Hemoperitoneum as the Sole Indicator of Abdominal Visceral Injuries: A Potential Limitation of Screening Abdominal US for Trauma 1

Emergency Radiology Kathirkamanathan Shanmuganathan, MD Stuart E. Mirvis, MD Caroline D. Sherbourne, MD William C. Chiu, MD Aurelio Rodriguez, MD Index terms: Abdomen, CT, 70.12112, 70.12115, 80.12112, 80.12115 Abdomen, hemorrhage, 791.41 Abdomen, injuries, 70.41, 80.41 Abdomen, US, 70.1298, 80.1298 Trauma, 70.41, 80.41 Radiology 1999; 212:423 430 Abbreviation: FAST focused abdominal sonography for trauma 1 From the Department of Diagnostic Radiology (K.S., S.E.M.) and the Shock Trauma Center (W.C.C., A.R.), University of Maryland Medical Center, 22 S Greene St, Baltimore, MD 21201 and the Department of Radiology, University of Texas Southwestern, Parkland Memorial Hospital, Dallas (C.D.S.). Received June 22, 1998; revision requested August 13; final revision received December 10; accepted January 19, 1999. Address reprint requests to K.S. (e-mail: kshan@radiology.ab.umd.edu). RSNA, 1999 Hemoperitoneum as the Sole Indicator of Abdominal Visceral Injuries: A Potential Limitation of Screening Abdominal US for Trauma 1 PURPOSE: To determine, at screening ultrasonography, the prevalence, severity, and clinical outcome of clinically important abdominal visceral injuries, without associated hemoperitoneum, that result from blunt abdominal trauma. MATERIALS AND METHODS: Computed tomography (CT) was performed at admission in 466 patients with visceral injury. A retrospective review was performed of findings from surgery and contrast material enhanced spiral and conventional CT performed to verify abdominal visceral injuries in 467 (4%) of 11,188 patients with blunt trauma. These patients were admitted to a level I trauma center over 33 months to determine the presence of hemoperitoneum and to identify the grade of injury. Medical records of patients with abdominal visceral injury without hemoperitoneum were reviewed for the management required and for results of focused abdominal sonography for trauma (FAST). RESULTS: A total of 575 abdominal visceral injuries were identified at CT and/or surgery. Findings of CT at admission (n 156) and of surgery (n 1) revealed no evidence of hemoperitoneum in 157 (34%) patients with abdominal visceral injury; 26 (17%) of whom also had negative FAST studies. Abdominal visceral injuries diagnosed in patients without hemoperitoneum included 57 (27%) of 210 splenic injuries, 71 (34%) of 206 hepatic injuries, 30 (48%) of 63 renal injuries, four (11%) of 35 mesenteric injuries, and two (29%) of seven pancreatic injuries. Surgical and/or angiographic intervention was required in 26 (17%) patients without hemoperitoneum. CONCLUSION: Reliance on the presence of hemoperitoneum as the sole indicator of abdominal visceral injury limits the value of FAST as a screening diagnostic modality for patients who sustain blunt abdominal trauma. Author contributions: Guarantors of integrity of entire study, K.S., S.E.M.; study concepts and design, all authors; definition of intellectual content, all authors; literature research, K.S.; data acquisition, K.S., S.E.M.; manuscript preparation, editing, and review, K.S., S.E.M., C.D.S. Clinical findings are often unreliable and have low sensitivity for diagnosis of intraperitoneal injuries following blunt abdominal trauma (1,2). It is challenging, even for an experienced trauma surgeon, to determine the extent of abdominal injury and the need for surgical intervention on the basis of clinical presentation alone. Historically, most trauma centers in the United States have used diagnostic peritoneal lavage and/or computed tomography (CT) to diagnose abdominal injuries in patients with acute blunt trauma. Ultrasonography (US) has been recognized as a valuable primary imaging modality in Europe and in Asia for more than 20 years, but it was not until the 1990s that it gained popularity in the United States for the evaluation of trauma injuries (2 12). In the United States, surgeons and emergency physicians have developed an interest in US and are attempting to incorporate it as an initial diagnostic study in the examination of patients with blunt trauma or as an ancillary study to either CT or diagnostic peritoneal lavage. The use of bedside US to evaluate patients with blunt trauma is based on the assumption that clinically important abdominal injuries are associated with free intraperitoneal fluid 423

