Blunt Abdominal Trauma: Should US Be Used to Detect Both Free Fluid and Organ Injuries? 1

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1 Emergency Pierre A. Poletti, MD Karen Kinkel, MD Bernard Vermeulen, MD François Irmay, MD Pierre-François Unger, MD François Terrier, MD Index terms: Abdomen, injuries, 78.41, Abdomen, US, , Trauma, 78.41, Published online before print /radiol ; 227: Abbreviations: AAST American Association for the Surgery of Trauma NPV negative predictive value PPV positive predictive value 1 From the Division of Radiodiagnostic and Interventional (P.A.P., K.K., F.T.), Division of Medico-Surgical Emergencies (B.V., P.F.U.), and Clinic/ Polyclinic of Digestive Surgery (F.I.), Hôpital Cantonal, University of Geneva, 24 rue Micheli-du-Crest, 1211 Geneva-14, Switzerland. Received February 20, 2002; revision requested April 23; revision received June 15; accepted July 25. Address correspondence to P.A.P. ( pierre -alexandre.poletti@hcuge.ch). Blunt Abdominal Trauma: Should US Be Used to Detect Both Free Fluid and Organ Injuries? 1 PURPOSE: To evaluate abdominal ultrasonography (US) for indirect (with free fluid analysis only) and direct (with free fluid and parenchymal analysis) detection of organ injury in patients with blunt abdominal trauma, with findings at computed tomography (CT) and/or surgery as the standard of diagnosis. MATERIALS AND METHODS: Abdominal US was performed at hospital admission in consecutive patients with blunt abdominal trauma. The presence of free peritoneal fluid and organ injury were recorded and compared with results of abdominal CT in all hemodynamically stable patients. When US results were considered falsenegative for free fluid or organ injury compared with CT results, repeat US was performed within 6 hours. Admission and second US results were compared with CT and/or surgical results to determine sensitivity, specificity, negative predictive value, and positive predictive value of US with regard to the presence of free intraperitoneal fluid and/or organ injury. RESULTS: Two hundred five hemodynamically stable patients underwent abdominal US and CT. CT revealed free fluid in 83 patients and organ injury in 99. Thirty-one (31%) of 99 patients with organ injury did not have free fluid at CT. Three (10%) of the 31 patients required surgery or angiographic embolization. The sensitivity of admission US was 93% (77 of 83 cases) for the diagnosis of free fluid, 41% (39 of 99) for directly demonstrating organ injury, and 72% (71 of 99) for suggesting organ injury by means of both free fluid and organ analysis. At second US, these sensitivities were 96% (80 of 83 cases), 55% (54 of 99) and 84% (83 of 99), respectively. CONCLUSION: US is highly sensitive for the detection of free intraperitoneal fluid but not sensitive for the identification of organ injuries. In hemodynamically stable patients, the value of US is mainly limited by the large percentage of organ injuries that are not associated with free fluid. RSNA, 2003 Author contributions: Guarantors of integrity of entire study, P.A.P., F.T.; study concepts, P.A.P., K.K., F.I., F.T.; study design, P.A.P., B.V., K.K.; literature research, P.A.P., B.V.; clinical studies, P.A.P., K.K., F.I.; data acquisition, P.A.P., B.V., K.K.; data analysis/interpretation, P.A.P., B.V., K.K., F.I.; statistical analysis, K.K.; manuscript preparation, P.A.P., K.K., B.V.; manuscript definition of intellectual content, F.T., P.A.P., K.K., P.F.U.; manuscript editing, P.A.P., K.K.; manuscript revision/review, P.F.U., F.I., F.T.; manuscript final version approval, all authors. RSNA, 2003 Ultrasonographic (US) examination of the abdomen for blunt trauma has been performed in Europe for almost 30 years (1). Because it is a rapidly performed, repeatable, noninvasive, and inexpensive study, US has been advocated by many as an effective triage tool in the evaluation of blunt abdominal trauma (2 5). There has been particularly high interest in the use of screening US in the pediatric population (6,7). In the population of adult patients with blunt trauma, the role of US is more difficult to assess. Some authors, mainly in the United States and Canada, advocate the use of focused assessment US for trauma in which examination is limited to evaluation for free intraabdominal fluid, without organ assessment, and the examination is performed or the results are interpreted by radiologists (5,8) or nonradiologists (9 11). This method is regarded as a rapid diagnostic examination in the triage of victims of blunt abdominal trauma that can lead to a reduction in the number of abdominopelvic computed tomographic (CT) and deep peritoneal lavage procedures performed, providing that the US operator has been sufficiently trained (4,5,8,12 14). 95

