HELICAL CT OF ABDOMINAL TRAUMA

ADVANCES IN EMERGENCY RADIOLOGY I

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HELICAL CT OF ABDOMINAL TRAUMA Robert A. Novelline, MD, James T. Rhea, MD, and Timothy Bell, MD

Trauma is the third most common cause of death in the United States and the leading cause of death of men and women under 40 years of age. Approximately 10% of all trauma deaths are due to abdominal injuries. The diagnosis of abdominal injuries due to blunt trauma is challenging because the injuries may not manifest themselves clinically during the initial assessment and because the presence of other more obvious injuries may divert the attention of the initial assessor from potentially life-threatening intra-abdominal pathology. Two different mechanisms may cause injury with blunt abdominal trauma: (1) compressive forces and (2) deceleration forces. Compressive forces result from blows or external compression against a fixed object, such as the spine. These forces can cause lacerations and subcapsular hematomas of solid parenchymal organs, such as the spleen and liver, or they can deform and increase the intraluminal pressure in hollow organs, such as the bowel, resulting in rupture. Deceleration injuries cause stretching and linear shearing forces between fixed and more freely moveable objects resulting in lacerations or injuries of structures, such as the renal arteries and mesenteric blood vessels. Penetrating injuries may be produced by a variety of devices, such as knives and high-velocity projectiles; each is associated with a different injury pattern. Approximately one third of stab wounds penetrate the peritoneal cavity and any organ in the path of the penetrating object may be injured. A major advance in the management of patients with abdominal trauma has been the rapid and accurate diagnosis now provided by CT. Since the first reports of the early 1980s; CT has proved to be an excellent technique for identifying abdomi-

nal injuries. The rapid diagnostic capability afforded by CT has not only contributed toward a decrease in morbidity and mortality from abdominal injuries, but also a decrease in nontherapeutic laparotomies in patients who can be managed conservatively. Hernoperitoneum is easily identified by CT, as are injuries of the spleen, liver, gallbladder, kidneys, pancreas, boweI, mesentery, and diaphragm.6,19,21,24,31, % 36. 37 CT can differentiate intraperitonal hemorrhage from retroperitoneal hemorrhage and can differentiate hernoperitoneum from water-dense, posttraumatic peritoneal fluid collections, such as urine with intraperitoneal bladder rupture or bile with gallbladder rupture. CT can identify active arterial bleeding as sites of intravenous (IV) contrast material extravasation,= and bowel rupture as sites of oral contrast material extravasation.= The aorta, inferior vena cava, and other vascular structures can be assessed from their opacification with IV contrast material. Bony injuries of the lumbar spine and pelvis may be identified on slices reviewed with bone window settings. The accuracy of CT in the diagnosis of blunt abdominal trauma has been reported to be as high as 97.6%.% The major advantage of helical CT in abdominal trauma imaging has been the increased speed of the CT examination, subsequently decreasing the scanning time for injured patients. A helical CT scanner located in or adjacent to the emergency center may make possible the CT evaluation of seriously injured patients who might not have been previously taken to CT for the lengthy examinations of the past. In multiple trauma patients, rapid successive CT scans of various body parts can be performed on the same patient. With helical

From the Department of Radiology, Massachusetts General Hospital; and Harvard Medical School, Boston, Massachusetts

RADIOLOGIC CLINICS OF NORTH AMERICA VOLUME 37 * NUMBER 3 M A Y 1999

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CT respiratory and other motion artifacts are diminished and there is improved vascular and parenchymal opacification with IV contrast material. Reconstructions with overlapping spacing permit better evaluation of small injuries, as well as improved coronal and sagittal reformations for displaying injuries and anatomic relationships in the craniocaudad direction, as in the diagnosis of diaphragmatic trauma,” traumatic avulsion of the gallbladder, and Chance fracture of the spine. Abdominal vascular trauma, such as traumatic renal artery occlusions~5is well shown by the excellent vascular opacification provided by helical CT and three-dimensional reformations can provide excellent CT angiograms.

eas. If no cervical spine fracture is identified at CT, the scan is followed by a lateral cervical spine plain film with the collar removed in order that any signs of possible ligamentous injury may be demonstrated. Multiple trauma patients who require CT imaging of the head should have their head CT scans performed prior to abdominal CT because the IV contrast material required for abdominal CT could interfere with the interpretation of the head CT. IV contrast opacification of cortical bleed vessels can mimic subarachnoid hemorrhage. If thoracic aortic injury is also suspected on the basis of trauma history or suspicious abnormalities on the portable chest film, then a combined chest-abdomen-pelvis CT can be performed as one procedure utilizing one injection of contrast material.

PATIENT SELECTION

Helical CT examinations of the abdomen are recommended for trauma patients with suspected abdominal injuries who are sufficiently hemodynamically stable for transportation from the trauma suite of the emergency center to the CT scanner. Unstable patients may be imaged with a portable ultrasound examination. If these patients later become stable following fluid and other resuscitative measures, they can be taken to CT after ultrasound. The bedside ultrasound examination for abdominal trauma has been referred to as focused abdominal sonogram for trauma. This examination can quickly and noninvasively identify free intraperitoneal fluid with accuracy equivalent to diagnostic peritoneal lavage. Another advantage over peritoneal lavage is that ultrasound can diagnose many subcapsular and intraparenchymal solid organ injuries in both the peritoneal cavity and retroperitoneum. Parenchymal organ injuries, however, are less accurately diagnosed by ultrasound than with CT. Bowel injuries and free air are generally not diagnosed with ultrasound. The success of emergency ultrasound examinations is operator dependent and further limited by the patient’s body habitus, presence of excessive bowel gas, presence of open wounds, and limited ability to move and roll the patient. A portable chest film and screening portable lateral cervical spine film are usually performed on multiple trauma patients prior to CT. Some trauma centers also obtain a portable pelvic film, although this may be unnecessary in patients who will shortly be examined with an abdominal CT scan that includes the pelvis. Any major chest injury needing immediate treatment, such as a pneumothorax requiring a chest tube, can be identified on the portable film and treated prior to CT. Any major unstable injury of the cervical spine may be detected prior to movement of the patient to the CT scanner. At our emergency center we are now clearing the cervical spine of trauma patients with a helical CT examination instead of plain films if the patient will be transported to CT for examination of the head, abdomen, or other anatomic ar-

HELICAL CT PROTOCOLS FOR ABDOMINAL TRAUMA

The performance of high-quality abdominal CT examinations with oral and IV contrast materials ensures the best accuracy in the identification of abdominal injuries. Oral contrast material is needed for optimum detection of bowel injuries; IV contrast material is needed for optimal detection of parenchymal organ and vascular injuries. IV contrast material is also valuable in identifying sites of active hemorrhage. Figure 1 illustrates the excellent parenchymal organ and bowel obtainable with oral and IV contrast agents. For oral contrast material the authors administer three cups of 0.25 oz of melgumine diatrizoate (Gastrografin, Bristol-Meyers Squibb, Wallingford, CT) in 10 oz of water. Because trauma patients may have a bowel rupture, we prefer to use watersoluble bowel contrast agents rather than dilute barium sulfate agents, which are less well tolerated by the peritoneum. We do not delay the CT examination for the passage of oral contrast material but administer the contrast material and scan as soon as possible. Usually, one cup is injected down the patient’s nasogastric tube (less severely injured patients without nasogastric tube can drink the contrast mixture) while the patient is still in the trauma room of the emergency department, another cup is injected while in transit to the CT scanner suite, and a third cup is injected while the patient is being positioned on the CT table. In this time period generally only the stomach, duodenum, and proximal small bowel are opacified; fortuitously, many bowel injuries with blunt trauma involve the proximal gastrointestinal tract. If an injury of the distal small bowel is suspected, then a repeat scan with additional oral contrast material is performed 1 to 2 hours later. If a colon injury is suspected on the basis of a flank or back penetrating injury, or on the basis of hematochezia in a patient with pelvic fractures, then the initial scan is performed with rectal contrast material; this examination is referred to as a

