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Original Research |
1 Emergency Department, Radiology Unit, S. Orsola-Malpighi Hospital, University
of Bologna, Via Massarenti 9, 40138 Bologna, Italy.
2 Internal Medicine Department, S. Orsola-Malpighi Hospital, University of
Bologna, Bologna, Italy.
3 Emergency Department, Medicine Unit, S. Orsola-Malpighi Hospital, University
of Bologna, Bologna, Italy.
4 Radiology Department, S. Orsola-Malpighi Hospital, University of Bologna,
University Hospital, Bologna, Italy.
Received January 7, 2005;
accepted after revision February 28, 2005.
Address correspondence to M. Valentino
(valentino{at}aosp.bo.it).
Abstract
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SUBJECTS AND METHODS. Sonography, contrast-enhanced sonography, and CT were performed to assess possible abdominal organ injuries in 69 nonconsecutive hemodynamically stable patients with blunt abdominal trauma and a strong clinical suspicion of abdominal lesions. Sonography and contrast-enhanced sonography findings were compared with CT findings, the reference standard technique.
RESULTS. Thirty-two patients had 35 abdominal injuries on CT (10 kidney or adrenal lesions, seven liver lesions, 17 spleen lesions, and one retroperitoneal hematoma). Sixteen lesions were detected on sonography, and 32 were seen on contrast-enhanced sonography. The sensitivity and specificity of sonography were 45.7% and 91.8%, respectively, and the positive and negative predictive values were 84.2% and 64.1%, respectively. Contrast-enhanced sonography had a sensitivity of 91.4%, a specificity of 100%, and positive and negative predictive values of 100% and 92.5%, respectively.
CONCLUSION. Contrast-enhanced sonography was found to be more sensitive than sonography and almost as sensitive as CT in the detection of traumatic abdominal solid organ injuries. It can therefore be proposed as a useful tool in the assessment of blunt abdominal trauma.
Keywords: abdominal imaging • contrast media • CT • emergency radiology • sonography • trauma
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Sonography for blunt abdominal trauma was first described in 1971 [4], and it is currently the primary screening examination for blunt abdominal trauma in most trauma centers of Europe [5] and Asia [6] and in some centers in the United States [7-14]. Its main application is the detection of free abdominal fluid, and it plays an important role in the evaluation of pleural and pericardial fluid. This examination is known worldwide by the acronym FAST—focused assessment with sonography for trauma [15]. The advantages of sonography are that it is nonionizing, portable, and rapid and accurate in excluding intraperitoneal fluid without interrupting resuscitation. In previous studies, the sensitivity of sonography for the detection of free abdominal fluid ranged widely from 63% to 99% [11, 12] and was significantly lower for solid organ lesions [16]. Furthermore, some researchers have reported that 29-34% of solid organ lesions can occur in trauma patients without hemoperitoneum [17, 18]. CT therefore remains the radiologic standard for evaluating patients with abdominal trauma [19-21].
In recent years, a new sonography technique using contrast agents, contrast-enhanced sonography, has been developed. Contrast-enhanced sonography is based on contrast-specific software and technology, operating at a low mechanical index, and is able to analyze resonance signals originating from second-generation contrast agents without bubble destruction, thus allowing continuous real-time sonography during vascular perfusion of the contrast agent [22-25]. Contrast-enhanced sonography has been evaluated in the characterization of focal liver lesions in a large series of patients [26], and its role in the assessment of blunt abdominal trauma patients has been shown [27-29].
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Sixty-nine (8.2%) nonconsecutive hemodynamically stable patients with clinical suspicion of solid abdominal injuries or positive FAST examination (or both) underwent contrast-enhanced sonography and subsequently underwent CT examination. A clinical sign of organ injury (i.e., pain or biochemical changes) or Blumberg sign was present, respectively, in 29 (42.0%) and four (5.8%) patients.
The 69 patients examined consisted of 51 males (73.9%) and 18 females (26.1%); their average age was 38.4 ± 18.5 (SD) years (range, 15-89 years). Blunt abdominal trauma was caused by vehicle crashes or resulted from accidental trauma, trauma while working, or trauma from participating in sports, accounting for 55.6%, 27.0%, 12.6%, and 4.8% of the cases, respectively.
Informed consent was not routinely obtained for the FAST examination, whereas it was required for the contrast-enhanced sonography and CT examinations. None of the patients refused to undergo contrast-enhanced sonography or CT. The study was approved by the ethics review board of our institution.
Sonography and Contrast-Enhanced Sonography Examinations
The sonography and contrast-enhanced sonography examinations were performed
by sonographers with at least 5 years of experience. The FAST examinations
were performed using an Esaote Caris Plus machine (Ansaldo) equipped with a
3.5-MHz curved-array probe. The sonography trauma protocol used for all
patients in the present study consisted of evaluation of the right and left
upper quadrants of the abdomen, epigastrium, paracolic gutters,
retroperitoneal space, and pelvis. A filled bladder was requested. Attention
was focused on the presence of free fluid, and abdominal organs were also
evaluated for parenchyma abnormalities.
