Penetrating Trauma: Can “Triple-Contrast CT” Guide Nonoperative Management?

Historically, penetrating trauma of the abdomen or flank was evaluated with surgical exploration (laparotomy), laparoscopy to inspect for peritoneal violation, or local wound exploration. More recently, selected stable patients have been evaluated with so-called triple-contrast CT (CT with oral, IV, and rectal contrast). IV contrast in this setting serves the same functions as in blunt trauma, discussed in detail earlier. Oral and rectal contrast agents are used for the theoretical benefit of demonstrating leak of contrast from the bowel lumen into the peritoneum or retroperitoneum.

As we discussed earlier, oral contrast has not been shown to be diagnostically beneficial in blunt abdominal trauma. Theoretically, oral and rectal contrast might be more useful in penetrating injuries, in which bowel penetration is a more common injury, and in which larger defects in the bowel wall might be expected. However, multiple studies have failed to show contrast leak from the bowel lumen to be a sensitive indicator of hollow viscus injury. In one prospective study of 200 patients, only 19% of patients with proven bowel injury had contrast leak from bowel observed on CT. In comparison, a wound track near the bowel was 77% sensitive.²⁶ Given this, are oral and rectal contrast agents truly essential in the setting of penetrating trauma? A single study has evaluated the sensitivity and specificity of “single-contrast CT” (CT with IV contrast and no oral or rectal contrast) for penetrating abdominal or flank injuries.²⁷ Ramirez et al.²⁷ retrospectively reviewed 10 years experience with IV contrast–only CT for evaluation of penetrating torso trauma in 306 hemodynamically stable patients. CT predicted “need for laparotomy” with 98% sensitivity and 90% specificity, a positive predictive value of 84%, and a negative predictive value of 99%. In 222 patients with gunshot wounds, the authors reported 100% sensitivity and a 100% negative predictive value, whereas they found 92% sensitivity and a 97% negative predictive value in patients with stab wounds. Although the authors did not compare the sensitivity and specificity of CT with IV contrast to triple-contrast CT, their results are comparable to those reported in studies of triple-contrast CT, described later. Like many retrospective studies, this study suffers from a mixed criterion standard that includes laparotomy and clinical course. The authors did not report the duration of clinical follow-up and losses to follow-up, raising the possibility that some injuries might have been missed by CT. Unlike some other studies, this study focused on prediction of “need for laparotomy” rather than sensitivity for peritoneal violation. Unfortunately, the authors did not categorize the laparotomy results (therapeutic, nontherapeutic, and negative). Because the surgeons in this study were not blinded to the CT results, they assuredly were influenced by the CT findings in their decision to operate. As a consequence, the reported performance of the CT is affected by incorporation bias. Nevertheless, the authors pointed to significant time savings by avoiding oral and rectal contrast agents.

Demetriades et al.³⁷ prospectively studied alert hemodynamically stable patients without findings of peritonitis on examination following penetrating abdominal injury. Unstable patients, patients with peritonitis, and those who could not be evaluated clinically underwent immediate laparotomy. Of 152 patients, 61 (40.1%) met criteria for CT evaluation with IV but without oral or rectal contrast. Patients without CT findings of hollow viscus injury were observed with serial exams and laboratory evaluation for falling hematocrit or developing leukocytosis. The authors found that 43 patients with 47 solid organ injuries (liver, spleen, and kidney) had no CT evidence of hollow viscus injury by CT. Because of CT evidence of active bleeding, 4 patients underwent angiographic embolization of the liver. Whereas 41 patients (27% of total) were managed nonoperatively, 3 patients failed nonoperative management but recovered without complications after laparotomy, and 2 patients underwent laparoscopy to evaluate for possible diaphragm injury, given the relatively low reported sensitivity of CT for this injury pattern.

Inaba and Demetriades³⁸ reviewed the indications for laparotomy in penetrating abdominal injury. Hemodynamically stable patients without examination findings of peritonitis can be managed nonoperatively with careful observation. Gunshot wounds to the abdomen can be imaged with CT to determine projectile trajectory and likely injuries. Peritoneal violation on CT without evidence of organ injury can be managed nonoperatively with careful serial examinations. Solid organ injuries can be managed with endovascular therapies, primarily embolization for control of hemorrhage. Evidence of hollow viscus injury on CT warrants surgical exploration.

Mitra et al.³⁹ retrospectively reviewed all patients with penetrating abdominal injury over a 5-year period and found 36 hemodynamically stable patients undergoing CT for evaluation. The authors did not identify the CT protocol used, although they specified that triple contrast was not used. They reported a 77.8% combined sensitivity of CT and ultrasound in these patients.

Beekley et al.⁴⁰ retrospectively reported on 145 stable patients in a military combat support hospital without peritonitis following penetrating abdominal shrapnel wounds. Patients were routinely evaluated with CT with IV contrast; oral contrast was used “rarely” and rectal contrast was used in 2 cases. Patients with no CT findings of intraperitoneal or retroperitoneal penetration were managed nonoperatively. Based on CT, 85 (59%) of patients were managed nonoperatively, and 60 (41%) underwent laparotomy. The authors reported that 75% of laparotomies were therapeutic. Negative CT missed 1 patient with an intraabdominal injury requiring laparotomy (sensitivity = 97.8%, specificity = 84.8%, negative predictive value = 99%).

A number of studies have evaluated the safety and sensitivity of the triple-contrast CT approach. Multiple large series and a metaanalysis report good outcomes with conservative nonoperative management following a CT showing no evidence of bowel injury. We discuss these shortly, but first consider some limitations. First, publication bias may skew the reported literature on this topic, with authors not reporting failures of this technique. Second, many of the published studies suffer from limited clinical follow-up, raising the possibility of missed injuries not recognized by the researchers. Third, the indications for conservative management with CT include a reassuring physical exam. Because different physicians may interpret the physical examination differently, it is unclear how safe the practice would be outside of the major trauma centers that are the source of much of the data.

Hauser et al.²⁸ retrospectively reviewed 40 cases of posterior abdominal penetrating injuries evaluated with CT using IV, oral, and rectal contrast. They found 6 of the 40 cases to have abdominal injury by CT, confirmed by laparotomy. Although 34 patients without CT evidence of peritoneal or retroperitoneal organ injury were observed for 72 hours and discharged without laparotomy, lack of long-term follow-up prevents certainty that no injuries were missed.

Himmelman et al.²⁹ prospectively enrolled 88 hemodynamically stable patients with penetrating back or flank wounds. In 9 patients, CT suggested surgical injuries; 5 of these underwent laparotomy, with 2 having significant injuries. The other 79 patients had no CT findings suggesting need for surgery, and 77 of them were observed for 48 hours without complications. Because of positive DPL, the remaining 2 patients underwent laparotomy, negative in both cases. The authors concluded that a reassuring CT had a 100% negative predictive value for injuries requiring surgical repair.

McAllister et al.³⁰ reported on 53 hemodynamically stable patients with stab wounds to the back, evaluated with triple-contrast CT if local wound exploration showed muscle fascia penetration. Of the 53 patients, 51 had negative CT or injuries not requiring surgery and did well with nonoperative management. Two CTs demonstrated injuries requiring therapeutic celiotomy. The authors concluded that CT was accurate in detection of occult injury but was costly and did not contribute to clinical management decisions—a peculiar conclusion given that the authors did not assess the planned management from clinicians blinded to the CT results.

