BLUNT TRAUMA

Blunt trauma mechanisms leading to significant intra-abdominal injuries often include compression and deceleration forces. Motor vehicle collisions are the leading cause of injury, both in the United States and throughout the world. Other common mechanisms include falls from high altitudes, assaults, projectile injuries, and sports-related trauma. Although the likelihood of injuring an individual organ depends on the specific mechanism of trauma and the vulnerability of the patient at the time of the event, the data in the trauma literature have repeatedly demonstrated that the liver and spleen are the most frequently injured organs. Other potentially injured organs include the kidneys, bowel and mesentery, pancreas, adrenals, diaphragm, intra-abdominal vessels, and bladder.

Over the past 2 decades, improvements in imaging technology have considerably improved our ability to detect intra-abdominal injuries from blunt trauma. Of the available imaging modalities, CT and US are the two most commonly used imaging techniques when evaluating for acute traumatic abdominal injury. Other modalities, such as plain film radiography, magnetic resonance imaging (MRI), nuclear scintigraphy, and catheter angiography, are typically employed in specific circumstances for further characterization of injuries, for detection of complications from the initial injury, and for the treatment of such injuries.

Focused Abdominal Sonography for Trauma

Typically, US is used during the initial assessment of the poly-trauma patient, while CT images are obtained once the patient has been stabilized. Rapid assessment of the trauma patient can be performed at the bedside by experienced sonographers as part of the focused abdominal sonogram for trauma (FAST). Such scans can readily identify free fluid within the abdomen or pelvis and can help triage patients at the time of initial assessment. FAST evaluation consists of visualization of five spaces:

1. Pericardium (subxiphoid view)

2. Splenorenal and hepatorenal (i.e., Morrison’s pouch)

3. Right paracolic gutter (Fig. 3-1)

4. Left paracolic gutter (see Fig. 3-1)

5. Pouch of Douglas

Figure 3-1 Intraperitoneal hemorrhage due to blunt abdominal trauma. FAST scan of the abdomen shows complex free fluid in the left lower quadrant in this patient following motor vehicle collision.

Multiple studies have demonstrated the benefit of a FAST study in the emergent decision-making process of the acutely traumatized patient. The main use of FAST is in the detection of free fluid (acute hemorrhage in this setting) in the peritoneal, pericardial, or pleural spaces to direct immediate therapeutic interventions by the trauma surgeons in the unstable or marginally stable patient. More recently, the development of contrast-enhanced US has improved detection of solid organ injuries and active bleeding. This technique, although not commonly used in the United States, does have potential as a means of evaluating the trauma patient without the use of ionizing radiation.

Computed Tomography Technique

Once stabilized, the abdominal trauma patient can be more completely imaged by a CT examination. With multidetector CT (MDCT) scanners, imaging of the head, cervical spine, chest, abdomen, and pelvis is performed as a single examination (“panscan”). Although adequate evaluation is possible with 4- and 8-row detector scanners, most large trauma centers now use 16- or 64-row detector scanners for trauma and other emergency room applications. Specific protocols regarding slice thickness, volume of intravenous contrast administered, timing of image acquisition, and use of oral contrast are continually reconfigured and vary between institutions.

In general, optimal evaluation of the abdomen and pelvis is performed by acquiring the axial dataset of CT images following intravenous injection of iodinated contrast material during the portal venous phase of hepatic enhancement. Intravenous contrast, 100 to 150 mL injected at a rate of 3 to 5 mL per second, is routinely employed for CT imaging of the trauma patient. If a dual syringe power injector is used (and this is the preferred system), the contrast bolus is followed by a 30- to 50-mL bolus of normal saline solution, typically injected at the same rate as the contrast material. This saline “chaser” ensures delivery of the complete contrast bolus into the circulation, rather than it remaining in the tubing or wasted in the veins of the upper extremities or mediastinum.

Regardless of the scanning protocol employed, modern 16- and 64-row detector scanners share several definite advantages over earlier-generation scanners. The most important of these is their markedly improved temporal resolution. With the development of these multidetector-row scanners, thin images (1 to 2 mm) can be easily acquired while still keeping scan time at 8 seconds or less per body part. In order to facilitate review at the interpretation workstations, it is advisable to reconstruct a separate set of thicker axial images by “fusing” the thin sections. For example, images acquired with 0.625- or 1.25-mm thickness can be reconstructed at 3.75- or 5-mm thickness. In addition, sagittal and coronal reformations are now generated almost routinely, taking advantage of the rapid scan times that nearly eliminate motion artifact. These sagittal and coronal reformations are ideal for adequate evaluation of the diaphragm, long vascular territories, and thoracic and lumbosacral spine, and reduce the need for lumbosacral and thoracic spine radiographs in the vast majority of patients. All series are sent to the Picture Archival Computer System (PACS) and are available at the time of interpretation and for further postprocessing (if necessary). Other benefits include the ability to combine routine protocols with CT angiograms of multiple body parts while still using a single bolus of contrast. This is possible due to the increased scanner table length (2 m) available with many of the 64 MDCT scanners. Using the scout images of the whole body, multiple complex CT examinations (including CT angiograms of the neck or extremities) are planned and combined in succession into one scan using a single contrast injection (Fig. 3-2).

Figure 3-2 Multitrauma CT in a patient with injury following blunt trauma. A, Scout image obtained on a 64 detector CT scanner. Using the single scout image, multiple CT studies can be planned, including dedicated CT angiographic studies of focal areas of injury. Note the presence of a distal right femur fracture (arrow) in this patient who suffered significant trauma after being struck by a car. B, In this case, CT angiography of the extremities was requested to evaluate the peripheral arteries of the lower extremity. No injury was detected. C, Abdominal-pelvic CT was also obtained at the same time as the CT angiography. This coronal image was reconstructed from the axial dataset acquired during the portal venous phase of contrast enhancement.

The increased temporal resolution and decreased scan times of 16- and 64-row detector scanners have resulted in a modification in the time intervals applied between the start of contrast injection and image acquisition. To ensure that all body parts are scanned at the optimum peak of contrast enhancement, it is preferable to scan the chest (30 to 35 seconds) independently from the abdomen and pelvis (65 to 75 seconds), rather than with a continuous scan encompassing all three regions and starting at approximately 60 seconds. The split scan method avoids the potential need for rescanning the chest in order to obtain true CT angiography images of the thoracic aorta, essentially eliminating the need for catheter angiography for suspected thoracic aortic injury. Scan time for each body part is approximately 4 to 8 seconds (for 16- and 64-row detector scanners), and there is a pause of 30 to 35 seconds between scans of the chest and abdomen. The only drawback in separating the thorax from the abdomen and pelvis is in the generation of multiplanar reformations. These acquisitions are, for all intents and purposes, two different studies and necessitate separate multiplanar reformats, which makes image analysis slightly more tedious. However, the benefits of an optimal study of the aortic arch and great vessels outweigh this drawback. With the 4-row detector and helical CT scanners, most CT protocols include a single continuous acquisition of the chest, abdomen, and pelvis 30 to 40 seconds after intravenous injection of 100 to 150 mL of contrast material. With this delay, although optimal for the abdomen and pelvis, the aortic arch and great vessels are not visualized at the peak of the arterial phase. Not uncommonly, when there is a question about the integrity of these vessels, repeat CT angiography or catheter aortography is necessary. This requires injecting a second bolus of contrast and may cause potential delays in diagnosis.

In addition to portal venous phase imaging, the acquisition of delayed images has become an increasingly important part of the trauma CT evaluation. Delayed images can be useful in evaluating vascular injuries as well as injuries to both the solid organs and the bowel and mesentery. Delayed CT acquisitions allow for improved characterization of solid organ injuries by helping to differentiate contained injuries (such as arterial pseudoaneurysms and arteriovenous fistulas) from uncontrolled active extravasation of contrast-enhanced blood. On delayed images, areas of active extravasation persist as hyperattenuating foci (relative to the aorta) and change configuration as blood (with contrast) diffuses into a potential space (Fig. 3-3), whereas pseudoaneurysms show an attenuation coefficient that remains similar to the aorta, with no change in overall size or shape. Delayed images also improve detection and characterization of bladder and renal injuries, as discussed later in this chapter. Finally, delayed scans can help in the characterization of findings seen on portal venous phase images that could potentially represent foci of extravasation and could be related to the acute injury (Fig. 3-4). However, the routine use of delayed images is unnecessary and should be discouraged, since the majority of trauma CT scans performed in emergency rooms today show no evidence of abdominal injury and the additional radiation dose is unnecessary. As an alternative, delayed images can be acquired selectively and used only when solid organ or bowel injry is detected or suspected on the initial CT acquisition. Additionally, since the sole purpose of this delayed scan is to characterize an injury seen or suspected on the initial scan, it is possible to employ a reduced radiation dose technique, typically 100 milliAmpere second (mAs) (or similar dose reduction with automated dose modulation).

Figure 3-3 Active contrast extravasation following blunt abdominal trauma. A, CT obtained during the portal venous phase shows contrast extravasation into the peripancreatic region due to an acute vascular injury (arrow). B, On the 5-minute delay CT, the contrast continues to diffuse into the soft tissue at the site of injury (arrows).

Figure 3-4 Hemangioma in young female patient detected during trauma CT. A, Portal venous phase CT shows focal puddling of contrast in the posterior segment of the right lobe of the liver (arrow). Initially, there was some question as to the presence of a focal liver injury with active bleeding. Free fluid is present adjacent to the liver margin. B, The 5-minute delay CT shows retention of contrast within a focal liver lesion (arrow) which excludes focal liver injury. Instead, the diagnosis of a benign hemangioma was confirmed.

In the past, oral contrast was considered a mandatory component of trauma CT protocols. However, reports in the radiological and surgical literature have suggested that imaging by MDCT without oral contrast is similarly accurate for the detection of bowel and mesenteric injuries at the time of initial CT evaluation. Occasionally, the initial scan may be inconclusive as to the presence of a bowel injury. In this case, and if there is a specific question of bowel injury on the initial scan, a follow-up CT (typically 12 hours later) with oral contrast can be performed at the discretion of the interpreting radiologist. If oral contrast is used to opacify the bowel in the setting of acute trauma, patients generally receive water-soluble contrast agents due to the potential for contrast extravasation into the peritoneal cavity from an acute bowel injury. Oral contrast can be given by mouth or by insertion into an indwelling nasogastric tube. The method chosen depends on the level of consciousness of the patient and associated injuries. CT imaging should not be delayed while waiting for the contrast to migrate into the distal small bowel.

With isotropic voxel scanning, CT has truly become a multiplanar modality. As described above, sagittal and coronal reformations have become a common component of trauma CT protocols. As the number of images generated for trauma patients increases, review of multiplanar images is one possible solution for improving interpretation efficiency. Coronal and sagittal reformations are also a useful, intuitive tool for communicating with clinical colleagues, as large amounts of information are represented on fewer images. Multiplanar image review is particularly useful for several trauma applications: evaluation of potential spine injuries, a more complete appreciation of often-complex injuries of solid organs, hollow viscera, and diaphragm, and for CT angiography, where longer segments of vessels may be visualized in sagittal and coronal planes.

