank, but it has not been used routinely to evaluate penetrating injuries to the thoraco-abdominal region, abdomen proper, or pelvis. This article discusses the authors' experience with helical CT (single- and quad-detector helical CT) combined with oral, intravenous, and colonic contrast (triple-contrast) to assess hemodynamically stable patients who have penetrating injuries to the torso.

Ballistics

Most civilian gunshot wounds result from medium-energy handguns with a muzzle velocity <1000 ft/sec. The extent of tissue damage caused by a projectile is more severe if the missile has high kinetic energy, yaws (tilts) early in its path through tissue, is of high mass, strikes bone (creating secondary missiles), or expands, deforms, or fragments. ³ A permanent cavity results from the missile crushing the tissues it strikes. Temporary cavitation from stretching results within several milliseconds, following the passage of the bullet through the tissues. Severe damage results from formation of the temporary cavity in fluid-filled organs, such as the bladder or heart, as well as in organs with dense parenchyma, such as the liver (Figure 1), kidney, and brain. ⁴ More elastic tissue, such as lung parenchyma or muscle, resists severe damage from the temporary tissue cavity. Stab wounds are low-energy injuries that cause tissue damage only along the wound tract.

Surgical policy

Urgent laparotomy is the standard of care in the United States for patients with gunshot or stab wounds who are hemodynamically unstable or have overt clinical signs of peritonitis. Prior to the mid-1960s, mandatory laparotomy was performed routinely in all patients admitted with penetrating torso injuries. ^5-7 This approach was based on military experience since World War I. If this management is applied to all civilian penetrating injuries, 15% to 20% of abdominal gunshot wound victims and 35% to 53% of abdominal stab wound victims will have an unnecessary (nontherapeutic) laparotomy. ^5-8 Since the mid-1960s, most trauma surgeons have approached the decision of whether or not to perform a laparotomy on patients with penetrating trauma based on the significance of visceral injury or tissue damage, rather than simply on the presence or absence of peritoneal violation. ^8-11 This selective policy used to be applied more readily to patients with stab wounds and has been accepted more slowly for the management of hemodynamically stable patients with gunshot wounds. ⁸ A selective surgical approach should reduce the number of negative and nontherapeutic procedures without increasing the number, morbidity, or mortality of missed or delayed diagnosis of significant injuries. The optimal method to triage hemodynamically stable patients for peritoneal violation and significant visceral injury with equivocal peritoneal signs following penetrating torso (defined by the area between the inter-nipple line and upper third of the thigh) injury is controversial. The anatomic location of the entry wound and the local practice at a given trauma or emergency center may determine the triage method upon which selective management will be determined.

Selective surgical management

The two most commonly used methods to select patients with penetrating torso trauma for initial nonsurgical management include observation and local wound exploration followed by diagnostic peritoneal lavage (DPL). Other triage methods include ultrasound, CT, and diagnostic laparoscopy. Prior studies have shown that clinical observation with serial physical examination (ideally performed by the same examiner) may be practiced with excellent results to reduce the incidence of nontherapeutic laparotomy for penetrating trauma. ^7,10 These studies show that 34% to 72% of patients with penetrating injury to the anterior abdomen or back who are hemodynamically stable and without overt signs of peritonitis are suitable for observation alone. Missed injuries that require subsequent operation occurred in 4% to 6% of patients in the observation-only group; time of delay in treatment ranged from 3 hours to 5 days. Compared with mandatory laparotomy, this approach reduced the nontheraputic laparotomy rate of 53% down to 3% to 8% in some series. ^7,10

Assuming that the patient is hemodynamically stable with no or equivocal clinical signs of peritonitis, local wound exploration is performed initially in the admissions area under local anesthesia and sterile conditions to determine whether the peritoneum has been violated again. ^12-14 If the peritoneum has not been violated, the exploration site and skin are closed and the patient can potentially be discharged, given an isolated penetrating torso injury. If there is penetration of the peritoneum or if the wound exploration is equivocal for peritoneal violation, DPL is performed to determine if there is intraperitoneal blood. Unfortunately, a positive DPL result may occur from injury to the peritoneal lining itself or from very minor and self-limited parenchymal injury, making the result true-positive for hemoperitoneum, but leading to potentially unnecessary surgery.