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Figure 1. Splenic trauma with hemoperitoneum showing the sentinel clot sign. The traumatized spleen (S) is shown in A-F: Multiple splenic lacerations are present. Hemoperitoneum (H) can be seen at every level. The densest blood, representing thrombus (arrows), is seen closest to the site of injury in the perisplenic space and left abdomen. The more remote blood around the liver is less dense. Excellent opacification of the parenchymal organs and bowel are obtained with intravenous and oral contrast agents.

triple contrast scan, consisting of oral, IV,and rectal contrast materials. For rectal contrast we place 40 mL meglumine diatrizoate into a 1-L bag of normal saline and administer this mixture rectally through an IV line connected to a small pediatric rectal catheter. To opacify the entire colon (eg., right-sided penetrating injury) we inject 800 to 1000 mL in an adult patient; if only the left colon is of concern, this can be opacified with 400 to

500 mL. Colonic filling by this technique can be accomplished within 5 to 7 minutes. For IV contrast material we inject 135 mL of 60% contrast material with a power injector at 2 to 3 mL/s. We have obtained excellent opacification with this technique, although some trauma centers use larger volumes of 130 to 180 mL of 60% contrast material injected at 2 to 4 mL/s. Helical scanning is performed beginning 70 seconds after the

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start of IV contrast material injection, scanning from above the highest hemidiaphragm to below the kidneys, utilizing a collimation of 5 mm, a pitch of 1.5, and reconstructions at 5 mm of image spacing. When this helical sequence is completed, scanning is delayed an additional 70 seconds to improve opacification of the lower urinary tract. Then, nonhelical, axial scanning is performed from below the kidneys through the ischial rami with 5 mm of collimation and 8-mm increments of table movement. The nonhelical sequence contributes to improved opacification of the urinary tract and less helical artifacts in large or overweight patients. Switching to nonhelical technique also decreases tube heating. This is an especially important consideration in polytrauma patients requiring multiple, sequential scans. If tube heating is not a problem, then the delayed scan of the lower abdomen can be performed helically. All slices are filmed at soft tissue and bone windows and those that include the lungs are also filmed at lung windows. Bone window images provide improved identification of suspected and unsuspected spine and pelvic injuries. Lung window images of the abdomen may be particularly helpful in showing small amounts of traumatic extraluminal air in the peritoneal cavity or retroperitoneum. These can be viewed on the CT console or workstation as an alternative to filming. Similarly, narrow soft tissue windows may be viewed or filmed for the identification of subtle organ injuries. The patient’s Foley catheter is routinely clamped prior to scanning while the patient is still in the trauma room to optimize urinary bladder filling. It has been well recognized that an abdominal CT scan performed without maximal urinary bladder filling can overlook both intraperitoneal and extraperitoneal bladder rupture. If the bladder is not distended on the initial CT scan, especially in patients with an increased likelihood of bladder injury because of pelvic fractures or gross hematuria, a repeat CT scan of the pelvis is performed after the retrograde administration of bladder contrast material (CT cystogram). To perform this examination, the Foley catheter is unclamped, the bladder is allowed to drain, 300 to 400 mL of bladder contrast material (40 mL meglumine diatrizoate in a 1-L bag of normal saline) are administered through the Foley catheter, and then the pelvis is rescanned. It should be noted that the appearance of a full or distended bladder on the initial CT scan may be unreliable; a CT cystogram is recommended when any doubt exists regarding bladder integrity. Also, if blood was seen at the urethral meatus on the initial evaluation of the patient in the trauma room, then a retrograde urethrogram should be performed prior to Foley placement to rule out a urethral injury. For multiple trauma patients with a trauma history or chest film suspicious for thoracic aortic trauma, a combined helical chest-abdomen-pelvis CT scan with one bolus of IV contrast material

should be performed. For the usual abdominopelvic CT scan for trauma, one waits 70 seconds after starting the N contrast material injection before beginning the abdominal scan. It is possible with helical CT technology to scan the entire chest with excellent aortic opacification during this 70-second delay, beginning the chest CT scan at 25 seconds and the abdomen CT scan at 70 seconds after the start of the injection. The availability of helical scanning and the introduction of this combined scan protocol has significantly decreased the need for more lengthy and costly angiographic procedures in those patients with suspected aortic injury. A separate article on aortic emergencies describes this technique in greater detail elsewhere in this issue. To take best advantage of the speed of helical CT in the emergency setting requires sufficient staffing of the CT scanning suite. Two CT technologists are routinely scheduled together, so that one can set up the patient and injector while the other schedules the patient and programs the scanner. A radiology resident or staff is present for each scan to confirm the choice of protocol and to provide immediate scan interpretation. In many abdominal trauma cases the CT scan protocol may need to be altered or augmented. For example, if the bladder is not full in a patient with hematuria, then a CT cystogram should be performed, or if bowel injury is suspected on the basis of a small amount of intraperitoneal free air but no bowel injury is seen, then a delayed scan with additional oral contrast material may be needed. Another important staffing consideration is the team to manage the patient; potentially unstable trauma patients require the presence of emergency department nurses or physicians to monitor vital signs and provide any emergency therapies required while the patient is in the scanner suite. The CT technologists performing the scan and the radiologists monitoring and interpreting the scan are generally too occupied with scanning to optimally manage a seriously injured patient. HEMOPERITONEUM

Traumatic hernoperitoneum may be detected at CT anywhere in the peritoneal cavity (see Fig. 1). Measuring the CT attenuation of intraperitoneal fluid has proved exceedingly useful in its characterization, because intraperitoneal fluid collections in trauma patients may not always represent blood. Although there is variation with individual scanners, hernoperitoneum usually measures greater than 30 HV. By comparison, water-dense fluids in a trauma patient, such as ascites, urine, bile, or intestinal contents, measure 0 to 5 or 10 HV. The recognition of water-dense fluids can be assisted by visual comparison with a fluid-filled structure, such as the gallbladder, or the soft tissue density of abdominal wall musculature; however, one may be misled by appearance only.

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CT, extravasation of IV contrast media may be shown flowing into and mixing with the surrounding hematoma of a lower CT attenuation (Figs. 3, 4, 5). In most cases the CT attenuation of extravasated contrast media measures higher than 100 H. Shanmuganathan et a133reported in a series of trauma patients that the density of extravasated contrast media can range from 85 to 370 H with a mean of 132 H. The CT demonstration of IV contrast media extravasation is now recognized as one of the most important signs in abdominal trauma CT. In nearly every case it indicates active bleeding and the need for emergency surgery or emergency angiographic embolization. SPLENIC TRAUMA Figure 2. Splenic fracture with laminated sentinel clot. A

deep laceration extending to the hilum divides the spleen into two segments (S).Laminations of thrombus (arrows) are shown extending around the laceration, attempting hernostasis. Remote hemoperitoneurn (H) is seen around the liver.

Hernoperitoneum may display a variety of densities at CT, the recognition of which is essential for most accurate assessment of an individual patient. Unclotted blood usually measures about 30 to 45 HV, clotted blood about 40 to 60 HV, and blood mixed with IV contrast material (hyperdense hematoma) about 80 to 300 HV.In attempting hemostasis, blood clots usually form around sites of bleeding and can be recognized at CT adjacent to injuries as higher density sentinel clots (Figs. 1and 2). These are contrasted with the lower density, more remote, unclotted blood seen elsewhere in the peritoneal cavity. One can use the helpful rule that the densest blood is usually closest to the site of injury. When a trauma patient is actively bleeding at

The spleen is the most frequently injured organ in patients who have suffered blunt abdominal trauma, accounting for about 40% of abdominal organ injuries. Spleen trauma is always a consideration in patients who have suffered blows to the left lower chest and left upper quadrant of the abdomen. Left lower rib fractures are suggestive of this injury, although an intact rib cage does not rule out spleen trauma. The spectrum of splenic injuries includes subcapsular hematomas, lacerations, contusions, fragmentation of the splenic parenchyma, and disruption of the hilar blood vessels. CT can accurately diagnose splenic trauma', 5; detect the extent of splenic injury; estimate the volume of hernoperitoneum; and identify associated injuries of the chest, diaphragm, left kidney, and other adjacent structures. Splenic trauma is best demonstrated at CT performed with IV contrast material, which opacifies the splenic parenchyma to reveal lacerations, hematomas, and other injuries. Splenic lacerations appear at CT as linear or curved low-attenuation zones (blood attenua-

Figure 3. Large hepatic laceration with hemoperitoneum and active arterial bleeding. A deep liver laceration involving the right lobe of liver, with extension through the liver capsule and hemoperitoneum (H) is seen. The arrows point to extravasated intravenous contrast material, indicating active arterial bleeding on both the initial scan (A) and a delayed scan (B) obtained 5 minutes later.