Soto et al. reported on 32 stable patients examined with triple-contrast CT and serial ultrasound following penetrating abdominal stab wounds. One patient had CT findings of extensive hepatic laceration and massive hemoperitoneum and was managed operatively. The other 31 patients were managed nonoperatively based on CT and ultrasound findings and were asymptomatic at 28-day follow-up. Of these patients, 21 had some form of intraperitoneal injury but without evidence of bowel injury.³¹ The small number of patients in this series, and the limited number of significant injuries, limit the external validity of this study.

Chiu et al.³² retrospectively reviewed 75 hemodynamically stable patients undergoing triple-contrast CT following penetrating torso trauma. Patients with negative CT or isolated solid organ injury were observed, whereas those with any other evidence of peritoneal violation (free air or fluid, contrast leak, or nonsolid visceral injury) underwent laparotomy. In patients with negative CT, 47 of 49 (96%) had successful nonoperative management, 1 had negative laparotomy, and 1 had a left diaphragmatic injury. In patients with positive CT, 15 of 18 had therapeutic laparotomy. Whereas 5 patients had isolated hepatic injuries, 2 had hepatic and diaphragmatic injuries, managed with angiographic embolization and thorascopic diaphragmatic repair. The authors concluded that CT is useful in selecting patients for nonoperative management, although solid organ injuries and diaphragmatic injuries may require invasive therapies.

Shanmuganathan et al.³³ prospectively studied triple-contrast helical CT in predicting peritoneal violation and need for laparotomy following penetrating torso trauma in 104 hemodynamically stable patients (54 gunshot wounds and 50 stab wounds). A positive CT was defined as evidence of peritoneal violation or injury to the retroperitoneal colon, a major vessel, or the urinary tract. Laparotomy was performed in patients with a positive CT except in those patients with isolated liver injury or free fluid. Patients with negative CT were initially observed. Among those with positive CT, 19 (86%) had therapeutic laparotomy. Whereas 9 patients with isolated hepatic injury on CT were successfully managed nonoperatively, 67 of 69 patients (97%) with negative CT had successful nonoperative management. The authors reported 100% sensitivity and 96% specificity of CT, although they failed to account for the operative management in 2 patients with negative CT.

In a separate report, Shanmuganathan et al.²⁶ reported on 200 hemodynamically stable penetrating trauma patients without peritoneal signs or radiographic (x-ray) findings of pneumoperitoneum. The group included 86 patients with gunshot wounds, 111 with stab wounds, and 3 sharp impalements. Triple-contrast CT was prospectively evaluated by three radiologists for peritoneal violation and injury to intra or retroperitoneal solid organs, bowel, mesentery, vascular structures, diaphragm, and urinary tract. CT was 97% sensitive for peritoneal violation requiring laparotomy and diagnosed 28 hepatic, 34 bowel or mesenteric, 7 splenic, and 6 renal injuries. Laparotomy based on CT findings was therapeutic in 87% of patients. Two patients with negative CT required therapeutic laparotomy.

Conrad et al.³⁴ retrospectively reviewed the charts of 81 patients who had emergency department workup for penetrating truncal trauma using triple-contrast CT. Following negative CT, 62 patients were discharged from the emergency department. Two missed injuries were identified but had no complications according to the authors. The authors concluded that emergency department discharge is a safe disposition; unfortunately, nearly one third of those discharged had no follow-up, rendering uncertain the outcomes of this strategy. If a significant percentage of the patients lost to follow-up had missed injuries, emergency department discharge following a negative CT would be unacceptable.

Loberant and Goldfeld³⁵ provided a case report of a patient undergoing a negative laparotomy because of a bony fragment mistakenly identified as contrast extravasation on triple-contrast CT.

Dissanaike et al.³⁶ reported a series of 9 patients evaluated with triple-contrast CT, with no missed injuries following nonoperative management of patients with negative CT. Clearly, the small numbers of patients in this series limit the value of the study.

Goodman et al.⁴¹ performed a metaanalysis to determine the predictive value of CT for laparotomy in hemodynamically stable patients with penetrating abdominal trauma. They identified 180 studies but included only 5 because of methodologic concerns. The pooled sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were 94.90%, 95.38%, 98.62%, 84.51%, and 94.70%, respectively. This meta-analysis included studies using both single-contrast and triple-contrast techniques and thus does not clarify the necessity for contrast agents.

Overall, triple-contrast CT appears to be a safe management strategy in highly selected stable patients without peritonitis on examination. Losses to follow-up, variable inclusion criteria, and the likelihood of publication bias favoring positive outcomes in the published studies all contribute to a need for caution with a negative CT. Multiple studies have demonstrated the possibility of missed diaphragmatic injuries and, rarely, missed operative bowel injuries. Following a negative triple-contrast CT, observation or close follow-up should be ensured. Further study is needed to determine the true diagnostic value of oral and rectal contrast in this setting.

Approach to Abdominal CT

For the emergency physician, a systematic and targeted approach allows rapid and accurate identification of important injuries on abdominal CT. Because multiple injuries are common following abdominal trauma, it is extremely important to inspect all major abdominal structures. A common pitfall is to end the search after detection of a single injury. Three window settings are useful in evaluating abdominal structures: soft-tissue (sometimes called abdominal or vascular) windows, lung windows, and bone windows. Soft-tissue windows are used to assess solid organs and hollow organs, to detect free fluid, and to detect free air. Lung windows are used to assess for pneumothorax (recall that the lower lungs and pleural spaces are visible on the cephalad-most abdominal CT slices) and pneumoperitoneum, as described later. Bone windows are used to assess for fractures but can also reveal pneumoperitoneum. We recommend evaluating soft-tissue windows first, followed by lung windows, followed by bone windows. Window settings are discussed in more detail in Chapter 9. In the descriptions of traumatic injuries that follow, soft-tissue windows are the appropriate setting for evaluation unless stated otherwise.

On soft-tissue windows, evaluate each organ in turn, rather than attempting to evaluate multiple structures on each slice. For example, follow the spleen through all CT slices in which it appears, evaluating for splenic injury. Do not attempt to evaluate the liver, kidneys, or pancreas during this process, even though they are visible, because this may distract you from a splenic injury. After completing evaluation of the spleen, repeat this process with other organs.

Common and Serious Injury Patterns on Computed Tomography

Imaging Findings of Shock: Inferior Vena Cava and Bowel

In cases of severe volume depletion (generally from hemorrhagic shock following trauma), the infrahepatic inferior vena cava (IVC) appears flattened (Figure 10-6; see also Figure 10-20).⁴² This appearance can occur in patients before the development of clinical hypotension or hemodynamic collapse and demands immediate volume resuscitation. Rarely, it may be a normal variant. In a series of 100 trauma patients, a flattened IVC occurred in 7, 6 of whom had other evidence of severe blood loss. In 100 patients without trauma, a flattened IVC was not seen.⁴²

Figure 10-6 Inferior vena cava (IVC) flattening, a sign of hypovolemia and shock.