HEPATIC TRAUMA

The liver is one of the most commonly injured organs in the abdomen, with the prevalence of injury in patients who have sustained multiple blunt trauma on the order of 1% to 8%. Despite the wide array of hepatic injuries, the vast majority of patients are treated conservatively, without the need for direct therapeutic intervention. Patients with extensive and complex lacerations and large parenchymal hematomas are increasingly being managed with observation and supportive measures alone. Endovascular therapy with embolization is reserved for definitive treatment of patients with significant vascular injury and active bleeding. The growing trend toward successful nonsurgical management of liver injuries is in part related to major advances in imaging technology and CT techniques in the past decade. Specifically, the focus is to rapidly demonstrate areas of potentially life-threatening active bleeding that require immediate attention. MDCT and US are the main modalities employed for initial detection and characterization of hepatic injuries. Other modalities, such as MRI with MR cholangiopancreatography (MRCP), hepato-biliary scintigraphy, and endoscopic retrograde cholangiopancreatography (ERCP), are reserved for detecting subacute or delayed complications, such as bile duct leaks, bilomas, and biliary strictures. Since CT with proper technique is sufficient to demonstrate the extent and significance of essentially all liver injuries, catheter angiography is reserved for confirmation of CT findings that suggest major vascular injury and, especially, as a means to treat those lesions that require intervention via embolization.

Ultrasonography

Sonographic evaluation for hepatic injuries is mostly limited to screening the trauma patient for indirect signs of injury, such as free fluid adjacent to the liver (as part of the FAST scan). When fluid is detected along the margin of the liver, it can appear complex and can contain echogenic clot due to its hemorrhagic nature. Although a careful inspection of the liver can demonstrate lacerations and contusions as focal areas of parenchymal distortion, various factors limit the use of US beyond the search for free peritoneal fluid. These include technical limitations such as difficult access to appropriate sonographic windows and the variability in operator experience and availability. However, advances in US technology and the development of sonographic contrast agents has led to increased use of this modality for direct evaluation of the solid parenchymal organs, including the liver, especially in European countries. On noncontrast US examinations, hepatic parenchymal injuries can produce three different morphological patterns. The most common pattern is that of a focal area of increased echogenicity with respect to the background liver, which is thought to correspond to the focal lacerations or hematomas seen on CT. The other two are a more diffuse area of increased echogenicity and focal areas of decreased echogenicity. Liver lacerations can be difficult to detect on initial exams, often appearing more prominent in the days following the initial injury (Fig. 3-5). The advent of sonographic contrast agents has increased the ability of ultrasound to detect acute hepatic injuries. Generally, the contrast agent is given in a bolus and the area of interest is scanned continuously for 4 to 6 minutes. On contrast-enhanced US, liver injuries are best seen during the portal venous phase of imaging. Liver lacerations can also appear as focal linear or branching hypoechoic areas, often oriented perpendicular to the liver surface. Contusions may appear as geographic areas of decreased echogenicity, often with ill-defined borders. Similar to active contrast extravasation on CT, active bleeding can be detected by the presence of micro-bubbles (contrast material) extending into a hematoma. In general, despite recent advances in technology, US is still considered an adjunctive test.

Figure 3-5 Liver laceration detected by ultrasound. Sagittal image of the right upper quadrant demonstrates a focal linear echogenic abnormality in the liver, compatible with an acute liver laceration (arrow).

A subcapsular hematoma is typically hypodense to the enhancing liver parenchyma and appears elliptical, conforming to the confines of the liver capsule (Fig. 3-6). Such collections are usually easily distinguished from perihepatic fluid. Intraparenchymal hematoma appears as an ill-defined hypoattenuating region within the liver. If seen on noncontrast CT, hematomas are typically hyperdense to the background liver parenchyma. Liver lacerations appear as hypoattenuating linear, often branching, and complex regions within the parenchyma of the liver (Fig. 3-7). Extension to the hepatic surface is very common. Even small lacerations can be associated with perihepatic blood. It is important to identify lacerations that extend to the periportal region, since these patients are at an increased risk for the development of delayed bile leaks due to injury of the biliary ductal system.

Figure 3-6 Subcapsular hematoma following blunt abdominal injury. Axial CT acquired during the portal venous phase shows a focal subcapsular elliptical hematoma in the right lobe of the liver.

Figure 3-7 CT depiction of liver lacerations following blunt abdominal trauma. A, Portal venous phase axial CT image demonstrates a focal liver laceration in the right lobe of the liver (solid arrow) with perihepatic blood in Morrison’s pouch (dashed arrow). B, Portal venous phase CT in a different patient following motor vehicle accident shows a more complex liver laceration (white arrows) with a focal area of active contrast extravasation (black arrow).

CT can also readily identify hepatic vascular injuries. Active extravasation of intravenous contrast, when seen during routine portal venous phase images, suggests ongoing hemorrhage from a hepatic arterial or portal venous source. Active extravasation may be confined to the hepatic parenchyma or may be seen as hyperattenuating collections of contrast-enhanced blood accumulating in the perihepatic spaces. On delayed CT images, the focus of active extravasation typically increases in size as the material continues to diffuse throughout the area of expanding hematoma (Fig. 3-8). In the past, active extravasation was considered an indication of the need for prompt surgical management. Currently, the demonstration of a sizable focus of active extravasation is more likely to trigger a response from the vascular interventional team for catheter angiography and coil embolization (see Fig. 3-8). Even patients with high-grade injuries can be managed conservatively using such techniques. Injuries to major hepatic vessels may also be directly depicted with CT. For example, direct evidence of portal venous injury may be seen as abrupt termination of a branch of an intrahepatic portal vein. Parenchymal injuries may extend centrally to involve the hepatic veins and inferior vena cava, seen on CT as abrupt termination of the hepatic veins, which may just begin to enhance during routine portal venous phase images. Such major venous injuries are more likely to require surgical management, since they can cause continued bleeding and hemodynamic instability, and are not readily treated by interventional radiology techniques (Fig. 3-9). Major venous injuries are also commonly associated with hepatic arterial trauma. Complications of hepatic vascular injuries include traumatic fistulas between various hepatic structures, including arterioportal, fistulas between hepatic arteries and biliary ducts, and, rarely, between a hepatic artery and adjacent bowel. Hepatic pseudoaneurysms can also occur as a result of hepatic injury and are extremely important to detect and document since they are at risk for delayed rupture, a potentially lethal complication. Hepatic artery pseudoaneurysms were considered rare, but are now detected more frequently due to improvements in the spatial resolution of CT and the ability to scan at the peak of contrast enhancement throughout the scan routinely (Fig. 3-10). Pseudoaneurysms appear as hyperattenuating foci on the early phase images and demonstrate washout on delayed phase images. If delayed rupture and hemorrhage are suspected based on clinical or laboratory parameters, CT is also the best method to detect subacute hemorrhage. On follow-up CT, delayed hemorrhage presents as an increase in the size of a previous hematoma. The more acute hemorrhage appears as focal hyperattenuating material in a previously documented hematoma or along the margin of the liver, the so-called “sentinel clot” sign. In addition to pseudoaneurysm formation and delayed hemorrhage, other complications of hepatic trauma result from associated bile duct injury and include the development of bilomas and abscess collections, persistent bile leaks with bile peritonitis, and bile duct strictures.

Figure 3-8 Active contrast extravasation following acute abdominal trauma. A, Axial CT obtained during the portal venous phase shows a complex liver laceration with active contrast extravasation (arrow). B, The 5-minute delay CT shows ongoing bleeding with contrast continuing to diffuse into the area of injury (arrow). C, Selective catheterization of the superior mesenteric artery (due to a replaced right hepatic artery) shows active bleeding as a large blush of contrast in the right lobe of the liver. D, After embolization, the postprocedure angiogram shows resolution of the contrast blush with adequate control of active bleeding.

Figure 3-9 Portal venous injury following blunt abdominal trauma. Axial CT obtained during the portal venous phase shows a complex injury involving the left lobe of the liver with active contrast extravasation. At surgery, a laceration of the left portal vein was detected that required surgical repair.

Figure 3-10 Hepatic arterial pseudoaneurysm following a motor vehicle accident. Axial CT obtained during the portal venous phase shows a large hematoma in the porta hepatis (asterisk) with a small pseudoaneurysm of the left hepatic artery (arrow). This injury required surgical intervention to repair a laceration of the left hepatic artery.

GALLBLADDER AND BILE DUCT TRAUMA

Blunt trauma may result in injury to the biliary tract, including the gallbladder and intrahepatic or extrahepatic bile ducts. The gallbladder and extrahepatic ducts are protected by the liver, and this may explain the low frequency of injury to these structures with blunt trauma. The most common location of extrahepatic biliary tract injuries is the gallbladder, followed by the common bile duct. Gallbladder injury is almost invariably associated with additional significant injuries. Liver, splenic, and duodenal injuries are most common, occurring in up to 91%, 54%, and 54% of cases, respectively. Extrahepatic bile duct injuries are very rare and are also usually associated with injuries to other organs. Gallbladder and bile duct injury may occur due to torsion, shearing, or compression forces. Certain factors may predispose to gallbladder injury. These include distention of the gallbladder in a preprandial state, which makes the gallbladder more vulnerable to compression injury. Injuries to the gallbladder are classified into three main categories: contusion, laceration/perforation, and complete avulsion. In general, contusions are considered to represent intramural hematomas, are the mildest form of gallbladder injury, and are treated conservatively. Lacerations and perforations are full-thickness wall injuries, requiring cholecystectomy. Avulsion of the gallbladder may involve variable portions of the gallbladder and cystic duct. Any of these lesions can be associated with transection of the cystic artery and major blood loss.

Extrahepatic duct injuries may occur at sites of anatomic fixation, such as the intrapancreatic portion of the common bile duct, and are frequently caused by blunt impact or acute deceleration, possibly with compression against the spine. Elevation of the liver following blunt trauma may cause stretching of the relatively fixed common duct. Injuries to the intrahepatic bile ducts are seen in patients with severe liver lacerations.

Delayed complications of gallbladder or bile duct injury, such as sepsis, may result from leakage of bile into the peritoneal cavity and subsequent infection. Sterile bile within the peritoneum undergoes continuous peritoneal reabsorption and may initially lead to surprisingly few symptoms. Since bile in the peritoneum usually does not cause symptoms until infected, bile leakage may occur for weeks or months before being detected clinically. When signs and symptoms are present, they are nonspecific and include vague abdominal pain, nausea, vomiting, and occasionally jaundice. With extrahepatic bile duct injury, diagnosis may be particularly difficult; up to 20% of such injuries are not detected at surgery. Injury to either extra- or intrahepatic bile ducts may also result in biliary strictures. Patients may present weeks, months, or even years later with signs of biliary obstruction or infection due to the development of foca l strictures at the site of injury.