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Figure 4. Active arterial bleeding after a liver biopsy. This patient experienced right upper quadrant pain and fainting 12 hours after a percutaneous liver biopsy. A, CT showed active bleeding at the biopsy site (arrow) and hemoperitoneum (H). L?, Slightly lower scan shows active bleeding (arrow) into the peritoneal cavity and hemoperitoneum (H). Also shown at this level is a denser collection of blood in the subcapsular space (S), which slightly indents the right margin of the liver.

Figure 5. Gallbladder avulsion showing value of coronal and sagittal reformations. A, CT scan at level of gallbladder fossa shows hemoperitoneum and hemorrhage in the gallbladder fossa; the gallbladder is not visualized at this level. A site of active bleeding (arrow) is seen within the gallbladder fossa. B, Slightly lower CT scan showing the gallbladder (arrow) at a lower than expected level. The cystic artery must be patent as the gallbladder wall is opacified. C and 0,Coronal and sagittal reformations clearly show that the gallbladder (white arrows) has been avulsed from the gallbladder fossa (black arrows). Hemorrhage (H) is seen around the liver and in the gallbladder fossa.

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tion, 35 to 45 H) traversing the splenic parenchyma (see Figs. 1 and 2). When lacerations extend through the splenic capsule hemoperitoneum results; if the capsule is intact, a subcapsular hematoma or intrasplenic hematoma may be demonstrated. Subcapsular hematomas appear as crescentic regions of low attenuation that compress the adjacent contrast-opacified splenic parenchyma. Intrasplenic hematomas appear as rounded low-attenuation zones within the splenic parenchyma; these may be homogeneous or inhomogeneous. A shattered spleen shows multiple crossing lacerations at CT. A splenic injury extending through the capsule is often seen surrounded by hemoperitoneum in the perisplenic space; actual laminated thrombus may be demonstrated (see Fig. 2), which has formed to induce hemostasis. Attempts have been made by several investigators to grade the CT appearance of splenic injuries in order to predict those patients whose splenic injuries can be treated conservatively and differentiate them from those who require emergency surgery.', 13,20 Most CT classification systems are based upon anatomic criteria, such as number and size of parenchymal lacerations, rather than physiologic criteria, such as rate of and continuation of bleeding. They have met with only variable success. Young patients (under 20 years of age) may do well with very severe degrees of injury, whereas older patients (over 55 years) may require surgery for the lowest grade of injury. Furthermore, the CT findings often inconsistently correlate with operative findings: CT frequently underestimates the actual extent of splenic injury, as compared with the findings at surgery. Although the CT grading of splenic trauma is not predictive of the need for

Figure 0: Multiple liver lacerations without capsular extent. Three hepatic lacerations (black arrows) are shown in a patient who suffered blunt abdominal trauma. The lacerations appear to join at the porta hepatis in a "bearclaw" configuration. The lacerations have irregular margins and are filled with blood density material; compare with the smooth margins of the normal fissure for the ligamentum teres (white arrow) which is filled with lessdense fat.

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surgical management, the CT grade of injury does relate to the rate of healing2 The lowest grades of injury typically heal within 4 months, whereas the higher grades of injury may take up to 6 to 11 months to heal. HEPATIC TRAUMA

Nearly 20% of organ injuries with blunt abdominal trauma involve the liver.31 The spectrum of hepatic injuries includes laceration, subcapsular hematoma, parenchymal contusion, hepatic venous injury, hepatic arterial injury, or disruption of the hepatic biliary system. Blunt trauma usually produces parenchymal lacerations, which may or may not extend through the liver capsule (Figs. 3, 6-9); those that do extend through the capsule are usually associated with hemoperitoneum. Intraperitoneal bleeding with liver injuries may be marked due to the dual blood supply to the liver and decreased ability for hemostasis due to constriction of hepatic veins.31Subcapsular hematomas of the liver more commonly result from penetrating trauma. Active bleeding may be demonstrated after blunt (see Fig. 3) or penetrating (see Fig. 4) trauma. Liver lacerations more frequently involve the posterior segment of the right lobe (Figs. 3, 7, 8) and this may relate to the proximity of this portion of the liver to the rib cage and spinal column. Injuries of the left lobe are frequently in a vertical orientation and result from anterior compression of the left lobe of the liver against the spine (see Fig. 9). These may be associated with other compression injuries of the pancreas, small bowel, duodenum, and transverse colon. Lacerations may involve important hepatic vascular structures, such as large hepatic vein and portal vein branches. These may be suggested by the proximity of lacerations to these structures or the presence of signs of active bleeding on the CT scan. The bare area of the liver is an irregular, rhomboid-shaped zone over the posterior surface of the liver that is devoid of peritoneal covering. Liver lacerations extending to the liver surface at the bare area result in extraperitoneal bleeding into the retroperitoneum, rather than peritoneal bleeding. The classic peritoneal findings on physical examination may be absent and peritoneal lavage may be negative. A CT scan shows the liver laceration, usually involving the posterior segment of the right hepatic lobe combined with retroperitoneal hemorrhage. Hemorrhage is often seen in the anterior right perirenal space, around the right kidney (see Fig. 7), right adrenal gland, or inferior vena cava. In a series of 155 patients whose CT scans showed liver trauma reported by Patten et a1,% in 25 (16%) the capsular extent was limited to the bare area. In 22 (88%) of the 25, right-sided retroperitoneal hemorrhage was seen; 5 (20%) had intraperitoneal hemorrhage. The patients whose liver injuries were confined to the bare area did well on conservative management. Important to

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Figure 7. Hepatic laceration extending into the bare area. A, A horizontal laceration (large arrow) of the posterior right lobe of liver is shown extending into the bare area (small arrows), where hemorrhage can be identified. B, Hemorrhage is seen in the right perirenal space (arrows). No renal or other retroperitoneal injury is present.

remember is that the CT scan of a liver laceration involving the bare area may suggest a retroperitoneal injury when none is present. Careful CT assessment of the retroperitoneal organs helps resolve this concern. Zones of low CT attenuation shown in the liver paralleling the course of the portal vein and its branches (periportal tracking) have been described in a variety of clinical conditions including hepatitis, liver transplantation, cardiac failure, cardiac tamponade, malignant tumors of the liver, and hepatic trauma. In nontraumatic conditions, periportal tracking has been attributed to lymphatic obstruction and dilatation of the lymph channels. With liver trauma the low-attenuation zones had been thought to represent dissection of blood along the course of the portal veins. Although periportal tracking is commonly seen on abdomi-

nal CT scans with liver trauma, it has been observed on the CT scans of many trauma patients without liver injury. In these cases it is considered to represent periportal lymphedema or a consequence of elevated central venous pressure caused by the rapid expansion of intravascular fluid volume during intravenous resuscitation. In reports by Patrick et alZ7and Shanmuganathan et aPZmultiple patients with blunt abdominal trauma were cited whose CT scans showed periportal tracking without evidence of liver injury. On the other hand, the authors referred to patients with liver injury whose CT scans also showed no evidence of periportal tracking. With liver trauma, periportal tracking is more frequently focal and associated with an adjacent liver laceration or hematoma. In nontraumatic cases, periportal tracking diffusely involves the entire liver.

