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EDUCATION EXHIBIT |
Department of Radiology, University of Alabama at Birmingham, Birmingham, Alabama
Being only human, radiologists remain reluctant to accept change despite the many changes that have taken place in the practice of diagnostic imaging in the past 20 years. We are comfortable with the procedures with which we are familiar and that we know are accurate and effective. To rationally evaluate a proposal for a new method of diagnosing a particular disorder, it is helpful to use three basic principles: (a) Consider the larger picture. (b) Do not force a new test to exactly replicate a tried and true test. (c) Keep in mind the advice derived from the Hippocratic oath: First, do no harm.
As correctly stated in the preceding article by Ali et al (1), urethral injury is not uncommon, especially in males, seen in approximately 10% of males with pelvic fractures. RUG remains the accepted standard of evaluation. It is both sensitive and specific in determining the type of injury (2,3). In the only publication of which I am aware that addresses the possible use of CT for diagnosis of urethral injury, Kane et al (4) concluded: "Our results ... suggest that CT may be as sensitive as cystography in detecting bladder injuries, but urethrocystography is superior to CT in the detection of urethral injuries." However, Ali et al (1) state that certain CT findings are specific for the various types of urethral injury. What is the truth?
The first basic principle to be applied is "consider the larger picture." Although this is probably always true, it is particularly important with trauma victims to consider the patient as a whole. Only by considering all the injuries, often prioritizing the most urgent, can one accomplish the larger goal, which is survival of the patient with the smallest residual disability, within reasonable limits of cost. It is possible that use of a test that is superior to another for accurate diagnosis of a specific injury could result in worse overall outcome, if use of that test compromises detection or management of other more significant injuries. CT has become so widely and frequently used in trauma evaluation because it is very effective in evaluating multiple systems. Most designated trauma centers have installed CT in the trauma area in such a fashion as to allow scanning of even clinically unstable patients, because of its proven effectiveness not only for diagnosis but for selection of patients for surgery and planning of the appropriate surgical intervention.
However, the standard teaching in genitourinary trauma imaging has been that RUG must be the first study in a patient suspected of having urethral injury and must be performed prior to placement of a Foley catheter. The experience at my institution, which is a level 1 trauma center, appears to parallel that implied by Ali et al (1). Because of the recognized value of CT, including CT cystography, as well as the general advantages of having a bladder catheter to monitor urine output, it is very common for a bladder catheter to be placed prior to performance of RUG. Frequently, this is done at another institution before the pa-tient is transferred to our trauma center. Unless the patient has signs indicating a very high likeli-hood of urethral disruption, such as blood from the urethral meatus and fractures of the pubic rami, urethrography is commonly performed after CT (perhaps 24–48 hours after and sometimes after surgical intervention), usually as pericatheter urethrography. In general, this approach is effective; although it is possible that a urethral injury may be initially missed or mistreated, this would not usually be life threatening. Conversely, performing RUG before CT to allow early and correct diagnosis of a urethral injury in a patient with an aortic injury or active bleeding from a liver or splenic injury could compromise the patient’s survival.
The second principle to be applied is "do not force a new test to exactly replicate a tried and true test." Specifically, it is not necessary to see the same key findings for the test to be accurate and effective. When I was a resident in the late 1970s, we learned to recognize retroperitoneal masses on the basis of displacement of the ureters at intravenous urography. Today, even though such displacement is still shown at CT, nobody looks for it—because the mass itself is directly visible.
In the study by Kane et al (4), diagnosis of urethral injury with CT was found to be inaccurate due to failure to demonstrate extravasation of contrast material from the urethra. As stated by Ali et al (1), extravasation from a urethral injury will be seen at CT only if prior RUG was performed (in which case the CT evidence is not needed) or if the patient voids on the table inadvertently, not a reliable procedure. However, Ali et al (1) did not rely on the key finding from RUG but rather first carefully evaluated the normal anatomy of the subvesical and periurethral regions and then looked for alterations of this normal anatomy. Ali et al (1) correlated certain features with the occurrence of urethral injury. Obscuration of the UGD fat plane was seen in 88% of patients with pelvic fracture and urethral injury versus only 3% of those with pelvic fracture but no urethral injury. Hematoma of the ischiocavernosus muscle was seen in 88% with urethral injury but only 17% without urethral injury. Obscuration of prostatic contour was seen in 59% with urethral injury but only 7% without urethral in-jury. Obscuration of the bulbocavernosus muscle was seen in 47% with urethral injury but only 10% without urethral injury. Hematoma of the obturator internus muscle was seen in 53% with urethral injury but only 13% without urethral injury.