Helical CT

In the past decade, triple-contrast CT has become the standard imaging study to evaluate patients with penetrating injuries to the back and flank ^15-18 due to its capacity to optimally reveal injuries to the retroperitoneal organs. The principal purpose of the CT study is to divide these injuries into those that are superficial; those with retroperitoneal penetration without significant visceral injury; or those with significant retroperitoneal and intraperitoneal injuries. Isolated retroperitoneal injuries infrequently cause critical injury to the retroperitoneal viscera. Retroperitoneal injuries often do not present with overt clinical signs or symptoms on admission and are poorly detected by DPL alone. ^15,18 Oral and intravenous contrast material is used routinely for the CT study of flank and back penetrating injury to optimize detection of injuries to the intraperitoneal bowel, solid organs, mesentery, genitourinary system, and retroperitoneal portions of the duodenum and colon. Most patients with dermal or superficial muscle injury are discharged within a short time. Patients with minor or low-risk injuries (small retroperitoneal hematoma or minor renal injury) are managed with short-term observation. Patients with major visceral injuries might be managed nonoperatively, but may require surgery or angiography. ¹⁵ Triple-contrast CT is a popular technique to triage patients with penetrating flank and back injuries because of its excellent sensitivity (89% to 100%), negative predictive value (89% to 100%), and accuracy (92% to 96%) to identify patients likely to require intervention for injury. ^15-18 Triage by CT leads to a very low rate of subsequent nontherapeutic laparotomy (2.3%). ^15-18

Concerns regarding the accuracy of CT to diagnose hollow viscus injuries have, in the past, diminished trauma surgeons' enthusiasm to request CT to triage patients with penetrating injuries to other anatomic regions in the torso. The bowel is the most commonly injured abdominal organ resulting from penetrating trauma. ^12,19 In some studies, surgeons have used DPL or observation as an adjunct to CT to diagnose potential intraperitoneal injuries. ^15,17 However, recent retrospective studies by Grossman et al ²⁰ and Ginzberg et al ²¹ have shown that helical CT is accurate in determining the trajectory of gunshot wounds and the presence of peritoneal violation in patients with nonflank and back wounds of the torso. In the retrospective study performed by Ginzberg et al, ²¹ triple-contrast CT was used as the initial screening study to detect peritoneal violation and minimize nontherapeutic laparotomy. Patients with equivocal helical CT results for peritoneal violation had cavitary endoscopy to verify CT findings. There were no missed injuries among 53 patients with negative CT who were observed for 23 hours. For abdominal wounds, CT had a specificity of 54%, a negative predictive value of 100%, and an overall accuracy of 71%; for flank wounds, CT had a specificity of 98%, a negative predictive value of 100%, and an overall accuracy of 98%. ²¹ Both retrospective studies concluded that CT was safe and effective as an initial screening study to detect peritoneal violation in hemodynamically stable patients with torso gunshot wounds. ^20,21

Prospective studies were performed at the authors' level-1 trauma center to evaluate triple-contrast helical CT in patients with penetrating torso trauma. ^22,23 These studies found that CT is highly accurate in demonstrating peritoneal violation and in predicting the need for subsequent laparotomy. ^22,23 In this research, CT studies were positive for peritoneal violation or a significant retroperitoneal injury in 34% (35 of 104) of patients and negative in 66% (69 of 104) of patients. Among patients with a negative CT, 97% (67 of 69) were managed nonoperatively without missed injuries. CT had 100% (19 of 19) sensitivity, 96% (69 of 72) specificity, 100% (69 of 69) negative predictive value, and 97% (101 of 104) accuracy in predicting the need for laparotomy. ²²

CT technique

Triple-contrast multidetector spiral CT is obtained from the inter-nipple line to the symphysis pubis, following administration of intravenous contrast material. CT was performed using an MX 8000 (Philips Medical Systems, Best, Netherlands) with a collimation of 2.5 mm (2.5 * 4 images per rotation) and a table speed of 10 mm/sec. Intravenous contrast material (300 mg iodine/mL, 150 mL) is administered at 3 mL/ sec using a power injector (Medrad 4, Medrad, Pittsburg, PA). A total volume of 600 mL of 2% sodium diatrizoate (Hypaque sodium, Amersham Health, Princeton, NJ) oral contrast material is administered 30 minutes before and again immediately before initiation of CT. An enema of 1 to 1.5 L of 2% sodium diatrizoate is also administered to opacify the colon on the CT table before scanning. Delayed images are obtained routinely in the renal excretory phase to evaluate the renal collecting system and to verify evidence of active arterial extravasation or pseudoaneurysm.

Exclusion criteria

At the authors' institution, any patient with hemodynamic instability, evidence of peritonitis on clinical examination (rigidity, rebound, tenderness, or considerable tenderness away from the wound site), or evisceration must undergo laparotomy. Other indications for surgery include free intraperitoneal fluid on focused abdominal sonography for trauma (FAST), rectal bleeding, hematemesis, or pneumoperitoneum diagnosed by chest or abdominal radiography.

