HELICAL CT OF ABDOMINAL TRAUMA

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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,7 CT has proved to be an excellent technique for identifying abdominal 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. Hemoperitoneum is easily identified by CT, as are injuries of the spleen, liver, gallbladder, kidneys, pancreas, bowel, mesentery, and diaphragm.6, 19, 21, 24, 31, 34, 36, 37

CT can differentiate intraperitonal hemorrhage from retroperitoneal hemorrhage and can differentiate hemoperitoneum 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,34 and bowel rupture as sites of oral contrast material extravasation.33 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%.38

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 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,11 traumatic avulsion of the gallbladder, and Chance fracture of the spine. Abdominal vascular trauma, such as traumatic renal artery occlusions,25 is well shown by the excellent vascular opacification provided by helical CT and three-dimensional reformations can provide excellent CT angiograms.

Section snippets

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

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

HEMOPERITONEUM

Traumatic hemoperitoneum 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, hemoperitoneum usually measures greater than 30 HV. By comparison, water-dense fluids in a trauma patient, such as ascites, urine, bile, or

SPLENIC TRAUMA

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,

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

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

BOWEL AND MESENTERIC TRAUMA

Bowel and mesenteric injuries are found in approximately 5% of all patients undergoing surgery after blunt abdominal trauma.30 Their 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.22 Although extraluminal air in the peritoneal cavity or retroperitoneum has been considered a specific sign for bowel rupture

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 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

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

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

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

BLADDER TRAUMA

Injury of the urinary bladder is a frequent and important complication of pelvic trauma. Three different types of injury are recognized: (1) bladder contusion, (2) extraperitoneal bladder rupture, and (3) intraperitoneal bladder rupture. Contusion represents an intramural injury with hematoma within the bladder wall, which 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

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 al16 reported on a series of 60 patients with blunt abdominal trauma

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

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

    *

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

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    Copyright © 1999 W. B. Saunders Company. Published by Elsevier Inc. All rights reserved.