2 If depiction of free peritoneal fluid at US in a hemodynamically stable patient results in the need to further examine the patient with CT, the value of negative focused assessment US for trauma is more problematic. Some researchers have raised concern about this method of triage while reporting a large number of organ injuries, including severe injuries, that were not associated with free fluid (15,16). Other researchers advocate performing an entire abdominal US examination that includes organ analysis (3,17,18). However, the value of systematic parenchymal analysis in the detection of solid organ injuries at US compared with the value of detection of solid organ injuries on the basis of free fluid analysis alone is difficult to assess and subject to controversy (19,20). In most previous series, US findings were not compared with CT or surgical findings as the sole standard of diagnosis (3,17,18,20); findings during relatively short periods of clinical follow-up were used as the standard of diagnosis instead. Therefore, in these series, the value of US in the detection of parenchymal injuries is probably overestimated due to an underestimation of false-negative results. Indeed, even potentially life-threatening injuries, such as splenic lacerations, can have a favorable clinical outcome without specific treatment. The purpose of our study was to evaluate the use of abdominal US for the depiction of organ injury indirectly (by means of analysis of free fluid only) and directly (by including parenchymal analysis) in patients with blunt abdominal trauma, with findings at CT and/or surgical follow-up as the standard of diagnosis. MATERIALS AND METHODS Patients and US Examination This prospective study was conducted during a 22-month period (January 2000 to October 2001) at a level I emergency trauma center. Patients enrolled in the study included all consecutive adolescents and adults (15 years old and older) who were admitted for suspicion of blunt abdominal trauma and who subsequently underwent abdominal CT or surgery or both. At the time of their arrival in the emergency department, all patients were assessed clinically by the emergency team. This was followed, within 30 minutes after admission, by an abdominal US examination performed by a trained senior radiology resident or fellow. TABLE 1 CT and/or Surgical Findings in 110 Patients with Solid Organ Injuries Organ No. of Injuries No. Requiring Surgical Repair or Angiographic Embolization Spleen 49 (37) 15 (43) Liver 43 (32) 3 (8.6) Kidney and/or adrenal gland 20 (15) 3 (8.6) Bowel and/or mesentery 14 (11) 11 (31) Bladder 3 (2.7) 2 (5.7) Pancreas 3 (2.7) 0 Diaphragm 1 (1.0) 1 (2.9) Total 133 (100) 35 (100) Note. Numbers in parentheses are percentages. Percentages do not add up to 100 due to rounding. All senior radiology residents (n 15) were required to attend at least 300 supervised US examinations in our institution before they began working in the emergency radiology unit. In the daytime including during the weekends all trauma US examinations were performed with the supervision of the emergency radiology fellow (n 1). At night, US examinations were performed by a senior resident alone. US examinations were performed with an SSD 2000 multiview unit (Aloka, Tokyo, Japan) and a 12-inch monochrome display monitor. A 3.5-MHz convex sector probe was used. The frequency could be changed to 2.5 or 5.0 MHz for obese or thin patients, respectively. Film copies were obtained for each patient. US examinations were completed within minutes. The presence of free intraperitoneal fluid was assessed in the perihepatic area, the Morison pouch, the perisplenic region, the paracolic gutters, and the Douglas pouch. The retroperitoneum was also assessed for the presence of fluid. Intraabdominal organs (ie, the liver, spleen, kidney, adrenal glands, pancreas, mesenteric root, and bladder area) were specifically evaluated for evidence of injury. The urinary catheter was clamped until the US examination was completed. US results were recorded on a written form, and this form was placed in the mailbox of the attending radiologist (P.A.P.) before CT of the abdomen and pelvis was performed. The quality of the US examination was rated as high each time the following conditions were present: The radiologist had enough time to perform the examination; the patient was cooperative, not overweight, and had a well-filled bladder; there was no air distention of the bowel loops and there were no fixed plasters on the abdomen; and the lighting in the room was reduced. The quality of the US examination was rated as medium whenever all these requirements were not met but there was no major impediment to analysis of the entire abdomen and the radiologist was quite confident in his or her results. The quality of the US examination was rated as low when it did not enable precise analysis of the entire abdominal cavity. In the latter case, the reason for the low quality of the examination was indicated. Each time an organ injury was depicted, the lesion was reported as being either hyperechoic, hypoechoic, or normoechoic but with architectural disruption of the vessels of the parenchyma at color Doppler US. Patients admitted after blunt trauma who had a Glasgow Coma Scale score higher than 13 and had (a) either no clear history of abdominal involvement or normal clinical abdominal examination results (eg, no pain at palpation, no guarding), (b) no rib fracture, and (c) a blood glutamic oxaloacetic transaminase level within the normal range. They also underwent routinely performed abdominal US, as reported on the written form. However, according to the standard of care in our hospital, these patients were not selected for further abdominal CT unless US results were considered positive for the presence of free fluid or organ injury. If there was no other reason for hospitalization, these patients were immediately discharged from the emergency department after they had been instructed to return if their condition deteriorated. The protocol of this study was approved by the ethics review board of Hôpital Cantonal. Since the routine care of trauma patients was not altered because of our study, patient informed consent was not required. 96 April 2003 Poletti et al