Computed Tomography

Gallbladder injuries are most often diagnosed at the time of the initial trauma CT scan. Contusions appear as diffuse gallbladder wall thickening. The presence of pericholecystic fluid is not specific, but may be an associated finding. High-attenuation fluid within the gallbladder lumen suggests hemorrhage and is a good indicator of acute injury. However, differentiation between high-attenuation sludge and blood may be difficult. Lacerations of the gallbladder wall are seen as focal disruption of the normal mural enhancement of the gallbladder wall. Dense contrast material in the gallbladder lumen or in the gallbladder fossa suggests active bleeding from injury to the cystic artery. If the gallbladder is avulsed from its pedicle, it may be displaced from the gallbladder fossa (Fig. 3-11). Injury of the extrahepatic bile ducts can be difficult to diagnose on CT, since perihepatic fluid is often caused by injury to other organs in the abdomen. Intrahepatic biliary ductal injury may be suggested on follow-up CT by the development or persistence of low-attenuation perihepatic fluid collections, usually with an obvious associated hepatic injury.

Figure 3-11 Avulsion of the gallbladder due to blunt trauma. CT obtained during the portal venous phase shows incomplete enhancement of the gallbladder wall with blood adjacent to the gallbladder. The gallbladder appeared inferiorly displaced at the time of CT. At surgery, avulsion of the gallbladder was confirmed requiring cholecystectomy.

(Reprinted with permission from Gupta A, Stuhlfaut JW, Fleming KW Blunt trauma of the pancreas and biliary tract: A multimodality imaging approach to diagnosis. RadioGraphics 24:1381–1395, 2004.)

Hepatobiliary Scintigraphy

Once the patient with complex liver trauma has survived the acute phase of hepatic trauma, when bleeding and possible exsanguination are the main concerns, the possibility of developing bile leaks with complicating abscess and sepsis must be considered and treated. Persistent perihepatic fluid collections and increasing low-attenuation intraperitoneal fluid are common indicators of bile leaks that require direct therapy. Biliary scintigraphy is a simple and useful method for detecting and characterizing bile duct injuries. Hepatobiliary radiopharmaceutical agents are taken up by hepatocytes and excreted into the bile ducts. Sequential imaging over 1 to 2 hours identifies extraluminal collections that develop as the radiotracer is excreted into the biliary system and drains into the small bowel lumen. In some cases, images delayed 4 hours are necessary when there is no evidence of injury on the initial image acquisition. On hepatobiliary scintigraphy, accumulation of the radiopharmaceutical agent outside the bile ducts is indicative of a bile leak, which can be either contained (Fig. 3-12) or free if it extends into the peritoneal cavity. Small bilomas can be treated conservatively and followed, whereas larger collections may require percutaneous drainage, especially if there is superimposed infection. Early detection of bile leaks allows proper treatment by either percutaneous drainage or by ERCP with sphincterotomy and stent placement (see Fig. 3-12). A possible delayed complication of bile duct injury is the development of a bile duct stricture with obstruction and infection. MRCP is an ideal method for following hepatobiliary injuries for possible development of strictures.

Figure 3-12 Biliary leak with biloma following blunt abdominal trauma. A, Coronal CT image obtained several days following the initial trauma demonstrates two focal fluid collections in the intrahepatic and perihepatic regions (arrows). B, Coronal thick slab MR cholangiopancreatography (MRCP) also demonstrates the presence of several extraluminal fluid collections as focal areas of increased signal on this fluid sensitive sequence (arrows). C, Hepatobiliary scan obtained in the anterior projection confirms the presence of bilomas with radiotracer located outside the expected lumen of the biliary tree (arrows). D, Endoscopic retrograde cholangiopancreatography (ERCP) was performed to further characterize the injury and for possible stent placement and confirms the presence of bile duct injury.

SPLENIC TRAUMA

The spleen is the most commonly injured organ in the abdomen as a result of blunt trauma. In the past, exploratory laparotomy with splenectomy was the dominant treatment for splenic injuries. However, improvements in our understanding of the natural history of splenic injuries as well as in the quality and access to imaging methods have modified treatment algorithms. Nonoperative management is used initially for the vast majority of splenic injuries. Splenectomy is reserved for the most complex injuries in unstable patients who do not respond to resuscitative efforts and for patients in whom conservative therapy fails. Patients who would otherwise be candidates for conservative management, but who require laparotomy for other abdominal injuries, may still undergo a splenectomy.

Splenic trauma is typically difficult to detect clinically. Patients can present with left upper quadrant pain, although associated severe injuries may confound the clinical picture or distract attention from the spleen or abdomen. Instead, most injuries are detected with imaging studies performed in these trauma patients, by either US or CT. The admission portable radiograph may demonstrate left rib fractures and alert trauma surgeons to the possibility of underlying splenic injury. However, plain film radiographs have no role in the direct demonstration of splenic injury. Once an injury is detected, and while the resuscitation process is ongoing, the interventional radiology team should be alerted, as catheter angiography may become necessary for treating vascular injuries, thus avoiding the need for splenectomy. However, splenectomy may still become necessary if the injury is severe and bleeding cannot be controlled by nonoperative means.

Splenic injuries are characterized as either hematomas or lacerations. As it has for the liver, the AAST has developed a scale for grading splenic trauma that is still commonly used for describing specific patterns of injury (Table 3-2). The prognostic implications of this scale are limited, since even complex injuries can heal without specific therapy. It is important to describe the type of injury, the location (parenchymal versus subcapsular), the size of the hematoma or laceration, and all associated complications. Severe injuries can affect the hilar vascular structures, leading to total or subtotal organ devascularization. Injuries to the splenic artery or branch vessels can cause active bleeding, which can be easily demonstrated with current MDCT examinations. Finally, splenic injuries can lead to the development of pseudoaneurysms, which are extremely important to note, since these patients have an increased risk of delayed morbidity and mortality due to pseudoaneurysm rupture.

Table 3-2 AAST Classification of Traumatic Splenic Injury

Ultrasonography

Splenic injuries can be detected by US evaluation of the abdomen and may be suspected based on the results of the initial FAST scan. However, the parenchymal injury can be difficult to detect. Instead, indirect evidence of injury is often identified, including hemoperitoneum and focal echogenic clot adjacent to the spleen. Splenic hematomas appear as heterogeneous and hypoechoic compared with the background spleen (Fig. 3-13). The borders are ill-defined and there is no associated mass effect or vessel displacement. Lacerations appear as linear or branching areas of decreased echogenicity compared with the normal spleen, often extending to the splenic surface. Although not commonly used in many countries, sonographic contrast agents have been shown to improve the ability to detect splenic injuries. The spleen can be readily imaged by contrast-enhanced US since it retains contrast for up to 5 to 7 minutes following intravenous injection. If the vascular pedicle is injured, there may be total or subtotal loss of enhancement in the spleen. Active contrast extravasation can be identified as a hyperechoic collection that develops in the early phase after contrast injection.

Figure 3-13 Splenic hematoma. A, Focused ultrasound of the left upper quadrant demonstrates a focal region of heterogeneity in the spleen (arrows), suggestive of an acute splenic injury. B, CT performed following the initial ultrasound confirms the presence of an acute splenic hematoma.

Computed Tomography

MDCT is the main imaging modality used to detect, characterize, and follow splenic trauma. Most splenic injuries are optimally detected on portal venous phase images of the abdomen following intravenous contrast injection. Splenic hematomas appear as focal areas of decreased attenuation compared with the background-enhancing splenic tissue (Fig. 3-14). Hematomas can be intraparenchymal or subcapsular in location. Lacerations appear as linear, irregular, and often branching areas of decreased attenuation (Fig. 3-15). Higher-grade injuries tend to be larger and involve more of the total volume of the spleen (Fig. 3-16). Injuries of the vascular pedicle lead to focal wedge-shaped areas of decreased enhancement, while severe injuries of the vascular pedicle may produce a markedly decreased or absent enhancement of most or all of the spleen on CT. In addition to describing the type of injury, it is important to note the presence of either active contrast extravasation or pseudoaneurysm formation. Active contrast extravasation in the spleen is characterized on CT by contrast density outside the expected lumen of the vessel, similar or higher in attenuation as compared with the adjacent vessels (Fig. 3-17). The shape is often irregular, with poorly defined margins due to the diffusion of the contrast material into the site of injury. Typically, contrast extravasation is identified within the splenic parenchyma or in a hematoma adjacent to the site of laceration in the perisplenic spaces. In contrast, splenic pseudoaneurysms are contained extraluminal collections that often have a more round or ovoid appearance (Fig. 3-18). These injuries are usually confined to the splenic parenchyma. In some cases, it is difficult to distinguish between active extravasation and pseudoaneurysms. If there is any question, delayed images are often useful in making this differentiation. On delayed CT images, active contrast extravasation shows a change in shape and usually an increase in size as the material continues to diffuse into the site of injury (see Fig. 3-17). On the other hand, pseudoaneurysms do not change in size or shape at different points in time, and the attenuation of the pseudoaneurysm tends to follow that of adjacent arteries such as the splenic artery or aorta (see Fig. 3-18). Other focal vascular injuries include the development of arteriovenous fistulas. Such injuries can be difficult to distinguish by CT alone, and are better characterized with catheter angiography. Once active contrast extravasation or a focal vascular injury such as a pseudoaneurysm is detected, the need for catheter angiography and possible endovascular therapy should be carefully assessed. Although practices vary among institutions, patients with proved active extravasation are more likely to undergo splenectomy, whereas contained vascular injuries such as pseudoaneurysms are more amenable to endovascular therapy with coil embolization.

Figure 3-14 Splenic hematoma following motor vehicle collision. Axial CT during the portal venous phase demonstrates a wedge-shaped hypodense region in the spleen (arrow), consistent with a subcapsular hematoma and characterized as a grade II injury according to the AAST trauma scale (see Table 3-2).

Figure 3-15 Splenic laceration following motor vehicle accident. Axial CT image obtained during the portal venous phase of contrast enhancement demonstrates a focal linear laceration in the spleen (arrow) that extends from the anterior to posterior surface, fracturing the spleen into two fragments. Perisplenic hematoma (asterisk) is evident posterior to the area of injury.

Figure 3-16 Shattered spleen. Axial CT image obtained during the portal venous phase of contrast enhancement following motor vehicle injury. There is no definable splenic tissue in the left upper quadrant. Instead, the shattered splenic tissue is surrounded by a large amount of perisplenic hematoma that extends to the midline. Blood is also present along the surface of the right lobe of the liver. The patient required emergent splenectomy to control the severe blood loss from this acute splenic injury.