CT with IV contrast, soft-tissue window. The size of the IVC has been suggested as a surrogate for intravascular volume status. A flattened IVC can indicate impending hemodynamic collapse and should prompt immediate volume resuscitation. In this 77-year-old trauma patient, who had been traveling in a car struck by a train, the IVC is extremely flat, suggested marked hypovolemia. Compare with the aorta, which has a normal caliber (2 cm). The patient had multiple injuries noted on CT, including pulmonary contusions, a periaortic hematoma, free fluid around the liver, and pelvic superior rami fractures. She also suffered a closed head injury with subarachnoid and subdural hemorrhage. Her initial lactate was elevated. Three hours after CT, the patient suffered a pulseless electrical activity arrest and could not be resuscitated. Autopsy found more than 500 ml of hemoperitoneum, as well as mediastinal hemorrhage.

Shock bowel is a term for secondary bowel injury resulting from sustained systemic hypotension. The CT appearance includes diffuse bowel wall thickening, visible on CT without oral contrast (Figures 10-7 and 10-8). This is in contrast to primary small-bowel traumatic injuries, which usually show focal regions of bowel wall thickening. Shock bowel is variably associated with IVC and aortic flattening, abnormal pancreatic enhancement and peripancreatic fluid, and poor enhancement of the spleen and liver because of hypotension. This constellation of findings is sometimes called the CT hypotension complex and has been reported in other conditions, including head and spine injury, post–cardiac arrest, septic shock, and diabetic ketoacidosis.⁴³

Figure 10-7 Shock bowel, a sign of severe sustained hypotension.

A and B, CT with IV contrast viewed on soft-tissue windows, demonstrating shock bowel in a trauma patient. Shock bowel refers to the appearance of bowel that has been hypoperfused for an extended period. Under these conditions, the bowel ceases peristalsis and assumes an appearance similar in some respects to small-bowel obstruction. In other respects, the bowel appears similar to a case of mesenteric ischemic—but the process is diffuse, rather than being restricted to a single vascular territory. As bowel becomes ischemic, it develops edema of the bowel wall, and the bowel wall develops a hyperenhancing pattern following administration of intravenous contrast, resulting from microvascular leak of the injected contrast. The bowel wall thus looks thick and bright, unlike its normal inconspicuously thin appearance. Loops of fluid-filled bowel are common, and the internal structure of the bowel becomes exaggerated. Sometimes plicae circularis become visible; at other times, the degree of bowel edema is so great that the lumen becomes effaced. This patient developed hemorrhagic shock from a traumatic amputation of his right arm, leading to shock bowel. By the time of the CT, the patient had been volume resuscitated, as indicated by the prominent inferior vena cava (compare with Figure 10-6).

Figure 10-8 Shock bowel.

CT with IV contrast, soft-tissue window. No oral contrast has been given. A-C, Another example of shock bowel. This patient underwent exploratory laparotomy to assess for traumatic bowel injury because some free fluid was noted in the abdomen on CT. No abdominal injuries were found at laparotomy. C, Close-up from B.

Pneumoperitoneum

Pneumoperitoneum is rare following blunt abdominal injury but can indicate bowel perforation. When detected on CT, it is not specific for bowel injury because air tracking from thoracic injuries can collect in the abdomen.^2-3 Following penetrating abdominal injury, pneumoperitoneum detected on CT is likely to indicate bowel perforation and prompts laparotomy in most cases.

On soft-tissue windows, air including pneumoperitoneum appears black (Figures 10-9 and 10-10; see also Figure 10-24). Large amounts of pneumoperitoneum are usually visible on this window setting, but smaller collections are more difficult to recognize because intraperitoneal and retroperitoneal fat appears quite dark on soft-tissue windows. On lung windows, all soft tissues and bones appear white, leaving only air black—thus emphasizing both pneumoperitoneum and bowel gas (see Figures 10-10 and 10-24, B). On bone windows, bone appears white or light gray, and all soft tissues are an intermediate gray, making black air readily visible. During trauma CT, the patient is generally supine, so pneumoperitoneum collects in the anterior midline and perihepatic spaces preferentially (60% in one study) rather than in a subdiaphragmatic location, as occurs on upright chest x-ray.⁴⁴ Air can collect in other locations, including the pelvis and mesentery. CT can detect air collections as small as 1 mm.⁴⁵

Figure 10-9 Penetrating abdominal injury with hemothorax.

This patient sustained a right upper quadrant gunshot wound. The trajectory of the bullet crossed the liver and diaphragm, entering the thorax. A, Chest x-ray shows a retained bullet and increased density of the right thorax, consistent with hemothorax. No meniscus is seen because this is a supine chest x-ray. B, CT with IV and oral contrast (soft-tissue window) shows a large hypodense area indicating hepatic laceration. Always consider chest injury with abdominal or flank gunshot wounds because the trajectory of the missile is unpredictable.

Figure 10-10 Intraperitoneal gas.

Same patient as the prior figure. Penetrating abdominal injuries can introduce exogenous air into the peritoneum and retroperitoneum. In addition, if perforation of a viscus occurs from a penetrating injury, air may escape into the peritoneum as a result. This patient sustained a gunshot wound to the right upper quadrant. CT shows air in the subcutaneous tissues, as well as air within the large hepatic laceration that resulted from the injury. Air appears black on all CT window settings, regardless of the administration of contrast. However, sometimes small collections of air may be difficult to identify on soft-tissue windows (A) because peritoneal fat is dark, nearly black, on this setting. Two other settings are useful to highlight air: bone and lung windows. On bone windows, bone is white, air is black, and all other tissues are intermediate gray. B, The same slice as A viewed on a lung window. Air is nearly black, whereas all other tissues appear white.

Hemoperitoneum and Free Abdominal Fluid

CT is believed to be highly sensitive for abdominal hemorrhage and free fluid. Hemoperitoneum is approximately 30 to 45 Hounsfield units (HU) in density and appears dark gray on CT soft-tissue windows (Figures 10-11 to 10-19 and 10-21 to 10-24).¹⁸ The density of fluid can be measured using the PACS cursor. Simple fluids such as urine or ascites have densities around 0 HU. Free fluid may also accumulate because of bowel injury and may have an intermediate density between the density of water and that of blood. Free fluid or hemoperitoneum generally collects by gravity in dependent regions of the abdomen and pelvis, so the location does not necessarily correspond to the source of bleeding. Inspect the perihepatic and perisplenic regions, including the hepatorenal recess (Morison’s pouch) and splenorenal recess. In addition, inspect the pelvic, paracolic gutters, and central abdomen because these regions may contain free fluid. Free fluid may be seen outlining bowel loops (see Figures 10-21 and 10-22).

Figure 10-11 Spectrum of splenic injuries.

Injuries to the spleen are generally easy to recognize as hypoattenuated (dark) regions on CT with IV contrast. With the administration of intravenous (IV) contrast, the normal spleen enhances quite homogeneously to a fairly bright gray. Injured areas within the spleen (variously referred to as lacerations, contained hematomas, or contusions) fail to enhance with IV contrast, because they are avascular. Depending on the timing of the CT relative to the injection of contrast, normal vessels within the spleen may appear brighter than surrounding parenchyma and should not be confused with active bleeding. Active bleeding (demonstrated in Figure 10-12) appears as a blush of bright contrast but is typically surrounded by hypodense areas of injury. A, Uninjured spleen. B, Minimally injured spleen (grade I). This injury is unlikely to cause hemodynamic compromise acutely because it is small, contained within the spleen, shows no active hemorrhage, and does not involve the hilum. C, Moderately injured spleen (grade III or IV). This injury, though relative small, involves the splenic hilum and may become life-threatening. This injury type is often treated with angiographic embolization to prevent further bleeding. D, Severely injured spleen (grade V). This spleen is shattered and may require embolization or splenectomy.