Wound tracts and peritoneal violation

CT can demonstrate the extent of a wound tract accurately by showing air (Figure 2), hemorrhage (Figure 1), bone (Figure 2), or bullet fragments along the wound. ^20,22,23 Prior knowledge of the wound entry site and use of optimum CT windows and level (window = 550, level = 75) assist in identifying subtle wound tracts and identification of visceral injury sites. ²² Low-energy knife wound tracts may be subtle compared with high-energy gunshot wound tracts that are seen clearly on CT from the presence of larger amounts of hemorrhage, air, and metal fragments.

CT findings of peritoneal violation include the presence of a wound tract outlined by air, hemorrhage, or bullet fragments due to the missile or knife entering the peritoneal cavity (trajectory of missile or knife); intraperitoneal free air or free fluid (Figure 3); bullet fragments; or intraperitoneal organ (Figures 1, 3, and 4), mesenteric, or vascular injury. The most common CT finding among patients with peritoneal violation is intraperitoneal free fluid. ²² Other CT signs useful to diagnose peritoneal violation include intraperitoneal visceral injury seen in 60% (21 of 35) of patients and free intraperitoneal air seen in 43% (15 of 43) in the authors' study. ²² These two signs are more often associated with gunshot wounds than with stab wounds. ²²

At the authors' institution, the CT scan is considered positive if there is evidence of peritoneal violation; injury to the renal collecting system, retroperitoneal colon, or duodenum; or major vascular injury. CT studies are considered negative when there is no evidence of peritoneal violation (Figure 5), with or without minor extraperitoneal injuries (minor renal injuries, small retroperitoneal or pelvic hematomas). Prospective studies have reported that CT is highly accurate in excluding peritoneal violation and can be used reliably to select patients for selective nonsurgical management without a high likelihood of significant missed injuries. ^22,23

Solid organ injury

Injuries to the liver and spleen are seen more frequently following penetrating injuries to the thoracoabdominal region (Figures 1, 3, and 4), upper abdomen, and flank. ^22-24 The liver is the most commonly seen injured solid organ in patients with penetrating trauma to the torso. ^22-24 On contrast-enhanced CT, intraparenchymal hematomas are seen along the wound tract as low-attenuation areas compared with the normal enhancing parenchyma of the liver or spleen. Intraparenchymal hematomas (Figure 1) seen along the wound tract are usually larger as a result of the higher energy gunshot wound, causing more tissue damage than a stab wound. Subcapsular hematomas are seen as low-attenuation collection(s) between the parenchyma and capsule. Subcapsular hematomas cause direct compression of the underlying normal parenchyma. Lacerations occur along the wound tract, as a result of the crushing of the parenchyma. On contrast-enhanced CT, acute lacerations are seen as linear low-attenuation areas compared with the normal enhancing parenchyma (Figure 3).

CT has proven very helpful in selecting patients with isolated liver injury from thoracoabdominal penetrating trauma for successful nonoperative management in studies reported by Renz and Feliciano ²⁴ and the current authors. ^22,23 In these studies, nonoperative management was successful in all patients with isolated penetrating liver injury. No patient needed laparotomy or developed complications requiring intervention. In the study performed at the authors' trauma center, adjunctive angiography and embolization were required for 3 patients to treat active hepatic hemorrhage shown by CT in 1 patient, and clinical evidence of ongoing hemorrhage in 2 others. Triple-contrast spiral CT provided valuable information permitting attempted nonsurgical management, including determination of bullet trajectory, identification of the extent of liver injury, and, principally, exclusion of other injuries that would mandate celiotomy.

Bowel and mesenteric injuries

Unlike in cases of blunt trauma, hollow viscus injuries are the most common injuries seen following all penetrating trauma. ^8,12,19 The concerns about the varying sensitivity and specificity of CT in diagnosing bowel injury have limited the use of CT to evaluate penetrating torso injury for the past decade. At the authors' institution, routine administration of oral and rectal contrast material is used to help to opacify the bowel and increase the sensitivity of CT to detect small amounts of intermesenteric fluid, mesenteric contusions, or infiltration of the mesenteric fat that may provide the only evidence of bowel injury. Also, adequate distention of the bowel by gastrointestinal contrast material enhances the ability to demonstrate bowel-wall pathology. Specific CT findings of bowel or mesenteric injury in patients with penetrating trauma include extravasation of oral or colonic contrast (Figure 6), bowel-wall thickening (Figures 3 and 7), mesenteric bleeding, discontinuity or defect in the bowel wall, or focal mesenteric hematoma or infiltration. A wound tract extending up to the wall of a hollow viscus (Figure 2) is also considered a sign of bowel injury on CT.

