V

Fig. 2. Complex interlobar hepatic transection (a, b) Axial MDCT images obtained during portal venous phase of scanning show a complex laceration (L) extending between the right and left hepatic lobes. Moderate hemoperitoneum (large arrow) is present. a Laceration extends to involve the retrohepatic inferior vena cava (arrowheads). b More inferiorly, laceration involves the main portal vein with blood tracking along the right and left portal branches (arrowheads)

Active hemorrhage, pseudoaneurysms and arteriovenous fistulas appear as areas of increased density relative to the normally enhancing hepatic parenchyma during the portal venous phase, reaching a similar attenuation value to an adjacent major artery, generally within 10 HU (i.e., CB). Traumatic injury may also result in segmental or complete hepatic devascularization.

Though CT grading of hepatic injury has thus far proven to be unreliable in predicting the need for surgery, CT has to be helpful in guiding management, and to have a positive correlation between grade of injury and the increased likelihood of failed nonoperative management. Vascular injuries, including post-traumatic pseudoaneurysm and arteriovenous fistula as well as active extravasation, are strong predictors of failure of nonoperative management. Injuries extending to the regions of the portal and hepatic veins are more likely to require surgery (Fig. 2). Injuries extending to involve the retrohepatic vena cava are particularly lethal, with a mortality rate of 90-100% due to the difficulty in exposing and controlling hemorrhage in this region. Some of these injuries may be further characterized and managed by angiography. At least one major trauma center in the U.S. performs an-giography on any of the following: 1) any grade III to V hepatic injury with extension into the region of a portal or hepatic vein, 2) any patient with active hemorrhage or vascular injury (i.e., a CB on portal venous phase) regardless of grade of injury, or 3) in any patient requiring multiple transfusions because of ongoing hepatic hemorrhage (Tab. 2).

Delayed complications may be seen in 10-25% of patients with hepatic injury. Hemorrhage, hepatic abscess and biloma are the most common complications. Delayed hemorrhage is seen in 1.7-5.9% of patients managed non-operatively. These patients are usually managed with an-giography or surgery. Hepatic abscess is seen in 0.6-4% of patients with hepatic injury, but more commonly in those patients managed nonoperatively. These patients are usually managed with percutaneous abscess drainage. Biloma is seen in less than 1% of patients with hepatic injury. Symptomatic patients are usually managed with percutaneous or endoscopic drainage. Asymptomatic pa-

Table 2. CT hepatic injury grading scale

CT Grade I Laceration(s) < 1 cm deep

Subcapsular hematoma < 1 cm diameter

CT Grade II Laceration(s) 1-3 cm deep

Subcapsular or central hematoma 1-3 cm diameter

CT Grade III Laceration(s) 3-10 cm deep

Subcapsular or central hematoma 3-10 cm diameter CT Grade IV Laceration(s) > 10 cm deep

Subcapsular or central hematoma > 10 cm diameter Lobar maceration or devascularization

CT Grade V Bilobar tissue maceration or devascularization

Modified from Mirvis et al. (1989)

tients are managed expectantly since bilomas usually resolve without intervention over the course of weeks to months.

Renal Injury

The kidneys are the third most commonly injured solid organ in the setting of blunt abdominal trauma, representing approximately 10% of all blunt injuries to the abdominal viscera in adults. However, the kidney is the most commonly injured solid organ in the setting of blunt abdominal trauma in children. During the 1950s and 60s, surgical exploration of the injured kidney often led to nephrectomy. As with splenic and hepatic injury, the improved ability to diagnose and monitor renal injuries by CT has facilitated the shift toward nonoperative management of these injuries among hemody-namically stable patients. Absence of hematuria can be reliably used to exclude significant renal injury in the setting of blunt abdominal trauma, but this does not hold true for penetrating trauma. Today, approximately 98% of all patients with renal injury are managed non-operatively.

Renal injury may be manifest on CT as parenchymal contusion, intraparenchymal, subcapsular or perinephric hematomas, intraparenchymal lacerations, vascular injuries including pseudoaneurysms and arteriovenous fistulas, and active arterial hemorrhage. Additionally, injuries may extend to and disrupt the collecting system, resulting in urinary extravasation (Fig. 3).

Renal contusions are seen as ill-defined round or ovoid hypoattenuating regions on the portal venous phase of scanning, or as persistent contrast staining on delayed images obtained in the pyelographic phase. Subcapsular hematomas are generally seen as well defined elliptical or crescentic collections of blood that reside immediately below the renal capsule, often compress the subjacent renal parenchyma and are of lower attenuation than the enhancing renal parenchyma. Perinephric hematomas are often poorly defined blood attenuating fluid collections contained between the kidney and Gerota's fascia that rarely deform the renal parenchyma. Renal lacerations are seen as linear or complex and branching areas of low attenuation coursing through the normally enhancing renal parenchyma, where as intrarenal hematomas are seen as low attenuation collections within the renal parenchyma. Active hemorrhage, pseudoaneurysms and arteriove-nous fistulas appear as areas of increased density relative to the normally enhancing renal parenchyma during the portal venous phase of scanning. The attenuation of these injuries is generally within 10 HU of the renal artery. Traumatic renal injury may also result in segmental or complete renal devascularization.