Figure 10-12 Grade IV spleen injury with hemoperitoneum and active extravasation of contrast material.

A, B, This 20-year-old male was ejected 15 feet from a vehicle and was found to have a high-grade splenic injury on CT with IV contrast. This injury was called “large” by the radiologist, “grade IV” by the surgeons. In this text, we focus on identifying injuries and accurately estimating severity, but specific scores are given less importance. CT findings include marked fragmentation of the spleen, gross hemoperitoneum, and active extravasation of injected contrast. Several points bear emphasis. First, note the quantity of fluid (blood) surrounding the liver even though the spleen is the injured organ. The location of free fluid is determined by gravity and tissue planes, not necessarily by the location of the injured organ. Free fluid appears dark gray compared with the brighter solid organs after administration of IV contrast. This is because of enhancement of the solid organ, which is receiving blood flow carrying contrast material. The free fluid accumulated before the administration of IV contrast and thus does not enhance. An exception is a region of active bleeding, which shows a bright blush of injected contrast at the moment of CT acquisition. This patient has such as blush, indicating active bleeding, in the bed of the spleen. How can active extravasation be discriminated from the normal appearance of vessels within the liver and spleen? These are, after all, extremely vascular organs. Depending on the timing of the CT scan relative to the injection of contrast material, the liver may show enhancement of hepatic arteries or veins, as well as portal veins. The liver parenchyma may remain somewhat enhancing, even after the major vessels have cleared of contrast. However, in each case, normal contrast enhancement of vessels can be recognized and discriminated from active extravasation. Active extravasation occurs in a location with an injury, which is hypodense (darker than surrounding tissue). In general, this means that the blush of active extravasation is surrounded by a darker tissue density of unenhancing fluid (blood) or poorly perfused injured tissue. Look for the bright spot with a dark background. The patient underwent exploratory laparotomy that confirmed a splenic injury with bleeding from the short gastric arteries. No other injuries were detected, and the patient underwent splenectomy. Grade IV and V splenic injuries are occasionally treated with embolization rather than splenectomy, even in the presence of active contrast extravasation, although the evidence for this approach is limited (see Chapter 16). Figures 10-13 to 10-15 explore this patient’s injury in more detail.

Figure 10-13 Hemoperitoneum in the setting of a grade IV spleen injury.

CT with IV contrast. These images are more caudad than those in Figure 10-12 for the same patient. A, Hemoperitoneum is present in a perihepatic location, including Morison’s pouch between the liver and the right kidney. This patient would have a positive FAST examination with fluid detected in the right upper quadrant. The liver itself was uninjured in this patient; the location of hemoperitoneum does not indicate its source. On the patient’s left, this slice is now below the level of the spleen, but a large amount of hemoperitoneum is present in this location as well. B, Still farther caudad, free fluid (hemoperitoneum) is seen in both paracolic gutters. Again, this would be seen on a FAST examination. A thin strip of fat separates the free fluid from the abdominal wall and from the kidneys, which are retroperitoneal. A common point of confusion is the appearance of fluid on CT, perhaps because emergency physicians use ultrasound so frequently. Whereas fluid appears black on ultrasound, on CT fluid appears an intermediate to dark gray (using soft-tissue windows). Fat appears nearly black on this window setting.

Figure 10-14 Hemoperitoneum in the setting of a grade IV spleen injury.

CT with IV contrast, soft-tissue window. These images are more caudad than those in Figure 10-13 for the same patient. Free fluid (hemoperitoneum) is seen in both paracolic gutters (A, B), extending into the pelvis (B). Again, this would be seen on a FAST examination. A thin strip of fat separates the free fluid from the iliacus muscle, which hugs the internal surface of the iliac bone of the pelvis, and the psoas muscle, which is paravertebral. Fat plays an important role as a contrast medium here, because without the interposed fat it would be difficult or impossible to identify the limits of the hemoperitoneum.

Figure 10-15 Grade IV spleen injury with hemoperitoneum and active extravasation of contrast material.

CT with IV contrast, soft-tissue window. Same patient as Figures 10-12 through 10-14. A, B, Coronal CT reconstructions are shown. Although these were not needed to make the diagnosis, they help illustrate the degree of hemoperitoneum, the fragmentation of the spleen, and the active extravasation of contrast indicating ongoing bleeding.

Figure 10-16 Grade I spleen injury.

CT with IV contrast, soft-tissue window. A-C, This 14-year-old male fell 15 feet from a tree. CT showed a subtle spleen injury. This injury would be characterized as grade I. Is free fluid present in Morison’s pouch? The patient did have pelvis fractures that could be a source. The patient was observed and did well without intervention. C, Close-up from B.

Figure 10-17 Spectrum of liver injuries.

CT with IV contrast, soft-tissue windows. In A, oral contrast is also present in the stomach. The normal liver enhances relatively uniformly with administration of intravenous contrast. Depending on the timing of the CT acquisition relative to the injection of contrast, portal and hepatic vessels are visible as bright linear markings. Injuries to the liver are generally easy to recognize as hypoattenuated (dark) regions because these regions have lost their blood supply and do not enhance. Areas of injury may be referred to by terms including hematoma, contusion, and laceration, which are essentially synonymous when describing CT findings. Hepatic injuries are graded from I to VI (see Table 10-3), but for the emergency physician, the key discriminatory categories are normal, low-grade injuries not requiring invasive therapy, and moderate- to high-grade injuries likely to require intervention (angiographic embolization or laparotomy). A, Uninjured liver. Dark areas here represent the normal anatomic divisions of the liver. B, Minimally injured liver (grade I). This injury is unlikely to cause hemodynamic compromise acutely because it is small, contained within the liver, shows no active hemorrhage, and does not involve the major vascular structures. C, D, Moderately to severely injured liver (grade III). C, The hematoma appears contained. D, The liver surface appears torn, and there is associated hemoperitoneum (dark gray crescent surrounding the liver). These injuries may progress, requiring embolization or laparotomy.

Figure 10-18 Hilar liver laceration.

CT with IV contrast, soft-tissue window. This patient sustained multiple life-threatening injuries in a motor vehicle collision, including a multifocal liver laceration extending to the liver hilum (A, B). Hemoperitoneum is present, particularly around the spleen. The patient was treated with angiographic embolization. Patients with higher grades of liver injury are sometimes too hemodynamically unstable even to undergo CT. The FAST examination may be positive, and the liver injury may be diagnosed during laparotomy or angiography.

Figure 10-19 Gallbladder and biliary injuries.

A-L, Series of computed tomography (CT) slices, with close-ups from each slice. This patient sustained a single stab wound to the right upper quadrant. CT with intravenous contrast demonstrates a wound track through the liver into the gallbladder. The gallbladder has high-density material within it consistent with clot—higher in density than normal bile. The liver laceration, though small, shows evidence of active contrast extravasation. The patient underwent laparotomy, confirming a through-and-through gallbladder laceration that was treated with cholecystectomy.

Figure 10-20 Bowel injuries or perforation from penetrating trauma.