Figure 8. Right package of blunt abdominal trauma. This patient suffered a blow to the right trunk. Chest film showed right rib fractures and a right pneumothorax. A, Lacerations (arrow) are shown in the posterior right lobe of liver. B, Slightly lower scan also shows a right renal laceration. Hemorrhage is seen in the right perirenal space (white H) and peritoneal cavity (black H).

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Figure 9. Midline package of blunt abdominal trauma. This patient suffered a blow to the midline upper abdomen from a steering wheel in a deceleration accident. The pancreas and left lobe of liver were compressed against the spine. A, White arrow indicates a vertical laceration of the left lobe of liver associated with hemoperitoneurn (H).The black arrow indicates the site of pancreatic fracture. The body and tail of the pancreas (P) are completely separated from the pancreatic head. B, Scan at the level of the pancreatic head (P). Hemorrhage (H) from the pancreatic fracture can be seen in the right anterior pararenal space. (From Hochberg E, Novelline RA, Rhea JT Computed tomographic diagnosis of a “midlinepackage” of abdominal trauma: Two illustrative cases. Emerg Radio1 2:319-322, 1995; with permission.)

GALLBLADDER TRAUMA

Trauma to the gallbladder is rare and occurs with blunt trauma when the gallbladder is full or distended. Many cases of gallbladder trauma have associated injuries of the liver and duodenum. The spectrum of injuries includes contusion of the gallbladder wall, gallbladder rupture, and gallbladder avulsion. Traumatic perforation may produce fluid collections of water density on CT scans representing bile within the peritoneal cavity, although blood density fluid may be identified from associated hemorrhage. Alternatively, because the gallbladder is extraperitoneal, bile leak from a ruptured gallbladder may be contained within the extraperitoneal gallbladder fossa. In these cases the peritoneal signs of bile leak may be absent, peritoneal lavage is negative, and the CT scan shows pericholecystic fluid.% The CT findings of gallbladder injury include pericholecystic fluid (the most common sign); blurring of the gallbladder contour; focal thickening or discontinuity of the gallbladder wall; or the finding of a mucosal flap within the lumen. Hemorrhage may be seen within the gallbladder lumen and hemorrhage may be seen tracking in the adjacent periportal zones of the liver.35A ruptured gallbladder may be collapsed at CT. Gallbladder avulsion may be associated with significant bleeding from lacerations of the cystic artery or its branches (see Fig. 5). Helical CT is particularly helpful in demonstrating gallbladder avulsion out of its fossa on coronal and sagittal reformations. BOWEL AND MESENTERIC TRAUMA

Bowel and mesenteric injuries are found in approximately 5% of all patients undergoing surgery

after blunt abdominal trauma.30Their diagnosis is critical in that life-threatening hemorrhage may result from disrupted mesenteric blood vessels and peritonitis may result from bowel rupture. CT has been shown to be accurate in the detection of bowel and mesenteric injuries.z2Although extraluminal air in the peritoneal cavity or retroperitoneum has been considered a specific sign for bowel rupture (Figs. 10-13), it is less common than extraluminal fluid and may be seen in trauma patients when no bowel rupture is present. The most specific CT sign of bowel rupture is extravasated oral

Figure 10. Gastric rupture with intraperitoneal air and oral contrast material. This 3-year-old child suffered blunt trauma with a ruptured stomach in an automobile accident. A large volume of free air (A) and extravasated oral contrast material (C) can be identified in the peritoneal cavity. The more dependent contrast material outlines the right lobe of liver.

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Figure 11. Ruptured duodenum with free air in the retro-

peritoneum. Multiple collections of extraluminal free air (arrows) can be seen in the retroperitoneum, adjacent to the duodenum (D) and surrounding the right kidney. This patient suffered a traumatic rupture of the second portion of the duodenum. contrast material (Figs. 10, 12, 14). Bowel wall thickening, bowel wall discontinuity, and mesenteric hematoma have also been recognized as excellent signs of bowel i n j ~ r y Other .~ CT signs of bowel injury include abnormal bowel thickening and bowel wall enhancement with IV contrast material (see Fig. 14). In addition to mesenteric hematoma, mesenteric injuries at CT may show evidence of mesenteric infiltration and interloop fluid (fluid in the leaves of the small bowel mesentery).15 Interloop fluid (see Fig. 14) may be seen with both bowel and mesenteric injury. Gastric rupture (see Fig. 10) often occurs with blunt trauma after a recent meal with a full stomach. It occurs more frequently in children than adults. The anterior wall of the stomach is the

Figure 12. Duodenum rupture with extraluminal air and oral contrast material. This patient suffered a rupture of the fourth portion of the duodenum near the ligament of Treitz. Note the extravasated air (A) and oral contrast material (arrows) on this delayed CT scan. The second portion of the duodenum (D) is normal.

most common site of rupture, followed by the greater curvature, the lesser curvature, and least frequently the posterior wall. Trauma to the left side has occurred in many patients and the most commonly associated injury involves the spleen.z2 Grossly bloody aspirate may be obtained through the nasogastric tube. Pneumoperitoneum as well as extravasated oral contrast material and gastric contents may be seen at CT (see Fig. 10). Blunt trauma to the duodenum usually involves its second or third portions resulting from compression of the horizontal segment of the duodenum against the spine. Differentiating duodenal perforation from duodenal hematoma is important clinically because perforation requires emergency surgery, whereas hematoma can generally be treated conservatively. With duodenal rupture extraluminal gas or oral contrast material is seen in the right anterior pararenal space of the retroperitoneum, often with spread to other retroperitoneal compartments (see Fig. 11).When perforation occurs near the ligament of Trietz, extravasated oral contrast material or gas may be seen within the peritoneal space (see Fig. 12).In patients with duodenal hematoma the CT scan may show a mass (hematoma) within the duodenal wall, compressing the duodenal lumen (Fig. 15). The clinical presentation of duodenal hematoma may also be helpful because these patients present with vomiting from obstruction of the duodenal lumen. It should be noted, however, that thickening of the duodenal wall and blood-density fluid may be seen within the anterior pararenal space in both conditions. Because duodenal injuries have an increased likelihood of associated pancreatic injuries, because the two organs are in such close proximity to one another, the pancreas always must be evaluated carefully. The jejunum and ileum are commonly injured at or near a point of fixation, such as the ligament of Treitz or the ileocecal valve. With rupture one may see extravasation of oral contrast material, bowel wall thickening, bowel wall hyperemia, and triangular-shaped collections of blood in the interloop space between fat-density leaves of mesentery (see Fig. 14). Rupture occurs most frequently along the antimesenteric border. Colonic injuries frequently result from compression injuries of the upper abdomen. The most frequent sites of injury are the transverse colon, sigmoid colon, and the cecum. Injuries to the transverse colon may cause intramural hematomas and serosal tears without spillage of colon contents. Colonic lacerations, however, can occur as well as colonic mesentery and vascular injuries, which may interrupt the blood supply to a colonic segment. Traumatic ventral or lateral abdominal wall herniations may also be associated with colonic injuries (see Fig. 13).With perforating injuries of the flank and back, a triple-contrast abdominal CT scan should be performed utilizing rectal contrast to opacify the large bowel. Stab wounds of the retroperitoneum in stable patients without co-

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Figure 13. Rupture of left abdominal wall with rupture of sigmoid colon. A and 6,A severe blunt blow to the abdomen produced a rupture of the left abdominal wall with traumatic herniation of the sigmoid colon (S). Extraluminal gas (arrows), especially adjacent to the herniated sigmoid, indicates that bowel rupture has occurred.

Figure 14. Ruptured jejunum with extravasated oral contrast material and interloop hemorrhage. A, Multiple signs of bowel injury are shown in this patient who suffered a jejunal injury. Note the thickened and hyperemic walls of the injured jejunal loop (arrows). Extravasatedoral contrast material (C) indicates that rupture has occurred. 6,The injured loop shown at a slightly lower level. The wall and valvulae conniventes are thickened and hyperemic. C,Below the injured loop, a triangular opacity of blood density can be identified, representing hemorrhage (H) between fat-density leaves of mesentery. (From Hochberg E, Novelline RA, Rhea JT: Computed tomographic diagnosis of a “midline package” of abdominal trauma: Two illustrative cases. Emerg Radio1 2:319-322, 1995; with permission.)

