What is the best imaging study to rule out urethral injury in trauma?

Retrograde Urethrography is the Best Imaging Study to Rule Out Urethral Injury in Trauma

Retrograde urethrography is the diagnostic procedure of choice and should be performed before attempting any urinary catheterization when urethral injury is suspected in trauma patients. 1

Clinical Indications for Suspected Urethral Injury

Urethral injury should be suspected in patients with:

• Blood at the external urethral meatus
• Suprapubic fullness
• Perineal laceration
• Scrotal hematoma
• Urinary retention
• Difficulty or inability to insert a urinary catheter
• Superiorly displaced prostate on rectal examination 1
• Pelvic fractures, especially with pubic symphysis disruption 2
• Straddle injuries 1

Diagnostic Algorithm

1. Initial assessment: Evaluate for clinical signs of urethral injury
2. If urethral injury is suspected: Perform retrograde urethrography before any urinary catheterization
3. If hemodynamically unstable: Defer urethral investigations and place a suprapubic catheter 1
4. If retrograde urethrography shows injury: Manage according to injury type (partial vs. complete)

Imaging Modalities for Urethral Trauma

First-Line Imaging

• Retrograde urethrography: Gold standard for diagnosing traumatic urethral injuries 1
  • Highly sensitive for detecting urethral disruption
  • Should be performed before attempting urinary catheterization
  • Essential for documenting a normal urethra prior to catheterization in high-risk cases 1

Alternative/Adjunctive Imaging

• Flexible urethroscopy: Alternative diagnostic modality 1

  • Preferred over retrograde urethrography in cases of associated penile injuries 1
  • Also preferred in female patients due to short urethra 1

• CT with delayed phase:

  • Not as sensitive or specific as retrograde urethrography for urethral injuries 1
  • May show indirect signs of urethral injury (hematoma, extravasation) 3

• MRI:

  • Not indicated in acute trauma setting 1
  • Useful for anatomic definition during post-traumatic period 1

Interpretation of Retrograde Urethrography

• Extravasation of contrast: Indicates urethral injury 1
• Incomplete lesions: Characterized by extravasation of contrast that also fills the bladder 1
• Complete lesions: Extravasation of contrast without bladder filling 1

Special Considerations

• Hemodynamic instability: In unstable patients, all urethral investigations should be postponed and a suprapubic catheter should be inserted 1

• Intraoperative setting: If urethral injury is suspected during emergency laparotomy, it should be investigated directly whenever feasible 1

• Pediatric patients: Similar principles apply, with retrograde urethrography being the study of choice for suspected urethral trauma 1

• Female patients: Due to shorter urethra, urethroscopy is recommended over retrograde urethrography 1

Common Pitfalls

• Blind catheterization: May convert a partial urethral tear to a complete transection, worsening the injury 4, 2

• Relying solely on clinical signs: Clinical features alone have a sensitivity of only 66.7% for urethral trauma, potentially missing injuries 2

• Delaying diagnosis: Delayed diagnosis may have significant long-term morbidity including urinary incontinence, voiding dysfunction, urethrocutaneous fistula, urethral stricture, and erectile dysfunction 5

• Focusing only on life-threatening injuries: Urethral injuries can be overlooked in polytrauma patients when attention is directed to more immediate life-threatening conditions 5

By following this evidence-based approach with retrograde urethrography as the primary diagnostic tool, clinicians can accurately identify urethral injuries and prevent iatrogenic complications in trauma patients.