Retrograde Urethrogram

The retrograde urethrogram (RUG) is a radiographic or fluoroscopic study of the male urethra in which water soluble iodinated contrast (about 20 to 30 mL of a 300 mg iodine in each mL agent, undiluted or diluted by half) is injected through the external urethral meatus while the penis is stretched along the thigh and images are taken in an oblique position (about 30 to 45 degrees).

The contrast outlines the anterior urethra (the fossa navicularis, penile and bulbar urethra) and fills the membranous and prostatic urethra under pressure when the external sphincter relaxes.

It is often combined with a voiding cystourethrogram or a suprapubic cystogram (a combined study) to show the posterior urethra and the length of a stricture or the distance between the two ends after trauma. The effective dose is about 0.5 to 2 mSv, mainly to the gonads, and screening time is kept short.

Urethral strictures affect about 1 in 1000 men, mostly due to infection, instrumentation and trauma. Urethral injury occurs in about 4 to 14% of pelvic fractures, and in straddle injuries. The retrograde urethrogram remains the first line test for the anterior urethra, defining the site, length, number and severity of strictures, and for suspected urethral injury, and the surgeon's choice of dilatation, urethrotomy or open urethroplasty depends on the length and position of the stricture.

Indications. Suspected or known urethral stricture (poor stream, hesitancy, recurrent infection, retention, abnormal uroflow). Urethral trauma after pelvic fracture or straddle injury (blood at the external meatus, high riding prostate, perineal haematoma, inability to void), before attempting a urethral catheter. Failed or difficult catheterisation.

Urethral fistula, false passage, or diverticulum. Assessment before and after urethroplasty or urethrotomy. Suspected urethral tumour or foreign body. Post-prostatectomy anastomotic stricture (combined with cystography). Congenital anomalies (anterior urethral valves, megalourethra, hypospadias repair). Not routinely for lower urinary tract symptoms with a normal flow rate.

Contraindications and precautions. Active urinary tract infection or acute urethritis, prostatitis, or epididymitis (treat first, and give antibiotic cover). Known allergy to iodinated contrast (the dose absorbed is small but reactions occur). Recent urethral instrumentation or catheter (wait for 1 to 2 weeks if possible to avoid false defects).

Urethral trauma: the study is done before catheter insertion, with gentle low pressure injection. Haemodynamic instability: resuscitation is the priority. A catheter tip balloon inflated in the fossa navicularis may rupture the urethra, so only a small inflation (1 to 2 mL) is used. Sterile technique, local anaesthetic gel, and privacy are used.

Preparation and technique. No fasting is needed and the patient is asked to void beforehand if possible. A control film of the pelvis is taken. A catheter with a small balloon (or a Knutsson clamp or a syringe with a tip) is placed at the meatus, the penis is stretched along the thigh to unfold the bulbar urethra and the patient is rotated 30 to 45 degrees.

Contrast is injected slowly under fluoroscopy while spot films are taken, and the injection continues until the posterior urethra and bladder neck fill (if the sphincter relaxes) or the contrast reaches the point of obstruction. A voiding film follows when needed, and a suprapubic catheter may be used to fill the bladder for a combined study.

Normal appearances. The anterior urethra is a smooth tube about 15 to 20 cm long. The fossa navicularis at the glans is a normal dilatation. The penile urethra is uniform, 6 to 8 mm wide when distended.

The bulbar urethra is wider (up to 12 to 15 mm), and the narrowest point is the membranous urethra at the urogenital diaphragm, which is often narrowed by the external sphincter contraction and then opens on voiding. The glands of Littre and Cowper duct orifices may fill as small outpouchings (normal), and the verumontanum in the posterior urethra appears as a filling defect.

The prostatic urethra is about 3 to 4 cm long, and contrast flows into the bladder when the sphincter relaxes.

Interpretation.

