Abdomen Trauma

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CHAPTER 3 Abdomen Trauma

Blunt and penetrating abdominal trauma are two of the more common indications for radiologic investigation in the emergency room setting and are common causes of morbidity and mortality among patients admitted to trauma centers. Many of these patients have multisystem injuries resulting from high-velocity mechanisms, and the full extent of these injuries is often difficult to detect clinically. A variety of imaging and nonimaging methods have been used to aid the clinician in the evaluation of abdominal trauma patients, but in recent years ultrasonography (US) and computed tomography (CT) have become the cornerstones of diagnosis and management. The almost universal use of CT, and of US in specific settings or circumstances, has modified the diagnostic approach of the poly-trauma patient and has relegated diagnostic peritoneal lavage to almost a historical procedure. This state-of-the-art imaging allows rapid detection of potentially life-threatening injuries that can be difficult or impossible to detect clinically, especially when the presence of associated injuries may mask overt clinical manifestations or divert the attention of the admitting physician away from major intra-abdominal bleeding.

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:

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).

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).

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.

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.

Table 3-1 AAST Classification of Traumatic Liver Injury

Grade Description
I

II

III IV V VI

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

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.

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

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

Grade Description
I

II III IV V

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

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