Figure 3-17 Splenic injury following blunt abdominal trauma. A, Axial CT image obtained during the portal venous phase of contrast enhancement demonstrates a complex splenic injury containing both complex lacerations and parenchymal hematoma. Active contrast extravasation is present (arrow). B, Delayed image obtained 5 minutes later with decreased radiation dose (100 mAs) confirms the presence of active extravasation (as opposed to a focal pseudoaneurysm) by demonstrating continued diffusion of the contrast into the surrounding parenchymal hematoma (arrow).

Figure 3-18 Splenic pseudoaneurysm. A, Axial CT obtained during the portal venous phase demonstrates a focal collection of contrast in the spleen (arrow) with enhancement similar to the aorta. B, The contrast collection is contained on the 5-minute delay CT and has decreased in density similar to the aorta (arrow), consistent with the presence of a focal splenic pseudoaneurysm.

PANCREATIC INJURY

Traumatic injuries of the pancreas are much less common than injury of the liver and spleen. In fact, pancreatic injury is reported to occur in less than 1% of all patients suffering blunt abdominal trauma. However, detection of such injuries is critical, since a delay in diagnosis can be a cause of significant morbidity and mortality. Unlike most injuries to the liver and spleen, injuries of the pancreas can be extremely difficult to detect and require a careful evaluation of MDCT images and use of complementary studies, such as MRCP and ERCP.

The pancreas is vulnerable to crushing injury from impact against the adjacent vertebral column. Two thirds of pancreatic injuries occur in the pancreatic neck (junction of body and head) and body, and the remainder are equally distributed between the head and tail. Isolated pancreatic injuries are rare; injuries to other organs, especially the liver, stomach, duodenum, and spleen, occur in more than 90% of cases. Not uncommonly, three or more organs are involved. In adults, more than 75% of blunt injuries to the pancreas are due to motor vehicle collisions. In children, bicycle injury is a common mechanism, and child abuse should be suspected in cases of infants with pancreatic trauma. Clinical findings are not very helpful in detecting such injuries, and more often the injury is suspected when amylase and lipase levels are found to be elevated. However, CT is still the mainstay for diagnosing pancreatic injury in trauma patients.

Injuries to the pancreatic head are almost twice as likely to be fatal (28%) than are injuries to the tail (16%), due to associated involvement of the inferior vena cava, superior mesenteric vein, or portal vein in the latter. In addition, the location of injury influences the surgical approach. Removal of more than 50% of the gland may lead to glucose regulation abnormalities or frank diabetes, and pancreas-sparing procedures are often attempted. Duct injuries occurring in the tail of the pancreas may be treated successfully by partial pancreatectomy with little risk of endocrine or exocrine dysfunction.

The main source of delayed morbidity and mortality from pancreatic trauma is disruption of the main pancreatic duct. The risk of abscess and fistula formation in patients with disruption of the pancreatic duct approaches 25% and 50%, respectively. Conversely, patients without duct injuries develop abscess or fistula in less than 10% of cases. Disruption of the pancreatic duct is treated surgically or by therapeutic endoscopy with stent placement, while injuries without duct involvement are usually treated nonsurgically. As such, it is critical that imaging focus on determining the integrity of the pancreatic duct directly or on indirect findings that suggest damage to the duct.

The imaging appearance of pancreatic trauma usually mimics the type of injury present. The role of ultrasonography is limited, but gland lacerations and transection can be seen as hypoechoic linear defects within the pancreatic parenchyma (Fig. 3-19). CT diagnosis of pancreatic injury is often difficult, with a reported sensitivity of 65% to 75% (although the sensitivity with newer MDCT scanners may be higher). Pancreatic injuries are typically detected on portal venous phase CT images of the abdomen. It is important to closely inspect the pancreas on thin-section images with liberal use of multiplanar reconstruction when available, since the many clefts of the pancreas can mimic or hide subtle injuries.

Figure 3-19 Pancreatic laceration. Ultrasound of the abdomen in a patient with pain following acute trauma shows a focal hypoechoic line (arrow) extending into the parenchyma of the pancreas, consistent with a focal laceration.

On contrast-enhanced CT, crush injuries (contusions) may show focal or diffuse enlargement and edema within the pancreas, characterized by areas of low attenuation extending through the planes of tissue within the gland (Fig. 3-20). Lacerations are detected as focal low-attenuation lines, most often perpendicular to the plane of the gland and duct (Fig. 3-21) and which may extend completely through the pancreas (termed pancreatic transection; Fig. 3-22). Additional indirect signs of injury include peripancreatic fluid/stranding as well as retroperitoneal hematoma in the peripancreatic region. A crucial part of the imaging characterization of pancreatic injury is to determine the depth of a laceration and any possible involvement of the main pancreatic duct. With modern MDCT technology,the pancreatic duct can be seen directly in the majority of patients. The depth of a laceration is also a useful predictor of main duct involvement: involvement of more than 50% of the anteroposterior thickness of the gland is often associated with duct transection (Fig. 3-23). While not commonly used, at least one CT grading system that parallels the surgical classification of Moore has been suggested: grade A, pancreatitis or superficial laceration (less than 50% pancreatic thickness); grade B1, deep laceration (greater than 50% pancreatic thickness) of the pancreatic tail; grade B2, transection of the pancreatic tail; grade C1, deep laceration of the pancreatic head; and grade C2, transection of the pancreatic head. Delayed complications, such as arterial pseudoaneurysms, abscesses, and pseudocysts, are all readily imaged by CT. Pseudoaneurysms typically appear as focal collections of contrast that enhance similarly to the aorta on all phases of imaging (Fig. 3-24). Pseudocysts and abscesses appear as focal pancreatic fluid collections of varying size. Percutaneous sampling under imaging guidance is very useful to confirm the diagnosis of superimposed infection.

Figure 3-20 Pancreatic trauma after blunt rugby injury. Axial CT during the portal venous phase shows a contusion of the pancreatic head (arrow). This patient was managed conservatively without the need for surgical intervention.

Figure 3-21 Pancreatic laceration. CT obtained in the portal venous phase demonstrates a focal low attenuation line (arrow) running through the pancreatic parenchyma in the tail of the pancreas, consistent with a focal pancreatic laceration.

Figure 3-22 Pancreatic transection. Trauma CT demonstrating complete transection of the body of the pancreas (arrow) due to blunt traumatic injury.

Figure 3-23 Pancreatic laceration with main duct injury. A, Axial CT obtained at the time of initial evaluation demonstrates a complex laceration of the pancreatic head–neck junction with near-complete transection. Injury of the main pancreatic duct was suspected. B, ERCP obtained to evaluate the extent of injury demonstrates contrast extravasation at the site of injury (arrows), confirming the presence of injury to the main pancreatic duct.

Figure 3-24 Pancreatic pseudoaneurysm following blunt trauma. A, Axial CT performed during the portal venous phase demonstrates a focal contained collection of contrast in the pancreatic head/neck region (arrow) at the site of previous pancreatic laceration with enhancement similar to the aorta. B, The delayed CT image obtained 5 minutes following the initial contrast injection confirms the presence of a pseudoaneurysm, with the focal collection (arrow) now decreased in attenuation as it mirrors enhancement characteristics of the adjacent vessels (including the aorta). This pseudoaneurysm resolved several days later and did not require further intervention.

One potential pitfall to be avoided is the misinterpretation of isolated low-attenuation fluid around the pancreas, without direct evidence of parenchymal trauma, as evidence of pancreatic injury (Fig. 3-25). In the trauma population, this can be the result of accumulation of fluid in the retroperitoneum from rapid or excessive administration of fluids for resuscitation. If there is a question, a repeat CT 24 to 48 hours later is advisable. Fluid related exclusively to exogenously administered replacements will decrease or resolve, whereas true pancreatic injuries lead to growing fluid collections and hematomas. Also, pancreatic lacerations may be very subtle on initial CT scans. Thus, if the patient develops abdominal pain after admission, a repeat CT with special attention to the pancreas is indicated.

Figure 3-25 Retroperitoneal fluid mimicking pancreatic injury. A, Axial CT image during the portal venous phase following motor vehicle accident shows low-density fluid (arrows) in the retroperitoneum posterior to the pancreas tracking anterior to the inferior vena cava and posterior to the duodenum. The possibility of pancreatic or duodenal injury was initially raised, although the patient did not exhibit clinical signs of either injury. Thus, follow-up CT was requested. B, Axial CT image with oral and intravenous contrast obtained 24 hours later shows that the fluid has nearly resolved, suggesting that the initial CT findings were due to fluid resuscitation and not to pancreatic or bowel injury.

Once injury to the pancreas is identified, MR and MRCP can help in further assessing the status of the main pancreatic duct, especially for follow-up of pancreatic injuries in these typically young patients in whom unnecessary radiation should be avoided if possible (Fig. 3-26). Common MR pulse sequences acquired include fat-suppressed T1- and T2-weighted sequences and MRCP, performed by using heavily T2-weighted breath-hold or non-breath-hold sequences. Fast spin-echo (two-dimensional or three-dimensional) and rapid acquisition with relaxation enhancement (RARE) sequences performed in the coronal and axial planes are usually sufficient. In addition to evaluating the pancreatic duct, MR can be used to assess for pancreatic fluid collections that may have developed due to the pancreatic ductal injury (Fig. 3-27). Hemorrhagic components are also easily detected with MR. Although MRCP is useful for evaluating the pancreatic duct, ERCP is important because of its potential to definitively confirm communication of an apparently interrupted duct with surrounding fluid collections (see Fig. 3-23). In addition, ERCP provides a means for possible endoscopic therapy of pancreatic duct leaks and fluid collections.

Figure 3-26 MR appearance of pancreatic injury. A, Axial T1 with chemical fat saturation demonstrates a focal laceration (arrow), which appears as low signal intensity on this pulse sequence. B, Axial fat-saturated T2-weighted sequence shows the laceration as focal linear increased signal in the tail of the pancreas (arrow). The fluid-sensitive T2 sequence also shows the presence of peripancreatic fluid (asterisk).

Figure 3-27 Pancreatic fluid collections, MR appearance. Axial fatsaturated T2 pulse sequence demonstrates two distinct fluid collections (arrows) as high signal intensity. The collections developed secondary to a pancreatic laceration with ductal injury that occurred at the time of the initial trauma.

BOWEL AND MESENTERIC INJURY

Injuries to the bowel and mesentery are uncommon but potentially devastating, since they are difficult to diagnose both clinically and with imaging. Most blunt injuries are secondary to motor vehicle collisions, although other mechanisms, including assaults and sports-related trauma, produce such injury. Injury of the small bowel is much more common than injury of the colon or stomach in the setting of blunt trauma (Box 3-1).

