CHAPTER 3 Abdomen Trauma
BLUNT TRAUMA
Computed Tomography Technique
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).
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).
HEPATIC TRAUMA
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.
Computed Tomography
CT is the dominant imaging modality in emergency rooms in the United States and most other Western countries. Improvements in the rate of CT detection of liver injuries, as well as in the proper characterization of most injuries, are some of the reasons that support the trend toward conservative management of such injuries. As previously mentioned, liver injuries are optimally seen on CT performed during the portal venous phase of contrast enhancement. Once identified, it is important to document the type and location of such injury. In addition, it is especially important to note the presence of active extravasation of contrast-enhanced blood and the potential for injury to central hepatic vessels such as the hepatic veins and inferior vena cava. Hepatic injuries are typically characterized as either lacerations or hematomas (subcapsular or parenchymal). While many radiologists rely exclusively on morphological descriptors in their report, it is useful to understand the liver injury scale developed by the American Association for the Surgery of Trauma (AAST) (Table 3-1). This grading scale takes into account features such as the size of subcapsular or parenchymal hematomas and lacerations, as well as evidence of active extravasation and major vascular injuries of the liver; these findings are all readily identified on well-performed CT examinations. The value of this scale lies more in the ability to communicate properly with trauma surgeons about the extent of the injury than in the ability to predict individual patient prognosis or the type of therapy necessary.
| Grade | Description |
|---|---|
| I |
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.
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.
GALLBLADDER AND BILE DUCT TRAUMA
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.
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.
SPLENIC TRAUMA
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.
| Grade | Description |
|---|---|
| I |
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.
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