3 TABLE 2 US Findings Compared with CT or Surgical Findings in 205 Hemodynamically Stable Patients US Findings vs CT or Surgical Findings Sensitivity Initial US Examination Specificity PPV NPV Second US Examination* Sensitivity Free fluid at US vs free fluid at CT (n 83) 93 (77/83) 95 (115/121) 93 (77/83) 95 (115/121) 96 (80/83) 98 (118/121) Free fluid and/or organ injury at US vs organ injury at CT or surgery (n 99) 72 (71/99) 88 (93/106) 85 (71/84) 77 (93/121) 84 (83/99) 87 (106/122) Free fluid at US vs organ injury at CT or surgery (n 99) 65 (64/99) 82 (87/106) 77 (64/83) 71 (87/122) 68 (67/99) 73 (87/119) Organ injury at US vs organ injury at CT or surgery (n 99) 41 (39/99) 94 (100/106) 87 (39/45) 62 (100/160) 55 (54/99) 72 (115/160) Spleen injury (n 44) 27 (12/44) 98 (157/161) 75 (12/16) 83 (157/189) 34 (15/44) 85 (160/189) Liver injury (n 41) 51 (21/41) 99 (158/159) 95 (21/22) 89 (158/178) 73 (30/41) 94 (164/175) Kidney/adrenal gland injury (n 20) 40 (8/20) 98 (182/186) 67 (8/12) 94 (182/194) 55 (11/20) 95 (185/194) Other organ injuries (n 12) 8.0 (1/12) 100 (193/193) 100 (1/1) 95 (193/204) 33 (4/12) 96 (193/201) Note. Numbers in parentheses are the data used to calculate the percentages. Patients who underwent immediate surgery after the initial US examination and did not undergo CT were excluded from this analysis. * The specificity and PPV of findings at second US could not be calculated because the radiologist was aware of CT results at the time of this examination. Numbers are those of patients verified to have this finding at CT or surgery. Only parenchymal injuries, not the presence of free fluid, were considered. Including bowel, mesenteric, bladder, and pancreatic injuries. NPV CT Scanning and Second US Examination CT scanning was performed with one of two single-section spiral CT units (PQ 5000, Marconi Medical Systems, Cleveland, Ohio; or CT/i High Speed, GE Medical Systems, Milwaukee, Wis), typically within 30 minutes after US. CT was routinely performed after contrast material had been injected intravenously as a power-injected bolus of 140 ml of 240 mg of iodine per milliliter at a rate of 3 ml/sec. A uniphasic injection of intravenous contrast material with a scan delay of 60 seconds was used. Whenever possible, given the clinical circumstances, oral contrast material (diatrizoate sodium, 1% Hypaque) was administered in a dosage of 300 ml 15 minutes before scanning and an additional 100 ml immediately before scanning. CT scanning was performed from the lung bases to the pelvis with 5-mm contiguous sections and a table speed of 5 mm/sec (pitch, 1). CT images were initially interpreted by the in-house radiology resident and were reviewed a second time by members of the attending radiology staff (P.A.P., K.K.). CT results were interpreted without knowledge of US results. Organ injuries were scored with regard to their severity. Spleen and liver injuries, respectively, were scored according to the American Association for the Surgery of Trauma (AAST) injury scale classification and an AAST-adapted CT-based classification (21,22). Serious and potentially life-threatening injuries were defined as lesions that required surgery or embolization as well as splenic injuries of grade II or higher and liver injuries of grade III or higher because of the potential of such splenic and liver injuries to result in massive delayed bleeding, even when clinical follow-up is uneventful (23 25). All patients with a false-negative US result for free fluid or organ injury underwent a second US examination that was performed within 6 hours after CT by an attending radiologist (P.A.P. or K.K.) with the same equipment used at admission US. The purpose of the second US examination was to enable retrospective identification of the specific organ injury (or free fluid) that was overlooked at admission US. Therefore, the radiologist who performed the second US examination was aware of the CT findings. The second US examination was performed in the best possible environmental conditions (eg, in a dark room, with removal of plasters if possible, and with no time limitation) in an isolated examination room in the emergency or intensive care department. Any time the culde-sac was not clearly visualized and no free intraperitoneal fluid was depicted elsewhere, the bladder was filled with saline. A hard-copy film was obtained to illustrate the presence or absence of new US findings. The purpose of the second US examination was to assess whether the lesion was conspicuous or still undetectable at US in optimal conditions. Color Doppler examination of injured areas was systematically performed during the second US examinations. Follow-up and Data Analysis Results of clinical and surgical followup, as recorded in medical and surgical records, were obtained for each patient up to the time of discharge from the hospital. US results were compared with CT and/or surgical results the standards of reference so that we could determine the sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of US for demonstrating free peritoneal fluid only, organ injury only, and both free peritoneal fluid and organ injury. If the initial US examination revealed the presence of free fluid that was not seen at subsequent CT but was confirmed at the second US examination, it was considered to have yielded a true-positive result. The amount of free fluid was assessed only when CT revealed fluid that was missed at initial US. For patients with multiple organ injuries, the US examination was considered to have yielded a true-positive per-patient result for organ injury analysis if at least one of the injuries was demonstrated at admission US. When evaluated for the presence of both free fluid and organ injury, the results of admission US were considered true-positive if at least one organ injury or the presence of free fluid was depicted. If the second US examination revealed injury and/or free fluid that was not seen at admission US, the admission US result Volume 227 Number 1 US in Blunt Abdominal Trauma 97