A, This patient sustained a gunshot wound to the left chest, which entered the left upper abdomen, injuring the splenic flexure and descending colon. B, The area of injury has been enlarged to allow inspection for small foci of air and metal shrapnel. On soft-tissue windows, metallic material is bright white (remember, calcium in bone is technically a metal). Air is black. Air is visible in the subcutaneous tissues, in the abdomen around the region of the spleen, and scattered outside the colon. The splenic flexure and descending colon appear ill-defined, with a hazy appearance of the surrounding fat—inflammatory stranding. Without a history of trauma, a case of colitis or diverticulitis could have a similar appearance. One of the metal fragments appears to lie within the colon. Laparotomy confirmed perforation of the distal transverse colon, which was resected. The spleen also shows a lack of enhancement (compare with the liver and kidneys)—suggesting a splenic arterial injury resulting in hypoperfusion. The inferior vena cava (IVC) is flattened, suggesting hypovolemia.

Figure 10-21 Penetrating bowel and mesentery injuries.

A, B, This male sustained a gunshot wound to the right hip. CT with intravenous contrast reveals free fluid throughout the abdomen, as well as extravasation of intravenously injected contrast in the right lower quadrant in the region of the small-bowel mesentery. Several areas of bowel wall thickening are visible. These findings indicated the need for laparotomy, which confirmed both mesentery and distal ileal injuries. The CT findings are explored in more detail in Figures 10-22 and 10-23.

Figure 10-22 Penetrating bowel and mesentery injuries with active bleeding.

Same patient as in Figures 10-21 and 10-23. Several clues on this CT with IV contrast suggest active bleeding. A, Fluid surrounding the liver and bowel is high density, more suggestive of blood than of serous fluid such as ascites. Compare the appearance of the fluid surrounding the liver to the appearance of lower-density fluid (bile) in the gallbladder. On CT scan, regardless of window setting, denser substances are brighter (whiter) and less dense substances are darker. Fluid is identifiable around the liver because it is less dense than the solid liver but denser than retroperitoneal fat, which is nearly black on this soft-tissue window setting. Dark retroperitoneal fat surrounds the right kidney. B, Injected contrast is seen extravasating in the right lower quadrant. How can this be identified as active bleeding? This patient received no oral contrast, so high-density material in this region must be injected contrast. The contrast does not have the typical well-circumscribed, rounded shape of contrast within vessels (compare with other vessels on this image). On the digital PACS, the blush of contrast does not communicate with a well-defined vessel as we search cephalad and caudad through the stack of images.

Figure 10-23 Penetrating bowel and mesentery injuries with active bleeding.

CT with IV contrast, soft-tissue windows. Coronal reconstructions from the same patient as in Figures 10-21 and 10-22. help illustrate the extent of intraabdominal hemorrhage and the location of the active bleeding. B, Close-up from A. D, Close-up from C.

Figure 10-24 Penetrating mesenteric injuries.

CT with IV contrast. This patient sustained a gunshot wound below the umbilicus. On a soft-tissue window (A), intravenous contrast extravasation is seen just left of the midline, indicating active bleeding. Free air is seen well on the same slice using a lung window (B). Air is present just deep to the rectus muscles in the peritoneal cavity, as well as just anterior to the sacrum. This air does not appear to be contained in bowel.

When free fluid is seen, a careful search for accompanying solid organ, bowel, and mesenteric injury must be performed. Although solid organ injury is the most common source of free fluid following trauma, the presence of a solid organ injury does not rule out concomitant hollow viscus or mesenteric injury. When free fluid is observed in the absence of solid organ injury, bowel or mesenteric injury must be strongly suspected. Unfortunately, the finding is nonspecific. In a study of 259 pediatric blunt trauma patients, 24 patients (9%) had free fluid as the only abnormal finding. Among the 16 patients with a small amount of free fluid, only 2 (12%) required laparotomy. Among the 8 patients with a moderate amount of free fluid, including free fluid in multiple areas on CT, 50% required operation.⁴⁶ In a study of 2299 adult blunt trauma patients, 90 patients had free abdominal fluid without solid organ injury, but only 7 (8%) had documented intestinal injuries.⁴⁷

Pancreatic Injuries

Pancreatic injuries are rare, occurring in around 2% of blunt trauma patients, and can be difficult to recognize on CT.⁵⁶ Single-detector CT was reportedly only about 80% sensitive for pancreatic injuries, and reports of the sensitivity of multidetector CT with narrow slice thickness are lacking.⁵⁶ A common mechanism for pancreatic injury is a direct blow to the epigastrium as in a handlebar injury or crush injury against the underlying spine. Pancreatic injuries are rarely isolated (<10%) and can accompany bowel injury. CT findings include abdominal free fluid with or without other solid organ injury, peripancreatic stranding or fluid, and direct evidence of pancreatic parenchymal injury (Figure 10-25). Like other solid organs, the normal pancreas is well perfused and enhances with IV contrast. Injured regions are hypoperfused and appear hypoattenuated or dark gray on soft-tissue windows. The body of the pancreas may appear completely transected or comminuted. Active hemorrhage is sometimes seen. Fluid between the splenic vein and the pancreas also suggests pancreatic injury. Injury to the pancreatic duct, which requires repair, can be difficult to recognize but is strongly suggested by deep lacerations of the pancreas (>50% of the pancreatic thickness).^56-57

Figure 10-25 Pancreatic injuries.

A, This patient sustained multiple gunshot wounds to the left thorax, resulting in injuries to the diaphragm, transverse colon, and pancreas that were confirmed at laparotomy. CT with intravenous contrast (soft-tissue window) shows air in the subcutaneous tissues of the left chest wall. The pancreas (small arrows) can be seen in its usual position, draped over the portal vein and celiac artery and then crossing just anterior to the left kidney. Air is present along the anterior border of the pancreatic tail, perhaps having been introduced by the gunshot wound or having escaped from the injured colon. The fat plane that normally separates the pancreas and kidney is obscured by stranding. The inferior vena cava also is flattened, consistent with blood loss. B, Close-up from A.

Adrenal Injuries

Injury to the adrenal glands can occur in blunt trauma. In addition, adrenal hemorrhage is thought to occur spontaneously in some patients with shock and may subsequently lead to adrenal insufficiency. The normal adrenal glands are thin, lambda-shaped structures capping the kidneys bilaterally (Figure 10-26). Adrenal hemorrhage usually results in an enlarged, rounded appearance (see Figure 10-26). The normal adrenal glands enhance with IV contrast, whereas contained adrenal hematoma is usually hypoattenuating. Stranding around the adrenal glands may also occur.^58-60

Figure 10-26 Adrenal injuries.

A, CT with IV contrast, soft-tissue window. This patient sustained an adrenal hematoma in the setting of severe blunt trauma that also resulted in multiple rib fractures, thoracic spine fractures, and a pneumothorax. Adrenal hematomas may result from the stress of severe injury, rather than from direct trauma to the gland. No injury to the surrounding liver, kidney, or adjacent ribs or vertebrae occurred. The inferior vena cava is anterior to the adrenal hematoma and filled with contrast. B, Close-up from A. C, CT with IV and oral contrast in a different patient. Normal adrenal glands for comparison. The adrenal glands are normally inconspicuous and may be difficult to locate. They usually lie just cephalad of the kidneys and have a lambda (λ) shape. D, Close-up from C.

Retroperitoneal Injuries

Retroperitoneal injuries such as psoas muscle hemorrhage are readily seen on CT. The presence of retroperitoneal fat assists in recognition of these injuries, acting as a natural contrast agent. Fat appears nearly black on soft-tissue windows, whereas the normal psoas muscle appears an intermediate gray. Blood in the retroperitoneum has a similar density to psoas muscle and can obscure fat planes (Figure 10-27).