The organ injury scale (OIS) of the American Association for the Surgery of Trauma (ASTT) is used to calculate the injury severity score (ISS) since the ISS correlates with patient outcome and likelihood of death.

Renal Trauma

However, the CT classification of renal trauma includes important injuries that can be identified at imaging, but that are not explicitly specified in the OIS system. These include: 1) subtotal or segmental renal infarction, 2) traumatic thrombosis of the main renal artery, 3) active extravasation of vascular contrast material, and 4) uretero-pelvic junction (UPJ) avulsion.

The majority of renal injuries, approximately 85%, are comprised of grade I and II injuries that are considered relatively minor and do not typically require any intervention. Conversely, grade IV and V renal injuries always require treatment to repair the renal collecting system, arrest hemorrhage, and/or restore renal perfusion. Grade III injuries may or may not require intervention, depending on the presence of CT findings of active bleeding or clinical signs and symptoms suggesting continued bleeding.

Fig. 3. Gunshot wound to right flank with renal injury. Axial MDCT images obtained during portal venous phase (a) and delayed scanning performed during the pyelographic phase (b, c). a, b Gunshot entry wound is readily identified in the right anterior flank (concave arrowheads) with intraperitoneal fluid confirming peritoneal violation. a Perinephric hematoma (arrowheads) appears contained by Gerota's fascia posteriorly but is less well marginated anteriorly. a, b Active arterial extravasation is noted anterior to the right kidney (large arrows) with increased contrast accumulation on the delayed phase of scanning. c More inferiorly, pyelographic extravasation (large arrows) confirms injury to the renal collecting system

Pancreatic Injury

Pancreatic injury is rare. One retrospective review that included 16,188 Level I trauma center admissions over a ten year study period found an incidence of pancreatic injury of 0.4%. In this same study, approximately two thirds (63%) occurred as a result of penetrating trauma, whereas only one third of cases (37%) were due to blunt abdominal trauma. Therefore, the relative incidence of pancreatic injury in penetrating trauma was found to be 1.1% as compared to an incidence of only 0.2% among blunt abdominal trauma patients.

Though CT has been widely used as the primary means of evaluation for blunt abdominal trauma in hemodynami-cally stable patients, only recently has it begun to gain wider acceptance for evaluation of patients with penetrating mechanisms. Given the low overall incidence of pancreatic injury, coupled with the historically less frequent evaluation of patients with penetrating trauma and the recent advances in MDCT, it remains unclear what role CT may have in excluding or accurately grading pancreatic injury.

Pancreatic injury may be manifest on CT as parenchy-mal contusion, intraparenchymal or peripancreatic hematomas, intraparenchymal laceration or pancreatic transection (Fig. 4), vascular injuries including post-traumatic pseudoaneurysm, and active arterial hemorrhage. CT has an established role for the evaluation of abdominal trauma, therefore it is most important that the radiologist remain alert to the possibility of pancreatic injury, particularly among those patients with penetrating injuries. Further, among those patients suffering blunt trauma, the relatively protected central position of the pancreas means that pancreatic injury is rarely isolated. Injury to the midline pancreatic body is commonly associated with left hepatic lobe and duodenal injury. Injury to the pancreatic tail is commonly associated with splenic injury. Injury to the pancreatic head is commonly associated with major hepatic, vascular (retrohepatic inferior vena cava, aorta, portal vein and superior mesenteric vessels), and/or duodenal injury. Greater scrutiny of the pancreas when b c

Fig. 4. Pancreatic laceration after motor vehicle collision. a, b Axial MDCT images obtained during portal venous phase show a pancreatic laceration near the junction of the pancreatic body and tail (arrowheads). Fat stranding is present posterior to the pancreas. A small amount of fluid is present in Morrison's pouch

Fig. 4. Pancreatic laceration after motor vehicle collision. a, b Axial MDCT images obtained during portal venous phase show a pancreatic laceration near the junction of the pancreatic body and tail (arrowheads). Fat stranding is present posterior to the pancreas. A small amount of fluid is present in Morrison's pouch these associated injuries are present may improve detection of pancreatic injuries. Post-traumatic complications of pancreatic injury may include pancreatitis, pancreatic fistula, pseudocyst or intra-abdominal abscess formation.