4 was reclassified as true-positive rather than false-negative. Since the sonologist was aware of the CT results when the second US examination was performed, it was not possible to calculate specificity and PPV in this setting. Results for patients who were hemodynamically unstable at or soon after admission were analyzed separately from those for patients who remained hemodynamically stable after admission. RESULTS Patient Characteristics Among the 439 patients who underwent abdominal US during the 2-year study period, 222 were considered free of intraabdominal injury and did not undergo further abdominal investigations. None of these patients was readmitted to our hospital with abdominal complaint due to trauma. The 217 other patients were included in this series. There were 150 men and 67 women. One hundred fifty-three (71%) of the 217 injuries were due to motor vehicle accidents; 40 (18%), to falls; and the remaining 24 (11%), to interpersonal violence (n 5), skiing accidents (n 3), or miscellaneous other causes (n 16) (percentages do not add up to 100 due to rounding). Fifty-one percent (110 of 217) of patients had at least one visceral injury that was confirmed at CT, surgery, or autopsy. Table 1 illustrates the frequency of organ injuries in our study population. Two hundred five patients were hemodynamically stable and underwent subsequent CT. At least one intraabdominal organ injury was found in 99 (48%) of the 205 patients. Sixty-nine (70%) of the injuries were considered life-threatening, and 28 (28%) required either surgical repair or angiographic embolization. Twelve patients were hemodynamically unstable and underwent immediate surgery after the initial US examination was performed. Ten (83%) of them were found to have a severe abdominal injury at surgery. Value of US in Hemodynamically Stable Patients Free fluid detection. Table 2 shows the US results in hemodynamically stable patients. Admission US did not depict free fluid in six (7%) and second US did not depict free fluid in three (4%) of 83 patients found to have free fluid at CT or surgery. In all false-negative cases, the quantity of free fluid was very small and the quality of the US examination was Figure 1. Images in an 18-year-old man who was admitted to the hospital after interpersonal violence and who complained of mild abdominal pain. The results of admission US (not shown) were normal except for the presence of a small amount of free fluid. (a) Subsequently obtained transverse CT scan of the abdomen demonstrates a grade III laceration (arrow) of the posterior aspect of the spleen. (b) Sagittal oblique long-axis image of the spleen obtained at a second US examination does not demonstrate any parenchymal abnormality. The admission and second US examinations were considered to have yielded a false-negative result for organ injury. reported as low. Two of the six patients in whom admission US did not depict free fluid were obese. Organ injury detection. When compared with CT results, admission US failed to depict at least one organ injury in 60 (29%) of the 205 patients. Admission US was 41% (in 39 of 99 cases) sensitive in the demonstration of at least one organ injury, regardless of whether free fluid was present or not. Therefore, 60 patients were considered to have falsenegative results for organ injuries and underwent a second US examination (Figs 1 3). Sensitivity increased to 55% (54 of 99 cases) at the second US examination. Liver lacerations or contusions were more easily detected at US than any other visceral abdominal injury, as shown in Table 2 and Figure 4. In no case did US reveal a parenchymal injury that was not depicted at CT. In two patients, an injury to the small bowel was not shown at CT but was found at subsequent surgery. Since both patients underwent a second US examination, results of which were considered normal, their US results were considered false-negative for organ injury. Forty (89%) of the 45 liver or splenic lacerations that were detected at admission or second US appeared as hyperechoic areas (Fig 4); five (11%) appeared as hypoechoic areas (Fig 5). At color Doppler US, decreased vessel visibility was observed within hyper- or hypoechoic parenchymal lesions, but never in normoechoic lesions. Therefore, compared with conventional US, color Doppler US did not depict any additional parenchymal lesions at either the admission or the second US examination. Table 3 shows the sensitivity of admission US in the depiction of splenic and liver lacerations or contusions with regard to the severity of the injury and the diagnostic criteria used. Admission US results were considered positive for organ injury if free fluid and/or a parenchymal abnormality was visible. The sensitivity of US in the depiction of parenchymal injuries increased with the grade of the lesion. Compared with analysis of free fluid alone, parenchymal analysis did not increase the sensitivity of US for splenic lesions at any grade. Compared with analysis of free fluid alone, parenchymal analysis did improve the detection of true-positive cases of injury by 17% in livers with grade II or grade III lacerations. Detection of organ injuries without associated free fluid. Thirty-one (31%) of 99 patients with CT- or surgically proved organ injuries had no associated free fluid at the time CT was performed. Free fluid was later depicted in six (19%) of these patients at second US. In other words, the presence of free fluid was never demonstrated in 25 (25%) of 99 patients with organ injury. Fifteen (22%) of 69 patients with life-threatening injury and three (11%) of 28 patients who underwent surgery or angiographic embolization did 98 April 2003 Poletti et al