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Figure 15. Duodenal hematoma. A large hematoma (arrows) is seen in the third portion of the duodenum, which was compressed against the spine. The patient suffered a midline blow to the anterior abdomen.

lonic perforation (Fig. 16) can be treated conservatively, whereas when colonic perforation is demonstrated (Fig. 16) the patient requires surgical intervention. The presence of extraluminal air in the peritoneal cavity of abdominal trauma patients has traditionally been attributed to bowel rupture, and the radiologic demonstration of free air has been an indication for emergency laparotomy. It has been increasingly recognized, however, that CT shows extraluminal free air in many blunt trauma patients who do not have bowel rupture. Kane et all2 reported that in a series of 18 abdominal CT scans for blunt trauma, only 4 (22%) proved to have bowel rupture. Hamilton et a19 reported that in a series of 118 consecutive abdominal CT scans for blunt trauma, free extraluminal air was seen in 7 patients and none had bowel perforation. In both of these series nearly all the patients with pneumoperitoneum also had chest trauma with a pneumothorax or chest tube, or were on mechanical ventilation. It is postulated that the pneumoperito-

neum shown by CT in patients without bowel rupture represents dissection of air from the chest into the peritoneal cavity. Previous reports have documented pneumoperitoneum on plain films following pneumothorax, mechanical ventilation, cardiopulmonary resuscitation, and tracheostomy. The other proposed mechanism for pneumoperitoneum is that it arises from intestinal microperforations that rapidly seal off after injury without any clinical sequellae. Oral contrast material is exceedingly important for the accurate CT diagnosis of bowel injuries. With oral contrast one can identify bowel rupture at sites where contrast extravasation is seen, better identify bowel wall thickening, and differentiate fluid-filled loops of bowel from free fluid within the peritoneal cavity. Bowel contrast is also helpful in the diagnosis of pancreatic trauma; peripancreatic edema or hemorrhage, both important signs of pancreatic trauma, can be mimicked by unopacified fluid-filled loops of bowel. At many trauma centers, however, oral contrast material is not routinely utilized because opponents of oral contrast have raised concerns regarding potential aspiration, especially in obtunded patients or those about to undergo general anesthesia. This should not be a problem, however, with patients whose airways are protected by endotracheal tubes and in those in whom the oral contrast is administered by a nasogastric tube and removed from the stomach by nasogastric tube suction at the completion of the examination. Opponents of oral contrast have also warned that extra time is lost waiting for the passage of oral contrast. Waiting is not necessary, however, because most bowel injuries involve the duodenum and proximal jejunum; these segments of bowel are routinely opacified with oral contrast material even when administered immediately prior to the CT scan. The colon can be opacified quickly with rectal contrast material. Most trauma radiologists have observed that the routine use of oral contrast material seems quite safe. In a report by Federle et als of 506

Figure 16. Value of rectal contrast material with flank stab wounds. A, Negative examination in a patient stabbed in the right flank. Hemorrhage (arrow) is seen in the right retroperitoneum; however the ascending colon is intact. B, Positive examination in a patient with a left stab wound. Extravasated rectal contrast material (arrow) indicates that perforation of the descending colon (D) has occurred.

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abdominal trauma CT scans performed with oral and IV contrast material, no patients had aspiration of contrast medium or gastric contents attributable to the performance of the CT scan. There are two postulated mechanisms for mesenteric injury with blunt abdominal trauma. The mesentery can be injured, along with the intestines, by crushing forces against the spine. In addition, tangential shearing forces may tear them from points of fixation.23Both mechanisms produce mesenteric lacerations that may cause severe bleeding and hypovolemia. The CT scan may show hematoma within the mesentery with hemoperitoneum (Fig. 17). Signs of IV contrast material extravasation may identify sites of active bleeding. Also, a laceration can interrupt the blood supply to a segment of bowel causing bowel ischemia, which may lead to bowel necrosis and peritonitis if severe. At CT devascularized loops of bowel show hyperemia if the arterial supply to the bowel remains intact but the draining mesenteric veins are interrupted (Fig. 18). A small mesenteric laceration may remain clinically silent initially, but later the patient may present with a posttraumatic ischemic bowel stricture. Unrepaired mesenteric lacerations may also present a risk for later internal herniation. With minor mesenteric injuries the CT scan may show only a streaking or hazy mesentery, representing minimal mesenteric infiltration with hemorrhage or edema. THE INFERIOR VENA CAVA IN ABDOMINAL TRAUMA

When performing abdominal trauma CT it is valuable to note the shape and caliber of the inferior vena cava as a useful indicator of the patient's intravascular fluid volume. When the inferior vena cava is oval and plump, it usually implies that fluid replacement therapy has been sufficient for

Figure 17. Mesenteric injury. Arrow indicates a spherical hernatorna within the mesentery, displacing adjacent

loops of bowel. Stranding is seen next to the hernatorna. The high density center indicates active bleeding that was confirmed at surgery.

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the patient's needs. When the inferior vena cava is thin and flat on multiple CT slices, however, it generally indicates insufficient fluid management and impending shock. The CT recognition of a flat inferior vena cava can show evidence for hypovolemia before this condition is clinically manifested by hypotension and tachycardia. This observation is particularly helpful in children and young adults who can maintain nearly normal blood pressure and pulse even when severely volume depleted due to their ability for massive vasoconstriction. Inferior vena cava injury after blunt trauma is rare but may occur. The CT findings include retroperitoneal hemorrhage with the inferior vena cava at its epicenter, irregularity of the caval contour, and extravasation of intravenous contrast material from the site of caval injury.26 PANCREATIC TRAUMA

Pancreatic injury is uncommon with blunt abdominal trauma, and when it occurs it is usually associated with injuries of other organs, such as the duodenum and liver (see Fig. 9). The usual mechanism of injury is an anterior midline blow causing traumatic compression of the pancreas against the vertebral column. The compressive forces may produce a pancreatic contusion, hematoma, laceration, or fracture. In motor vehicle accidents, anterior compression is often caused by the steering wheel or seatbelts. Pancreatic injury is more common in children and young adults. The decreased incidence in older adults may be associated with a thicker envelope of fat tissues surrounding the pancreas, which may serve as a protective cushion. Lacerations and fractures that interrupt the pancreatic duct require emergency surgical intervention with repair or resection of the pancreas distal to the site of injury. If these injuries are overlooked, or their diagnosis delayed, the consequences may be recurrent distal pancreatitis, pancreatic pseudocyst formation, or pancreatic abscess.14 At CT pancreatic lacerations and fractures appear as interruptions in the pancreatic parenchyma with associated fluid, representing hemorrhage, in the anterior pararenal space (Figs. 19 and 20). Helical technology has improved the CT diagnosis of pancreatic lacerations and fractures by providing improved IV contrast enhancement of the pancreatic parenchyma at the time of scanning. Subtle pancreatic injuries, such as contusion and hematoma, may appear as pancreatic enlargement, pancreatic masses, or irregularity in the pancreatic contour, which may be associated with peripancreatic fluid collections. More remote signs of pancreatic trauma include fluid around the superior mesenteric artery, fluid in the transverse mesocolon or lesser sac, fluid between the pancreas and the splenic vein, and thickening of the left anterior pararenal fascia.35

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Figure 18. BoweVmesenteric injury and Chance fracture. This young woman suffered an anterior abdominal injury in a deceleration automobile accident; she was wearing a lap-type seat belt. The duodenum and several loops of jejunum were injured, and a laceration of the superior mesenteric vein was found that was actively bleeding. A, CT scan shows a thick-walled hyperemic duodenum (D), with adjacent right anterior pararenal hemorrhage. The jejunum (straight arrow) is also injured with hyperemic, thickened walls. The curved arrow points toward extravasated intravenous contrast material in the peritoneal cavity, indicating active bleeding. B, Slightly lower scan shows the injured jejunum (shorf arrows) and hernoperitoneum (H), and an unexpectedfracture of the L l vertebra (long arrow.) C, Targeted, bone window scan of L1 shows fractures of the body and posterior elements. 0, Sagittal reformation of the L1 CT scan through the left facets joints shows the horizontal splitting (arrow) of the posterior elements through the pars interarticularis,characteristic of Chance fracture.

