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1
Department of Radiology, Children's Memorial Hospital, 2300 Children's Plaza,
Chicago, IL 60614.
2
Department of Radiology, University of Chicago Children's Hospital, 5841 S.
Maryland Ave., Chicago, IL 60637.
3
Present address: Department of Radiology, Loyola University Medical Center,
2160 S. First St., Maywood, IL 60153.
4
Department of Surgery, University of Chicago Children's Hospital, Chicago, IL
60637.
5
Present address: 7129 Jahnke Rd., Richmond, VA 23225.
Received July 6, 1999;
accepted after revision November 2, 1999.
Address correspondence to E. C. Benya
Abstract
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SUBJECTS AND METHODS. Fifty-one consecutive children with blunt abdominal trauma requiring abdominal CT were prospectively examined with sonography. Sonograms and CTs were independently evaluated by two radiologists for fluid and organ injury; CT examinations were considered abnormal if either was identified. Differences in CT interpretation were settled by a third observer. Using CT as the truth standard, we calculated the sensitivity, specificity, and negative predictive value of sonography for both observers. Agreement of the sonographic interpretations was evaluated using kappa statistic.
RESULTS. In 33.3% of patients, CT revealed fluid, organ injury, or
both. The sensitivity and specificity of sonography when detection of fluid
was the sole parameter evaluated was 58.8% and 79.4%, respectively, for
observer 1 and 47.1% and 79.4%, respectively, for observer 2. In contrast, the
sensitivity and specificity of sonography when detection of both fluid and
organ injury was evaluated was 64.7% and 79.4%, respectively, for observer 1
and 70.6% and 70.6%, respectively, for observer 2. The negative predictive
value of sonography was 79.4% and 75.0% with evaluation limited to detection
of fluid and 81.8% and 82.8% with evaluation of fluid and organ abnormality
for observers 1 and 2, respectively. Agreement was excellent for sonographic
identification of fluid (
= 0.82) but poor for detection of organ
injury ( = 0.34).
CONCLUSION. The low sensitivity and negative predictive value of sonography when assessing for either fluid alone or fluid and organ injury suggest that a normal screening sonography alone in the setting of blunt abdominal trauma fails to confidently exclude the presence of an intraabdominal injury.
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Twenty-seven of the 51 children presented after having been struck by a motor vehicle while either walking or riding a bicycle. Additional mechanisms of injury included falls in 13, motor vehicle collisions in eight, apparent nonaccidental trauma in two, and assault with a blunt object in one.
Forty-nine of 51 CT examinations of the abdomen and pelvis were performed helically on a HiSpeed Advantage CT scanner (General Electric Medical Systems, Milwaukee, WI) during dynamic bolus administration of IV contrast material with slice collimation ranging from 5 to 10 mm, depending on the size of the child. Two children underwent abdominal CT at outside institutions before being transferred to our institution for further examination and treatment. Oral contrast material was administered to 50 of the 51 patients.
Abdominal sonography was performed with a 128XP10 or Sequoia (Acuson, Mountain View, CA) using a 2.5- to 8-MHz transducer (Acuson), depending on the child's size and body habitus. In all patients, abdominal sonography was performed after abdominal CT. The pediatric radiologist or sonographer performing the sonography was not aware of the clinical history, physical examination, or CT and laboratory results. In all patients, the standard sonographic examination included longitudinal and transverse images of both upper quadrants of the abdomen and transverse views of the pancreas, bladder, and both lower quadrants to the abdomen to detect intraperitoneal and retroperitoneal fluid. A variable number of supplemental transverse and longitudinal images of the solid organs in the upper abdomen were subsequently obtained.
The sonograms and CT examinations were evaluated independently by two
pediatric radiologists. The standard sonograms were first assessed for the
presence or absence of intraabdominal fluid. At the same image-interpretation
session, all sonograms were reviewed for the presence or absence of solid
organ injury and fluid. In 49 of the 51 sonographic examinations, observer 1
performed the sonography and the interpretation of the images was based on
real-time and static images. In the remaining two sonographic examinations,
which were performed by a pediatric sonographer, the interpretation of images
by observer 1 was based on the static images. Observer 2 based interpretation
of the 51 sonographic examinations on static images alone. CT findings were
considered abnormal if either fluid or organ injury was identified, with
differences in interpretation settled by a third observer in 15 cases. Data
analysis included calculation of the sensitivity, specificity, and negative
predictive value for sonographic detection of fluid alone and, subsequently,
sonographic detection of fluid and organ injury using CT as the truth
standard. Additionally, evaluation of the agreement of sonography
interpretations was assessed using the kappa statistic to measure
reproducibility. A value greater than 0.75 denotes excellent
reproducibility and a kappa value of less than 0.4 denotes marginal
reproducibility.
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In all patients, abdominal CT was performed first, followed by sonography. The time between CT and sonography could be accurately measured in 47 children; the mean interval between examinations was 4 hr and 42 min, with a range of 9 min to 15 hr and 43 min. Malfunction of the clock on the sonographic machine resulted in an inability to accurately determine the interval between examinations in four children. The interval between examinations was less than 24 hr in all children.