5 not have associated free fluid at the time CT was performed. The majority of cases of organ injury without associated free fluid were not detected at US. Table 4 shows the results of US in patients with organ injury but no associated free fluid. The organ injury group includes both patients with life-threatening injury and those who underwent surgery or embolization; the group of patients with lifethreatening injury includes the group of patients who underwent surgery or embolization. Table 5 shows the results of the admission and second US examinations in hemodynamically stable patients with regard to the reported quality of the admission US examination. The main reason for the low quality of 19 examinations was obesity in seven (37%), distracting environmental conditions in five (26%), restlessness of the patient in three (16%), air distention of the bowel loops in three (16%), and the patient s intense abdominal pain in one (5%). Six (32%) of these 19 patients were found to Figure 2. Images in a 54-year-old woman who was admitted to the hospital after a motor vehicle collision. (a) Oblique long-axis image obtained at admission US does not demonstrate any injury of the right kidney. (b) Subsequently obtained transverse CT scan demonstrates a large laceration (arrow) of the right kidney that is surrounded by an extensive hematoma (arrowheads). (c) Oblique long-axis image obtained at second US reveals a slightly heterogeneous area (between crosshairs) in the lower portion of the right kidney. The admission US examination was considered to have yielded a false-negative result for kidney injury (demonstrated at CT and second US) in this patient. have an organ injury at CT; admission US results were false-negative in four (67%) of these six patients, and second US results were false-negative in three (50%). Detection of free fluid and/or organ injury. Results of 72% percent of the admission US examinations were truly positive (ie, in 71 of 99 cases) and results of 84% of the second US examinations were truly positive (ie, in 83 of 99 cases) for either free fluid or organ injury with regard to the presence of an organ injury at CT or surgery. The presence of free fluid at admission US had a sensitivity of 65% (64 of 99 cases) and a specificity of 82% (87 of 106 cases) in heralding the finding of visceral injury at CT or surgery. In this setting, a positive US result for free fluid in the absence of organ injury was considered a false-positive result. Fifteen (7%) of the 205 hemodynamically stable patients had free fluid at admission US but no associated parenchymal injury at CT. Free fluid was not revealed at CT in four (27%) of these patients. However, the presence of free fluid in these four patients was confirmed at review of results from both the admission and the second US examinations. These US results were considered truepositive. The presence of free fluid could be explained in nine of the 15 patients; these nine patients either had a concomitant pelvic fracture or were women who were in the middle of their menstrual cycles. Clinical follow-up of five (83%) of the six patients with unexplained isolated free fluid was uneventful. One of the six patients developed pneumoperitoneum 3 days after admission; perforation of the small bowel was revealed at surgery. Value of US in Hemodynamically Unstable Patients Twelve patients were hemodynamically unstable at or soon after admission. Two died immediately after admission. Autopsy did not reveal any abdominal injury in either patient. Ten other patients had abdominal organ injury with a large amount of free intraperitoneal fluid and underwent immediate surgery (without subsequent CT or US). When the results of surgery were used as the standard of diagnosis, the sensitivity and specificity of admission US in the depiction of free fluid were each 100% (10 of 10 cases and two of two cases, respectively). The sensitivity and specificity of admission US in the demonstration of organ injury in these 10 patients were 50% (five of 10) and 67% (two of three), respectively. DISCUSSION This investigation was focused on assessment of the limitations of US as a triage tool for patients suspected of having blunt abdominal trauma. With CT findings as the standard of diagnosis, the sensitivity of US for the demonstration of free fluid was 93% (77 of 83 cases) in hemodynamically stable patients and was 100% (10 of 10 cases) in hemodynamically unstable patients. These excellent results are in accord with those of previous studies, in which sensitivity values for the demonstration of intraperitoneal free fluid ranging from 84% to 98% were observed when results of CT, deep peritoneal lavage, and clinical follow-up were used as the standard of diagnosis (5,17,26). However, the results of the present study demonstrated that admission US has low sensitivity in the depiction of organ injuries. The value of US in revealing an organ injury varied greatly with the location of the lesion: Splenic injuries were missed more often (sensitivity, 27% [12 of 44 cases]) than liver injuries (sen- Volume 227 Number 1 US in Blunt Abdominal Trauma 99