or hemoperitoneum. Most studies of the use of US to evaluate injuries from blunt trauma to the torso have used hemoperitoneum as the sole criterion of abdominal organ injury. The reported sensitivity and negative predictive value for US in depicting hemoperitoneum vary from 78% to 99% and from 93% to 99%, respectively (8 10,12 16). However, previous smaller studies have shown abdominal injuries can occur without hemoperitoneum in up to 7% of patients with blunt trauma (15 17), but none or only a few of these patients need laparotomy to treat their abdominal visceral injuries. At our level I trauma center, Shock Trauma Center, University of Maryland Medical Center, Baltimore, CT is primarily used to screen patients for organ injury following blunt trauma, and our experience with CT suggests a high number of clinically important abdominal organ injuries do occur without associated hemoperitoneum. We undertook a large retrospective study of patients with blunt trauma who were admitted to our level I trauma center to determine the frequency, severity, and clinical outcome of important organ injuries that occur without free fluid or hemoperitoneum identified at the initial diagnostic evaluation. MATERIALS AND METHODS During 33 months, 11,188 patients with blunt trauma were admitted to our level I trauma center. The trauma registry database was reviewed (by K.S., S.E.M., and C.D.S.) to find all intraabdominal injuries involving the spleen, liver, kidney, diaphragm, mesentery, bowel, pancreas, urinary bladder, aorta, and inferior vena cava (18). During the study period, traumatic intraabdominal injuries were identified in 467 patients (4%). CT was performed at admission in 466 patients with abdominal injuries. CT and surgery reports on the 467 patients with abdominal injuries were retrospectively reviewed (by C.D.S., S.E.M., and K.S.) to determine the presence of hemoperitoneum. Three radiologists (C.D.S., S.E.M., K.S.) retrospectively reviewed the CT scans at the same time, by consensus, and were blinded to the results of focused abdominal sonography for trauma (FAST) in all patients whose initial CT interpretation included no hemoperitoneum. The abdominal and pelvic CT scans were reviewed, and the presence of hemoperitoneum, its location, and the grades of organ injuries were determined by consensus. TABLE 1 American Association for the Surgery of Trauma Splenic Injury Scale (1994 Revision) Grade* Type of Injury Description of Injury I Hematoma Subcapsular, 10% surface area Laceration Capsular tear, 1-cm parenchymal depth II Hematoma Subcapsular, 10% 50% surface area; intraparenchymal, 5 cm in diameter Laceration 1 3-cm parenchymal depth that does not involve a trabecular vessel III Hematoma Subcapsular, 50% surface area or expanding; ruptured subcapsular or parenchymal hematoma Laceration 3-cm parenchymal depth or involving trabecular vessels IV Laceration Laceration involving segmental or hilar vessels producing major devascularization ( 25% of spleen) V Laceration Completely shattered spleen Vascular Hilar vascular injury that devascularizes spleen * Advance one grade for multiple injuries, up to grade III. TABLE 2 American Association for the Surgery of Trauma Hepatic Injury Scale (1994 Revision) Grade* Type of Injury Description of Injury I Hematoma Subcapsular, 10% surface area Laceration Capsular tear, 1-cm parenchymal depth II Hematoma Subcapsular, 10% 50% surface area; intraparenchymal, 10 cm in diameter Laceration 1 3-cm parenchymal depth, 10 cm in length III Hematoma Subcapsular, 50% surface area or expanding; ruptured subcapsular or parenchymal hematoma; intraparenchymal hematoma 10 cm or expanding Laceration 3-cm parenchymal depth IV Laceration Parenchymal disruption involving 25% 75% of hepatic lobe or 1 3 Couinaud segments within a single lobe V Laceration Parenchymal disruption involving 75% of hepatic lobe or 3 Couinaud segments within a single lobe Vascular Juxtahepatic venous injuries (ie, retrohepatic vena cava and/or central major hepatic veins) VI Vascular Hepatic avulsion * Advance one grade for multiple injuries, up to grade III. The scale devised by the Organ Injury Scaling Committee of the American Association for the Surgery of Trauma was used to grade injuries of the spleen and liver (Tables 1, 2) (19). The method described by Mirvis and Gelman (20) was used to grade injuries to the kidney. Abdominal and pelvic extraperitoneal hematomas were diagnosed by consensus as small, moderate, or large. Large hematomas were those that distended the extraperitoneal compartment and exerted a mass effect on adjacent organs. Medical records were reviewed (by C.D.S., S.E.M., and K.S.) to determine the surgical findings, FAST results, management, and clinical outcome for all patients who had organ injury without hemoperitoneum diagnosed at CT, surgery, or US. CT was performed with a Hi-Q or Somatom Plus 4 scanner (Siemens Medical TABLE 3 Abdominal Injuries Organ or System No. of Injuries in All Patients No. of Injuries in Patients without Hemoperitoneum* Spleen 210 57 (27) Liver 206 71 (34) Kidney 63 30 (48) Mesentery 35 4 (11) Pancreas 7 2 (29) Gastrointestinal 6 1 (17) Bladder 21 0 (0) Vascular and/or retroperitoneal hematoma 20 14 (70) Gallbladder 7 0 (0) Total 575 179 (31) * Numbers in parentheses are percentages. 