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EDUCATION EXHIBIT |
Department of Diagnostic Imaging and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, Maryland
I thank Dr Olmsted for the opportunity to comment on the well-written article by Körner et al (1) in this issue of RadioGraphics, one of several excellent articles about emergency radiology that have come from the University Hospital of Munich in recent years. The use of US in the setting of acute abdominal trauma has a long and controversial history. Issues of concern include the precise role that US should play in the imaging of acute trauma, the level of training required to attain high accuracy in performing the examination and interpreting the results, and the utility of the results (assuming an appropriate level of expertise of the sonographer and interpreting physician) for making triage decisions.
The use of US for the assessment of blunt abdominal trauma is a routine clinical practice in Japan and Europe, and US is the main triage tool in some European countries. FAST was adopted more recently in the United States (2). Surgeons and emergency physicians viewed the procedure as a logical extension of the physical examination, allowing a quick, painless, and low-cost evaluation of the abdomen for free fluid as an indicator of probable intraperitoneal injury. Others saw the potential of US for evaluating the intraperitoneal and retroperitoneal organs, as well, to acquire more precise information for decision making about further imaging studies and treatment (3). In the United States, the FAST approach was emphasized because the presence or absence of hemoperitoneum was considered the key factor in deciding whether to continue observation and monitoring of the patient or to undertake further imaging examinations and, possibly, intervention (4). Over time, inspections for pleural and pericardial fluid and for pneumothorax became additional indications for US in the acute trauma setting. Slowly, a consensus has been developing around the "best" applications of abdominal US in trauma. Of course, there are dissenting views.
With regard to the question of who should perform US, the answer depends more on staffing practices in the institutional emergency department than on control by a particular specialty. Although radiology department staff tend to view US as part of their domain, as a diagnostic method that requires radiology residency training to achieve accurate results, it has been shown that relatively little supervised experience may adequately prepare a physician to perform US with high accuracy (5). Perhaps several hours of didactic training in physics, common diagnostic pitfalls, proper use of scanning equipment, and interpretation of findings, followed by a written examination, should be required before the US examination of patients is attempted. As reflected in the literature, at least 20–30 supervised patient examinations then should be performed, followed by periodic quality performance "check-ups" (5). The radiology department could and should help in the training process and performance evaluation. Where possible, FAST could be performed by radiology department staff or radiologists in training as part of the trauma team, and this approach might be considered optimal practice. In settings where this is not feasible, other physicians working in the admissions area could perform the US examination. In any case, the study must be done expeditiously, especially in patients whose condition is unstable. Sometimes a combination of initial US performed by a radiologist or a technologist, followed by a repeat US study performed by the clinical physician, offers the best diagnostic and training opportunity. US equipment should be approved by the radiology department before it is used, and regular quality checks of equipment should be performed by sonographers or technologists. It is important also to recognize that in the interpretation of FAST images, as in the interpretation of most diagnostic images, accuracy is not only operator dependent but also involves many other factors, such as the equipment used, the conditions of the examination, and the quantity of fluid present.
Some studies indicate that US of blunt trauma should include an inspection of individual organs in addition to the assessment for intraperitoneal fluid (3). Poletti et al performed an excellent study with results that are germane to this issue. In their study, US was performed by staff radiologists at admission and within 6 hours after admission, under optimal study conditions, to diagnose both intraperitoneal fluid and direct organ injury in 205 hemodynamically stable patients. The results of the initial US examination at admission were correlated with the outcomes of CT and surgery (6). The sensitivity of US for depicting free fluid was 93%, but that for direct depiction of organ injury was only 41%. These statistics improved to 96% and 55%, respectively, at the subsequent US examination. The authors concluded that US, even when performed by well-trained operators, is clearly inappropriate for the triage of patients with acute blunt abdominal trauma when triage is based on the presence and severity of organ injuries (6). The use of contrast material–enhanced US in the diagnosis of organ injuries was not addressed in that study.
Although the accuracy of US for the detection of free fluid generally has been high, there are limitations, as noted in the article by Körner et al. A study performed by Shanmuganathan et al showed that among 466 patients with blunt abdominal visceral injury identified at CT or surgery, 157 (34%) had no evidence of hemoperitoneum and 26 (17%) of these 157 patients had negative results at FAST (7). In a more narrowly focused study by McGahan et al, FAST was not proved accurate for the identification of renal injury (8). FAST images from only seven (35%) of 20 patients with isolated renal injuries showed free fluid in the abdomen, whereas the images from 13 (65%) of 20 patients showed no evidence of free fluid. All seven patients with US findings of free fluid had moderate or severe renal injuries. Renal parenchymal abnormalities were identified at US in eight (22%) of 37 patients with renal injuries. The renal abnormalities were detected more often in cases of severe injury (60%). Isolated renal injuries frequently occur without the presence of free fluid in the abdomen. Furthermore, the US appearance of the kidney often is normal in the presence of acute renal injuries (8).