6 Figure 3. Images in a 51-year-old woman admitted after a motor vehicle accident. (a) Sagittal oblique image obtained at admission US reveals a diffusely thickened hypoechoic duodenal wall (between crosshairs) that contains hyperechoic material consistent with blood and is surrounded by free fluid (arrowhead). (b) Subsequently obtained transverse CT scan reveals an area of thickening of the duodenal wall (black arrowheads) that is surrounded by free fluid (white arrowhead). A pancreatic injury (arrow) is also seen. The admission US examination was considered to have yielded a true-positive result for bowel injury. Figure 4. Images in a 21-year-old woman admitted to the hospital with diffuse abdominal pain after trauma. (a) Transverse image obtained at admission US shows a hyperechoic area (arrowheads) in the right lobe of the liver. (b) Subsequently obtained transverse CT scan of the abdomen reveals a grade III liver laceration (arrowhead). The admission US examination was considered to have yielded a truepositive result for liver laceration. sitivity, 51% [21 of 41 cases]). This discrepancy can be explained by the larger size of the liver and the fact that it can be more easily accessed with the US probe, enabling US to be performed even in the presence of, for example, plasters or gaseous abdominal distention. As reported in the literature, the spleen was the most frequent site of organ injuries in our series. This result is sobering, because trauma to the splenic parenchyma can result in massive and unpredictable delayed bleeding (23,24,27,28). In the current series, if patients with admission US results that were negative for both free fluid or organ injury had been discharged to their homes without first undergoing CT, 12 (24%) of 49 splenic injuries and 10 (23%) of 43 liver injuries would have been missed. Nine (18%) of these splenic injuries and four (9%) of these liver injuries were considered potentially lifethreatening. The low sensitivity of US in the demonstration of splenic lesions did not substantially increase at the second US examination, which was performed in ideal conditions of use. Indeed, 29 (66%) of 44 splenic lesions were still missed at the second US examination, even though the operator was aware of the CT results. Therefore, the results of our study suggest that the limitations of US in the depiction of splenic injuries are related more to the US technique itself than to possible distractions in an emergency department environment. The results outlined in Table 3 indicate that the diagnosis of possible splenic injuries at US depends on the grade of the lesion and the presence of free fluid. Analysis of the parenchyma alone at US revealed mainly grade IV and grade V lesions (sensitivity, 65% [11 of 17 cases]). However, splenic lesions would have been diagnosed in 37 (76%) of 49 cases on the basis of the presence of free fluid at admission US. For the depiction of renal and adrenal injuries, US had moderate sensitivity compared with its sensitivities for the depiction of liver and splenic injuries. Other intraabdominal injuries, which mainly consisted of bowel and mesenteric abnormalities, were usually not detected at admission US. In our study, only four (33%) of 12 such injuries could be detected at second US. Similar observations for bowel and mesenteric injuries have already been reported (19,29). However, bowel and mesenteric injuries often occur in more severely ill patients and do not carry a high potential for sudden massive bleeding. An important finding of this study is that the presence of free fluid in hemodynamically stable patients is not well correlated with the presence or absence of an abdominal organ injury. Indeed, 31 (31%) of 99 patients with organ injuries did not have associated free fluid. Because depiction of free fluid at US in hemodynamically stable patients is generally considered an indication for subsequent CT, a sensitivity of 65% (64 of 99 cases) for the finding of free fluid at US in the indirect diagnosis of organ injury is disappointing. Repeating US to try to detect free fluid that had been revealed at CT improved the sensitivity by only 3.6% (three of 83 cases). This poor result is easily explained by the high number of organ injuries that did not have concomitant hemoperitoneum or hemoretroperitoneum: 31 (31%) of 99 injuries at admission US and 25 (25%) at second US. Our findings are in accord with those of a study by Shanmuganathan et al (16), who reported that 34% of patients with blunt trauma with organ injury did not have associated free fluid at admission CT. However, 17% of them required surgery or angiographic embolization (16). In our study, 15 (48%) of 31 instances of organ injury without free fluid were considered potentially life threatening, and three (20%) of those 15 instances had to be treated with surgery or angiographic embolization. Subsequent free fluid was seen at second US in six of 31 patients without free fluid at admission due to the time between CT and second US. However, in the remaining 25 patients, the second US examination still failed to de- 100 April 2003 Poletti et al