Bowel and Mesentery Injury

Bowel and mesenteric injury are relatively rare among patients with blunt abdominal trauma. According to the largest retrospective study to date, the incidence of small bowel injury is 1.1%, and the incidence of colonic injury is 0.3% among these patients. Most frequently injured are the jejunum and ileum at the ligament of Treitz and the ileocecal valve, respectively, as these are sites of transition between fixed and mobile bowel segments, making them prone to the forces of deceleration injury. The next most commonly injured areas are the colon and rectum, followed by the duodenum and stomach. Surgical exploration remains the primary means by which any bowel perforation is treated.

Unequivocal findings of full thickness bowel injury on MDCT include direct visualization of bowel wall discontinuity with or without extravasation of bowel contents, including oral contrast material. Pneumoperitoneum, though strongly suggestive of full thickness bowel injury in the appropriate clinical setting, is a well-known cause of false positive CT interpretation. Air may be introduced into the peritoneal cavity by alternate means, including diagnostic peritoneal lavage, Foley catheter placement in the setting of intraperitoneal bladder rupture, and translocation of air from the thoracic cavity in the presence of thoracic injury (e.g., pneumothorax or pneumomedi-astinum). Nonetheless, pneumoperitoneum without an identified source should be considered indicative of full thickness bowel injury until proven otherwise. Focal bowel wall thickening (Fig. 5) usually reflects partial thickness injury (i.e., bowel wall contusion or hematoma) that is most often self-limited in the absence of less equivocal clinical findings (e.g., adjacent pneumoperitoneum or bowel content extravasation). In the absence of solid organ injury, the presence of isolated nonphysiologic quantities of free fluid is associated with an 84.2% incidence of small bowel injury. When coupled with pneumoperi-toneum, sensitivity for detecting small bowel perforation increases to 97%. When confronted with nonspecific findings such as focal bowel wall thickening or unexplained free fluid in the setting of blunt abdominal trauma, a thorough CT evaluation of the bowel using water-soluble oral contrast material should be strongly considered among patients for whom surgical exploration is deferred.

Mesenteric injury may or may not be associated with bowel injury. CT findings of mesenteric injury may include ill-defined focal areas of fat stranding that reflect mesenteric contusion, focal collections of blood attenuat-

Small Bowel Trauma

Fig. 5. Small bowel injury. Axial MDCT image obtained during portal venous phase shows circumferential thickening of a small bowel loop in the mid abdomen (arrowhead). Interloop fluid is present. Patient went to laparotomy for other intra-abdominal injuries (obviating need for repeat scan with oral contrast material), at which time the small bowel injury was found to be nontransmural

Fig. 5. Small bowel injury. Axial MDCT image obtained during portal venous phase shows circumferential thickening of a small bowel loop in the mid abdomen (arrowhead). Interloop fluid is present. Patient went to laparotomy for other intra-abdominal injuries (obviating need for repeat scan with oral contrast material), at which time the small bowel injury was found to be nontransmural ing mesenteric hematoma or active mesenteric arterial extravasation. Isolated mesenteric contusion is usually managed nonoperatively. Active mesenteric arterial extravasation usually undergoes emergent laparotomy. Mesenteric hematoma management may vary based on its size and association with other injuries. Mesenteric injury can also result in devascularized segments of bowel. As with nonspecific findings of bowel injury, CT evaluation using water-soluble oral contrast material should be strongly considered among patients with mesenteric injury for whom surgical exploration is deferred.

Bladder Injury

Bladder injury is relatively uncommon, with a reported incidence of 1.6% among blunt abdominal trauma patients. Approximately 90% of bladder injuries are the result of motor vehicle collisions or pedestrians struck by car. The remaining 10% are related to falls, pelvic crush injuries (often occupational and/or industrial), and severe blows to the lower abdomen. The likelihood of bladder injury is almost certainly related to its degree of dis-tention at the time of trauma. Hematuria is present in es sentially all cases of bladder rupture, and most have gross hematuria.

Bladder rupture can be classified as extraperitoneal (EBR, 57%), intraperitoneal (IBR, 36%), or combined (EBR and IBR, 5-7%). Approximately 7-9% of patients with pelvic fracture will have bladder rupture. Conversely, 83-89% of patients with bladder rupture will have pelvic fracture. Pelvic fracture is almost uniformly present if the bladder rupture is extraperitoneal. Previously, the strong association of EBR with pelvic fracture was mechanistically explained as resulting from direct bladder perforation by bony spicules resulting at the fracture site (Fig. 6a, b). However, at least one study has shown that the site of bladder injury was opposite the fracture site in 65% of cases. More recently, some authors have suggested that shearing forces related to pelvic ring disruption may tear the bladder at its fascial attachments. Whereas EBR more commonly occurs at the low anterior bladder, IBR more commonly occurs at the bladder dome. IBR most commonly results from a direct blow to a distended bladder that increases intravesicular pressure and causes the bladder to burst into the intraperitoneal space. IBR tears are typically much larger (5-10 cm) than those encountered with EBR.

