Introduction 

Retrograde Urethrography, a specialised diagnostic imaging procedure, plays a crucial role in unravelling the intricate details of the urethra. This article delves into the purpose, procedure, and significance of Retrograde Urethrograms, shedding light on its vital role in diagnosing and managing various urethral conditions.

Definition of retrograde urethrogram (RGU)

A Retrograde Urethrogram (RGU) is a medical imaging procedure used to evaluate the anatomy and function of the urethra. The urethra is the tube that carries urine from the bladder out of the body. This diagnostic test is typically performed to assess abnormalities or issues related to the urethra, such as strictures (narrowing), obstructions, or other structural abnormalities.

During a retrograde urethrogram, a contrast medium (a substance that shows up on X-rays) is introduced into the urethra. This contrast medium helps highlight the urethra on X-ray images, allowing the healthcare provider to visualise the structure and identify any abnormalities. The contrast medium is usually introduced into the urethra through a catheter. X-ray images are taken as the contrast fills the urethra retrogradely (backwards), moving from the external urethral meatus (opening) toward the bladder. RUG is typically used in men because it is not practical for use in females.¹

RUG is often recommended when symptoms or signs suggest urethral abnormalities, such as difficulty urinating, recurrent urinary tract infections, or blood in the urine. The information obtained from a retrograde urethrogram can aid in the diagnosis and treatment planning for conditions affecting the urethra. Before this procedure, patients must inform their healthcare provider of any allergies or previous adverse reactions to contrast media.

Basics of urethral anatomy

Overview of the male and female urethra 

The urethra is a crucial component of the urinary system responsible for transporting urine from the bladder to the external environment. Certain differences make the female urethra impractical for RUG. Here are the key distinctions between male and female urethras:

Length

RUG relies on a contrast agent travelling through the urethra to gain information. The male urethra is longer and more complex as it extends through the penis therefore, a lot of information is gained, unlike the female urethra, which is shorter and straighter.

Anatomy

The male urethra is located on the posterior and has an external structure; therefore, X-ray systems can view it clearly. Conversely, the female urethra is located behind the vagina. Its internal structure reduces the visibility of X-ray systems because it is deeper in the body.

Lower prevalence of certain conditions

Some conditions RUG aims to diagnose, such as prostate abnormalities or strictures in the male urethra, are less common or absent in females. Therefore, the clinical need for RUG in females is generally lower.

Key structures involved in urethral function 

Several key structures are involved in urethral function, each playing a specific role in the process of urine elimination. The primary structures include:

• Bladder: The bladder is the muscular organ that stores urine until it is ready to be expelled from the body. It contracts to push urine into the urethra during the voiding process
• Internal urethral sphincter: This involuntary smooth muscle sphincter surrounds the junction between the bladder and the urethra. It helps prevent the involuntary release of urine²
• External urethral sphincter: The external urethral sphincter is a voluntary skeletal muscle sphincter surrounding the urethra as it passes through the pelvic floor. Conscious control over this sphincter allows for voluntary initiation and interruption of urination
• Prostate gland (in males): In males, the prostate gland surrounds the prostatic part of the urethra. It secretes fluids that contribute to semen during ejaculation. The prostate's position also provides structural support to the male urethra
• Membranous urethra: This is the short segment of the male urethra that passes through the urogenital diaphragm. The external urethral sphincter surrounds it
• Spongy urethra: The longest part of the male urethra, it passes through the penis and is surrounded by erectile tissue. It carries both urine and semen during ejaculation
• Urethral glands: Various glands along the urethra, such as the bulbourethral glands (Cowper's glands) in males, contribute fluids to the urethra. These fluids help lubricate and neutralise acidity in the urethra
• Urethral mucosa: The inner lining of the urethra, the urethral mucosa, is composed of mucous membrane and transitional epithelium. This lining provides a protective barrier and aids in the smooth passage of urine
• External urethral orifice: The external urethral orifice opens the urethra to the external environment. It is located at the tip of the penis in males and anterior to the vaginal opening in females
• Common issues affecting the urethra: Several common issues that affect the urethra can be diagnosed using RGU. Some of these include
• "Urethral stricture: A narrowing of the urethra is often due to scar tissue formation. It can result in difficulty urinating, a weak urine stream, and increased frequency of urination
• Urinary tract infections (UTIs): Infections that can affect any part of the urinary system, including the urethra. Symptoms may include pain or burning during urination, increased urgency, and frequent urination
• Urethritis: Inflammation of the urethra, is commonly caused by infections (such as sexually transmitted infections like gonorrhoea or chlamydia).³ Symptoms may include pain, burning, and discharge
• Urethral trauma: Injuries to the urethra, which can occur due to accidents, pelvic fractures, or medical procedures. Trauma can lead to complications such as strictures or fistulas
• Incontinence: Loss of bladder control, which can result in involuntary urine leakage through the urethra. Stress incontinence and urge incontinence are common types
• Prostatitis: Inflammation of the prostate gland can cause symptoms like pain or discomfort in the pelvic region and may affect the urethra⁴

