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Urethral Trauma Imaging

Overview

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.
  Urethral injuries constitute 4% of urologic trauma injuries. In cases of pelvic fracture, urethral injury may be present in up to 25% of men and 4.6% of women. Presentation may include blood at the urethral meatus, suprapubic fullness, and urinary retention.
 (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.

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.

Preferred examination

If any of the clinical findings listed above are present, the possibility of urethral trauma should be properly investigated by retrograde urethrography (RUG).
This should always be done prior to the insertion of a urethral catheter.

indications for urethral imaging include an unstable pelvis, penile fracture, or significant perineal hematoma after straddle injury. Cystourethroscopy should be considered in women to evaluate the bladder neck, because injury to the bladder neck can result in urinary incontinence.

In cases of delayed urethral repair, repeat imaging with retrograde urethrography and voiding cystourethrogram  is necessary to help characterize the length and location of the defect. If visualization of the bladder neck is poor, flexible cystoscopy can be used through the suprapubic site to gain better visualization. MRI can also be used to further characterize the stricture and to estimate the length of the defect, the degree of prostatic misalignment, and the density of scar tissue

For most patients with widespread acute trauma, computed tomography (CT) scanning is performed as an initial diagnostic tool.
However, these scans are not traditionally used for diagnosing urethral trauma. Research indicates, however, that CT scanning may be useful as an initial screen for urethral injuries.

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 before evaluation for urethral trauma, it should not be removed 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.

Urethra, trauma. Normal retrograde urethrogram. Pe

Urethra, trauma. Normal retrograde urethrogram. Pericatheter retrograde urethrogram is negative for urethral trauma and shows continuous filling of contrast material through the extent of the urethra and into the bladder without extravasation.

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Urethra, trauma. Retrograde urethrogram reveals a

Urethra, trauma. Retrograde urethrogram reveals a type I urethral injury with minimal stretching and slight luminal irregularity of the posterior urethra. No extravasation of contrast material is present.

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Urethra, trauma. Retrograde urethrogram demonstrat

Urethra, trauma. Retrograde urethrogram demonstrates a less common type II urethral disruption. Extravasation of contrast material (solid arrow) from the posterior urethra is seen superior to an intact urogenital diaphragm (dashed arrow).

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Urethra, trauma. Retrograde urethrogram reveals a

Urethra, trauma. Retrograde urethrogram reveals a type III urethral tear at the urogenital diaphragm (solid arrow) and a type IV urethral disruption at the bladder neck (dashed arrow).

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Urethra, trauma. Straddle injury. Retrograde ureth

Urethra, trauma. Straddle injury. Retrograde urethrogram shows a type V urethral injury with extravasation of contrast material from the distal bulbous urethra.

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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.

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