Although bowel and mesenteric injuries can occur in isolation, most patients present with injuries to other organ systems, typically the liver or spleen. Three different mechanisms have been described. The first type of injury, a crush injury, generally occurs due to impaction of the bowel between the anterior abdominal wall and the spine or other solid organ. This type of injury leads to bowel wall contusions, mural hematomas, and lacerations, and often involves the duodenum and transverse colon. The second type of injury, a shearing injury, occurs at the sites of fixed anatomic structures, such as at acquired adhesions or at normal points of bowel fixation (such as the ligament of Treitz and the ileocecal valve). During brief periods of rapid deceleration, mobile loops of bowel are pulled away from points of fixation, leading to shearing-type injuries, which include bowel or mesenteric lacerations, mesenteric vascular injuries, and degloving injuries where the serosa is stripped away from the rest of the wall. The third type of injury, the burst injury, is due to sudden increases in intraluminal pressure that lead to focal bowel perforation or laceration.

Delayed diagnosis of bowel or mesenteric injuries is a leading cause of morbidity and mortality in victims of blunt trauma. The clinical diagnosis of a focal injury to the bowel or mesentery can be extremely challenging. Trauma patients are often intoxicated and have distracting injuries, altered levels of consciousness, or closed head injuries that preclude the accurate detection of physical symptoms and may mask the clinical manifestations of bowel injury. In the past, trauma surgeons relied on invasive tests such as diagnostic peritoneal lavage as a means of detecting intestinal contents or blood in the peritoneal cavity. However, this test is invasive and not specific and often led to a large number of nontherapeutic exploratory laparotomies. Peritoneal lavage has been replaced by CT as the main diagnostic modality. Improvements in technology and increased awareness of the many (often subtle) CT signs of bowel and mesenteric injuries have resulted in earlier detection. Ultrasonography is not reliable for direct demonstration of the bowel injury, although the finding of free peritoneal fluid on the initial FAST scan may serve as indirect evidence of injury and heighten clinical suspicion.

CT diagnosis of injuries to the bowel and mesentery is not always straightforward. Unlike most solid organ injuries, which are often obvious, the radiologist needs to carefully inspect the images for direct and indirect signs, each having varying ranges of sensitivity and specificity. Numerous CT signs have been reported to occur in the setting of bowel and mesenteric trauma (Box 3-2).

Since the detection of bowel and mesenteric injuries is challenging, and so many reported CT signs must be carefully sought for, it may be more useful to consider the types of injury and the possible appearance of such injury on trauma CT scans. According to the AAST injury scale for the bowel (including stomach, duodenum, small intestine, and colon), injuries tend to vary from mild grade I injuries such as bowel wall hematomas to severe grade V injuries including devascularization and complete bowel wall transection. Mesenteric vascular injuries vary from grade I distal branch vessel injury to grades III and IV superior mesenteric trunk and celiac axis injuries, with grade Vinjury reserved for major abdominal vessel (aortic, caval, or extrahepatic portal vein) injury. Thus, the frequency of individual CT signs found in bowel and mesenteric injuries depends on the type and severity of injury that has occurred.

Bowel wall hematomas and contusions, when visible by CT, typically present with focal thickening of the bowel wall. The area of thickening may appear hyperattenuating relative to the normal bowel wall due to the presence of acute blood (Fig. 3-28). Depending on the severity of the injury, the hematoma may be eccentric or concentric in appearance. More severe injuries, which include lacerations of the bowel wall, are only rarely directly seen on CT as focal wall interruptions or frank discontinuity. Instead, other secondary signs of bowel laceration may be present to suggest such an injury. Free intraperitoneal air is one of the more common findings in patients with focal bowel wall lacerations (Fig. 3-29). However, the overall sensitivity of this finding varies between 20% and 75%. Free air may be found locally, adjacent to the site of perforation, or remotely in the upper abdomen near the surface of the liver or along the undersurface of the peritoneum. The presence of free air is not 100% specific for bowel injury, and other benign iatrogenic and traumatic causes (such as bladder rupture and air introduced at the time of Foley catheter placement) must be considered (Box 3-3).

Figure 3-28 Bowel wall hematoma. Axial CT without oral contrast demonstrates focal bowel wall thickening (arrows) in this patient following motor vehicle collision. The bowel wall is thickened and increased in density compared with the adjacent muscle.

Figure 3-29 Free intraperitoneal air due to bowel injury. A, Axial CT performed with oral and intravenous contrast shows focal wall thickening of the distal ileum (black arrows) with small bubbles of free air in the lower abdomen (white arrow). A focal 1-cm ileal perforation was confirmed at surgery. B, Axial CT performed during the portal venous phase shows a large collection of free air in the upper abdomen (arrows). A sigmoid laceration was detected at surgery.

Free intraperitoneal fluid is another sign associated with bowel and mesenteric trauma. In fact, it has been reported as the most common individual finding. This fluid can be seen adjacent to the site of the injury within the leaves of the mesentery, or diffusely throughout the abdomen and pelvis. While often present in combination with other CT findings, the significance of isolated free fluid on trauma CT scans is controversial, but it appears to be less commonly associated with bowel and mesenteric injuries than was once thought (see discussion on free fluid later in this chapter). However, isolated small puddles of free fluid trapped within the mesentery, seen on CT as small triangles outlining the mesenteric leaves (Fig. 3-30), should prompt a very careful review of the bowel loops for direct evidence of injury.

Figure 3-30 Mesenteric hematoma. Axial CT in this patient demonstrates a focal triangular-shaped hematoma in the bowel mesentery (arrow). Mesenteric hematomas are often subtle, so careful inspection of the mesentery is required to exclude the presence of injury. The presence of mesenteric hematoma should raise the index of suspicion for associated bowel injury.

In addition to extraluminal air and fluid, oral contrast may also escape into the peritoneal cavity when a bowel laceration is present (Fig. 3-31). Unfortunately, this is an uncommon finding, with reported sensitivities as low as 6%, and is highly unlikely to be present as an isolated finding. This is the main reason why the mandatory use of oral contrast in blunt trauma has been questioned, and there is now a growing trend toward non-oral contrast CT for this indication. It should be noted that focal lacerations of the duodenum may produce free air and free fluid that is isolated to the retroperitoneum (Fig. 3-32). Close inspection of the duodenal wall should be made when such findings are present.

Figure 3-31 Bowel wall laceration involving the jejunum. Acute bowel wall injury in this patient was confirmed by the presence of oral contrast outside the expected lumen of bowel (arrow).

Figure 3-32 Duodenal laceration after a motor vehicle accident. Axial CT image during the portal venous phase demonstrates a small bubble of air in the retroperitoneum (solid arrow) with associated retroperitoneal fluid (dashed arrow). A duodenal injury was suspected based on the CT findings and a focal laceration was confirmed at the time of surgery.

Bowel injuries may also produce focal changes in the appearance of the bowel wall itself that can be readily detected with MDCT. Partial thickness injuries may allow air to escape into the bowel wall, producing focal pneumatosis. Other findings include focal wall thickening and focal abnormal wall enhancement following intravenous contrast administration (Fig. 3-33). Enhancement may be increased or decreased, as occurs with severe devascularization from degloving injuries. Focal abnormal wall enhancement almost always indicates that an injury requiring surgical intervention has occurred. Colonic injuries may also manifest as focal wall thickening, usually with surrounding mesenteric hematoma (Fig. 3-34).

Figure 3-33 CT findings suggestive of focal bowel wall injury. A, Axial CT obtained at 5-minute delay shows focal thickening of the jejunum (solid arrows) with fluid in the mesentery (dashed arrow) due to a focal jejunal laceration that required surgical repair. B, Axial CT in another patient with a distal ileum laceration shows abnormal enhancement of the bowel wall greater than the adjacent psoas muscle.

(B, Reprinted with permission from Stuhlfaut JW, Lucey BC, Varghese J Blunt abdominal trauma: Utility of 5-minute delayed CT with a reduced radiation dose. Radiology 238:473–479, 2006.)

Figure 3-34 Focal colon injury after blunt trauma. Axial CT demonstrates focal bowel wall thickening of the ascending colon (arrow) with adjacent mesenteric hematoma. This patient required surgery to repair a focal laceration.

Blunt trauma can result in significant injuries that are isolated to the mesentery, such as lacerations and vascular injuries. Mesenteric lacerations cannot be directly seen; however, they often produce indirect CT signs, such as mesenteric “stranding” (focal ill-defined increase in attenuation) or the formation of a frank mesenteric hematoma due to small vessel injury (Fig. 3-35). When larger vessels are injured, active contrast extravasation may be present (Fig. 3-36). Additionally, mesenteric lacerations can lead to the development of internal hernias. Close clinical follow-up of mesenteric injury is mandatory, because even small hematomas associated with small vessel injury can produce vascular compromise of the associated segment of bowel. The resulting bowel ischemia may be seen as a focal hypoenhancing segment by CT; however, delayed presentation of such injuries, such as bowel obstruction secondary to an ischemic stricture, is possible.

Figure 3-35 Mesenteric hematoma after motor vehicle blunt trauma. Axial CT image following administration of intravenous contrast demonstrates a focal hematoma in the mesentery (arrow) without evidence of bowel injury. A mesenteric laceration that required repair was identified at surgery; no bowel injury was detected.

Figure 3-36 Mesenteric injury with active bleeding. A, Axial CT obtained during the portal venous phase demonstrates mesenteric stranding with a focal collection of extraluminal contrast (arrow) consistent with active extravasation. B, Catheter angiography was requested. A single digital subtraction image following selective injection of SMA branch vessels demonstrates a focal blush of contrast (arrow) that confirms the presence of active bleeding. This patient was treated with coil embolization.

FREE PERITONEAL FLUID

Previous studies have shown that isolated free fluid is present in approximately 3% of all trauma CT scans. In the past, trauma surgeons often elected to surgically explore this subset of patients to fully evaluate the bowel for the presence of injury. However, these patients are now increasingly being managed nonoperatively. One study found that only 27% of patients with isolated free fluid require therapeutic laparotomy. Often, such patients are managed expectantly unless other clinical criteria are present to suggest acute bowel injury. The appearance and location of free fluid are often helpful in selecting patients for nonoperative management. Isolated free pelvic fluid in females is often of no clinical significance; there is also growing evidence to suggest that small amounts of low-attenuation fluid in male patients may be a benign finding, not associated with significant bowel or mesenteric injury (Fig. 3-37). However, large amounts of free fluid in males or females (especially if high in attenuation), focal mesenteric fluid, and free fluid in more than one space or location may be indicative of an underlying injury and may warrant surgery (Fig. 3-38), close clinical observation, or CT follow-up.

Figure 3-37 Free pelvic fluid in a male patient after blunt trauma. Axial CT demonstrates a small amount of free fluid in the recto-vesicle space (arrow) in this male patient following a motor vehicle collision. No solid organ injury or bowel injury was detected, and the patient recovered without the need for further imaging or intervention.