The procedure of retrograde urethrogram

This section will review the steps you should expect in an RGU procedure:

• Patient preparation: The patient is typically briefed on the procedure, and any questions or concerns are addressed 
• Positioning: The patient is positioned on the X-ray table, either lying on their back or in a lithotomy position (for females) with their feet placed in stirrups. Proper positioning is essential for obtaining precise and accurate images
• Catheter insertion: A small, flexible catheter is gently inserted into the urethra. In males, the catheter may need to navigate through the prostate, while in females, it passes into the urethra without obstruction from the prostate
• Contrast injection: A radiopaque contrast medium, visible on X-rays, is injected through the catheter into the urethra. The contrast fills the urethra retrogradely, moving towards the bladder. This helps highlight the urethral anatomy
• Fluoroscopy or X-ray imaging: As the contrast fills the urethra, real-time X-ray images(fluoroscopy) or static X-ray images are captured. These images reveal the structure of the urethra, allowing the healthcare provider to identify any abnormalities or issues
• Dynamic imaging (optional): In some cases, dynamic imaging may be performed during voiding. This involves capturing X-ray images as the patient empties their bladder. Dynamic imaging helps assess urethral function and may reveal issues such as reflux or leakage
• Image analysis: A radiologist or urologist carefully analyses the obtained images to assess the anatomy of the urethra and identify strictures, diverticula, stones, or any other abnormalities
• Catheter removal: Once the imaging is complete, the catheter is gently removed, and the patient is typically allowed to empty their bladder
• Post-procedure observation: The patient may be monitored briefly after the procedure, and any immediate concerns or side effects are addressed

Interpretation of retrograde urethrogram

After the procedure, a radiologist must examine the images to identify abnormalities and make a diagnosis. Here are some things they look for:

• Normal urethral anatomy
  • The images provide a clear view of the normal anatomy of the urethra, including the prostatic, membranous, and spongy (penile) segments in males
• Urethral stricture
  • Narrowings or strictures in the urethra may be visualised as areas of constriction, which can help determine the location and extent of the stricture
• Urethral fistula
  • Abnormal connections between the urethra and adjacent structures can be visualised, providing information about the location and size of the fistula
• Urethral tumours
  • Tumours or growths in the urethra may appear as irregularities or masses on the images. The size, location, and characteristics of the tumour can be assessed
• Urethral trauma
  • In cases of trauma, disruptions or injuries to the urethra may be evident in the images. The extent of damage and any associated complications can be identified
• Voiding dysfunction
  • The images can reveal abnormalities in urethral function during voiding, such as reflux or incomplete emptying
• Postoperative changes
  • Following urethral surgeries, RUG can help assess the procedure's success, identify any complications, and visualise changes in the urethral anatomy

Alternatives and complementary procedures 

Although the retrograde urethrogram is an excellent diagnostic tool, it is often used with other modalities to aid in diagnosis. Other imaging modalities are sometimes preferred depending on the specific clinical scenario. Some alternatives and complementary procedures are

• Voiding cystourethrogram (VCUG)
  • This procedure combines antegrade and retrograde imaging. A contrast medium is introduced into the bladder. X-ray images are taken during the filling (antegrade) and voiding (retrograde) phases⁵
• Urethroscopy (cystoscopy)
  • A flexible or rigid tube with a light and camera (urethroscope) is inserted into the urethra to visualise the interior directly. Urethroscopy allows for detailed examination and biopsy of the urethra
• Ultrasound of the urethra
  • Ultrasound imaging may be used to visualise the urethra, especially in cases where real-time imaging is required. It is non-invasive and can help identify obstructions or abnormalities
• Computed tomography (CT) urography
  • CT urography combines CT imaging with contrast medium to provide detailed images of the urinary tract, including the urethra. It is useful for evaluating urinary stones, tumours, or other abnormalities

Summary

• Retrograde Urethrography (RUG) is vital for diagnosing and managing urethral conditions by evaluating anatomy and function.
• The article covers the basics of urethral anatomy, emphasising differences between male and female urethras in length, anatomy, function, and infection susceptibility.
• Common urethral issues, like strictures and infections, are explored, shedding light on associated symptoms and health concerns.
• The RUG procedure involves patient prep, catheter insertion, contrast injection, fluoroscopy or X-ray imaging, and optional dynamic imaging, with detailed steps outlined.
• Radiologists interpret RUG images to identify normal anatomy, strictures, fistula, tumours, trauma, voiding dysfunction, and postoperative changes. The article also discusses alternatives to RUG in specific clinical scenarios.

RUG is essential in accurately diagnosing and treating urinary problems by allowing us to see and pinpoint structural issues. A solid grasp of how the urethra works and what can go wrong enables healthcare professionals to offer specific and efficient solutions. As technology advances, combining RUG with other imaging methods ensures a well-rounded evaluation of the urinary system. RUG's role in improving diagnostic accuracy and tailoring treatments is vital, promising better outcomes and a higher standard of care in the field of urinary health.