Injury to the urethra is usually associated with severe pelvic trauma in males. The results of such an injury can have enduring consequences that include stricture, impotence, and incontinence. (See the images below.) 
A diagnosis of urethral trauma should be investigated in the presence of pelvic fracture, straddle injury, penetrating trauma in the vicinity of the urethra, or penile fracture. While there are no findings specific for urethral trauma, there are many that suggest its presence. Findings can include blood at the urethral meatus, gross hematuria, an inability to spontaneously void, and a high riding prostate on rectal examination. [2, 3, 4, 5]
For many patients with urethral injury, extravasation of blood contained within different fascial planes is also present. On examination, patients with injuries to the urethra distal to the urogenital diaphragm and not contained by the Buck fascia typically have a butterfly hematoma, which forms as blood collects in the superficial perineum.  Scrotal enlargement is also common in this injury, as extravasated fluids are bound by only the Colles fascia. For patients with anterior urethral trauma with extravasation confined by the Buck fascia, edema and ecchymosis of the penile shaft is common.  In some cases, however, a hematoma is not seen until at least an hour after injury. 
If any of the clinical findings listed above are present, the possibility of urethral trauma should be properly investigated by retrograde urethrography (RUG). [2, 4, 7] This should always be done prior to the insertion of a urethral catheter.
For most patients with widespread acute trauma, computed tomography (CT) scanning is performed as an initial diagnostic tool. [8, 9] However, these scans are not traditionally used for diagnosing urethral trauma. Research indicates, however, that in the future, CT scanning may be useful as an initial screen for urethral injuries. [8, 10, 11]
In the past, diagnostic catheterization was used to check for urethral disruption. This has been universally dismissed as an acceptable diagnostic tool.  A urethral catheter risks converting a partial urethral tear into a complete urethral disruption, it can increase the extent of hemorrhaging, and it increases the possibility of contaminating a sterile hematoma.  If, however, a urethral catheter is properly in place prior to evaluation for urethral trauma, it should not be removed in order to perform urethrography. In such a case, a pericatheter urethrogram may be obtained.
After a diagnosis of urethral trauma has been made, management and repair can be planned with the possible aid of other imaging modalities, such as magnetic resonance imaging (MRI) and ultrasonography. MRI has some utility in planning surgical approach for posterior urethral disruptions, and ultrasonography has been used at times to aid in the repair of urethral trauma. [12, 13, 14, 15, 16, 17]
Limitations of techniques
While RUG provides clinically valuable information on the presence, location, and severity of urethral extravasation, it provides limited information about the details of surrounding soft tissue damage. Furthermore, imaging of the proximal urethra can occasionally be inadequate. This is usually caused by subpar contrast-agent filling of the proximal urethra or by gross extravasation of contrast blocking visualization of the proximal urethra. 
In contrast, MRI has proven clinical utility in its ability to define damage to soft tissue neighboring the urethral trauma. Alone, however, MRI should not be used to investigate urethral extravasation or to define urethral trauma as partial or complete. [13, 14]
The standard imaging method used to diagnose urethral trauma is RUG. [2, 4] While various techniques have been described to implement RUG, the most common utilizes a Foley catheter. [6, 15] With this method, the patient is ideally positioned for imaging in an approximate 45° oblique angle with the penis stretched so that the meatus points cephalad. This produces a C configuration from the bladder level to meatus tip. If the penile shaft points caudad, the femur may obscure the opacified urethra.
For some patients with multiple injuries, this position is unobtainable. In this case, the patient should be supine with the penis stretched perpendicular to the leg. When the image is obtained in this anteroposterior projection, however, the urethra can appear foreshortened, allowing for possible errors in interpretation of extravasation. [3, 6, 18]
The Foley catheter is then placed inside the urethra with the balloon inflated in the fossa navicularis. Approximately 20-30 mL of 30% contrast material are injected into the urethra, with the exposure being made during the active injection of the last few mL of contrast. Obtaining the image during the injection allows for maximum filling of the deeper bulbar, membranous, and prostatic urethral sections. (See the image below.) [3, 7]
In the most ideal conditions, the entire procedure should be performed under fluoroscopic control; however, in the emergent environment this is often impossible.
Classification of RUG findings
The most accepted and unified classification of RUG findings for urethral injuries is the Goldman classification, with its foundation in the earlier system developed by Colapinto and McCallum. [19, 20] The Goldman classification of urethral trauma is defined entirely on the anatomical findings of the injury and not on its mechanism. This system defines five major types of urethral injuries as seen in RUG.
Type I urethral injury results when the puboprostatic ligament is ruptured, and the prostate is allowed to move superiorly. The urethra remains intact however, and is only severely stretched by the movement of the prostate. No extravasation of contrast material is seen with radiography, and continuity is maintained with the bladder (see the image below). True cases of Type I urethral injury are uncommon. 