Bladder Injury Mdct

Fig. 6. Extraperitoneal bladder injury. a Axial MDCT image obtained during portal venous phase shows low attenuation fluid anterior and lateral to the bladder (arrowheads). b Coronal reformation shows left superior pubic ramus fracture (arrowhead) with a bony spicule directed toward the bladder. Note the absence of free fluid within the peritoneal cavity. c Sagittal reformation after retrograde administration of bladder contrast via indwelling Foley catheter shows ex-traperitoneal extravasation of contrast material into the prevesical space (white arrowheads) through a defect (black arrowhead) in the low anterior bladder. d Axial image obtained at CT cystography shows the 'molar tooth' sign (arrowheads) related to extravasation of bladder contrast material anteriorly and laterally. (Images courtesy of Dr. Peter Clarke, Boston)

CT is an excellent means of bladder evaluation when injury is suspected based on mechanism, presence of pelvic fracture and/or hematuria. The standard method for CT cystography, as described earlier, has a reported sensitivity/specificity of 92%/99.6% for IBR, and a sensitivity/specificity of 100%/99.3% for EBR. The most classic finding for EBR is referred to as the 'molar tooth sign' (Fig. 6c, d). This is present when extravasat-ed bladder contrast tracks anteriorly and laterally around the distended bladder, creating the profile of a molar tooth. Extraperitoneal contrast can also track into the anterior abdominal wall, flank, scrotum and thighs. IBR is first suspected by the presence of low attenuation urine ascites during the initial portal venous phase of scanning. Following CT cystography, ex-travasated bladder contrast resides within the peritoneal cavity and confirms intraperitoneal rupture (Fig. 7).

Bladder Trauma Cystography

Fig. 7. Intraperitoneal bladder injury in a repeat study performed on a transfer trauma patient whose outside imaging did not accompany them. Axial MD-CT image obtained during portal venous phase

(a) and coronal MPR

(b) show a large volume of high-density contrast material pooling in the paracolic gutters (arrowheads) and between bowel loops (large arrow), confirming intraperitoneal bladder rupture. No solid visceral injury was present. Note absence of oral contrast material within the stomach. (Images courtesy of Dr. Peter Clarke, Boston)

False negatives are known to occur when bladder distention is inadequate for whatever reason (technique, patient tolerance, bladder compression by pelvic hematoma). If CT cystography is not timed correctly in the patient's evaluation, extravasated oral or intravenous contrast material may be mistaken for bladder injury leading to false positive diagnoses.

Intraperitoneal bladder rupture is universally treated by surgical repair. Otherwise, these typically large bladder lacerations continue to decompress and spill urine into the peritoneal cavity where it is resorbed by peritoneal surfaces and leads to uremia. Extraperitoneal bladder rupture is typically managed by catheter drainage. Surgical repair remains an option if adequate drainage cannot be accomplished, injury is in close proximity to the bladder neck, there are associated rectal or vaginal injuries, or the patient undergoes open reduction internal fixation of an anterior pelvic fracture. Approximately 85% of EBR heal by the tenth day, and almost all heal within 3 weeks of injury.

Diaphragmatic Injury

Diaphragmatic injury is present in 1-6% of patients sustaining blunt abdominal trauma. The force required for diaphragmatic injury accounts for the frequent coexistence of other abdominal injuries in 75-100% cases. Diaphragmatic injury is twice as common with penetrating trauma as compared to blunt abdominal trauma. Left diaphragmatic injury is more common than right whether due to blunt (approximately 75%) or penetrating (approximately 56%) mechanisms. Left predominance may be slightly overestimated, since right diaphragmatic injury is more likely to go undiagnosed among nonsurgical cases. Bilateral diaphragmatic injuries occur in 1-5% of patients. The posterolateral aspect of the diaphragm is the most frequent site of injury given the congenital weakness in this region. Diaphragmatic injury is frequently missed in the acute setting.

Diaphragmatic injury may be suspected or diagnosed on the portable chest radiograph obtained as part of a routine trauma series. If gas-containing viscera are identified within the thorax, and particularly if said viscera are constricted at the site of diaphragmatic tear (the 'collar sign'), then diaphragmatic injury can be reasonably assumed. Passage of a nasogastric tube into the stomach can help to confirm its abnormal position in the chest cavity and further establish the diagnosis of diaphragmatic injury.

CT signs that are specific for the diagnosis of diaphragmatic injury include: 1) herniation of abdominal viscera into the thorax (Fig. 8), and 2) focal constriction of the diaphragm around abdominal viscera, the so-called 'CT collar' sign. Nonspecific CT signs of diaphragmatic injury include: 1) discontinuity of the diaphragmatic crus, 2) thickening of the diaphragm, and 3) the 'dependent viscera' sign. Routine use of sagittal and coronal re-

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