Figure 3-38 Free intraperitoneal fluid. Sagittal reformatted image in this male patient after a motor vehicle collision demonstrates a large amount of dense fluid in the left lower quadrant and in the perisplenic region (arrows). While no injury to the bowel, mesentery, or solid organs was identified, the patient was taken to surgery based on the CT findings. A laceration of the middle colic artery was found and repaired at the time of exploration.

Unfortunately, the surgeon and radiologist are often faced with patients whose clinical evaluation and CT examination, although not entirely normal, do not conclusively confirm the presence of a bowel injury that warrants laparotomy. These include findings such as questionable focal wall thickening, small isolated mesenteric hematomas, or isolated free intraperitoneal fluid. These patients should be admitted for close clinical observation. If the patient develops signs or symptoms consistent with peritoneal irritation, surgical intervention is then advised. Otherwise, a repeat CT with water-soluble oral contrast 12 to 24 hours after the admission CT should be considered before discharging the patient. Given the high morbidity associated with a delayed diagnosis of bowel injury, this careful approach is recommendable.

Finally, in addition to focal bowel injury, the initial trauma CT may show a diffuse abnormality of the bowel that can be seen in patients with hypovolemic shock (so-called shock bowel). Typically, the small intestine is diffusely thickened and there is increased enhancement of the small bowel mucosa (Fig. 3-39). The etiology of the intense mucosal enhancement is not completely understood, although it is thought to be due to increased vascular permeability of the bowel mucosa due to hypoperfusion. Occasionally, the bowel may appear dilated. This appearance is fairly classic and is usually reversible once the patient is appropriately resuscitated. In addition to small bowel abnormalities, profound hypovolemia is also associated with flattening of the inferior vena cava, decrease in caliber of the abdominal aorta, pancreatic swelling, and increased enhancement of the adrenal glands (typically greater than adjacent vascular structures), which maintain normal size and shape.

Figure 3-39 Hypovolemic shock, CT appearance. A, Axial CT obtained in the portal venous phase demonstrates diffuse mural thickening and intense enhancement of the small bowel mucosa in this patient with profound hypovolemic shock following a motor vehicle accident. B, In addition to the bowel findings in A, this patient has a flat IVC and small-caliber aorta, and there is increased enhancement of the adrenal glands (arrow depicts abnormal right adrenal, the left is partially imaged at this level), all signs of hypovolemic shock.

RENAL AND URETERAL TRAUMA

Ultrasonography

Sonography is particularly limited for evaluation of the kidneys following blunt trauma. Acute hematomas are typically hyperechoic and difficult to differentiate from the echogenic renal sinus or perirenal fat (Fig. 3-40). Although early experience suggests that detection of parenchymal injuries is enhanced with the use of ultrasound contrast agents, their use in practice is limited, as is the case for most trauma applications. When seen, renal lacerations appear as linear hypoechoic defects within the parenchyma and may extend to the renal capsule. Injury to the vascular pedicle may be identified by total lack of enhancement of the kidney following contrast injection.

Figure 3-40 Shattered kidney. A, Ultrasound of the left flank demonstrates increased echogenicity in the expected location of the left kidney (arrow), without readily identifiable renal parenchyma. B, CT performed following the initial ultrasound confirms the presence of a shattered kidney. The increased echotexture on ultrasound corresponds to hematoma, which appears as low density on this CT.

Computed Tomography

On CT, renal contusions appear hypoattenuating relative to the surrounding enhanced parenchyma and are optimally seen on the nephrographic phase of contrast enhancement, which typically occurs 90 to 120 seconds following initiation of intravenous contrast infusion. However, most injuries are also well seen in the portal venous phase of hepatic contrast enhancement, the timing used for most abdominal trauma CT scans. A contused kidney is often hypofunctioning, and CT demonstrates a delay in enhancement relative to the normal-functioning contralateral kidney or the ipsilateral noncontused areas (Fig. 3-41). On later phases, the contused kidneys may show a persistent nephrogram with delayed excretion of contrast into the collecting system. Renal laceration represents a tear in the parenchyma and manifests as a focal area of linear low attenuation on CT. The laceration typically extends to the surface and is often associated with a perirenal hematoma or fluid collection (Fig. 3-42). Once a laceration is identified, delayed images are extremely important for demonstrating a potential leak of urine containing dense contrast material into the perinephric space (Fig. 3-43). In addition, some lacerations are associated with active extravasation of contrast-enhanced blood (Fig. 3-44). Unless there is associated major vascular injury, most lacerations will heal without any specific therapy.

Figure 3-41 Renal contusion. Axial CT image obtained following blunt abdominal injury during the portal venous phase of contrast enhancement. There is a focal area of hypodensity (arrow) in the upper portion of the right kidney with minimal stranding due to blood in the perirenal fat. This injury is typical of a renal contusion and typically requires no further management.

Figure 3-42 Renal laceration. Axial CT in patient after a motor vehicle collision demonstrates a focal low density line (arrow) in the renal cortex diagnostic of a focal renal laceration. Perinephric hematoma is present in the fat adjacent to the injury.

Figure 3-43 Renal laceration. Axial CT in this patient was obtained at 5-minute delay to assess the integrity of the collecting system. In addition to a small laceration with perinephric hematoma, a focal collection of contrast (arrow) is present in the perinephric space, consistent with a small urine leak.

Figure 3-44 Complex renal injury with active contrast extravasation. Axial CT obtained during the portal venous phase demonstrates a complex right renal laceration with pooling of extraluminal contrast (arrow) within a large perinephric hematoma. This patient underwent coil embolization to repair this vascular injury.

A renal fracture represents a severe form of laceration in which the kidney is separated into at least two complete independent fragments. If the kidney is fractured into more than three parts, the injury is typically described as a shattered kidney. This injury is often easier to characterize with the help of multiplanar reformations, which afford the opportunity to identify fracture lines running in different planes. Once detected, any significant perirenal hematoma or focus of active contrast extravasation should be noted since these patients may require further intervention. If the patient is stable and surgery can be avoided, catheter angiography is often helpful to identify isolated arterial injuries that may benefit from embolization. Shattered kidneys more often require surgical intervention and nephrectomy to control bleeding from multiple injured branch vessels.

Finally, injury of the vascular pedicle typically represents either an acute traumatic dissection or transection of the renal artery or vein (Fig. 3-45). When such an injury occurs, the kidney will show an absence or near absence of contrast enhancement on the portal venous phase CT exam and there may be associated perirenal hematoma. This injury is severe, and patients may present in hypovolemic shock due to profound blood loss. This injury may be treated by surgical revascularization if detected early (typically within the first 6 hours following the initial trauma); otherwise, nephrectomy is indicated as the kidney is unsalvageable if the diagnosis is delayed or if the patient presents too long after the time of initial injury.

Figure 3-45 Renal vascular pedicle injury. Axial CT image in this patient following a high-speed motor vehicle collision demonstrates diminished enhancement in a large portion of the right kidney due to this vascular pedicle injury.

Ureteral Injury

The ureter is the least commonly injured segment in the genitourinary system, accounting for less than 1% of all injuries. Most ureteral injuries are penetrating injuries such as gunshot wounds. Injury can occur anywhere along the course of the ureter, and most often is confined to one side of the body. Similar to other organs of the genitourinary system, ureteral injuries often present clinically with gross or microscopic hematuria. However, hematuria may not be present in up to 25% of patients with ureteral trauma. Thus, these injuries may not be suspected at the time of abdominal CT or exploratory surgery (especially in the case of penetrating trauma). In the past, intravenous urography (IVU) was the imaging test of choice for detecting ureteral injuries; however, CT has essentially replaced IVU in that setting.

Typically, the trauma IVU consists of a scout radiograph of the abdomen followed by hand injection of a water-soluble intravenous contrast agent. A second image is then taken approximately 10 to 15 minutes later to assess the integrity of the collecting system and ureters. A normal IVU is a good indication that there is no major injury of the genitourinary system. Ureteral injury is identified as contrast-filled urine accumulating in the retroperitoneal space. It is important to evaluate the entire ureter to exclude distal injuries within the pelvis.

More commonly, the ureter is evaluated with the routine trauma CT. When a focal injury of the collecting system or ureter is suspected, delayed CT images are mandatory. These are typically obtained 5 to 7 minutes following contrast injection to avoid unnecessary delay in patient care while the patient is undergoing diagnostic imaging evaluation. Early portal venous phase images may show abnormal fluid or stranding adjacent to the ureter; delayed images show extravasation of urine with contrast at the site of injury (Fig. 3-46). Multiplanar reformations are useful in highlighting the site of injury and may aid the urologist in treatment planning.

Figure 3-46 Ureteral trauma. Coronal reformatted image obtained at 5-minute delay demonstrates abrupt termination of the proximal right ureter with extraluminal contrast just lateral to the site of injury, adjacent to the lower pole of the right kidney (arrow). This patient required stent placement to treat the injury. (Reprinted with permission from Stuhlfaut JW, Soto JA, Lucey BC Blunt abdominal trauma: Performance of CT without oral contrast material. Radiology 233:689–694, 2004.)

ADRENAL TRAUMA

Injury of the adrenal gland is uncommon. It occurs in approximately 1% of all patients sustaining abdominal trauma. Isolated adrenal injury is even rarer, occurring in less than 5% of all patients with adrenal trauma. Instead, most patients with adrenal injuries also have injury to one or more other solid organs in the abdomen, most commonly the liver, spleen, or kidney. Ipsilateral rib fractures are also common. Adrenal injuries typically occur on the right side and are much less commonly seen in isolation in the left adrenal gland. Possible explanations for this discrepancy that have been offered include the position of the right adrenal gland in relatively tight quarters between the spine and the liver and the right adrenal gland being subject to higher venous pressure than the left when increased abdominal pressure occurs at the time of injury. The right adrenal gland might see relatively higher venous pressures transmitted from the vena cava, while venous pressures are filtered by the left renal vein before reaching the left adrenal gland. Regardless, injury to the adrenal gland can be readily identified on routine trauma CT imaging. Typically, adrenal injuries appear as round or ovoid nodules replacing the normal adrenal gland. Not uncommonly, there is a fracture of an ipsilateral transverse process (Fig. 3-47). These hematomas can be associated with surrounding periadrenal fat stranding on CT. It is important to distinguish adrenal hematomas from incidental adrenal nodules, which are commonly seen in the trauma population (and in the general population). It is helpful to measure the attenuation of the lesion. Most adrenal hematomas have attenuation coefficients higher than 50 Hounsfield units (HU). Adrenal injuries typically have a higher HU than other adrenal lesions such as adenomas, which often have attenuation measurements less than 10 HU. If available, delayed images (10 to 15 minutes after contrast injection) can help characterize the lesion by determining the washout characteristics. If there is any question, follow-up imaging can be obtained to assess for interval change in the suspected adrenal injury. On follow-up CT, adrenal hematomas typically regress or calcify. In addition, pseudocysts can develop as sequelae of adrenal injury. Rarely, patients with bilateral adrenal injury can develop clinical manifestations of adrenal insufficiency.