424 Radiology August 1999 Shanmuganathan et al

Figure 1. Flow diagram of patients admitted for blunt trauma. a. b. c. d. Figure 2. Grade IV splenic laceration without hemoperitoneum. (a) Axial CT image obtained at admission shows a grade IV splenic laceration (arrows). (b, c) Axial CT images show no hemoperitoneum in the (b) region of the hepatorenal fossa or (c) pelvis. (d) Angiogram shows a pseudoaneurysm (arrow) of the splenic artery with intraparenchymal extravasation of contrast material. The pseudoaneurysm was successfully embolized. a 100 120-second delay was instituted between abdominal and pelvic scanning. Conventional CT was performed with a scanning time of 2.0 seconds or less, with contiguous axial scans obtained with 10-mm collimation from the lower part of the chest to the iliac crest and with 10-mm collimation at 20-mm table increments from the iliac crest to the symphysis pubis. Contrast material (Hypaque 60% [diatrizoate meglumine] or Omnipaque 240 [iohexol]; Nycomed Amersham, Princeton, NJ) was intravenously power injected (Mark IV; Medrad, Indianola, Pa) as a 150-mL bolus at a rate of 3 ml/sec for spiral CT and as an initial bolus of 100 ml at a rate of 1.5 2.0 ml/sec followed by an injection of an additional 50-mL bolus at a rate of 1 ml/sec for conventional CT. All patients orally received contrast material consisting of 5 g of Hypaque powder (diatrizoate meglumine; Nycomed Amersham) in 300 ml of water 30 45 minutes prior to imaging, and, if time permitted, a second dose was given in the scanning suite, either orally or through a nasogastric tube. FAST was performed and the images were interpreted by the attending trauma surgeon or trauma fellow in the admitting area during the initial evaluation of the patient. US was performed with a Sonoline model SI-400 system (Siemens Medical Systems) by using a 3.5-MHz convex sector transducer. Hard copies of the studies were not reviewed by either the radiology resident or the staff radiologist. A nonrandomized, nonconsecutive subset of patients underwent FAST at the discretion of the attending trauma surgeon. FAST was aimed at the depiction of hemoperitoneum in three regions, including the hepatorenal fossa (Morison pouch) and right subdiaphragmatic space; the left upper quadrant, with attention to the splenorenal recess and left subdiaphragmatic space; and the pelvis, with attention to the rectouterine pouch (pouch of Douglas). FAST results were interpreted as positive if hemoperitoneum was depicted in any of the three regions scanned and were interpreted as negative if no hemoperitoneum was found in these regions. All patients underwent further abdominal evaluation at CT or exploratory laparotomy, as indicated by the overall clinical presentation. RESULTS Systems, Iselin, NJ). The abdomen was scanned from the lower part of the chest to the iliac crest, and the pelvis was scanned from the iliac crest to the symphysis pubis. Spiral CT was performed with 10-mm collimation and a table speed of 10 mm/sec (pitch of 1). To visualize the excretion of contrast material in the pelvic ureters and bladder, Of the 11,188 consecutive patients who were admitted with blunt abdominal trauma, 467 (4%) had visceral injuries that were ultimately diagnosed at contrast material enhanced CT and/or surgery. A total of 575 injuries were identified (Table 3) among the 467 patients. Of these patients, 157 (34%) had visceral injuries without hemoperitoneum diag- Volume 212 Number 2 Hemoperitoneum to Indicate Abdominal Visceral Injuries: Limitation of US 425