Type II urethral trauma is the classically described posterior urethral injury in which the urethra is torn superior to the urogenital diaphragm. In such an injury, contrast-agent extravasation is seen within the extraperitoneal pelvis, but contrast material is not present within the perineum (see the image below). Here, the urogenital diaphragm is intact, preventing the spread of contrast material inferiorly. This type exists in approximately 15% of urethral trauma cases resulting from pelvic crush injuries. 
The most common type of urethral trauma has proven to be type III urethral injury. [4, 20] Type III urethral injury, like type II, shows disruption above the urogenital diaphragm. Unlike type II, though, this injury extends through the urogenital diaphragm and includes the proximal bulbous urethra. In this injury, extravasation can be found within the extraperitoneal pelvis and within the perineum. (See the image below.)
The amount of contrast material found above or below the urogenital diaphragm depends upon the exact location of the injury and the degree of disruption to the perineal membrane. 
Some investigators believe that type I, II, and III urethral disruptions may be seen as the same mechanism of trauma, with varying degrees of severity.  Indeed, there has been at least 1 report of a delayed rupture of type I urethral trauma. 
Type II or III urethral injury can be further classified as a partial or complete urethral tear.  With RUG, partial tears are diagnosed when extravasation of contrast material occurs with the presence of contrast material in the bladder. Complete tears are diagnosed when extravasation is present and no contrast agent is present in the bladder or in the proximal torn end of the urethra. The relative frequency of partial tears versus complete tears is highly variable in the literature, and no reason for this variance has been agreed upon. 
Type IV urethral trauma is a tear to the bladder neck that extends into the proximal urethra. Contrast-agent extravasation is seen in the extraperitoneal pelvis around the proximal urethra (see the image below). Such injuries can damage the internal urethral sphincter, resulting in incontinence.  Proper diagnosis is therefore essential to ensure adequate patient care.
A related injury, as described in the Goldman classification, is type IVA. This is not a urethral injury; however, it can easily be mistaken for a proximal urethral tear. In this case, the base of the bladder is disrupted, with periurethral extravasation of contrast agent. The resulting radiographs can easily mimic those of a true type IV urethral trauma. Distinguishing the 2 conditions is important because type IV injury is typically treated surgically and type IVA injury is not.  Dynamic RUG under fluoroscopic control facilitates the differentiation.
Type V urethral trauma describes all cases that are isolated to the anterior urethra. Such an injury occurs distal to the urogenital diaphragm and is more associated with perineal crush or straddle injuries.  The resulting urethral injury is usually a partial tear of the bulbous urethra, though complete tears can also occur.
In this case, contrast-agent extravasation occurs inferior to the urogenital diaphragm (see the image below). If the Buck fascia remains intact, the extravasation is limited to its confines, ie, the penile shaft. If the Buck fascia is disrupted, the contrast material contained within the limits of the Colles fascia. [3, 6] In this case, contrast agent might be found in the lower abdomen and in the scrotum. 
Under certain circumstances, all of the clinical signs of urethral disruption may be present, but contrast extravasation may be completely absent. In such a case, a diagnosis of urethral contusion is often made. 
Degree of confidence
Specific degrees of confidence for diagnosing male urethral trauma by RUG are not documented.
With regard to females, contradictory opinions exist about the diagnostic dependability of urethrography, with some believing that diagnosis should be made with urethroscopy.
As discussed above, type IV urethral injuries involving the proximal urethra can be radiologically indistinguishable from type IVA injuries that do not involve the urethra. Careful evaluation is necessary to distinguish these two injuries.
Similarly, reflux of contrast agent into Cowper ducts, which connects to the bulbous urethra, should not be confused with extravasation of the anterior urethra. 
There have been some investigators who have questioned the accuracy of RUG in distinguishing partial and complete urethral tears. They have suggested that contrast material proximal to a partial rupture could be prevented by spasm of the external urethral sphincter. 
Despite the prevalent use of CT scanning as the initial screening modality for general acute trauma, the literature has historically described few applications of CT in diagnosing urethral injuries.  In one small study of CT and the ability to identify patients with bladder and posterior urethral injuries, CT identified only 1 of 3 patients with urethral trauma.  The authors of the study suggested that the presence of a Foley catheter might have prevented adequate contrast-agent extravasation in the undiagnosed cases.
One report has shed new light into the important potential clinical value for CT in diagnosing urethral trauma.  In this retrospective review, Ali et al reviewed 97 patients examined over an 11-year period. Seventeen patients had pelvic fractures and urethral injury (confirmed during urethroscopy or surgery), 30 patients had pelvic fractures with no associated urethral injury, and 50 patients had neither pelvic fracture nor urethral injury. As a result of their investigation, the authors were able to identify findings specific for type I, II, and III urethral injuries as well as findings highly associated with general urethral trauma.
