Pelvic fractures are usually caused by high energy injuries, such as traffic accidents or falls from a height. They place patients at risk for associated urethral injury, known as pelvic fracture urethral injury (PFUI), which is caused by avulsion of the membranous urethra from the bulbar urethra. Most patients with PFUI eventually develop urethral stenosis, regardless of initial treatment. Delayed anastomotic urethroplasty with the sequential use of ancillary techniques has become the standard treatment for PFUI and remains a challenging urological surgery. ¹ This is because pelvic anatomy is markedly changed by the injury, and surgeons are forced to make a precise anastomosis in a deep and small operative field.

Figure 1. Representative preoperative MRI findings (dashed arrows) and corresponding urethrogram in patients with urethral gap after PFUI. Solid arrows indicate location of distal urethral end ( DE) and proximal urethral end ( PE). A, lateral displacement of disrupted urethral ends (coronal T2-weighted fat-suppressed image). B, bulging of rectum into urethral gap (sagittal T2-weighted image). C, close proximity of dorsal venous complex (dashed line) to urethral ends (sagittal T1-weighted, contrast enhanced image). D, false passage from DE to bladder neck created during failed endoscopic primary realignment (sagittal T1-weighted, contrast enhanced image). Note that none of findings seen on MRI were visible in urethrogram.

Accurate preoperative assessment is crucial for the proper selection of surgical approach and for a successful outcome. A combined antegrade and retrograde urethrography is the cornerstone of preoperative evaluation. However, it has several drawbacks. ² First, the measurement of urethral gap length on urethrography is operator dependent, and accurate estimation is difficult in the case of poor filling of the posterior urethra by contrast material. The bladder neck sometimes does not open on antegrade urethrography, especially in patients with prolonged suprapubic catheterization or decreased bladder capacity. Second, the proximal end of the displaced urethra can be displaced in a horizontal as well as vertical direction, and urethrography cannot accurately determine the degree of displacement 3-dimensionally. Third, the anatomical relationship of the urethra with its surrounding structures (such as the rectum and dorsal venous complex) or periurethral problems (such as minor fistulae or cavitation) cannot be well detected by urethrography. To overcome the limitations of urethrography, magnetic resonance imaging (MRI) has emerged as a noninvasive, multiplanar and high resolution modality for the evaluation of PFUI. ²

Figure 2. Representative MRI findings of PUA in patients with PFUI (sagittal T2-weighted images). A, patient with relatively small PUA who required both corporal separation and inferior pubectomy during delayed anastomotic urethroplasty. B, patient with large PUA who needed only bulbar urethral mobilization. ³PE, proximal urethral end. Arrows indicate inferior pubic ramus.

Important information, such as the bulbar urethral length, the site of the ends of the disrupted urethra and the urethral gap length, can be accurately measured in the sagittal view of an MRI. These results show better correlation with intraoperative findings than urethrography. ² The degree of lateral urethral displacement, which cannot be assessed by urethrography, is easily estimated in the coronal view (fig. 1, A). The greatest advantage of MRI over urethrography is its ability to evaluate periurethral anatomy. In patients with complete urethral disruption, the rectum can protrude into the space between the displaced urethral ends. This can be clearly seen on MRI but is not visible on urethrography (fig. 1, B). Without this information, surgeons may encounter unexpected rectal injuries during urethroplasty. The disrupted proximal end of the urethra can also be in close proximity to an intact dorsal venous complex ventrally. If this association is not known preoperatively, rough handling may lead to increased blood loss (fig. 1, C). Furthermore, MRI can clearly demonstrate minor periurethral fistulae that may be missed on urethrography (fig. 1, D).

Figure 3. Comparison of 2D ( A) and 3D ( B) MRI (sagittal T2-weighted images) in patient with PFUI. Note clearly visible urethral lumen in 3D image. Dashed arrows indicate distal urethral end ( DE) and proximal urethral end ( PE). Solid arrows indicate bulbar urethra.

MRI findings may have an impact on the decision about the type of urethroplasty. The most challenging aspects of delayed anastomotic urethroplasty are determining the location of the proximal urethral end and creating an anastomosis in the limited operative space of the pelvis. If the proximal urethral end is not found after mobilizing the bulbar urethra, or anastomotic tension is present due to a long urethral gap, surgeons should consider using ancillary techniques. These include techniques such as corporal separation, partial pubectomy and urethral rerouting, done to increase the exposure and to straighten the bulbar urethra and reduce anastomotic tension. These methods are often necessary when the proximal urethral end is displaced upward and is hidden behind the inferior pubic arch. Therefore, we believe that identifying the location of the proximal urethral end in reference to the pubis is the key to determining the need for ancillary techniques.

We have proposed the use of a novel MRI parameter to pubo-urethral stump angle (PUA, fig. 2), defined as the angle between the long axis of the pubis and the line joining the proximal urethral end to the lower border of the inferior pubic ramus (measured in the sagittal plane in T2-weighted MRI). ³ In our single-surgeon series of 74 PFUI patients, PUA was an independent predictor of the need for more complex ancillary techniques. ³ Although a long-held belief has been that the need for ancillary techniques can be determined only based on findings at surgery, MRI might help surgeons to predict the same preoperatively. In addition, we recently introduced a 3-dimensional (3D) T2-weighted turbo spin echo MRI using the volume isotropic turbo spin echo acquisition (VISTA) technique to obtain more detailed information. ⁴ The quality of the 3D MRI is superior to conventional 2-dimensional (2D) MRI, which enables clear visualization of the urethral lumen (fig. 3).

Despite these advantages, there are several problems with using MRI in the assessment of PFUI, the most critical of which is its cost. The cost of an MRI is approximately 5 times higher than that of urethrography. In addition, the presence of internal fixators for a fractured pelvis or metallic orthopedic hardware can cause artifacts and prevent accurate assessment. Although MRI is not necessary for the preoperative evaluation of every case, information obtained from it can be beneficial for an inexperienced surgeon. It is also useful in the management of complex PFUIs, such as after a failed previous urethroplasty, rectourethral fistula or a long gap. ⁵ The appropriate use of MRI and its cost-effectiveness require confirmation from future studies.