• Urethral stricture: a short or long segmental narrowing of the urethral lumen with a proximal dilated urethra; length is measured with a scale or marker (under 1 cm short, 1 to 2 cm intermediate, over 2 cm long); the commonest site is the bulbar urethra (mainly after infection and trauma), followed by the penile, membranous and fossa navicularis. Multiple strictures, a "beaded" or irregular pattern, and complete obliteration are seen after infection (gonococcal, tuberculous) or catheter injury. A stricture with periurethral extravasation, fistula or false passage indicates a complex disease.
• Lichen sclerosus (balanitis xerotica obliterans): long, tight strictures of the meatus and fossa navicularis, extending into the penile urethra.
• Urethral trauma: extravasation of contrast outside the urethra, graded as: stretching without extravasation (grade I), contusion with no extravasation, partial disruption with extravasation but contrast also passing into the bladder, complete disruption with extravasation and no passage of contrast to the bladder, and bladder neck or prostatic involvement. Posterior urethral injury (proximal to the urogenital diaphragm) is associated with pelvic fracture, a high riding prostate, and a distance between the ends (defect length) that the surgeon measures with a combined study; bulbar injury is typically from a straddle injury.
• Urethral fistula and false passage: contrast tracking outside the main lumen into the corpus spongiosum, the perineum, the rectum, or the scrotum, usually after instrumentation or infection.
• Urethral diverticulum: a contrast filled pouch, congenital (anterior, in the penoscrotal region) or acquired (distal to a stricture, after urethroplasty).
• Posterior urethral valves and anterior urethral valves: a dilated posterior urethra with a distal narrow jet or a dilated anterior urethra proximal to the valve.
• Urethral tumour and calculi: a filling defect or an irregular narrowing with an irregular outline (squamous cell carcinoma), and urethral calculi as opaque stones that fill the lumen.
• Periurethral abscess and urethral extravasation with infection: collections of contrast in the periurethral tissue.
• Intravasation: contrast entering the periurethral veins, the corpora or the prostatic veins when the urethra is inflamed or injury is present.

Critical values and findings needing immediate action.

• Urethral rupture with extravasation: suprapubic catheter drainage and urology referral; avoid blind urethral catheterisation.
• Urethral injury with pelvic fracture and haemodynamic instability: resuscitation, pelvic stabilisation, haemorrhage control and trauma team review.
• Extravasation with infection and perineal swelling (urinary extravasation, Fournier gangrene): urgent debridement, broad spectrum antibiotics and surgical review.
• Intravasation of contrast (rare): observe for systemic reaction and sepsis, and treat.
• Complete urethral obstruction with retention: suprapubic drainage and urology referral.
• Acute urinary sepsis after instrumentation (rigors, fever, hypotension): cultures, antibiotics and resuscitation.

Limitations and artefacts.

• Technical errors produce false strictures: inadequate stretch of the penis or poor oblique rotation foreshortens and overlaps the bulbar urethra, an inadequately distended segment appears narrowed, and spasm of the external sphincter mimics a membranous stricture.
• Contrast injected too rapidly or at high pressure causes intravasation or extravasation of a normal urethra; air bubbles mimic stones and filling defects.
• The study shows the lumen, not the periurethral scar (spongiofibrosis), whose extent affects surgical choice; sonourethrography or MR provide this.
• The posterior urethra is not shown reliably in a retrograde study unless the sphincter relaxes; a combined retrograde and voiding study is needed.
• The study underestimates stricture length in some cases, and the surgeon confirms the length in theatre.
• Contrast reactions are uncommon, and urinary tract infection or urosepsis can follow instrumentation, so antibiotics are used in high risk patients.
• Radiation dose is low, but is not trivial for the gonads in young men.

Special groups.

• Trauma patients: the RUG is done before catheterisation if urethral injury is suspected, and a suprapubic catheter is used if the urethra is disrupted.
• Children: urethral injuries are rare, and posterior urethral valves are imaged by voiding cystourethrography rather than retrograde study.
• Patients with diabetes or immunosuppression: higher risk of infection, and prophylaxis is given.
• Women: urethral disease is imaged by voiding cystourethrography or MRI, because retrograde study is technically difficult in the short female urethra, and double balloon catheters are rarely used.
• Pregnancy: avoid.
• Regions: urethral stricture from gonococcal, tuberculous, and schistosomal infection, and from traditional circumcision or instrumentation, is common in men; pelvic fracture from road traffic injury accounts for many posterior urethral injuries; delayed presentation with chronic retention and renal damage is common.

Follow up tests. Voiding cystourethrogram or suprapubic cystogram (a combined study), sonourethrography or MR urethrography for spongiofibrosis and periurethral disease, uroflowmetry and post-void residual ultrasound, urethroscopy and cystoscopy, urine culture and microscopy, urethral swab and tests for gonorrhoea, chlamydia and tuberculosis, renal and bladder ultrasound,

serum creatinine and electrolytes, prostate specific antigen when relevant, and referral to urology for dilatation, urethrotomy or urethroplasty.