Figure 3-47 Adrenal injury. A, Transverse CT image in this patient following blunt trauma depicts a right adrenal hematoma (arrow) with stranding of soft tissue in the periadrenal region. B, Adrenal injuries are often associated with fractures of the transverse process, as was evident in this patient at a level below the site of adrenal injury (arrow).

PELVIC TRAUMA

Although the pelvis communicates with the peritoneal and extraperitoneal compartments of the abdominal cavity and is imaged concomitantly with the abdomen at the time of admission CT, the unique anatomic disposition of the pelvic ring and the types of injuries encountered deserve a separate discussion in this chapter. In most settings, a portable radiograph of the pelvis is obtained upon arrival of a multiple-trauma patient to the trauma bay. If a displaced (and possibly unstable) fracture of the pelvic ring is demonstrated, the pelvic cavity should be investigated carefully for associated injuries to the vascular structures, rectum, bladder, or urethra. Strong forces are necessary to disrupt the osseous pelvic ring; the radiographic evaluation of trauma to the bony pelvis is discussed in detail in chapter 4 on trauma of the extremities.

The possibility of vascular injury and major (sometimes life-threatening) bleeding should be considered in every patient with a disruption of the pelvic ring. CT has been shown to be valuable in evaluating for vascular injury in patients with pelvic trauma. Large hematomas and foci of active extravasation are the main findings that may prompt a consult to the interventional radiology service for possible endovascular therapy via embolization. Multiphasic CT imaging provides a temporal assessment of change in the size of the hematoma, and provides an indirect means of estimating the rate of bleeding (Fig. 3-48).

Figure 3-48 Complex pelvic fracture with active bleeding. A, Transverse CT obtained as part of a CT angiogram demonstrates a complex fracture of the left ilium with a large pelvic hematoma and active contrast extravasation (arrow). B, CT obtained at 5-minute delay shows an increase in size of the hematoma with continued diffusion of blood and contrast (arrow) into the site of injury.

Bladder Trauma

Bladder injuries result from blunt (70% to 80%) or penetrating trauma (20% to 30%). Common causes of bladder rupture include direct impact with the steering wheel or seatbelt in motor vehicle accidents and assaults to the lower abdomen by a kick or blow. The likelihood of bladder trauma is directly related to the degree of distention at the time of the injury, with a full bladder more likely to rupture than an empty one. A high clinical suspicion and timely diagnosis are the keys to successful medical or surgical treatment. Approximately 10% of patients with pelvic fractures have bladder injuries, and the likelihood of bladder injury is directly related to the severity of the fracture. There is also a high association between bladder rupture and urethral disruption.

Patients with signs and symptoms suggestive of a bladder injury typically have a history of pelvic trauma, often with a fracture evident on the admission radiograph. Although the clinical signs of bladder injury are nonspecific, a triad of symptoms is often present: suprapubic pain, gross hematuria, and an inability to void or difficulty in doing so. The hallmark of a bladder rupture is hematuria, which is almost invariably present. More than 95% of bladder ruptures are associated with gross hematuria, and 5% are associated with microscopic hematuria. Since some patients can still void, the ability to urinate does not exclude bladder injury or perforation. Whenever a bladder injury is suspected, the patient should be further evaluated with conventional cystography or CT cystography and the threshold for performing these tests should be very low.

Cystography

A well-performed cystogram begins with an abdominal radiograph (scout view). This serves to evaluate the pelvic bones and to determine if there is any displaced fracture that could limit the patient’s ability to position properly. Subsequently, a Foley catheter should be placed into the bladder. However, it is mandatory to carefully inspect the urethral meatus for evidence of gross blood before attempting to catheterize the bladder. Blood at the urethral meatus is an absolute indication for retrograde urethrography to assess urethral integrity before attempting to blindly pass a Foley catheter. Approximately 10% to 20% of men with a posterior urethral injury have an associated bladder injury. Blind passage of a urethral catheter may convert a partial disruption of the urethra into a complete tear. If a posterior urethral injury is present, placement of a percutaneous suprapubic catheter may be necessary to evaluate bladder integrity.

Once the lumen of the bladder has been catheterized, diluted water-soluble contrast material (usually 50% contrast and 50% sterile saline) is slowly instilled by gravity (approximately 75 cm above the pelvis). The examination should be performed under continuous fluoroscopic observation. If gross extravasation is noted, no further distention is necessary. If extravasation is absent, the remainder of the contrast is infused (to 300 to 400 mL total) until full distention is achieved. Spot fluoroscopic images should be obtained as necessary. Standard static projections include anteroposterior and oblique views of the bladder filled with contrast, along with another anteroposterior film obtained after drainage. Oblique films are often difficult to obtain in a patient with pelvic fractures and may be omitted in selected cases. The total volume of contrast administered is less important than ensuring that adequate bladder distention is achieved, in order to demonstrate small injuries that may otherwise go undetected. Some superficial lacerations may seal temporarily by wall edema or by an overlying hematoma, omentum, or adjacent segment of large or small bowel. Full distention helps prevent this false negative result. Also, the postdrainage film is a critical part of the study because it may disclose small foci of extravasation that may be hidden by the distended bladder. The accuracy of a well-performed cystogram ranges between 90% and 98%.

CT Cystography

Most patients with bladder injuries have suffered multiple trauma and require abdominal or pelvic CT scans as part of their evaluation. The CT scan of the pelvis provides information on the status of the pelvic organs and osseous pelvis. Occasionally, bladder rupture is shown on the initial pelvic CT images with contrast-filled urine accumulating in the perivesical space or peritoneal cavity (Fig. 3-49). However, bladder integrity is not confirmed until full distention of the bladder with homogeneously opacified fluid is achieved. A CT cystogram is performed after the abdominopelvic CT is completed. With a Foley catheter secured in the bladder, diluted contrast is instilled to achieve full distention. CT images limited to the pelvis are then obtained. Although CT cystography lacks the temporal, dynamic information provided by fluoroscopy, the superior contrast resolution compensates for this limitation, often showing small accumulations of extravesical contrast. In the majority of major trauma centers, CT cystography has replaced conventional cystography as the most widely used method to assess bladder integrity.

Figure 3-49 Extraperitoneal bladder rupture. Axial CT obtained 5 minutes after the injection of intravenous contrast demonstrates extraluminal contrast (arrows) in the space of Retzius secondary to a traumatic bladder rupture.

Types of Bladder Rupture

Bladder ruptures are classified as extraperitoneal, intraperitoneal, or combined (intra- and extraperitoneal). This distinction is critical, as management varies considerably: intraperitoneal ruptures require immediate surgical therapy, whereas extraperitoneal ruptures are usually managed with bladder drainage and delayed reconstruction, when necessary. Extraperitoneal injuries account for approximately 70%, intraperitoneal injuries account for approximately 20%, and combined perforations account for approximately 10% of all injuries. The proportion of intraperitoneal ruptures is considerably higher in children due to the predominantly intra-abdominal location of the bladder in this age group, as the bladder descends into the pelvis usually by the age of 20 years.

In blunt trauma, extraperitoneal bladder ruptures are almost invariably associated with pelvic fractures. Rupture may occur either from a direct perforation by a bony fragment (as with fractures of the anterior pubic arch) or from a burst injury or sudden shearing force from the pelvic ring at the time of the impact. The classic finding on cystography or CT cystography is contrast extravasation around the base of the bladder confined to the peri- and prevesical space (of Retzius); flame- or starburst-shape areas of contrast extravasation are characteristic (see Figs. 3-49 and 3-50). An associated pelvic hematoma may give the bladder a teardrop shape. With a more complex injury, the contrast material extends to the thigh, scrotum (or labia), penis, or perineum, or into the anterior abdominal wall (Fig. 3-51). Extravasation will reach the scrotum when the superior fascia of the urogenital diaphragm or the urogenital diaphragm itself has been disrupted. If the inferior fascia of the urogenital diaphragm is violated, the contrast material will reach the thigh and penis (contained by Colles’ fascia).

Figure 3-50 Cystographic and CT appearance of extraperitoneal bladder rupture. A, Anteroposterior image of the pelvis obtained after gravity-assisted bladder distention demonstrates contrast outside the expected lumen of the bladder (arrow). B, This finding is better depicted on the postdrainage film (arrow), which clearly depicts the extraperitoneal nature of this injury. C, On CT cystography, extraluminal contrast due to bladder injury is also readily identified (arrow).

Figure 3-51 Extraperitoneal bladder injury. Axial image from a CT cystogram demonstrates extraluminal contrast within the pre-vesicle space due to an acute extraperitoneal bladder injury. In addition, contrast has tracked inferiorly and laterally in the left inguinal region.

A typical intraperitoneal rupture results from a horizontal tear occurring in the dome of the bladder. The dome is the weakest and least supported area and the only portion of the adult bladder covered by peritoneum. The mechanism of injury is usually a direct blow to a fully distended urinary bladder. Initial CT images often demonstrate low-attenuation fluid within the peritoneal cavity, and gas if a Foley catheter has been introduced (Fig. 3-52). On cystography, contrast accumulates in the peritoneal cavity, outlines loops of bowel, and fills the paracolic gutters, pouch of Douglas, and other peritoneal spaces, including the subphrenic spaces. In combined intraperitoneal and extraperitoneal ruptures, cystography reveals contrast outlining the abdominal viscera and perivesical space. Combined ruptures are common after penetrating injuries from a high-velocity bullet or knife traversing the bladder.

Figure 3-52 Intraperitoneal bladder injury. A, Axial CT image demonstrates free air in the peritoneal cavity (arrow) in addition to free fluid along the liver margin. No bowel injury was detected. Prior to this CT, a Foley catheter had been placed and the free air was thought to be due to an acute bladder injury. B, Sagittal reformat from the subsequent CT cystogram depicts contrast in the peritoneal cavity (asterisk) due to an intraperitoneal bladder rupture.

Urethral Injury

Early recognition of urethral injuries is necessary in order to prevent serious long-term sequelae such as strictures that require recurrent interventions to prevent infectious complications. The vast majority of urethral injuries occur in men. Most urethral injuries are associated with major blunt trauma such as that caused by motor vehicle accidents or falls, but penetrating injuries, although rarely, may be the cause as well. Given the severity of the traumatic event that caused the urethral injury, many of these men have associated neurologic and orthopedic injuries that further complicate therapy. Iatrogenic causes, such as traumatic catheter placement or transurethral dilation, can also occur.

Urethral injuries are usually classified as belonging to one of two types, based on the anatomical site of the tear: posterior urethra or anterior urethra. Posterior urethral injuries are more common and usually occur at the junction of the prostatic and membranous segments, where the urethra is fixed by the attachments of the puboprostatic ligaments. Thus, posterior urethral injuries are typically caused by severe blunt trauma with fractures of the anterior pelvis; displacement of the bone fragments overstretches the short membranous segment. Male patients with pelvic fractures have a 5% to 10% incidence of posterior urethral injury.