A distance of 2 cm between the prostatic apex and urogenital diaphragm was specific for type I urethral injuries. The CT findings specific for type II and type III urethral trauma were contrast-agent extravasation above the urogenital diaphragm and extravasation below the urogenital diaphragm, respectively (see the images below). CT findings associated with, but not specific for, urethral trauma were distortion or obscuration of the urogenital fat plane, hematoma of the ischiocavernosus muscle, distortion or obscuration of the prostatic contour, distortion or obscuration of the bulbocavernosus muscle, and hematoma of the obturator internus muscle. 
Because many patients with generalized trauma undergo CT before a specific evaluation for urethral trauma, CT might serve as an initial screening examination for such injuries. Presently, no test supersedes RUG for the confirmation of urethral trauma. [8, 9] With information from reports, such as that by Ali et al, CT might help to exclude unnecessary RUG. Such a screening would require a thorough understanding of the relevant and intricate pelvic anatomy.
Some advocate performing CT-retrograde urethrography (CT-RUG) in patients who are scheduled for CT of the pelvis for other indications and have a high suspicion of urethral injury. CT-RUG can be performed with contrast that is more concentrated (eg, 40 mL of 60% contrast in 500 mL saline) than that typically used for CT cystogram, in order to help distinguish any extravasated contrast from vascular or bladder contrast extravasation. 
CT-RUG may also be useful in the preoperative evaluation of patients with complex urethral injuries. 
Degree of confidence
Because few studies have been conducted to evaluate the accuracy of CT in identifying urethral trauma, further investigation is necessary for a well-defined degree of confidence.
In the study by Ali et al described above, all specific findings were found only in patients with urethral trauma.  Among associated findings, distortion and obscuration of the urogenital fat plane was found in 88% of those with urethral trauma and in 3% without urethral trauma. Hematoma of the ischiocavernosus muscle was found in 88% with urethral trauma and in 17% without urethral trauma. Distortion or obscuration of the prostatic contour was present in 59% with urethral trauma and in 7% without urethral trauma. Distortion or obscuration of the bulbocavernosus muscle was present in 47% with urethral trauma and in 10% s without urethral trauma. Hematoma of the obturator internus muscle was found in 53% of patients with urethral trauma and in 13% without urethral trauma.
False-positive and false-negative results have not been thoroughly studied. It has been suggested that the presence of a Foley catheter in the urethra can produce false-negative findings for urethral trauma on CT studies. 
Magnetic Resonance Imaging
Traditionally, MRI has not been used as an initial diagnostic tool for urethral traumatic injuries; nevertheless, some researchers have demonstrated the advantage of using MRI as a preparatory tool when planning surgical repair of urethral disruption. [14, 19, 25, 26, 17]
Urethrography is the most commonly used preoperative evaluation; however, with this technique, information on prostatic displacement and the degree of scarring can be limited. Further, the exact length of the urethral defect can be inaccurately determined when the prostatic urethra is not optimally filled with contrast material. [14, 19]
MRI has shown positive results in evaluating the anterior-posterior, superior-inferior, and lateral displacement of the prostate; the degree of scar tissue around a urethral defect; and the precise length of a posterior urethral defect. In one study, the results of MRI preoperative evaluations changed the surgical repair approach in 26% of the patients studied. Because of its superiority in defining local disruption to adjacent tissues, MRI can be an important tool in combination with RUG in evaluating urethral trauma for management.
Degree of confidence
In the study mentioned above, the displacement of the prostatic apex was accurately measured by MRI to within 5 mm in 90% of patients. The length of the urethral defect was accurately identified within 5 mm in 85% of patients.  Large studies to determine a consensus degree of confidence are not available.
Like MRI and CT, ultrasonography alone has not yet proven to be adequate and is not typically used for the primary diagnosis of urethral trauma. [15, 27] However, a few reports suggest that ultrasonography can be used for defining the extent of urethral damage in certain cases and for preparing for surgical repair. [12, 28]
High-frequency probes used in sonourethrography provide a high spatial resolution; therefore, details of urethral anatomy can be studied after the injection of a saline solution. This saline solution technique uses a Foley catheter in a similar manner as described for RUG to promote distension of the urethra. The presence of saline in the urethra produces high contrast relative to the urethral mucosa. Thus, this technique allows accurate visualization of the urethral wall, as well as the urethral lumen. 
Only a limited number of reports exist in the literature regarding the usage of sonourethrography. Such cases include the use sonography for the diagnosis of urethral trauma associated with penile fracture and in evaluating anterior urethral trauma prior to delayed urethroplasty. Sonourethrography has been shown to accurately depict trauma to soft tissues surrounding the urethra, such as the tunica albuginea.  Other investigators have shown that sonourethrography can more accurately measure stricture length than RUG can.  This information could prove useful for planning surgical repair for specific cases.
Authors have also suggested that sonography demonstrates hematoma size and the extent of fluid extravasation better than RUG can.