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Figure 19. Pancreatic fracture. This patient suffered a blow to the anterior abdomen that fractured the pancreas against the spine. A, Arrow indicates fracture line. The body and tail of the pancreas (P) are separated from the pancreatic head. Hemorrhage (H) is seen in the right anterior pararenal space. B, Slightly lower scan shows hemorrhage (H) in the fracture line between the pancreatic head (PH) and pancreatic body (PB).

To determine the integrity of the pancreatic duct with pancreatic trauma may require additional examination with endoscopic retrograde cholangiopancreatography or MR imaging. Occasionally, the pancreas may appear normal at CT when lacerations or fractures are present, because the pancreas may return to its original contour after these injuries have occurred.39Consequently, endoscopic retrograde cholangiopancreatographyor MR imaging may be useful to rule out pancreatic trauma when only peripancreatic fluid collections are seen4 A follow-up, delayed CT scan may also be helpful to show more specific signs of pancreatic injury not present on the initial scan. RENAL TRAUMA

Kidney injuries are common with blunt abdominal trauma and they are frequently associated with

injuries of other organs (Figs. 8 and 21). The spectrum of injuries includes renal contusion, renal cortical laceration, fractured kidney, shattered kidney, subcapsular hematoma, traumatic renal artery occlusion, and traumatic renal vein thrombosis. Fortunately, 95% of kidney injuries represent cortical lacerations, contusions, and other conditions that can be treated conservatively without surgical intervention.18 Today even major cortical lacerations with urine leak in stable patients are managed conservatively, the patient treated nonsurgically with placement of a ureteral stent. At CT contusions appear as focal, patchy parenchymal zones of decreased IV contrast enhancement, or they may appear as a striated nephrogram similar to the nephrogram of pyelonephritis. Lacerations appear as irregular, linear, low-attenuation zones that extend from the periphery of the renal parenchyma toward the intrarenal collecting

Figure 20. Pancreatic laceration. A and B, This 12-year-old child fell out of a tree, suffering an anterior blow to the left abdomen. The pancreatic tail (P) was compressed against the spine, producing a laceration (arrows). Hemorrhage (H) is seen in the left anterior pararenal space around the pancreatic tail.

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Figure 21. Left package of blunt abdominal trauma. This patient suffered a blow to the left trunk. The chest film showed left lung air-space opacities representing contusion. A, CT scan shows a fracture (arrow) of the spleen and lack of perfusion of the upper pole of the left kidney (K). Hemorrhage can be identified in the left perirenal space and perisplenic portion of the peritoneal cavity. 6, Slightly lower scan confirms segmental renal artery occlusion. Most of the left kidney is ischemic (K) because of segmental renal artery occlusion. The segmental branches to the posterior parenchyma (arrow) remain intact.

system. Most lacerations are associated with hemorrhage in the surrounding perirenal space. Minor lacerations (Fig. 22) involve the cortex only, whereas major lacerations (Fig. 23) extend into the intrarenal collecting system and at CT show extravasation of urine and excreted contrast material into the renal parenchyma and perirenal space. Delayed CT images at 2 to 10 minutes may be required to demonstrate the extravasation of excreted contrast material when lacerations are associated with urine leak. The leakage of urine and excreted contrast material from the intrarenal collecting system with a major renal laceration may be confused with the arterial extravasation of IV contrast material shown with active renal bleeding. In differentiating these two possibilities it should be noted that the extravasated contrast material

with active bleeding is usually surrounded by less dense blood clot and may not be contiguous with the urinary collecting system. Also, active renal arterial bleeding is seen much earlier (40 to 80 seconds) than the extravasation of excreted contrast material from the renal collecting systems. Renal fracture is diagnosed when lacerations are shown connecting the medial and lateral cortical surfaces of the kidney through its hilum. A shattered kidney shows multiple lacerations traversing the kidney and fragmenting it into several components. Extensive leak of urine and excreted contrast material are generally present with renal fracture and shattered kidney. Subcapsular hematomas appear at CT as crescent-shaped zones of low attenuation that extend along the surface of the kidney beneath the renal capsule. They compress and

Figure 22. Small cortical laceration of right kidney. A, Black arrow indicates a triangular, lowattenuation zone representing a small cortical laceration containing hemorrhage associated with perirenal hemorrhage (white arrows). There is no extension into the intrarenal collecting system. 6, The surrounding rim of hemorrhage in the perirenal space (arrows) is better shown on a slightly lower scan.

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Figure 23. Large left kidney lacerations with extension into the intrarenal collecting system. A, Scan taken through mid-left kidney shows a ring of perirenal hemorrhage (arrows) around the left kidney, adjacent to the pancreas (P) and spleen (S). Hemorrhage (H) can also be seen anterior to the pancreas, in the left anterior pararenal space. B, Slightly lower scan shows deep lacerations of the left renal parenchyma, with left perirenal hemorrhage and hemorrhage (H) in the leff anterior pararenal space. C,Slightly lower scan shows extravasation of excreted intravenous contrast material (arrow) into the left perirenal space. 0,Scan just below the level of the kidneys shows hemorrhage in the inferior extension of the left perirenal and left anterior pararenal spaces.

distort the expected normal contour of the opacified renal parenchyma, and there is absence of hemorrhage in the perirenal space when the capsule remains intact. Traumatic renal artery occlusion usually results from deceleration injuries that stretch the proximal renal arteries producing intimal tears that thrombose, progressing on to complete renal artery occlusion. The findings at CT include absence of the parenchymal nephrogram on the affected side. A cortical rim sign of peripheral renal enhancement may be seen; renal capsular arteries that arise very early from the main renal artery, proximal to the site of occlusion, may supply blood and IV contrast material to the very peripheral renal cortex (Fig. 24). Helical CT may also show the renal artery occlusion itself.25Segmental infarction (see Fig. 21) may occur as a result of traumatic occlusion of one or several segmental arteries. In a review of 32 cases by Lewis et all7 a distinct upper pole predilection was noted. None of 30 surviving patients experienced delayed hemorrhage or deterioration

of renal function, indicating that segmental infarction can be managed nonoperatively. Traumatic renal vein thrombosis appears as a persistent nephrogram on delayed scans, and the thrombus may be seen directly within the renal vein at CT.35 COMBINATION INJURIES

With blunt abdominal trauma, combination injuries are common and they are often related to the mechanism of injury. An awareness of these combinations and a knowledge of the patient’s trauma history can be particularly valuable in the performance and interpretation of abdominal trauma CT. The radiologist can be certain that the CT protocols are custom-tailored to optimally show all of the suspected injuries, or rule them out. In addition, the CT scan can be more carefully and systematically scrutinized so as not to miss additional injuries after the first or most prominent injury has been detected.

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fort. In an accident these newer seat belts then act as a lap-type seat belt. Bladder injuries may also occur in these patients. On physical examination one may see a linear ecchymosis or seat belt bum (hematoma) across the patient’s abdomen. When this physical sign is present a CT scan and careful search should be made for injuries of the bowel, mesentery, spine, and bladder. Thin-collimationCT slices of the spine with sagittal and coronal reformation may be required to demonstrate the Chance fracture (see Fig. 18). A final combination is the association of bladder injury with pelvic fractures; this is described in the next section. BLADDER TRAUMA Figure 24. Traumatic occlusion of the right renal artery. This patient experienced sudden onset of right flank pain after deceleration trauma. CT scan shows lack of opacification of the right kidney (K), indicating traumatic occlusion of the right renal artery. Compare with the normal left kidney. The faint rim of contrast opacification (arrow) rewesents limited blood SUPPIY to the kidney periphew through patent cortical arteries ;hat originated -proximalto the site of occlusion.