nosed at CT on admission (n 156) or at laparotomy (n 1) (Fig 1). FAST was also performed in 26 (17%) of the 157 patients without hemoperitoneum and revealed negative results in 25 patients and falsepositive results in one patient with pelvic fractures and retroperitoneal and pelvic hematomas. Among all the abdominal visceral injuries identified at CT or at surgery in the entire population of patients admitted with blunt trauma, hemoperitoneum was not seen in 27% of the splenic injuries (Fig 2), 34% of the hepatic injuries (Fig 3), 48% of the renal injuries, 11% of the mesenteric injuries, and 29% of the pancreatic injuries (Table 3). Retrospective CT grades, determined by using the surgical scale of splenic and liver injuries diagnosed in patients without hemoperitoneum, are displayed in Table 4. Forty-one (58%) of the 71 hepatic and 23 (40%) of the 57 splenic injuries in patients without hemoperitoneum were classified as high-grade (grade III or higher) injuries on the American Association for the Surgery of Trauma scale. Fourteen patients without hemoperitoneum also had large extraperitoneal hematomas that were diagnosed at CT on admission. Active hemorrhaging was seen in six of these patients (21,22). Eight of the extraperitoneal pelvic hematomas occurred as isolated injuries. Among the 30 renal injuries that occurred in patients without hemoperitoneum were 19 (63%) minor and 11 (37%) major lesions. The major renal injuries included either large perinephric or subcapsular hematomas (n 5), renal lacerations involving the collecting system or a transected kidney (n 4), and renal vascular pedicle injuries (n 2). The minor renal injuries included small perinephric or subcapsular hematomas (n 8), segmental renal infarctions (n 3), and renal lacerations without involvement of the collecting system with small or no perinephric hematoma (n 8). Four major and six minor renal lesions occurred as isolated injuries, and the other renal lesions were associated with additional intraperitoneal traumatic lesions. Three of the four mesenteric injuries in patients without hemoperitoneum were diagnosed at CT at admission and were managed conservatively with clinical examinations and follow-up CT. One of the patients had a mesenteric injury that was diagnosed at surgery to repair a ruptured left hemidiaphragm that was depicted at CT of the chest at admission. The mesenteric injury was directly repaired without resection of the bowel. a. b. Figure 3. Grade IV hepatic laceration in a patient without hemoperitoneum. (a, b) Axial CT images obtained at different levels in the hepatic region show multiple lacerations (arrows) involving the right and left lobes. No hemoperitoneum is seen. Twenty-six (17%) of the 157 patients with abdominal injuries without hemoperitoneum required surgery (n 19) or angiographic embolization (n 8) to manage their injuries (Table 5). (One patient underwent both splenectomy and diaphragmatic repair.) Splenic injury (n 14) was the most common reason (Table 5) for celiotomy (n 9) or angiographic embolization (n 5) (Figs 2, 4). Five patients without hemoperitoneum needed surgery, including nephrectomy in four patients and thrombectomy and reanastomosis of a renal arterial injury in one patient, for major renal injuries. Three patients with pelvic fractures but no hemoperitoneum had sites of active bleeding within the extraperitoneal pelvic hematomas that required angiographic embolization. One patient underwent celiotomy to repair bilateral diaphragmatic injuries. In another patient, a transverse colostomy was performed for cecal and anal tears. Nontherapeutic celiotomies, associated with pancreatic injury, were performed in two patients without hemoperitoneum. At surgery, one patient had a pancreatic contusion, a nonobstructive contusion of the duodenum, and a hemostatic grade III splenic injury, whereas the other patient had a pancreatic contusion and a hematoma of the proximal jejunal wall. None of the abdominal lesions in these patients required surgical repair. One of the patients without hemoperitoneum with a large retroperitoneal hematoma died of massive, uncontrolled hemorrhage into the retroperitoneum. Twenty-nine (18%) patients without TABLE 4 Injuries in Patients without Hemoperitoneum Grade* Splenic Hepatic I 4 10 II 30 20 III 18 25 IV 5 15 V 0 1 * American Association for the Surgery of Trauma classification. TABLE 5 Surgery or Embolization Required in Patients without Hemoperitoneum No. of Patients Procedure (n 26) Splenorrhaphy 5 Splenectomy 4 Splenic embolization 5 Nephrectomy and/or renal arterial repair 5 Pelvic embolization 3 Diaphragmatic repair 3 Nontherapeutic laparotomy 2 Note. One patient underwent both splenectomy and diaphragmatic repair. hemoperitoneum had combined abdominal injuries (Table 6). Thirteen patients had combined visceral injuries and 19 patients had intraperitoneal and retroperitoneal injuries. The most common combined visceral injuries involved the liver and kidney (n 10). Five of the patients 426 Radiology August 1999 Shanmuganathan et al