The sensitivity, specificity, and negative predictive value of sonography
for the two observers using CT as the truth standard are shown in
Table 1. The sensitivity and
specificity of sonographic assessment limited to intraabdominal fluid alone
was 58.8% and 79.4%, respectively, for observer 1 and 47.1% and 79.4%,
respectively, for observer 2. In contrast, complete sonographic assessment for
detection of fluid and organ injury showed sonography to have a sensitivity
and specificity of 64.7% and 79.4%, respectively, for observer 1 and 70.6% and
70.6%, respectively, for observer 2. The negative predictive value of limited
sonography was 79.4% and 75.0% for fluid detection and 81.8% and 82.8% for
complete sonographic examination for observers 1 and 2, respectively. The
agreement was excellent for the sonographic identification of fluid ( =
0.82) but poor for sonographic detection of organ injury ( = 0.34) for
both observers.
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In the trauma setting, peritoneal fluid found by rapid sonographic screening may represent hemoperitoneum, bowel contents or urine after solid or hollow organ injury, or simply physiologic fluid [15]. This type of limited sonographic examination has been given the acronym FAST, for focused abdominal sonogram for trauma [16]. However, detection of fluid on sonography after blunt abdominal trauma is not sufficient to identify all children with intraabdominal injuries because as many as 36% of abdominal injuries caused by blunt abdominal trauma do not have associated free peritoneal fluid [15]. In our series, one child had a liver injury without associated free intraperitoneal fluid. Given this significant limitation of focused abdominal sonography for trauma, we designed our study to determine whether a more complete assessment for both fluid and organ injury on abdominal sonography would improve its accuracy. With abdominal sonography we prospectively examined only those children with blunt abdominal trauma whose mechanisms of injury, physical examination, or laboratory test results led the trauma surgeons to request CT. Thus, our comparison of sonography with CT was limited to patients with a high index of suspicion regarding significant abdominal injury. Unfortunately, neither focused sonography that assesses for fluid nor complete sonography that evaluates for fluid and organ injury is as accurate as CT.
Other investigators have suggested that complete sonography of the abdomen be performed in children after blunt abdominal trauma to fully image the abdomen and pelvis for organ injury in addition to looking for fluid [3,4,5]. In these studies by Luks et al. [3], Katz et al. [4] and Akgur et al. [5], those children in whom sonography failed to reveal intraperitoneal fluid or organ injury typically had no additional imaging to confirm the absence of injuries. Clinical follow-up was used as the truth standard regarding the presence or absence of intraabdominal injury in these studies. Luks et al. reported a sensitivity and specificity of 89% and 96%, respectively, with a negative predictive value of 95% for sonography in the setting of blunt abdominal trauma. These values are considerably better than those from our current study. These differences are best explained by differences in study design. In our series, the findings on abdominal sonography were compared with CT findings in all cases. We considered CT the truth standard against which sonography was measured because these children, in all cases but one, did not undergo surgical exploration. In the series by Luks et al., the truth standard against which sonography was assessed was overall diagnostic workup and clinical course with 44% of children receiving no additional testing to confirm the sonographic findings. Fifty-six percent of children underwent further examination with one or more additional diagnostic tests. In this group, nine children were found to have an injury when a subsequent diagnostic imaging test was performed. Currently, the time for clinical observation of a child by the trauma team is frequently less than 24 hr thus, initial screening test results are relied on to guide treatment decisions.
As expected, in our study population there was increased sensitivity for abnormalities with sonographic assessment for fluid and organ appearance compared with limited sonographic assessment for fluid alone. However, the negative predictive value of only 82-83% for complete sonographic assessment in our study sample suggests that potentially significant injuries in children may be missed with screening sonography even when a complete examination is performed (Fig. 1A,1B). Additionally, although the agreement between both observers was excellent regarding the sonographic detection of fluid, it was poor regarding the presence or absence of organ injuries on sonography, which might further add to the difficulty in determining the appropriate treatment of the injured child (Fig. 2A,2B). Nonoperative treatment of children with solid organ injury requires accurate detection of injuries followed by hospitalization, monitoring, and restriction of activities. Our study suggests that normal sonographic findings fail to assure the absence of intraabdominal injury and, thus, sonography is not adequately helpful to the pediatric trauma surgeon treating the injured child. The level and intensity of treatment varies for mild to severe organ injury, but the child with a solid organ injury is typically observed in the hospital and is not immediately discharged.
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It could be argued that our study was limited by the fact that sonography was performed after CT. However, the pediatric sonographer or radiologist performing the sonography was not aware of the CT results in an attempt to avoid any potential bias toward identifying abnormalities. Because of the absence of in-house sonographers, the decision was made to perform the clinically indicated abdominal CT first to not interfere with patient care. However, all members of the trauma team were made aware of this study and the need to keep the sonographers unaware of the clinical data and CT findings. All sonography was performed by an attending pediatric radiologist or a pediatric sonographer, thus, minimizing operator dependent-related issues of sonographic quality.
In conclusion, our series shows that the detection of abnormalities is improved with a complete sonographic assessment for fluid and organ appearance as opposed to a limited sonographic survey for fluid after blunt abdominal trauma. However, we believe the sensitivity and negative predictive value rate for abdominal sonography are too low for sonography to be suitable for the exclusion of abdominal injury in the hemodynamically stable child with blunt abdominal trauma. CT remains a better screening test in children with suspected injury after blunt abdominal trauma.
Acknowledgments
We thank Edwin Chen, Department of Biostatics, School of Public Health,
University of Illinois at Chicago, for advice on data analysis and David K.
Yousefzadeh, Department of Radiology, University of Chicago Children's
Hospital, for review of CT scans and for helpful comments.
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