Combination injuries of the upper abdomen may be categorized into three different groups, or packages, based on the site of the abdominal blow, be it the right side, left side, or midline.1° The right package (see Fig. 8) consists of some combination of a right lung contusion or laceration; right rib fractures; a right-sided pneumothorax or hemothorax; combined with right-sided abdominal visceral injuries of the liver, right kidney, right adrenal gland, or right hemidiaphragm. The left package (see Fig. 21) is similar but substitutes splenic injury for liver injury and may include the pancreas. The midline package (see Fig. 9) due to a direct blow to the midline can include injuries to the left lobe of liver; the sternum; lower ribs; heart; pericardium; transverse colon; small bowel; mesentery; and retroperitoneally the pancreas, duodenum, aorta, and inferior vena cava. In trauma centers the midline package has been noted to be a common abdominal injury. Patients may suffer a midline package when driving a motor vehicle without restraints and are struck by the steering wheel in a deceleration accident; or they may receive a blow to the midabdomen in an assault or sports injury. Again, the benefit of recognizing these packages is an awareness of the spectrum of injuries that may be present. Another combination injury seen in motor vehicle accidents is the association of a small bowel or mesenteric injury combined with a Chance-type fracture of the lumbar spine (See Fig. 18). Although this injury has been noted in the past primarily in patients wearing lap-type seat belts at the time of injury, they occur today in patients with over-the-shoulder type seat belts who choose to wear them under their arm for personal com-

Injury of the urinary bladder is a frequent and Of pelvic trauma* Three important different types of injury are recognized: (1)bladder contusion, (2) extraperitoneal bladder rupture, and (3) intraperitoneal bladder rupture. Contusion represents an intramural iniurv with hematoma within the bladder wall, wkch may be readily identified at CT; there is no extravasation of urine or extravasated IV contrast material. Contusion is managed conservatively. Extraperitoneal rupture (80% to 90% of cases) is more common than intraperitoneal rupture (15% to 20% of cases) and a combination of both (0% to 12% of cases) may occur. Differentiating intraperitoneal and extraperitoneal bladder rupture is of clinical importance because extraperitoneal rupture is usually managed conservatively, whereas intraperitoneal rupture requires emergency surgical intervention. Intraperitoneal bladder rupture occurs when the bladder is full at the time of lower abdominal trauma. Usually, the laceration involves the bladder dome. Extravasated urine and contrast material flow into the peritoneal cavity where these fluids can be seen at CT surrounding loops of bowel and pooling into peritoneal recesses. Extraperitoneal bladder rupture is commonly associated with pelvic fractures and may result from shearing forces at the bladder base or from direct injury to the anterior bladder wall by pelvic fracture fragments. Urine and excreted contrast material flow into the adjacent perivesical soft tissues and can extend into the perineum, scrotum, thighs, as well as superiorly within the anterior abdominal wall. It is important to recognize extravasation into the anterior prevesical space, a potential space between the transversalis fascia and parietal peritoneum. Extravasation of opacified urine in this potential space can extend cephalad within the abdominal wall, and can surround the anterior and lateral portions of the peritoneal cavity mimicking intraperitoneal rupture at CT. Extravasated urine can also flow into the retrorectal presacral space, showing at CT as contrast between the rectum and sacrum. Figure 25 illustrates the CT appearance of three different fluid collections occurring with bladder

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Figure 25. CT of bladder rupture: comparison of three different patients. A, lntraperitoneal bladder rupture. CT scan shows water-dense urine (U) in the peritoneal cavity. B, lntraperitoneal bladder rupture. Delayed CT scan shows excreted intravenous contrast material (opacifying the urine) in the peritoneal cavity. C,Extraperitoneal bladder rupture. Contrast-opacified urine is seen in the abdominal wall within a potential space between the transversalis fascia and parietal peritoneum. Extraperitoneal rupture into the anterior prevesical space permitted extension into the abdominal wall and extraperitoneal pelvis.

rupture: (1) urine as a water-density fluid within the peritoneal cavity with intraperitoneal rupture, (2) urine opacified with excreted IV contrast material within the peritoneal cavity with intraperitoneal rupture, and (3) urine opacified with IV contrast material within the extraperitoneal soft tissues with extraperitoneal rupture. To diagnose bladder rupture accurately by CT the bladder must be filled, or bladder rupture may be overlooked resulting in false-negative diagnoses. Therefore, when the bladder is not adequately filled by antegrade means after routine clamping of the Foley catheter prior to CT, then a CT cystogram, as described previously, should be performed (Figs. 26 and 27). In a report by Rehm et alZ9comparing retrograde cystography with CT for suspected bladder rupture, 21 of 21 patients were correctly diagnosed with a retrograde cystogram; however, in the 7 patients studied by CT, all 7 CT scans failed to show evidence of bladder rupture. In this report, however, the CT scans were not performed with a full bladder. By comparison, Sivit et als

performed abdominal trauma CT scans in children with a maximally filled bladder by clamping of the Foley catheter and delaying for 5 minutes between the IV contrast injection and scanning of the pelvis. In their series of 1500 trauma CT scans there were 7 cases of bladder rupture all correctly diagnosed by CT. WHEN CT SHOWS INTRAPERITONEAL FLUID AND NO OTHER INJURIES

When the CT scan of a patient with blunt abdominal trauma shows only intraperitoneal fluid and no other signs of injury, it is a challenge for the radiologist and referring physician to plan optimum management. The fluid could reflect only a tiny self-limited injury of a parenchymal organ, not requiring any treatment whatsoever, or could represent a serious injury like bowel rupture requiring emergency laparotomy. Levine et all6 reported on a series of 60 patients with blunt abdom-

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Figure 26. Extraperitoneal bladder rupture with pelvic fractures: value of the CT cystogram. A, CT scan through the bladder performed using the routine abdominal trauma protocol. The patient's Foley catheter was clamped before the CT scan, and the bladder was opacified with excreted intravenous contrast material. No bladder rupture is seen. 6,Repeat CT scan a few minutes later after the bladder had been drained and then filled with bladder contrast material (CT cystogram) shows extensive contrast material extravasation from an extraperitoneal bladder rupture.

Figure 27. CT cystogram of intraperitoneal bladder rupture. A and B, No bladder rupture was seen on the initial CT scan using the routine abdominal trauma protocol, although water-dense fluid was seen in the peritoneal cavity that could represent urine, bile, or bowel contents. A CT cystogram showed gross extravasation (short arrows) of bladder contrast material into the peritoneal cavity from an intraperitoneal bladder rupture. Long arrow indicates site of rupture.

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inal trauma whose CT scans showed only intraperitoneal fluid; of note, 6 patients (10%) required laparotomy for bowel or mesenteric injury. When only intraperitoneal fluid is seen at CT it is first recommended that the CT attenuation of this fluid be measured, because it may not represent blood (35 to 45 H). Water-dense fluids (0 to 5 H) detected in a patient with blunt abdominal trauma may represent urinary bladder rupture, gallbladder rupture, chyloperitoneum, or pre-existing ascites. When blood density is confirmed the CT scan should be scrutinized for other signs of abdominal injury, such as a small hepatic or splenic laceration. Bowel injury is more likely if other signs are present, such as extraluminal air, oral contrast medium extravasation, thickened or hyperemic bowel wall, and triangular fluid collections between leaves of mesentery. Because bowel rupture is one of the important diagnoses to rule out, a repeat CT with additional oral or rectal contrast material to opacify completely the gastrointestinal tract may be very helpful. Peritoneal lavage after CT may be useful in determining the nature of water-dense fluids (bile versus urine versus bowel contents) and with blood-density fluid determining whether bowel contents are present to indicated bowel rupture. Another alternative is a repeat CT scan in 12 to 24 hours to search for signs of abdominal injury that were not present on the initial scan. CONCLUSION CT is the imaging procedure of choice for detecting or ruling out the presence of abdominal injuries in trauma patients. With helical CT, abdominal scanning can be performed more quickly, minimizing patient movement, respiratory motion, and vascular pulsation. Helical CT requires less time for the completion of CT scans permitting examination of those trauma patients who require a rapid imaging work-up, as well as permitting the performance of multiple serial CT scans on the same trauma patient. Scanning can be provided more reliably during peak IV contrast enhancement of abdominal organs for better detection of injuries. A single, combined chest-abdomen-pelvis CT scan with one IV contrast bolus is possible with helical CT also permitting evaluation of the chest when aortic trauma is suspected. Improved sagittal and coronal reformations are possible with helical technology. High diagnostic accuracy depends on the routine use of optimal helical CT protocols and knowledge of the CT findings of abdominal trauma. References 1. Ashlock SJ, Harris JH, Kawashima A. Computed tomography of splenic trauma. Emerg Radiol 5:192202,1998