Figure 10-27 Retroperitoneal hemorrhage (iliopsoas hematoma).

This patient fell 12 feet from a ladder, sustaining transverse process spinal fractures and a pneumothorax. In addition, this CT with IV contrast (soft-tissue window) demonstrates a right iliopsoas muscle hematoma. The source of the hemorrhage is evident—a transverse process fracture of the adjacent L2-5 lumbar vertebrae. Hemorrhage can be subtle because fresh blood and muscle have similar density on CT—both appear medium gray on soft-tissue window settings. In this case, comparison with the normal left side reveals asymmetry of the right iliopsoas resulting from an adjacent hematoma. The retroperitoneal fat separating the right kidney from the right iliopsoas is also obscured. A, A slice through the level of the kidneys. B, Two lumbar levels lower.

Abdominal Wall or Flank Injuries

Muscles of the anterior abdominal wall or flank can be damaged, resulting in herniation of abdominal contents. On CT, abdominal contents may be seen in subcutaneous fat (Figures 10-28 and 10-29).

Figure 10-28 Abdominal wall injuries.

This 6-year-old boy was injured falling off a bicycle while riding down a hill and presented with right lower abdominal pain and a protuberant abdomen. CT shows a large hernia defect in the rectus muscle of the right abdominal wall, through which the bowel has herniated into the subcutaneous tissues. Laparotomy was performed, and the hernia was found to contain both the small and the large bowel, with a contusion of the terminal ileum and a serosal tear of the cecum, which was repaired primarily. Compare the injured side with the normal muscles of the left abdominal wall. The patient is tilted slightly in the CT scanner, accounting for the apparent asymmetry of the pelvis.

Figure 10-29 Penetrating abdominal trauma with abdominal wall injury.

This patient presented with a self-inflicted stab wound to the lower abdomen. A, C, CT with oral and intravenous contrast was performed. A, B, axial CT slices through the pelvis, viewed on soft-tissue windows. B, Close-up from A. D, Close-up from C. The CT shows fat stranding consistent with blood in the subcutaneous tissues deep to the stab wound. Compare with the normal appearance of uninjured subcutaneous fat (dark gray). Of greater concern, the bowel lies just deep to the rectus muscle. Though no definite bowel injury is seen, a second slice at a more caudad level (B) shows stranding of intraperitoneal fat just deep to the rectus muscle. This suggests the stab has penetrated the peritoneum, possibly injuring the bowel. In addition, a tiny focus of contrast may represent active bleeding. The patient was observed without laparotomy despite these findings and did well.

Diaphragm Injuries

Overt diaphragm injuries with herniation of abdominal contents into the thorax are readily detected by CT (Figures 10-30 through 10-34). However, when the chest x-ray is normal and the diaphragmatic injury is subtler, CT is less sensitive. Improvements in CT technology, particularly the use of helical CT and coronal and sagittal reconstructions, appear to have improved sensitivity. Nonetheless, studies of diaphragm rupture are limited by the rarity of this injury, with wide confidence intervals because of small studies (described later). Overall, CT likely has a sensitivity of around 60% to 80%, with a specificity of 80% to 100%.

Figure 10-30 Left-sided diaphragmatic rupture from blunt trauma.

A, supine portable AP chest x-ray. Several features of this x-ray strongly suggest traumatic diaphragm rupture. First, the left hemidiaphragm is elevated relative to the right. Normally, the right hemidiaphragm is slightly higher than the left because the liver is larger than the spleen. Second, the apparent gastric air bubble overlies the heart in the left chest. Third, the costovertebral angle is not clear on the left, though this is a nonspecific finding. The patient has multiple left posterior rib fractures, suggesting a high-energy trauma mechanism that might also produce diaphragm rupture. The patient’s CT is explored in Figures 10-31 and 10-32. B, Close-up from A.

Figure 10-31 Left-sided diaphragmatic rupture from blunt trauma.

Same patient as in Figures 10-30 and 10-32. CT with IV contrast, axial images. A, Soft-tissue window of a slice through the T6 level. The stomach is seen in the left chest abutting the heart. A gastric tube is seen passing through the stomach. These findings confirm diaphragm rupture, even without direct visualization of the diaphragm injury. These findings could be recognized without the use of any contrast agents. This patient received intravenous but not oral contrast. A soft-tissue contusion is seen in the left chest wall. A posterior fracture of the sixth rib is visible—this could be inspected in more detail on a bone window. B, Lung window showing subcutaneous air but no large pneumothorax.

Figure 10-32 Left-sided diaphragmatic rupture from blunt trauma.

Same patient as in Figures 10-30 and 10-31. A, In this coronal reconstruction, the stomach abuts the heart, having herniated through a diaphragmatic injury. B, Close-up from A.

Figure 10-33 Right-sided diaphragmatic rupture from blunt trauma.

AP supine chest x-ray. Though rarer than left-sided ruptures, right diaphragm ruptures can occur and must be recognized. This 17-year-old male presented in respiratory distress after a motor vehicle collision. He has herniated the entire liver and segments of colon into the right chest, resulting in mediastinal shift to the left. His respiratory distress is likely because of complete compressive atelectasis of the right lung, as well as compression of the left lung by the shifted mediastinum. The patient’s CT is explored in Figure 10-34.

Figure 10-34 Right-sided diaphragmatic rupture from blunt trauma.

Same patient as in Figure 10-33. CT with IV contrast, soft-tissue windows. A right diaphragm rupture has occurred. A, Axial image. At the level of the scapula, the liver is seen in the right thorax adjacent to the heart, which has been displaced into the left chest. Kinking of the superior mediastinum results, similar to the case in a tension pneumothorax. B, A coronal reconstruction highlights the mediastinal shift.

CT findings of subtle diaphragmatic injury include a discontinuous diaphragm and waistlike constriction of abdominal viscera (sometimes called the “collar sign”), the most common finding in one study.⁶¹ An additional finding, the “dependent viscera sign,” may also be sensitive for diaphragm injury and is described here. Normally, an intact diaphragm prevents the upper one third of the liver from contacting the posterior ribs on the right and the stomach and bowel from contacting the posterior ribs on the left. When the diaphragm is ruptured, these organs become dependent (hence the term dependent viscera sign) and contact posterior ribs in a patient positioned supine during CT.⁶¹ The diaphragm itself may be obscured by hemothorax or hemoperitoneum.⁶² In some cases, the presence of a diaphragm injury can be inferred from injuries on both sides of the diaphragm, though the diaphragmatic defect itself may not be seen (Figures 10-35 and 10-36).

Figure 10-35 Transhepatic gunshot wound with hemothorax and diaphragm injury.

This patient sustained a gunshot wound to the abdomen but was hemodynamically stable on arrival. Chest x-ray shows veiling of the right thorax, suggesting a hemothorax. This appearance is typical on a supine chest x-ray, whereas an upright chest x-ray usually would show a meniscus because of dependent thoracic fluid. The patient underwent abdominal CT, shown in Figure 10-36. Always consider chest injury with any penetrating abdominal or flank wound because the course of a penetrating injury may cross the diaphragm.

Figure 10-36 Transhepatic gunshot wound with diaphragm injury.

Same patient as in Figure 10-35. A, Axial view. B, Coronal view. CT with IV contrast (soft-tissue windows) shows a transhepatic gunshot wound with an associated hemothorax. The presence of simultaneous chest and abdominal injuries suggests a diaphragmatic perforation, which was confirmed at surgery.