The contrast-enhanced sonography studies were performed using an ATL HDI 5000 machine (release 10.4, Philips Medical Systems) equipped with a 5-2-MHz curved-array probe and contrast-specific software operating at a low mechanical index. The contrast medium administered was SonoVue (BR1, Bracco), a second-generation blood pool sonography agent that is available commercially in Europe. Because of its current availability in Italy, no further authorization was required. SonoVue consists of stabilized aqueous suspension of sulfur hexafluoride microbubbles with a phospholipid shell of a diameter that allows both pulmonary and sinusoidal passage. The low solubility of the gas of SonoVue and the high resistance of its shell to the mechanical effect of the ultrasound beam give this contrast agent a long duration; therefore, contrast-enhanced sonography can be used to evaluate all the vascular phases (i.e., arterial, venous, and parenchyma) in real time. By using a low mechanical index, the signals from stationary tissue are almost totally cancelled. The microbubbles produce a high-amplitude signal in well-perfused parenchyma. The microbubbles of the sonography contrast agents reflecting the ultrasound beam emit harmonics at twice the insonation frequency: a special transducer acquires this type of signal by separating the fundamental frequency from the second harmonic using inverted phase pulses (pulse-inversion imaging).
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Examinations lasted 4-6 min, and all were recorded as moving images on an optical disk. Interpretation of the study was contemporaneous with the investigation, on the basis of the alteration of the contrast enhancement of the parenchyma. Static images were also obtained to permit the measurement of the size of the lesions and their relation to the most important structures, such as the vessels and capsule. In accordance with the aim of the study, the examinations were finally reevaluated and compared with the CT findings.
CT Examination
For the whole study population, unenhanced and contrast-enhanced CT
examinations were performed within 30 min after contrast-enhanced sonography.
All CT examinations were performed by experienced radiologists who were
blinded to the results of both sonography and contrast-enhanced sonography.
The CT examinations were performed with a single-detector unit (Emotion,
Siemens Medical Solutions) with a 5-mm collimation, 7.5-mm/sec table speed,
and 5-mm reconstruction interval. A 150-mL dose of nonionic contrast medium
(Iomeron, Bracco) was injected at a rate of 2 mL/sec. The acquisition delay
was 60 sec.
All these studies were recorded on optical disk to permit reevaluation. The lesions were graduated according the Organ Injury Scale of the American Association for the Surgery of Trauma [30].
Data and Statistical Analysis
For statistical analyses, sonography or contrast-enhanced sonography
findings were considered positive if a parenchyma abnormality that could be
consistent with trauma was identified on CT. Positive sonography and
contrast-enhanced sonography findings were considered true-positive if CT
revealed evidence of the parenchyma injury; findings were considered
false-positive if the injury was not confirmed on subsequent CT. Negative
sonography findings were counted as true-negative if CT findings were negative
and the patient had an uneventful clinical course; findings were counted as
false-negative if CT revealed parenchyma injury.
A solid organ injury on sonography was considered if an intraparenchymal hyper- or hypoechoic area or a distortion of the normal echoic structure was seen (Fig. 1). Nontraumatic lesions, such as well-visualized simple cysts that allowed definitive diagnosis on sonography, were considered negative findings.
On contrast-enhanced sonography, organ injuries such as contusion appeared as a defect of vascularization in a well-perfused parenchyma: a slightly hypoechoic area with ill-defined borders (Figs. 2A and 2B). The appearance of a strongly hypoechoic area against the homogeneously increased echogenicity of the parenchyma with or without interruption of the profile was consistent with the presence of a laceration (Figs. 3A and 3B). The absence of parenchyma perfusion was a sign of hypovolemic shock or arterial injury (Figs. 4A and 4B). Focal extravasation of contrast medium suggested active hemorrhage (Figs. 5A and 5B).
At the end of the study, each examination was further evaluated for free fluid and abdominal lesions by an independent expert sonographer and radiologist.
Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for sonography and contrast-enhanced sonography with a bayesian calculator.
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Table 1 shows a comparison of the results obtained with CT and contrast-enhanced sonography. Sensitivity, specificity, positive predictive value, and negative predictive value of sonography and contrast-enhanced sonography versus CT are listed in Table 2.
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Sonography Findings
FAST examination depicted free fluid in 24 of the 30 patients found to have
free fluid on CT (80% sensitivity). Solid organ injuries were detected on
sonography in 16 of 35 CT-detected solid organ lesions, although these
included three false-positive findings that were angiomas, two in the liver
and one in the spleen. The sensitivity of sonography was therefore 45.7% and
its specificity, 91.8%; the positive and negative predictive values were 84.2%
and 64.1%, respectively. Sonography was able to reveal four of seven liver
lesions with a sensitivity of 57.1%, eight of 17 spleen lesions with a
sensitivity of 47.1%, and four of 10 kidney or adrenal lesions with a
sensitivity of 40%.