7 pict 11 potentially life-threatening injuries, two of which (18%) required surgery. In our series, the presence of free fluid was not depicted at admission US in two (25%) of eight grade III splenic lacerations and in seven (39%) of 18 grade III liver lacerations. These observations also substantiate the findings of Shanmuganathan et al (16), who reported that up to 40% of splenic or liver lacerations without concomitant free fluid were of a high AAST grade. Because of the limitations of using free fluid analysis at US to predict the presence of an organ injury, some authors advocate solid organ screening as part of the initial evaluation (3,8,17). In our series, adding analysis of parenchymal lesions to analysis of free fluid improved the sensitivity of admission US (72%, 71 of 99 cases) by only 7% compared with the analysis of free fluid alone (65%, 64 of 99 cases). Since US has been found to be very sensitive in the depiction of free fluid, this lack of improvement in sensitivity can be explained only by a lack of sensitivity for detecting parenchymal injuries. Indeed, admission US was only 41% (in 39 of 99 cases) sensitive in directly demonstrating an organ injury. Figure 5. Images in a 22-year-old man admitted to the hospital after a motor vehicle accident. (a) Sagittal long-axis image obtained at admission US demonstrates a normal-appearing spleen. A large amount of free fluid was also revealed at this examination (image not shown). (b) Subsequently obtained transverse CT scan depicts an extensive splenic laceration (arrowhead). Hemoperitoneum is seen in the perisplenic (white arrow) and perihepatic (black arrow) areas. (c) Sagittal oblique longaxis image obtained at second US reveals only a small hypoechoic lesion (arrowheads) in the splenic parenchyma. The admission US examination was considered to have yielded a falsenegative result for splenic laceration. Sensitivity improved at second US by only 15% (15 of 99 cases), despite the fact that the radiologist was aware of the CT findings and specifically sought to demonstrate them at US. One advantage of our study was the systematic use of results of CT or surgery as the standard of diagnosis in a consecutive series of patients. Therefore, the results of our study do not confirm the high sensitivity of 87% that has been reported for US in the identification of organ injuries in patients with blunt abdominal trauma (20). In the study of Yoshii et al (20), the true amount of false-negative US results is likely to have been underestimated. Our observations suggest that the utility of abdominal US in the assessment of blunt abdominal trauma is limited by the technique itself. Improving the conditions of use would only slightly diminish the rate of false-negative cases. Indeed, in the group of patients for whom the quality of the admission US examination was reported as good, the sensitivity of admission US and second US, respectively, in the depiction of organ injury did not exceed 77% (57 of 75 cases) and 85% (64 of 75 cases) (Table 5). One of the limitations of the present study was the limited follow-up of patients with negative results at admission US that were associated with negative results of physical and laboratory investigations. More than half (n 222) of all trauma patients admitted to our level I center during the study period who underwent abdominal US at admission fulfilled these criteria and did not undergo further radiologic investigations after US results were considered negative. This method of triage is considered cost-effective in our hospital, yielding a prevalence of organ injuries in our patient population of 48%. Therefore, CT was not performed systematically. Use of this method of triage (US and physical and laboratory investigations) can potentially lead to an underestimation of false-negative cases. Since none of the 222 patients in this study who underwent abdominal US without subsequent CT developed any abdominal problem, this possible selection bias should be limited to minor injuries only. The use of this method of triage most likely explains the absence of grade I liver lacerations detected at CT in our group of patients. However, since the main goal of our investigation was to perform a technical analysis of US limitations rather than a clinical evaluation of the method of triage, we excluded all patients who did not undergo CT or surgical follow-up. Because the time between US and CT varied, it is possible that some bleeding did occur in the short time intervals, thus leading to an overestimation of false-negative results at admission US. However, the sensitivity of admission US in the detection of free fluid was excellent (93%), and at second US this sensitivity was increased by only 3%. This means that the phenomenon of subsequent bleeding occurred in only a small number of patients in this study. Therefore, our results suggest that repeating the abdominal US examination after an initial normal US result will probably not boost the sensitivity of US in demonstrating a traumatic abdominal injury. In most studies in which the value of US in trauma patients is assessed, no differentiation is made between patients who are hemodynamically stable at admission and patients who are not (3,11, 17,20). However, the purpose of the US examination is different in these two patient populations. In hemodynamically stable patients, the main objective at US is to assess the presence of intraabdominal injury so that those patients who require further investigations or clinical Volume 227 Number 1 US in Blunt Abdominal Trauma 101