a. b. Figure 4. Progression of low-grade splenic injury to a higher grade injury needing angiography. (a) Axial CT image obtained at admission shows a grade II intraparenchymal splenic laceration (arrow). (b) Follow-up axial CT image obtained 5 days after admission shows multiple splenic lacerations (arrowheads) with a splenic pseudoaneurysm (arrow), which indicates progression to higher-grade (grade IV) splenic injury. (c) Angiogram shows a pseudoaneurysm (arrow) of the upper pole branch of splenic artery. The splenic pseudoaneurysm was embolized. c. without hemoperitoneum had three or more abdominal visceral injuries (Fig 5). Twelve (41%) of the 29 patients with combined abdominal injuries without hemoperitoneum needed laparotomy (n 11) or angiographic embolization (n 1) to manage their injuries. DISCUSSION The advantage of using US for the evaluation of patients with potential abdominal trauma is that it is a rapid, noninvasive modality that can be used at the bedside to depict hemoperitoneum. Serial US examinations can also be performed, if clinically warranted, at regular intervals. Unlike previous studies, the current study demonstrated that 34% of patients with abdominal visceral injuries following blunt abdominal trauma did not have hemoperitoneum at CT on admission or at surgery. In 17% of patients without hemoperitoneum in whom visceral injuries were ultimately diagnosed, both admission FAST and CT findings confirmed the absence of associated hemoperitoneum. The high frequency of visceral injuries occurring without hemoperitoneum in this study could be attributed to the lack of a reference standard test (CT and/or surgery) in most previous studies (2,3,8 10,12,14 17) to verify US findings obtained at admission. Also, the time from injury to diagnosis for most patients with trauma admitted to our trauma center is less than 1 hour. This brief time may not always be sufficient for intraperitoneal hemorrhaging to manifest from some intraperitoneal injuries. Since FAST relies on the presence of hemoperitoneum as the sole indicator of abdominal organ injury, 34% of the patients with blunt trauma and abdominal injuries (157 of 467 patients) would not have had their injuries diagnosed at US at admission if it were used as the sole screening modality. Fifty-eight percent of the hepatic and 40% of the splenic injuries in patients without hemoperitoneum were a surgical grade of III or higher. Fourteen patients with large extraperitoneal hematomas and 11 (37%) of 30 patients with renal trauma had major injuries but no hemoperitoneum. Our study findings demonstrate that substantial numbers of high-grade intraperitoneal or extraperitoneal injuries can occur without associated hemoperitoneum. Surgical or angiographic intervention was required to manage abdominal visceral injuries in 17% of patients who had no hemoperitoneum at CT on admission. The consequence of missing the injuries in the other 131 patients is difficult to extrapolate from our study findings, since all 131 patients were successfully managed with close observation of their hemodynamic status and with restricted activity. Most trauma centers that use US as a primary screening modality rely on the assumption that any missed injuries are low-grade lesions without serious clinical consequence (13,23). Although this may be true for most hepatic injuries, splenic injuries have a more unpredictable course (24). It has been shown that the use of a CT-based grading system to select patients for nonsurgical management of splenic injuries is unreliable (24 28). In up to 15% 20% of patients with lowgrade splenic injuries, conservative treatment has been shown to fail (24,29). It is well established that such injuries may clinically manifest later as delayed splenic ruptures (24,29,30). In a recent study (29), conventional and spiral CT results demonstrated that nonsurgical management failed in 15% of patients with splenic injury, and 82% of these patients had low-grade splenic injuries with vascular abnormalities, including pseudoaneurysm or hemorrhage within the splenic parenchyma at CT either at admission or at follow-up. Early surgical or angiographic intervention in such patients could have reduced the failure rate of conservative management of splenic injury to 4% (29). We have also observed the progression of initially low-grade splenic injuries to higher-grade