In another study, Udobi et al reviewed the results of FAST in 75 patients with stab or gunshot wounds, 41 of whom had a proved abdominal injury. Among 54 patients with a negative FAST result, 13 had hemoperitoneum and significant intraperitoneal injury, and another nine had no hemoperitoneum but had injuries requiring surgical repair (9). The overall sensitivity of FAST was a dismal 46%, with a 60% negative predictive value. These results strongly call into question the utility of FAST in patients who have penetrating flank, back, and abdominal injuries but who are not in need of emergency laparotomy. In the study by Udobi et al, positive results at FAST had a 94% specificity and a 90% positive predictive value. These statistics indicate the utility of FAST when results are positive. As in blunt trauma, FAST has a role in penetrating trauma only in the critical circumstance of hemodynamic collapse, to demonstrate or exclude the presence of free fluid in the thoracic or abdominal cavity as a prelude to immediate surgical exploration. In our practice at the University of Maryland Shock-Trauma Center, CT has shown far greater accuracy than FAST for the detection of peritoneal violation (hemoperitoneum) and the need for surgical exploration in cases of nonsuperficial penetrating injury (7).
In another study performed by McGahan et al (10), contrast-enhanced US provided greatly improved depiction of liver and spleen injuries in comparison with unenhanced US. Solid organ injuries usually appeared hypoechoic on contrast-enhanced US images, but a hyperechoic region surrounding the injury also was identified on images of liver injuries. The usefulness of contrast-enhanced abdominal US for the triage of hemodynamically stable patients with blunt abdominal trauma awaits further investigation.
Körner et al make clear that the time needed for extensive scanning and the skill needed for directly detecting or excluding parenchymal injuries make US impractical for that purpose in patients with major blunt trauma (1). Perhaps as important is the fact that many abdominal injuries can be managed nonsurgically (eg, with embolization) with a high success rate (11). When a patient’s hemodynamic status is unstable and cannot be stabilized, nothing except an expedited FAST examination is possible or advisable before proceeding to the operating room. However, in the modern acute trauma care environment, many if not most patients can be resuscitated and hemodynamically stabilized, allowing time to safely perform CT before necessarily proceeding directly to surgery. In some cases, CT may help identify an injury that is causing significant hemoperitoneum but that may be adequately managed with angiographic intervention. If an injury can be safely and successfully treated without laparotomy, the recovery period is typically shorter and there is less likelihood of postsurgical complications.
If US (FAST) is to be relied on, the occasions for its use must be clearly determined by the need for immediate surgical intervention, not transient instability. CT can be performed quickly today, as the CT suite is often close to the admission area where resuscitation and monitoring take place. Moreover, CT can provide a wealth of information about other injuries, such as those to the head, spine, chest, and face. More complete knowledge of the patient’s spectrum of injuries, beyond the mere presence or absence of peritoneal fluid, would likely make for better-informed prioritization of further diagnostic studies or immediate intervention. All patients with an appropriate history of major trauma or concurrent severe major injuries should undergo abdominopelvic CT to definitively identify or exclude significant injuries. A negative result at FAST alone cannot be relied on to exclude significant abdominal injury (12).
The primary extraabdominal application of US in the blunt trauma patient is the assessment of the pericardial and pleural spaces. However, US is less sensitive than CT for the detection of a minimal hemopericardium or a small pneumothorax, which might progress to a life-threatening cardiac tamponade or a tension pneumothorax, respectively, if not detected in the initial imaging work-up. During the global assessment of patients with major blunt trauma, these entities should be excluded with CT, which is far more accurate than radiography for these diagnoses (13).
Finally, my one major criticism of the article by Körner et al is that the authors’ inclusion and discussion of several US images showing direct parenchymal injury may mislead some readers. However, while they describe and illustrate the US appearance of organ injuries, the authors also emphasize that "dedicated" US is not indicated for the vast majority of patients with blunt trauma. I think this is the best take-home message in the article.
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Department of Clinical Radiology, University Hospital of Munich, Munich, Germany
The authors thank Dr Mirvis for his thorough commentary on our article. We fully agree with his argument. However, we would like to point out that at remote hospitals where major trauma is treated, especially in developing countries, the role of US might differ somewhat from that at a level I trauma center (1). If CT is not immediately available or if a patient’s injuries are clinically underestimated and he or she is admitted to a hospital that has no CT capability, US could be the only imaging modality for ruling out or confirming intraabdominal parenchymal injury, even if its sensitivity is considerably lower than that of CT (2–4). That is why we included images of organ lesions in our article. However, we agree that at specialized trauma centers where CT is readily available, US may be considered insufficient to safely rule out organ injury.
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