Contrast-Enhanced Sonography Findings
Solid organ injuries were detected on contrast-enhanced sonography in 32 of
35 solid organ lesions, giving to a sensitivity of 91.4%, a specificity of
100%, and a positive and negative predictive value of 100% and 92.5%,
respectively. Contrast-enhanced sonography was able to reveal seven of seven
liver lesions with a sensitivity of 100%, 17 of 17 spleen lesions with a
sensitivity of 100%, and eight of 10 kidney or adrenal lesions with a
sensitivity of 80%. It allowed the correct diagnosis of the sonography finding
that was a false-positive (Figs.
6A and
6B); however, two kidney
lesions and the retroperitoneal hematoma were missed.
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The value of sonography in revealing an organ injury varies greatly with the location of the lesion. In the detection of spleen injuries, the sensitivity of sonography varies from 27% to 68.6%. The larger size of the liver and easier approach to the liver explain the higher sensitivity of sonography for liver lesions, ranging from 51% to 87.5% in different studies. For kidney or adrenal injuries, however, sonography has a low sensitivity (25-40%) [33, 34].
In our study, the sensitivity of sonography in the detection of solid organ injuries was 45.7%, higher in the detection of liver and spleen lesions (57.1% and 47.1%, respectively), lower in kidney or adrenal lesions (40%). In contrast, sonography had three false-positive cases that were liver or spleen angiomas. In our experience, sonography was not able to show satisfactorily small parenchyma injuries or the involvement of the main structures, such as vessels and the capsule.
The advent of the sonography contrast agents and their application in the evaluation of liver lesions [26] have provided new tools for investigating abdominal parenchyma trauma. Catalano et al. [27] have shown that contrast-enhanced harmonic sonography is a promising tool in the evaluation of blunt splenic trauma and is more accurate and informative than standard sonography, correlating better with CT. Like the study of Catalano et al., the present study showed that the main advantage of contrast-enhanced sonography in a trauma setting is to increase the accuracy for detection of solid organ injuries as compared with sonography. In our study, in fact, contrast-enhanced sonography revealed parenchyma lesions that were not visible on sonography, thereby permitting more confidence in the clinical assessment of the trauma patients. The sensitivity with contrast-enhanced sonography improved from 45.7% to 91.4%. Contrast-enhanced sonography permitted a better definition of the limits of the lesion and the normal parenchyma and its extension to the capsule, which was an important criterion for surgery evaluation. Even very subtle lesions, especially inside the spleen, became evident after administration of the contrast agent. Moreover, contrast-enhanced sonography showed some angiographic findings unthinkable on sonography, such as contrast medium extravasation, parenchyma infarction, and vascular pedicle avulsion. Detection of these signs, previously unique to contrast-enhanced CT, was important in the subsequent treatment of the patient. These possibilities are important and represent an interesting application of this new technique.
The solid parenchyma injuries missed on contrast-enhanced sonography and revealed on CT consisted of one retroperitoneal hematoma and two kidney lesions. The retroperitoneal spaces represent sites that are difficult to investigate on both sonography and contrast-enhanced sonography. These areas can be depicted only on the rare occasions when fluid collects inside the peritoneal spaces [34]. For the detection of such injuries, CT therefore remains the reference technique [35]. The retroperitoneal hematoma did not, in any case, require any surgical treatment.
Two kidney lesions were missed on contrast-enhanced sonography, although the kidney is a well-defined organ and is clearly visible on contrast-enhanced sonography; in these cases, the two injuries went unnoticed because they were small and low-grade injuries (grade II on CT), and by the time of follow-up, the two lesions had resolved without any treatment. Therefore, the fact that the lesions were not detected on contrast-enhanced sonography did not change the management of these patients, which was conservative in all cases.
Unlike the findings reported by Poletti et al. [29], no major lesions (CT grade III or higher) were missed on contrast-enhanced sonography in our study. This can probably be explained by the improved sonographic technologies used in our study (release 10.4).
On the basis of these results, contrast-enhanced sonography can replace sonography in the triage of hemodynamically stable trauma patients. The examination is so rapid (4-6 min) that the time of assessment is not unduly prolonged. CT could be reserved for patients with negative findings on contrast-enhanced sonography and clinical suspicion of injury. Contrast-enhanced sonography can be also used in the follow-up of solid organ lesions being treated conservatively.
In conclusion, our study shows that contrast-enhanced sonography may be useful in a trauma setting to examine patients with clinical suspicion of parenchyma lesions. Contrast-enhanced sonography cannot completely replace CT, but it can reduce the use of CT as a screening method.
Acknowledgments
We thank, for his valuable help in writing this paper, Mr. Michael
Webb.
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