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2. Benya EC, Bulas DI, Eichelberger MR, Sivit CJ: Splenic injury from blunt abdominal trauma in children: Followup evaluation with CT. Radiology 195:685488, 1995 3. Breen DJ, Janzen DL, Swirewich CV, Nagy AG: Blunt bowel and mesenteric injury: Diagnostic performance of CT signs. J Comput Assist Tomogr 21:706-712, 1997 4. Clements RH, Reisser J R Urgent endoscopic retrograde pancreatography in the stable trauma patient. Am Surg 62446-448, 1996 5. Federle MI': Computed tomography of blunt abdominal trauma. Radiol Clin North Am 21:461-474, 1983 6. Federle ME Courcoulas AP, Powell M, et al: Blunt splenic injury in adults: Clinical and CT criteria for management, with emphasis on active extravasation. Radiology 206:137-142, 1998 7. Federle MI', Goldberg HI, Kaiser JA, et al: Evaluation of abdominal trauma by computed tomography. Radiology 138637444,1981 8. Federle MP, Peitzman A, Krugh J: Use of oral contrast material in abdominal trauma CT scans: Is it dangerous? J Trauma 38:51-53, 1995 9. Hamilton P, Rizoli S, McLellan B: Significance of intra-abdominal extraluminal air detected by CT scan in blunt abdominal trauma. J Trauma 39:331-333, 1995 10. Hochberg E, Novelline RA, Rhea JT Computed tomographic diagnosis of a "midline package" of abdominal trauma: Two illustrative cases. Emerg Radiol 2:319-322, 1995 11. Israel RS, Mayberry JC, Primack SL Diaphragmatic rupture: Use of helical CT scanning with multiplanar reformations. AJR Am J Roentgenol 1671201-1203, 1996 12. Kane NM, Francis IR, Bumev RE, et al: Traumatic pneumoperitoneum: Implic&ions of computed tomography diagnosis. Invest Radiol 263574578, 1991 13 Kohn JS, Clark DE, Isler RJ, Pope C F Is computed tomographic grading of splenic injury useful in the nonsurgical management of blunt trauma? J Trauma 36385-389, 1994 14. Lane MJ, Mindelzun RE, Jeffrey RB: Diagnosis of pancreatic injury after blunt abdominal trauma. Semin Ultrasound CT MR 17177-182, 1996 15. Levine CD, Gonzales RN, Wachsberg RH, Ghanekar D CT findings in bowel and mesenteric injury. J Comput Assist Tomogr 21:974-979, 1997 16. Levine CD, Pate1 LJJ, Wachsberg RH, et al: CT in patients with blunt abdominal trauma: Clinical significance of intraperitoneal fluid detected on a scan with otherwise normal findings. AJR Am J Roentgenol 164:1381-1385, 1995 17. Lewis DR, Mirvis SE, Shanmuganathan K Segmental renal infarction after blunt abdominal trauma: Clinical significance and appropriate management. Emerg Radiol 3236240,1996 18. Matthews LA, Spirnack JP: The nonoperative approach to major blunt renal trauma. Semin Urol 13:77-82, 1995 19. Mirvis SE, Gens DR, Shanmuganathan K: Rupture of the bowel after blunt abdominal trauma: Diagnosis with CT. AJR Am J Roentgenol 159:1217-1221, 1992 20. Mirvis SE, Whitley NO, Gens DR: Blunt splenic trauma in adults: CT classification and correlation with prognosis and treatment. Radiology 171:33-39, 1989 21. Murray JG, Caoili E, Gruden JF, et al: Acute rupture of the diaphragm due to blunt trauma: Diagnostic

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sensitivity and specificity of CT. AJR Am J Roentgenol 166:10351039,1996 Nghiem HV, Jeffrey RB Jr, Mindelzun RE: CT of blunt trauma to the bowel and mesentery. AJR Am J Roentgenol 16053-58, 1993 Nolan BW, Gabram SGA, Schwartz RJ, Lenworth L M Mesenteric injury from blunt abdominal trauma. Am Surg 61:501-506, 1995 Novelline RA: Abdomen: Traumatic emergencies. In Harris JH, Harris WH, Novelline RA (eds): The Radiology of Emergency Medicine. Baltimore, Williams and Wilkins, 1993 Nunez D Jr, Becerra JL, Fuentes D, Pagson S Traumatic occlusion of the renal artery: Helical CT diagnosis. AJR Am J Roentgenol 167777-780, 1996 Parke CE, Stanely RJ, Berlin A: Inferior vena caval injury following blunt trauma: CT findings. J Comput Assist Tomogr 17154-157, 1993 Patrick LE, Ball TI, Atkinson GO, Winn KJ: Pediatric blunt abdominal trauma: Periportal tracking at CT. Radiology 183:689-691, 1992 Fatten RM, Spear RE', Vincent LM, et al: Traumatic laceration of the liver limited to the bare area: CT findings in 25 patients. AJR Am J Roentgenol 1601019-1022,1993 Rehm CG, Mure AJ, O'Malley KF, Ross S E Blunt traumatic bladder rupture: The role of retrograde cystogram. Ann Emerg Med 20:845-847, 1991 Rizzo MJ, Federle MP, Griffiths BG: Bowel and mesenteric injury following blunt abdominal trauma: Evaluation with CT. Radiology 173:143-148, 1989

31. Shanmuganathan K, Mirvis SE: CT evaluation of the liver with acute blunt trauma. Crit Rev Diagn Imaging 36:73-113, 1995 32. Shanmuganathan K, Mirvis SE, Amoroso M: Periportal low density on CT in patients with blunt trauma: Association with elevated venous pressure. AJR Am J Roentgenol 160279-283, 1993 33. Shanmuganathan K, Mirvis SE, Reaney SM: Pictorial review: CT appearances of contrast medium extravasations associated with injury sustained from blunt abdominal trauma. Clin Radio1 50:182-187, 1995 34. Shanmuganathan K, Mirvis SE, Sover E R Value of contrast-enhanced CT in detecting active hemorrhage in patients with blunt abdominal or pelvic trauma. AJR Am J Roentgenol 161:65-69, 1993 35. Shuman WP: CT of blunt abdominal trauma in adults. Radiology 205:297-306, 1997 36. Sivit CJ, Cutting JP, Eichelberger M A CT diagnosis of localization of rupture of the bladder in children with blunt abdominal trauma: Significance of contrast material extravasation in the pelvis. AJR Am J Roentgenol 164:1243-1246, 1995 37. Sivit CJ, Eichelberger MR, Taylor GA, et al: Blunt pancreatic trauma in children: CT diagnosis. AJR Am J Roentgenol 1581097-1100,1992 38. Wing VW, Federle MP, Morris JA, et al: The clinical impact of CT for blunt abdominal trauma. AJR Am J Roentgenol 1451191-1194, 1985 39. Wong YC, Wang LJ, Lin BC, et al: CT grading of pancreatic injuries: Prediction of ductal disruption and surgical correlation. J Comput Assist Tomogr 21:24&250, 1997

Address reprint requests to Robert A. Novelline, MD Department of Radiology Massachusetts General Hospital Boston, MA 02114