injuries at follow-up CT (Fig 3). In this study, among the patients without hemoperitoneum with visceral injuries that were diagnosed at CT on admission, splenic injuries were the most common cause of hemorrhage that required surgery or angiographic embolization. Among patients with these injuries, six (43%) of 14 had grade I or grade II splenic injuries. Our study findings validate the importance of diagnosing low-grade splenic injuries that occur without hemoperitoneum in hemodynamically stable patients. It is important to treat these patients with careful observation and with Volume 212 Number 2 Hemoperitoneum to Indicate Abdominal Visceral Injuries: Limitation of US 427

TABLE 6 Combinations of Injuries in Patients without Hemoperitoneum Patient No. Hepatic* Splenic* Renal restricted activity and to document healing or progression of the splenic injury at follow-up CT. Like diagnostic peritoneal lavage, US has known limitations in evaluating the retroperitoneum (2,8). Optimal evaluation of injuries to the kidney, pancreas, or duodenum and detection of retroperitoneal hematoma could be time-consuming and limited secondary to overlying bowel gas from the paralytic ileus that results from retroperitoneal injury, softtissue emphysema, difficulty in differentiating intra- and extraperitoneal softtissue planes, or inability to alter the patient s position. A small amount of hemoperitoneum is not uncommon in patients with large retro- or extraperitoneal pelvic hematomas from red blood cells or plasma that enters the peritoneal cavity through a small tear or even through the intact serosal layer of the retroperitoneal lining (31). This could further add to the difficulty in determining the exact site of injury or hemorrhage (intra- vs retroperitoneal space). A large amount of hemorrhaging into the retroperitoneal structures is an important but not uncommon cause for the hemodynamic instability or occult blood loss in patients with blunt trauma. In this study, 11 patients had major renal injuries and 14 patients had large retro- or extraperitoneal pelvic hematomas without hemoperitoneum. Five of the retroperitoneal and three of the extraperitoneal pelvic hematomas occurred as isolated injuries. Surgery, including nephrectomy and repair of a renal vascular pedicle injury, was required in five (45%) of 11 patients with major renal injuries. Three of the patients with large extraperitoneal pelvic hematomas had sites of active bleeding that required angiographic embolization. At our trauma center, the FAST technique is not used routinely to evaluate the retroperitoneum. A substantial number of major retroperitoneal injuries that needed surgical or angiographic intervention occurred in this study. Although these injuries and sites of hemorrhage would have been missed at FAST, they were diagnosed correctly because, at our center, CT is used as the principal screening modality to evaluate these patients with blunt trauma. Hemodynamically stable patients with blunt trauma could have concurrent injuries in multiple abdominal and pelvic regions. Prior knowledge of the precise extent and grades of the coexistent injuries is helpful in identifying the predominant injury, which guides the surgeon through the decision tree of clinical management. Although it produces highly sensitive findings in well-trained hands, FAST, unlike CT, is not specific to the site of origin and extent of injury. Twenty-nine (18%) of 157 patients without hemoperitoneum had combined injuries, including concurrent intraperitoneal (n 19) or intra- and retroperitoneal (n 7) injuries (Table 6). CT was helpful in determining the predominant injury in 43% of the patients in the combined injury group and helped to prioritize patients for angiographic embolization or laparotomy. The goal of this retrospective study was to ascertain the prevalence of abdominal visceral injuries that occur without hemoperitoneum and to determine if a substantial number of these injuries may need surgical or angiographic intervention. This study was not undertaken to measure the sensitivity, specificity, or accuracy of FAST at our level I trauma center. Retroperitoneal Hematoma Other 1 II III Absent Absent Absent 2 III Absent Major Absent Absent 3 II Absent Major Absent Absent 4 III II Absent Absent Absent 5 Absent II Minor Absent Diaphragmatic 6 Absent IV Absent Absent Diaphragmatic 7 Absent IV Minor Absent Absent 8 Absent Absent Absent Absent Diaphragmatic and mesenteric 9 Absent Absent Absent Present Intestinal and mesenteric 10 III II Absent