UROGENITAL TRAUMA

Role of magnetic resonance imaging in assessment of posterior urethral distraction defects
Koraitim MM, Reda IS
Department of Urology, University of Alexandria College of Medicine, Alexandria, Egypt
Urology. 2007; 70: 403-6

• Objectives: To determine the clinical usefulness of magnetic resonance imaging (MRI) in the assessment of posterior urethral distraction defects.
• Methods: A total of 21 male patients, 6 to 35 years old, with posterior urethral distraction defects underwent MRI of the pelvis and combined antegrade retrograde urethrography before surgical repair. Repair was performed with a bulboprostatic urethral anastomosis through the perineum in 13 patients and transpubically in 8. The MRI and urethrographic findings were compared and correlated with the operative findings. The MRI findings were also correlated with the incidence of posttraumatic impotence.
• Results: On MRI, the length of urethral defect and type of prostatic displacement could be correctly determined in 86% and 89% of the patients, respectively. Also, MRI precisely delineated the extent of scar tissue, which varied according to the type and magnitude of the original trauma. Furthermore, MRI revealed the presence of paraurethral false tracks in 3 patients. In addition, MRI demonstrated avulsion of the corpus cavernosum, as well as lateral prostatic displacement in all 6 patients with posttraumatic impotence.
• Conclusions: Preoperative MRI can provide useful information that might help determine the appropriate surgical repair. It correctly estimates the length of the urethral defect, clearly demonstrates the type and degree of prostatic displacement, precisely delineates the site and density of scar tissue, and reveals the presence of paraurethral false tracks. Also, MRI can identify the cause of posttraumatic impotence such as avulsion of the corpus cavernosum and thus might predict the potency outcome in these cases.
  
  
• Editorial Comment
  Posterior urethral distraction defects were classically described as prostato-membranous disruption injuries by Turner-Warwick. In other words, posterior urethral injuries from pelvic fracture are not urethral strictures but scar tissues that fill the gap from the displacement of the prostate or the bulbar urethra. While many of the urethral injuries from pelvic fracture are at the prostato-membranous junction, roughly as many are at the bulbo-membranous junction. When preparing for a posterior urethroplasty, a well performed and simultaneous VCUG and RUG are needed. The keys here a properly performed study is to first perform a static cystogram to test the competence of the bladder neck, and then have the patient void, in order to fill the prostatic urethra. In this day and age with an aggressive initial management of primary realignment with flexible cystoscopes, the final distraction defect distance is typically < 2 cm and only occasionally > 2 to 3 cm. For such short distances, there is rarely the need for an abdominal perineal approach. The progressive perineal approach, as detailed by Webster, will typically bridge all gaps. In my personal experience with posterior urethroplasty, I have only needed to perform a pubectomy 2 times in over the last 10 years. In conclusion, while having a MR imaging of the urethra preop is nice, it is more of a luxury then a true necessity. The area that I have found the pelvic MR to be a value is when the prostate is displaced laterally and it is those circumstances that the prostatic urethra can be difficult to find. The other interesting finding from pelvic MR study, is that impotence after pelvic fracture may be due to avulsion of the corpus cavernosum from the ischium, and not necessarily a vascular injury at Alcock’s canal.

Dr. Steven B. Brandes
Associate Professor, Division of Urologic Surgery
Washington University in St. Louis
St. Louis, Missouri, USA
E-mail: brandess@wustl.edu