In the prospective study performed at the authors' institution, of the 35 patients in the study with peritoneal violation, 13 (37%) had bowel or mesenteric injury as shown on CT. ²² The wound tract extending adjacent to injured bowel was the most common CT finding seen in 69% (9 of 13) of the patients with bowel injury. Other CT findings of bowel injury included bowel-wall thickening in 54% (7 of 13) and oral or rectal contrast extravasation in 15% (2 of 13). All 7 patients with bowel-wall thickening had bowel injury that required intervention.

Unlike in cases of blunt trauma, the inability to use the presence of isolated free intraperitoneal air or fluid as a diagnostic or suspicious CT sign of bowel injury makes diagnosis of bowel injury far more challenging in the setting of penetrating trauma. In penetrating trauma, free intraperitoneal blood may result from bleeding from an injury to the abdominal wall (the peritoneal lining itself) or from extraperitoneal bleeding leaking through a defect caused by a wound tract into the peritoneal cavity. Free intraperitoneal fluid in the absence of a solid-organ injury should be considered a CT finding of peritoneal violation and not a nonspecific finding of bowel injury. The presence of pneumoperitoneum without evidence of a pneumo-thorax, pneumomediastinum, or retroperitoneal air decompressing into the peritoneal cavity is a specific CT finding of bowel injury and mandates surgery in cases of blunt trauma. However, free air may be introduced into the intraperitoneal cavity by a bullet or knife during violation of the peritoneum, thus pneumoperitoneum is a sign of peritoneal violation and also cannot be used as a specific CT finding of bowel injury in cases of penetrating injury.

Diaphragm injury

Patients with any penetrating injury to the thoracoabdominal region with radiographic or CT evidence of a wound trajectory extending in close proximity to the diaphragm are likely to have a diaphragmatic injury. Most patients sustaining diaphragm injury from blunt trauma have long lacerations often permitting immediate or early herniation of abdominal structures into the chest. Typically, lacerations of the diaphragm from penetrating injury are <2 cm long (particularly for knife wounds) and therefore may be extremely subtle. ^25,26 Murray et al ²⁶ reported a 24% (26 of 110) incidence of occult diaphragm injuries diagnosed prospectively by laparoscopy in 110 stable patients with penetrating injury to the thoracoabdominal region but no clinical indication for celiotomy. In this study, chest radiographs were normal in 62% (16 of 26) of the patients with diaphragm injury. All patients with a penetrating injury tract adjacent to the diaphragm should be considered to have a potential diaphragm injury. Suspicious CT findings of diaphragm injury in penetrating trauma include a wound track outlined by air, hemorrhage, or bullet fragments due to the missile or knife extending adjacent to the diaphragm; thickening of the diaphragm as a result of hematoma or edema; free air on the peritoneal aspect of the diaphragm in the absence of a hollow viscus injury; and a defect in the continuity of the normal diaphragm or crus with no clear evidence of hematoma or blood. Diagnostic CT signs of diaphragm injury include the CT collar sign (constriction of a herniating viscus at the diaphragmatic rent) (Figure 8), herniation of abdominal content into the thoracic cavity through a diaphragmatic rent (Figure 8), or the presence of contiguous organ injury on either side of the diaphragm in patients with a single gunshot or stab wound (Figure 7).

A review of CT findings in 19 patients with potential diaphragm injury at the authors' institution found that the most common diagnostic CT sign of diaphragm injury was contiguous organ injury on either side of the diaphragm from a single wound seen in 42% (8 of 19) of patients. ²² Herniation of abdominal fat through a diaphragm defect was seen in 1 patient. CT findings were diagnostic in 47% (9 of 19) of patients. Other CT findings suggestive of a diaphragm injury seen in the study include focal thickening of the diaphragm in 37% (7 of 19), and focal discontinuity of the diaphragm in 5% (1 of 19) of patients. Further prospective studies are needed to determine the sensitivity, specificity, and accuracy of CT signs to diagnose diaphragm injury in penetrating trauma.

Conclusion

Initial studies indicate that triple-contrast helical CT is highly accurate in excluding peritoneal violation in hemodynamically stable patients with penetrating trauma of the torso who have no other indication for laparotomy. Patients with isolated liver injury can be selected using helical CT for nonoperative management. In particular, further studies are necessary to determine the accuracy of triple-contrast helical CT in diagnosing the more challenging penetrating injuries to the bowel and the diaphragm. AR