8 TABLE 3 Value of US Performed at Hospital Admission for Diagnosis of Splenic and Liver Lacerations according to Severity of Injury and Diagnostic Criterion Used Injury and Severity* Free Intraabdominal Fluid Only observation can be identified. Therefore, the low sensitivity of US in the identification of organ injuries should moderate the role of US results in the decision to discharge patients without performing other investigations because of the risk that a life-threatening injury may be overlooked. In hemodynamically unstable patients who cannot be transported to CT facilities, the main purpose of abdominal US is to rapidly depict or enable the exclusion of the presence of massive hemoperitoneum as a source of bleeding and to direct the clinician to the most urgent lifesaving therapeutic procedure. In this context, missing an injury that is not associated with the presence of free fluid will have no substantial adverse effect. Indeed, it is unlikely that an injury without substantial hemoperitoneum will require an immediate surgical procedure. Once the patient has been treated, he or she will undergo temporally remote subsequent investigations and clinical observation. Logically, the amount of free fluid will be greater in the presence of a hemodynamic impairment, leading to a better performance of US in this setting. In our series, among the 12 patients with blunt abdominal trauma who were hemodynamically unstable at admission, 10 had a severe abdominal injury that was responsible for the bleeding. In these 10 patients, US yielded excellent sensitivity and specificity values at analysis of free fluid only. However, the number of patients in this group was small, and these results therefore have only an indicative value. In spite of the difficult conditions involved in the use of US in hemodynamically unstable patients, parenchymal injuries were revealed in 50% of such patients a rate slightly higher than that achieved in hemodynamically stable patients. This can be explained by the fact that severe injuries are easier to identify at US than are minor injuries. In conclusion, in most of the usual conditions of use, US is at least as effective as CT in the detection of free intraperitoneal fluid. This makes US a very useful tool for assessment of the presence of hemoperitoneum in hemodynamically unstable patients. In hemodynamically stable patients with blunt abdominal trauma, US is limited mainly by its low sensitivity in directly demonstrating organ injuries, especially splenic lacerations, even with optimal conditions of use. In this setting, up to 31% of CTproved intraabdominal injuries did not have associated free fluid. Methodologic improvements, such as the use of US contrast media, might increase the value of US in patients with abdominal trauma. Further studies are required to assess the potential of this approach. Diagnostic Criterion at US Organ Injury Only Free Intraabdominal Fluid and Organ Injury Splenic laceration Grade I (n 9) 6 (67) 0 6 (67) Grade II (n 15) 9 (60) 2 (13) 9 (60) Grade III (n 8) 6 (75) 3 (38) 6 (75) Grades IV and V (n 17) 16 (94) 11 (65) 16 (94) All grades (n 49) 37 (76) 16 (33) 37 (76) Liver laceration Grade II (n 14) 6 (43) 6 (43) 8 (57) Grade III (n 18) 11 (61) 9 (50) 14 (78) Grade IV (n 11) 11 (100) 7 (64) 11 (100) All grades (n 43) 28 (65) 22 (51) 33 (77) * Numbers of injuries are those observed at CT or surgery (the standards of diagnosis in this study). None of the patients in this study had a grade I liver laceration. Data are numbers of patients with this finding. Numbers in parentheses are percentages. Data are numbers of organ injuries directly visualized at US. Numbers in parentheses are percentages. Compared with analysis of free fluid only, analysis of organ injury only did not enable the detection of additional splenic injuries and was only of limited value in the detection of liver injuries. Data are numbers of instances in which both parenchymal and free-fluid findings at US indicated the presence of organ injury. Numbers in parentheses are percentages. TABLE 4 Value of US in Depicting CT-proved Organ Injuries That Were Not Associated with Free Fluid Organ Injuries without Associated Free Fluid Initial US Examination False-Negative Rate Second US Examination All injuries 84 (26/31) 68 (17/25) Life-threatening injuries* 80 (12/15) 64 (7/11) Injuries requiring surgery or embolization 100 (3/3) 50 (1/2) Note. Numbers in parentheses are those used to calculate the percentages. Depiction of free fluid and/or organ injury at US was considered a true-positive result. * Including nine splenic injuries, four liver injuries, and two other organ injuries. TABLE 5 US versus CT Results with Regard to Quality of Initial US Examination in 205 Patients Quality of Initial US Examination Sensitivity of Initial US vs CT Specificity of Initial US vs CT Sensitivity of Second US vs CT High (n 140) 77 (57/75) 95 (62/65) 85 (64/75) Medium (n 46) 69 (22/32) 86 (12/14) 81 (26/32) Low (n 19) 29 (2/7) 75 (9/12) 57 (4/7) Note. Numbers in parentheses are those used to calculate the percentages. Depiction of free fluid and/or organ injury at US was considered a true-positive result. The specificity of findings at second US could not be calculated because the radiologist was aware of CT results at the time of this examination. References 1. Goldberg BB, Clearfield HR, Goodman GA, Morales JO. Ultrasonographic determination of ascites. 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