There are some methodologic concerns with the preceding article. The authors retrospectively evaluated three groups: 17 patients with pelvic fracture and urethral injury, 30 patients with pelvic fracture but no urethral injury, and 50 patients with neither pelvic fracture nor urethral injury. The numbers of patients with specific types of urethral injury are relatively small (four with type I injury, four with type II injury, and seven with type III injury). The CT technique was somewhat variable. It is not clearly indicated how many patients underwent RUG prior to CT nor how many had undergone catheterization prior to CT. In addition, the time lapse from the instant of the trauma to the performance of CT is not given—which could affect the presence or conspicuity of hematoma or obscuration of normal tissue planes. In fact, the authors do not explicitly state the sen-sitivity and specificity of the CT findings for the specific types of urethral injury. Moreover, the features the authors describe as specific for type I, II, or III urethral injury depend on the presence and pattern of extravasation. The new findings they propose are nonspecific.
The third principle—First, do no harm—still must be considered. Although urethral injuries are usually not life threatening and thus proper care of the patient may involve prioritizing evaluation and treatment of other injuries, unrecognized or improperly treated urethral injuries can nevertheless lead to significant long-term disability. This is illustrated in the Figure. A 24-year-old man experienced fractures of the sacrum and pubic bones in a motor vehicle collision. He was initially seen at another institution. A Foley catheter was placed and stabilization of the pelvic fractures with external fixation devices was performed before transfer to our institution for definitive treatment. Standard trauma CT had been performed at the other institution but no urethrography or cystography. Two weeks after the trauma episode, we were asked to perform CT cystography (Figure, parts a–c), which showed that the balloon of the Foley catheter was in a subvesical location, with extensive extravasation consistent with a type III urethral disruption. Despite surgical realignment and repair of the urethra, the patient subsequently had incontinence due to disruption of the urethral sphincter mechanism (Figure, part d).
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Department of Radiology, State University of New York, Downstate Medical Center, Brooklyn, New York
Department of Surgery, Kings County Hospital Center, Brooklyn, New York
We thank Dr Kenney for his valuable commentary on our article. Without compromising the three important principles for conducting a study, as described by Dr Kenney, our efforts were directed to bringing attention to the following issues concerning evaluation of posterior urethral trauma.
Owing to the universal acceptance of RUG as the standard of reference for diagnosis of urethral injury, the role of CT has been understated in the current literature. We mentioned some instances where knowledge of normal and pathologic CT anatomy can be of paramount importance for an emergency department radiologist to produce an intelligent and comprehensive report. We believe that familiarity with these findings would be useful in alerting the radiologist of a possible urethral injury in cases like the one cited by Dr Kenney.
In our study, we analyzed the comparative percentages for the presence or absence of each sign in the presence or absence of urethral injury. We did not go into the statistics because in our view the number of positive cases was relatively small. However, our efforts were directed at identifying and describing these novel signs so that they can be used as a template for prospective studies in the future. Of course, all of the variables that Dr Kenney has mentioned and others must be evaluated and integrated into the study design for any future work.
We described some findings as being specific for the type of urethral injury due to their absolute lack in the absence of a particular type of urethral injury. In addition, there were no other plausible explanations for their presence in the particular cases. However, we did not go so far as to recommend that RUG may not be performed in these cases. We believe that a larger patient sample and a well-designed prospective study are needed to make that claim.
Another important point raised by Dr Kenney is the principle of not doing any harm. RUG does involve manipulation of an acutely traumatized urethra. The possibility of exacerbating an acute tear by inadvertent forceful injection of contrast material into the urethra and the introduction of infection are real concerns. In the future, if CT is found to be sensitive and specific enough, we might be able to avoid RUG and the associated risks in some cases.
As Dr Kenney stated, more work is needed to suggest any changes in the current management protocol for urethral injury. We hope our article will generate interest in the evolving role of CT.
Related Article
RadioGraphics 2003 23: 951-963.
This article has been cited by other articles:
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  P. Ramchandani and P. M. Buckler Imaging of Genitourinary Trauma Am. J. Roentgenol., June 1, 2009; 192(6): 1514 - 1523. [Abstract] [Full Text] [PDF]
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