Absent Absent 11 II Absent Minor Absent Mesenteric 12 II Absent Minor Absent Mesenteric 13 II II Absent Absent Absent 14 Absent III Major Absent Absent 15 Absent Absent Major Absent Diaphragmatic 16 III II Absent Absent Absent 17 III Absent Minor Absent Absent 18 II II Absent Absent Absent 19 Absent Absent Minor Absent Diaphragmatic 20 IV Absent Major and minor Absent Absent 21 III III Minor Absent Absent 22 IV Absent Minor Absent Absent 23 Absent III Minor Absent Absent 24 III Absent Major Absent Absent 25 Absent IV Minor Absent Absent 26 IV Absent Minor Absent Absent 27 Absent III Minor Absent Absent 28 Absent Absent Absent Present Diaphragmatic 29 Absent Absent Major Absent Mesenteric * American Association for the Surgery of Trauma grade. Mirvis and Gelman (20) grade. Required surgery. Required angiography. Only 17% of 157 patients with blunt trauma who had abdominal visceral injury without hemoperitoneum underwent both FAST and CT and/or surgery at admission; FAST revealed false-negative results in 25 patients. A prospective study, in which FAST was performed at admission in all patients with blunt trauma who were evaluated consecutively with CT or surgical correlation, would have been optimal to determine the sensitivity, specificity, and accuracy of FAST at our trauma center. CT and surgery are considered the standard or reference modalities for detecting hemoperitoneum in patients with trauma; CT and surgery were performed in all 157 patients with abdominal visceral injury without hemoperitoneum in this study (13,15,16,31 34). Prior study findings have indicated that a minimum of a liter of fluid should be present in the hepatorenal fossa for prompt, reliable detection of intraperitoneal fluid in 97% of patients at US in the trauma setting (11,35). 428 Radiology August 1999 Shanmuganathan et al

a. b. c. Figure 5. Combined injuries of both kidneys. (a) Axial CT image shows a grade IV liver laceration (arrows) involving the right lobe. Posterior pararenal hematoma is adjacent to the bare area (arrowheads) of the liver. (b, c) Axial CT images show a minor left (arrowhead in b) and a major right (solid arrow in c) renal injury with a large right paranephric hematoma (open arrows in c). No hemoperitoneum is seen. Most investigators in studies in which US is used as a screening tool for blunt abdominal injuries recommend clinical observation and monitoring of the patients with negative or indeterminate initial abdominal US results (23,36). None of these studies, however, define the indications for repeated US examinations, the intervals at which they should be repeated, and the number of negative results that are needed prior to discharging the patient. At our trauma center, if no injury is identified at initial CT, patients may be discharged as soon as 3 4 hours following admission. Findings from a multicenter prospective study (37) also indicate that abdominal CT has a negative predictive value of 99.63% for the need for celiotomy following blunt trauma and that CT enables reliable identification of patients who do not require admission to the hospital. Abdominal CT can prevent the unnecessary and potentially costly admission of patients without documented injury for observation only and helps to more precisely select patients with multiple trauma injuries for surgical, angiographic, or expectant management. Thirty-four percent of patients with abdominal visceral injury following blunt abdominal trauma had no hemoperitoneum at admission, but CT reliably depicted injuries that did not have associated hemoperitoneum. In this study, 17% of patients with abdominal and/or retroperitoneal injuries but without hemoperitoneum required surgical and/or angiographic intervention. Since FAST relies on the presence of hemoperitoneum as the sole indicator of abdominal visceral injury, it will fail to depict many intraperitoneal, as well as retroperitoneal, injuries. References 1. Branney SW, Wolfe RE, Moore EE, et al. Quantitative sensitivity of ultrasound in detecting free intraperitoneal fluid. J Trauma 1995; 39:375 380. 2. Lentz KA, McKenney MG, Nunez DB Jr, Martin L. Evaluating blunt abdominal trauma: role for ultrasonography. J Ultrasound Med 1996; 15:447 451. 3. Kretschmer KH, Bohndorf K, Pohlenz O. The role of sonography in abdominal trauma: the European experience. Emerg Radiol 1997; 4:62 67. 4. Bode PJ, van Vugt AB. Ultrasound in the diagnosis of injury. Injury 1996; 27:379 383. 5. Bode PJ, Niezen RA, van Vugt AB, Schipper J. 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