The sensitivity of CT for diaphragmatic injury has improved over the past 20 years due to technological improvements, while chest x-ray sensitivity has remained static. Gelman et al.⁶³ reported the sensitivity of chest x-ray as 46% for left-sided diaphragmatic rupture but only 17% for right-sided rupture. An additional 18% of left-sided ruptures had abnormalities not diagnostic of diaphragm rupture but prompting additional imaging. At that time (1991), CT was only 14% sensitive.

Smithers et al.⁵ (1991) reported a sensitivity of chest x-ray around 60% for diaphragm rupture within 48 hours after injury.

Murray et al.⁶² (1996) reported the performance of three radiologists for detection of diaphragm rupture on CT in a case-control study (11 cases, 21 controls). Sensitivity for detecting diaphragmatic rupture was 54% to 73%, and specificity was 86% to 90%. Average sensitivity for the three observers was 61% (95% CI = 41%-81%), and average specificity was 87% (95% CI = 76%-99%).

Killeen et al.⁶¹ (1999) reported on helical CT with sagittal and coronal reconstructions in 41 patients, 23 with proven diaphragm injury. Sensitivity for detecting left-sided diaphragmatic rupture was 78%, and specificity was 100%. Sensitivity for the detection of right-sided diaphragmatic rupture was 50%, and specificity was 100%.

Bergin et al.⁶⁴ (2001) described the dependent viscera sign (discussed earlier). In their sample of 28 patients, 10 with diaphragm injury, the finding was 100% sensitive for left-sided rupture and 83% sensitive for right-sided rupture. The authors claimed a consecutive sample of patients undergoing CT and laparotomy was studied, but the high incidence of diaphragm injury in this series (36%) far exceeds other reports and strongly suggests selection bias.

Allen et al.²² (2005) reported CT without oral contrast to have a sensitivity and specificity for diaphragm injury of 66.7% (95% CI = 29.9%-92.5%) and 100% (95% CI = 99.2%-100%), respectively, although their study included only nine injuries.

Vascular (Aorta and Inferior Vena Cava) Injuries

The abdominal aorta is relatively rarely injured with blunt mechanisms of trauma. However, severe trauma (e.g., falls from great height or extremely high-speed collisions) can disrupt the abdominal aorta. The normal aorta is circular in cross section, does not exceed 3 cm in diameter, and has a smooth contour. It has a uniform location anterior to the spine, making it easy to inspect. With IV contrast, the aorta should fill uniformly with contrast, with no filling defects or intimal flaps visible. In older patients, aortic aneurysms and mural thrombus may be incidentally detected, unrelated to trauma (see Chapter 11). In cases of trauma, the aortic contour may be irregular, and active extravasation of contrast may be seen as a bright blush (Figure 10-37). Any periaortic hematoma that accumulated before the administration of IV contrast appears dark gray, approximately 45 Hounsfield units. Aortic injuries from penetrating trauma have a similar appearance to those seen with blunt trauma, if the patient is stable enough to undergo CT.

Figure 10-37 Abdominal aortic injury from blunt trauma.

This patient sustained a traumatic L1-2 spinal subluxation resulting from a fall from great height. The abdominal aorta was torn at the site of spinal trauma, an unusual injury following a blunt mechanism. CT with IV contrast, soft-tissue windows. A, Axial view shows an absence of the normal circular cross section of the aorta, as well as the presence of abnormal contrast extravasation. B, Sagittal view shows the aortic discontinuity at the level of spinal injury. Following an emergent aortic repair, the patient survived with relatively normal neurologic and vascular function.

Injuries to the IVC are more common in penetrating trauma than in blunt trauma. The IVC has a uniform location to the right of the patient’s aorta. Its size is generally smaller than that of the aorta but varies with the patient’s intravascular volume status. The IVC may be circular or elliptical in cross section. In hemorrhagic shock, the IVC appears flattened (see Figures 10-6 and 10-20).⁴² Active extravasation of contrast can be seen with IVC injuries.

Is There a Role for Pan-Scan CT in Patients With Blunt Abdominal Trauma?

In contrast to the admonition for limited CT based on clinical decision rules, other authors have cautioned that significant injuries are often present in patients with no signs of symptoms of abdominal trauma. Several studies have concluded that so-called pan-scan CT (CT of the head, neck, chest, abdomen, and pelvis) is required following all blunt trauma—though these studies have serious methodologic flaws and have been widely criticized. We discuss some of these flawed studies here. Many of these studies suffer from both selection and spectrum bias. The studies are typically conducted in large, high-acuity, high-volume centers, and application of techniques developed in these settings is unlikely to yield similar results when used in centers with lower patient acuity and volume. In addition, studies of this type frequently suffer from poor collection of history and examination data. In one case, the authors titled their study “Whole Body Imaging in Blunt Multisystem Trauma Patients Without Obvious Signs of Injury,” but in questions following their oral presentation, the investigators admitted failing to assess for obvious physical findings such as chest and spine tenderness.⁶⁶ Some studies also included both patients with abnormal mental status and those with normal mental status—two populations whose examination findings may be different in their reliability.⁶⁶

Sampson et al.⁷⁴ reported a retrospective series of 296 patients undergoing comprehensive CT, including noncontrast CT of the head and cervical spine with contrast-enhanced CT of the chest, abdomen, and pelvis. The authors reported the detection of “unsuspected injuries,” including 19 cervical spine injuries, 97 pneumothoraces, and 19 splenic injuries. Whether these injuries were truly unsuspected based on history and examination is not clear from the study design and manuscript. Moreover, the clinical importance of some injuries, including small pneumothoraces detected by CT, is unknown and not measured in this study. It is possible that detection of subtle injuries resulted in worsened patient outcomes by prompting unnecessary interventions such as thoracostomy. Despite this, the authors advocated comprehensive CT in blunt trauma patients, with little evidence to guide their selection of patients. The authors stated that all hemodynamically stable blunt trauma patients with more than two body systems involved were imaged. However, this study is highly selection biased because only 296 patients in a 7-year period were imaged in this manner, with an annual emergency department census of 85,000 visits. It is likely that only relatively sick patients were selected to undergo comprehensive CT. Application of this imaging strategy to all blunt trauma patients in other practice settings would likely result in imaging of less injured patients, with less potential benefit from intensive imaging. The cost and radiation exposure of this strategy would likely not be warranted.

Huber-Wagner et al.⁷⁵ retrospectively reported survival in 1494 patients undergoing whole-body CT for evaluation of blunt trauma, compared with 3127 not undergoing whole-body CT. They reported a 25% reduction in mortality risk in patients undergoing whole-body CT, compared with the predicted mortality using previously published trauma scores. The authors concluded “whole-body CT… significantly increased the probability of survival in patients with polytrauma.” Unfortunately, retrospective studies such as this can demonstrate only association, not causation, as the authors suggested. Many confounding factors may cause studies such as this to reach precisely the wrong conclusions. Although the authors attempted to control for factors such as trauma-center type and year, this is not a randomized controlled trial and bias likely played an important part in outcomes in the two groups. Patients not undergoing whole-body CT may have differed in important but unmeasured ways from patients undergoing whole-body CT. For example, more stable patients may have been recognized by the treating physicians and selected for CT imaging, giving the false appearance that CT caused improved survival.⁷⁵ The type of physicians caring for the patients may have been the biggest determinant of outcome, with the use of CT as simply a marker of physician training. The local infrastructure at hospitals practicing whole-body CT may have differed from those not performing whole-body CT. The authors skipped an important step in demonstrating any cause–effect relationship when they failed to demonstrate injuries found on CT that plausibly could have been treated to reduce mortality. In commentaries upon this study, other authors pointed out that early deaths, before the completion of whole-body CT, could contribute to the worsened outcomes in the group not receiving whole-body CT.^76-79 In the first hour, 58 patients died in the non–whole-body CT group, compared with only 8 in the whole-body CT group. Although the authors of this study proposed a prospective randomized controlled trial, others have criticized them for aggressively suggesting whole-body CT based on their study.

