What is a retrograde urethrogram (RUG)?

Retrograde Urethrogram (RUG)

A retrograde urethrogram (RUG) is the gold standard diagnostic imaging procedure for evaluating male urethral injuries and strictures, performed by injecting contrast material into the urethra to visualize its anatomy and identify abnormalities. 1

Definition and Purpose

A RUG is a radiographic procedure that involves:

• Injection of water-soluble contrast material into the male urethra in a retrograde fashion
• Fluoroscopic imaging to visualize the entire length of the urethra
• Assessment of urethral integrity, strictures, extravasation, or other abnormalities

Key Indications

RUG is indicated in the following clinical scenarios:

• Suspected urethral injury, particularly after pelvic trauma 2, 1
• Blood at the urethral meatus 1
• Perineal or scrotal hematoma 1
• Difficulty or inability to insert a urinary catheter 1
• Suprapubic fullness or urinary retention 1
• Superiorly displaced or non-palpable prostate on rectal examination 1
• Evaluation of known or suspected urethral strictures 2
• Prior to urinary catheterization in high-risk patients 2

Technique

The procedure is performed as follows:

1. Patient positioning:

   • Patient is placed in an oblique position (30-45°) with the bottom leg flexed and top leg straight 1
   • If severe pelvic or spine fractures are present, patient may remain supine 1

2. Catheter insertion:

   • A 12Fr Foley catheter or catheter-tipped syringe is introduced into the fossa navicularis (distal urethra) 1
   • The balloon is not inflated, but the catheter tip is secured at the urethral meatus
   • Alternative: vacuum uterine cannula can be used to avoid urethral instrumentation in cases where manipulation must be avoided 3

3. Contrast administration:

   • 20-30 mL of undiluted water-soluble contrast material is injected 1
   • Injection should be performed under dynamic fluoroscopy
   • Excessive pressure should be avoided to prevent extravasation or intravasation 4

4. Image acquisition:

   • Multiple radiographic views are obtained during contrast injection
   • Oblique views are particularly helpful for visualizing the entire urethra

Interpretation

RUG findings are interpreted as follows:

• Normal: Smooth, continuous filling of the urethra with contrast
• Urethral injury: Extravasation of contrast outside the urethral lumen 1
  • Complete disruption: Extravasation without bladder filling
  • Incomplete disruption: Extravasation with some contrast reaching the bladder
• Stricture: Narrowing of the urethral lumen with proximal dilation 5
• Other findings: Diverticula, fistulas, false passages

Special Considerations

• Combined studies: RUG may be combined with voiding cystourethrogram (VCUG) for better visualization of posterior urethra 5
• Pediatric patients: Catheter size should be adjusted by age (median 5Fr for infants, 7Fr for ages 1-5, 8Fr for older than 5 years) 6
• Contraindications: Hemodynamic instability (suprapubic catheter preferred) 1
• Alternative imaging:
  • Urethroscopy is preferred over RUG for penile injuries and in female patients 1
  • Sonourethrography can provide three-dimensional assessment of stricture length and thickness 5

Complications and Precautions

• Blind catheter passage prior to RUG should be avoided to prevent worsening injury 1
• Excessive pressure during contrast injection can lead to:
  • Extravasation or intravasation into venous system
  • Risk of bacteremia, sepsis, contrast reactions
  • Worsening of strictures 4
• Ensure sterile urine before the study and elicit history of allergies 4

Accuracy and Limitations

• RUG has 89% sensitivity and 97% specificity compared to cystourethroscopy 6
• Technical difficulties may occur in approximately 8% of cases 6
• CT with delayed phase is less sensitive and specific than RUG for urethral injuries 1

RUG remains the cornerstone diagnostic procedure for male urethral pathology, particularly in trauma settings and for stricture evaluation, providing critical information for surgical planning and management.