Anterior urethral injuries affect the bulbar or penile segments and are usually the result of trauma to the perineum, such as straddle injuries. Relatively minor trauma can injure the bulbar urethra, but the diagnosis may be delayed by months or even years, when patients present with urethral strictures. Occasionally, tears of the penile urethra are seen in the setting of a penile fracture.

Diagnosis Retrograde Urethrogram

The possibility of a urethral injury should be considered in every patient with a pelvic fracture before blindly inserting a Foley catheter into the bladder. Other potential antecedent history, such as traumatic catheterization, straddle injury, or any penetrating injury near the urethra, should also raise suspicion. Symptoms include hematuria and an inability to void. However, these are rarely useful in the setting of major acute trauma, when patients are intubated and sedated or unconscious. On physical examination, the hallmark finding is presence of blood at the meatus or a high-riding prostate gland on rectal examination.

The diagnosis is confirmed with a retrograde urethrogram, which must be performed prior to insertion of a catheter into the bladder in order to avoid further injury to the urethra. For the retrograde urethrogram, a Foley catheter is generally preferred over the Brodney clamp. A 16-F catheter is placed into the distal urethra, and the balloon (3 mL) inflated within the fossa navicularis. Then 30 to 60 mL of water-soluble contrast material is injected under fluoroscopic guidance using a 60-mL piston syringe. Oblique views (when possible) are usually the most helpful.

Urethrography serves to assess integrity and to localize and characterize tears as complete or incomplete. In posterior urethral injuries, contrast material accumulates outside the urethra in the retropubic extraperitoneal space (Fig. 3-53). In partial rupture, there is at least some continuity, which allows partial filling of the bladder, in addition to the extravasated contrast. Complete tears are shown as an interruption of the urethra. Involvement of the urogenital diaphragm is assumed when contrast accumulates in the perineum. Partial tears of the posterior urethra usually heal uneventfully, whereas complete tears may heal with formation of a stricture. Other long-term symptoms associated with severe urethral injuries include impotence and, rarely, incontinence. These sequelae are more likely a reflection of the severity of the initial trauma, rather than caused by the urethral injury itself. In anterior urethral injuries, contrast may fill the corpora cavernosa or corpus spongiosum or it may reflux into the draining veins.

Figure 3-53 Posterior urethral injury following acute trauma. Image obtained at the time of retrograde urethrography demonstrates extravasation of contrast into the retropubic space (arrow) from a posterior urethral injury.

Rectal Injury

The rectum is rarely injured as a result of blunt trauma. When injured, there is often a history of direct perineal force at the time of the traumatic event, and patients often have associated pelvic fractures. Rectal injury can be difficult to detect clinically, although some patients present with bright red blood per rectum. Physical exam may detect the presence of blood or bone fragments in the rectal vault, indicating a high likelihood of injury. Often, patients with suspected injury are evaluated directly by rigid sigmoidoscope. However, rectal injuries are increasingly diagnosed at the time of diagnostic CT imaging. CT imaging may show focal rectal wall thickening (Fig. 3-54) or localized free air in the perirectal fat. In addition, hematoma may be present in the perirectal fat as a result of such injury. Water-soluble contrast administered as an enema may be necessary to demonstrate the site of perforation in questionable cases (Fig. 3-55).

Figure 3-54 Acute rectal injury. Sagittal reformat obtained after trauma CT shows focal thickening of the posterior rectal wall (arrow) with fluid in the presacral space. Rectal laceration was confirmed at surgery.

Figure 3-55 Acute rectal injury following blunt injury. A, Axial CT obtained during the initial trauma CT demonstrates stranding in the soft tissue posterior to the distal rectum, suspicious for an acute injury. B, After administration of water-soluble rectal contrast, a posterior laceration with contrast extravasation is readily identified.

PENETRATING ABDOMINAL TRAUMA

Penetrating abdominal trauma caused by stab or gunshot wounds is a frequent cause of admission to emergency departments in large urban centers. The pathophysiology involved in penetrating trauma is unpredictable and the pattern of injuries differs from blunt abdominal trauma. Compared with blunt trauma, injuries to the bowel, mesentery, and diaphragm are more common with penetrating trauma. Bowel injuries may remain clinically occult for several hours after trauma occurs. Thus, early detection of bowel injuries is a major concern in this patient group. In the past, exploratory laparotomy was considered mandatory for diagnosis and treatment of all patients with confirmed penetration of the peritoneum. This surgical approach is based on the following assumptions: laparotomy is necessary to exclude intra-abdominal injuries; diagnostic laparotomy is associated with little morbidity; and increased morbidity and mortality are associated with delayed treatment of injuries to the hollow viscera. Immediate laparotomy is still mandated when the penetrating injury is associated with definite signs of peritoneal irritation, hemodynamic instability, gastrointestinal bleeding, or evisceration. However, if all penetrating abdominal injuries are managed with surgery, even without clinical evidence to suggest visceral involvement, the frequency of negative or nontherapeutic laparotomy varies between 20% and 40%. The rate of complications is also high, in the range of 5% to 20%, for patients with negative or nontherapeutic laparotomy findings.

The high proportion of negative laparotomy findings and the relatively high frequency of complications led some surgeons to question the need for mandatory surgical exploration in this setting. Knowledge gained from conservative or nonsurgical treatment of blunt trauma has resulted in an extension of this alternative treatment to some victims of penetrating stab injuries and, more recently, to select groups of victims of gunshot wounds. With a conservative approach, penetrating trauma patients who do not have an indication for immediate laparotomy at presentation are admitted to the hospital and observed during 24 hours or more. During the period of clinical observation, laparotomy becomes necessary if the abdominal pain (which is almost invariably present at admission) worsens progressively or if the patient develops rebound tenderness, generalized abdominal guarding, hypoperistalsis, unexplained shock, or gastrointestinal bleeding. The downside is that the delay generated by the period of observation may increase the severity of peritoneal involvement and cause a longer postoperative course if laparotomy is eventually required and a hollow viscus injury found. Thus, this conservative approach has resulted in a growing interest in using diagnostic procedures and imaging tests such as peritoneal lavage, laparoscopy, US, and CT to identify patients with occult injuries that require operative management before they become clinically apparent. These include injuries to the hollow viscera, mesentery, large vessels, and diaphragm.

Peritoneal lavage has high sensitivity but low specificity. Use of an elevated cell count as a criterion for need for laparotomy is not uniform and has not been adjusted to the modern concept of nonsurgical treatment of wounds to the solid viscera. In general, patients with occult hollow viscus injury are not well evaluated by means of diagnostic peritoneal lavage. Laparoscopy is useful for diagnosis of peritoneal violation and wounds of the diaphragm, and, in some patients, therapeutic procedures can be performed at the same time. The downside is that this is an invasive procedure that requires general anesthesia and that the evaluation of the retroperitoneum is limited and visualization of all the hollow viscera incomplete.

Computed Tomography

Whereas CT is widely used for blunt trauma, it is not widely used in the evaluation of penetrating injuries. Initial reports on the use of CT for penetrating trauma were limited to asymptomatic patients with injuries in the back and flank, since they infrequently have associated injury to critical retroperitoneal viscera due to the good protection provided by the ribs, spine, and large paraspinal muscles. Given the higher frequency of hollow viscus injuries that occurs in penetrating trauma, it is mandatory that patients receive intravenous, oral, and rectal contrast material (“triple-contrast” CT) in order to maximize the diagnostic potential of CT for penetrating trauma. Typically, patients receive 600 to 800 mL of diluted (2% to 3% concentration) water-soluble (iodinated) contrast material orally and a 1- to 1.5-liter enema of similarly diluted water-soluble contrast material. Oral contrast should be administered within 30 minutes of CT data acquisition. Rectal contrast is typically administered on the CT table, immediately prior to CT scanning. Several studies have found this approach to be highly sensitive and specific for detecting and ruling out hollow viscus injuries. As for blunt trauma patients, delayed images (3 to 5 minutes following initiation of intravenous contrast material injection) should be acquired for a complete evaluation of the renal collecting system and ureters and for characterization of extravascular collections of contrast-enhanced blood.

The diagnostic criteria used for interpretation of blunt trauma CT scans cannot be applied to penetrating trauma patients. Presence of free intraperitoneal air or free peritoneal fluid is a sign of peritoneal violation but is not definitive evidence of bowel injury, since air can be introduced into the peritoneal cavity by a bullet or knife wound and free fluid can be the result of bleeding from the peritoneal lining itself (Fig. 3-56). The only unequivocal sign of hollow viscus injury is the presence of extraluminal collections of oral or rectal contrast material (Fig. 3-57). Other CT findings considered highly indicative of bowel injury include the presence of focal bowel wall thickening or discontinuity and a bowel wall hematoma. Mesenteric injuries are confirmed by finding active extravasation of contrast material, as shown by the portal venous and delayed phase scans, or a focal mesenteric hematoma. Injuries to solid organs resulting from penetrating injuries are similar in appearance to those from blunt trauma (Fig. 3-58). Injury to the diaphragm is suspected when the trajectory of the missile or sharp object appears to extend toward or to the diaphragm. More specific signs, however, include finding herniated abdominal content into the chest through the diaphragmatic rent (Fig. 3-59), the CT “collar” sign (focal constriction of herniated abdominal fat or viscera at the site of diaphragmatic defect), and the finding of injured organs on either side of the diaphragm when only one injury was inflicted (thoracoabdominal injury). CT findings of potential diaphragm injury include a penetrating injury tract that extends to the diaphragm, thickening of the diaphragm, and an isolated focal defect in the normal continuity of the diaphragm without adjacent hemorrhage. If a question concerning the presence of peritoneal penetration persists during the period of clinical observation, laparoscopy should be performed as a definitive test.

Figure 3-56 Penetrating injury with rectus abdominus hematoma. Axial CT obtained to evaluate a stab wound to the anterior abdomen demonstrates thickening of the left rectus muscle with active contrast extravasation. Free fluid is present in the right abdomen, but the bowel appeared completely normal. This patient recovered without need for exploratory surgery.

Figure 3-57 Bowel injury after penetrating trauma. Sagittal reformat CT obtained to evaluate a gunshot wound demonstrates extraluminal contrast (arrow) from an acute, full-thickness, small bowel injury.

Figure 3-58 Solid organ injury after acute gunshot injury. A, Axial CT obtained following the acute injury demonstrates a focal liver laceration in segment 7 (arrow). B, Sagittal reformat also demonstrates a focal renal laceration with large perinephric hematoma (arrow).

Figure 3-59 Diaphragmatic injury. Axial CT obtained following a gunshot injury demonstrates a focal rent in the diaphragm (arrow). The stomach has herniated into the left chest through the defect.