From the Guidelines
The best imaging to determine a urethral obstruction is retrograde urethrography (RUG), as it remains the study of choice for delineation of stricture length, location, and severity, according to the American Urological Association guideline 1. When evaluating a patient for urethral obstruction, it is essential to consider the patient's symptoms, physical examination, and urinalysis results. The initial evaluation may include a combination of patient-reported measures, uroflowmetry, and ultrasound post-void residual (PVR) assessment. However, if symptoms and signs suggest the presence of a stricture, noninvasive measures such as uroflowmetry may definitively delineate low flow, which is typically considered to be less than 12 mL per second and may indicate obstruction from the stricture.
Some key points to consider when choosing an imaging modality include:
- Urethro-cystoscopy, RUG, voiding cystourethrography (VCUG), or ultrasound urethrography can be used to make a diagnosis of urethral stricture, as recommended by the American Urological Association guideline 1.
- RUG, with or without VCUG, is the preferred method for assessing stricture length, location, and severity.
- Ultrasound urethrography may serve to diagnose the presence of urethral stricture, as well as describe the location, length, and severity of narrowing of strictures, but requires a skilled ultrasonographer.
- Determination of urethral stricture length and location is crucial for preoperative planning and informed discussion about treatment options, perioperative expectations, and expected outcomes following urethral stricture therapy, as stated in the American Urological Association guideline 1.
In summary, RUG is the gold standard for direct urethral assessment due to its high sensitivity for detecting obstructions and anatomical abnormalities, and it should be used in conjunction with other diagnostic tools to determine the best course of treatment for patients with suspected urethral obstruction, as supported by the American Urological Association guideline 1.
From the Research
Imaging Techniques for Urethral Obstruction
- Retrograde urethrogram (RUG) and voiding cystourethrogram (VCUG) are currently the gold standard imaging techniques for diagnosis of urethral stricture and determination of stricture location 2
- However, RUG and VCUG have limitations such as exposure to ionizing radiation, operator and patient dependence, and moderate invasiveness 2
- Novel imaging modalities like endoluminal ultrasound (ELUS) have been developed to accurately evaluate the presence, location, length, and lumen cross-sectional area of urethral stricture without ionizing radiation 2
- ELUS has shown excellent intra- and interobserver variability (r = 0.99 for both) and feasibility as a quantitative technique to determine healthy urethral lumen and stricture cross-sectional area 2
Alternative Imaging Techniques
- Magnetic Resonance Imaging (MRI) and MR voiding cystourethrography (MR-VCU) can be used to evaluate male primary bladder neck obstruction and provide useful anatomical and functional information 3
- MRI can substitute for standard cystourethrogram in patients with primary bladder neck obstruction, with a diagnostic accuracy of 87% 3
- MR urethrography has been shown to be effective in depicting obliterative urethral stricture, with significantly lower errors and better linear fit to surgical measurement compared to conventional retrograde urethrography combined with voiding cystourethrography 4
Common Findings and Indications
- Urethrography is an effective and cheap means of imaging the urethra, commonly indicated for strictures and lower urinary tract symptoms 5
- Urethral stricture is the most common abnormal finding, commonly affecting the bulbar urethra 5
- About 63.6% of patients with urethral strictures have short segment stricture, which is common at the bulbar urethra 5