Can Patients Be Safely Discharged Following a Normal CT for Blunt Abdominal Trauma? What Injuries Can Be Missed?

Historically, patients with blunt abdominal trauma were typically observed to allow repeat clinical examination and detection of evolving abdominal injuries. The introduction of CT allowed earlier detection of injury, but the safety of discharge following a normal abdominal CT was unknown. Reports of missed injuries such as bowel, mesenteric, and diaphragmatic injury prompted frequent admission even following a normal abdominal–pelvic CT.

Livingston et al.⁴⁷ (1998) prospectively studied 2299 adult blunt abdominal trauma patients using a standardized protocol with abdominal CT, followed by admission and observation. CT was negative in 1809 patients. Among these patients, 9 underwent celiotomy, including 6 therapeutic laparotomies for 3 bowel, 1 bladder, 1 kidney, and 1 diaphragmatic injury. Another 2 patients had nontherapeutic laparotomy, and 1 had a negative laparotomy. The negative predictive value of abdominal CT for celiotomy was 99.63% (lower 95% CI = 99.31%, lower 99% CI = 99.16%). The authors concluded that admission and observation are not required in patients following negative abdominal CT. This study benefits from its prospective design, protocol-driven follow-up, and high rate of injury (17% with abnormal CT). However, several important limits should be emphasized. Bowel injuries are rare following blunt abdominal injury, occurring in only 25 patients in this study (1% of patients). As a result, even a poor test will have an excellent negative predictive value for this injury. A fixed guess of “no bowel injury” will be correct in 99% of cases. However, in patients with a high pretest probability of bowel injury, a negative CT should be treated with caution. For example, a patient with increasing abdominal pain and tenderness and abdominal bruising should likely be observed despite normal CT. In this study, CT was only 88% sensitive for bowel injury, meaning that 1 in 8 patients with a bowel injury could be missed. The same principle applies to diaphragm injuries, which are also rare and difficult to detect with CT, with sensitivity as low as 66% in some studies.²²

In pediatric patients, the safety of discharge following a negative abdominal CT has also been investigated. Awasthi et al.⁶⁵ prospectively enrolled 1295 patients younger than 18 years undergoing CT with IV contrast for evaluation of blunt abdominal trauma. Of these patients, 210 had injuries detected on CT. The authors then followed the 1085 patients with normal abdominal CT. Only two intraabdominal injuries were noted in patients with normal CT: a mesenteric hematoma and serosal tear discovered during nontherapeutic laparotomy and a perinephric hematoma on repeat CT not requiring therapy. The negative predictive value of a normal abdominal CT was 99.8% (95% CI = 99.3%-100%). This study is strengthened by excellent follow-up, large numbers, and a high-risk population, with 16% of the initial cohort having an abnormal CT indicating injury. The authors concluded that the probability of an injury requiring intervention is low in pediatric patients with normal abdominal CT and that routine admission is not necessary. As with the adult population, observation should be considered for patients with a high suspicion for injury based on examination and history because of the limited sensitivity of CT for bowel, mesentery, and diaphragm injuries.

Can Patients Be Safely Discharged Following a Normal CT for Penetrating Abdominal Trauma? What Injuries Can Be Missed?

The sensitivity of CT for penetrating torso injuries was described in detail earlier in this chapter. Based on a meta-analysis, the sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were 94.90%, 95.38%, 98.62%, 84.51%, and 94.70%, respectively.⁴¹ However, multiple studies document missed bowel and diaphragm injuries, suggesting that observation should be strongly considered following a negative CT. Studies that claim good outcomes with emergency department discharge following a negative CT suffer from significant losses to follow-up that may invalidate their results.³⁴

Can CT Be Performed in Pregnant Patients With Abdominal Trauma? What Is the Radiation Risk?

In the pregnant female, radiation to the abdomen and pelvis should be minimized because of concerns for fetal effects. However, unrecognized abdominal or pelvic injuries pose a threat to both the mother and the fetus. Contrary to common physician belief, a single abdominal or pelvic CT delivers a radiation dose below the threshold known to cause teratogenic or neurologic effects.^81-82 If significant concern exists for maternal injury, CT should be performed. An increase in pediatric cancers, particularly leukemias, is a theoretical risk for in utero irradiation.^82-83 If possible, a well-considered imaging plan should be develop to avoid redundant radiation exposures. For example, if CT is required, plain radiographs of the pelvis and lumbar–sacral spine should be avoided because these deliver fairly high radiation doses and provide no information that could not be gleaned from CT. When the suspicion for maternal injury is lower, alternative strategies such as observation with serial physical examination, serial ultrasound, and trending of laboratory data can take the place of immediate CT.

What Is the Risk From Intravenous Contrast?

IV contrast crosses the placenta in small quantities. Animal studies do not show fetal teratogenic or mutagenic effects or effects on fertility.^83a

Are Special Findings Seen on CT During Pregnancy?

Pregnancy results in special findings on CT.⁸⁴ Hydronephrosis (resulting from compression of the ureters by the enlarged uterus) and enlarged ovarian veins are normal findings in later pregnancy. Diastasis of rectus abdominus muscles and widening of sacroiliac joints and pubic symphysis are normal in the third trimester. Nonenhancing regions of the placenta on IV contrast–enhanced CT (dark gray or hypoattenuating in appearance) can indicate placental infarction or abruption. These should not be confused with normal placental cotyledons that have central areas of low attenuation with surrounding high-attenuation rings. CT can demonstrate uterine rupture, characterized by extrauterine fetal parts or by oligohydramnios with free maternal abdominal and pelvic fluid. Fetal parts are not usually seen until late first trimester on CT, and direct detection of fetal injuries is rare. Hemorrhage in the amniotic cavity may be seen. Fetal loss is most often because of placental abruption or maternal hypotension.

Although MRI can be used to evaluate traumatic injuries, in most centers it is not rapidly available, making it impractical for patients with potentially serious and time-sensitive injuries.⁸⁴

Can Imaging Rule Out Placental Abruption?

Placental abruption can occur with even minor trauma and should be considered in every patient with blunt abdominal trauma beyond 22 to 24 weeks.⁸⁵ Ultrasound is considered insensitive for detection of placental abruption, with sensitivity, specificity, and positive and negative predictive values of 24%, 96%, 88%, and 53%, respectively.⁸⁶ Retroplacental hematomas can be isoechoic with the placenta and uterus and may not be recognized.⁸⁷ Consequently, even if ultrasound appears reassuring, patients should undergo fetal heart rate monitoring for several hours for signs of fetal distress, such as bradycardia or tachycardia, that may the earliest signs of abruption.⁸⁸