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Laparoscopic & Robotic European Urology - Magnetic Resonance Urethrography in Comparison to Retrograde Urethrography in Diagnosis of Male Urethral Strictures: Is It Clinically Relevant?
Laparoscopic & Robotic European Urology - Magnetic Resonance Urethrography in Comparison to Retrograde Urethrography in Diagnosis of Male Urethral Strictures: Is It Clinically Relevant? | European Urology - Magnetic Resonance Urethrography in Comparison to Retrograde Urethrography in Diagnosis of Male Urethral Strictures: Is It Clinically Relevant? |
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Volume 50, Issue 3, Pages 587-594 (September 2006) 1. Introduction: The male urethra is a tubular structure approximately 18–20cm long and runs from the bladder to the external urethral meatus. Traditional radiologic exams, such as retrograde urethrography (RUG) and micturition cystourethrography, are considered the standard imaging techniques for the morphologic and functional study of the urethra. Limitations of these studies include being invasive, poorly defining the accurate length of the stricture, and differing results between the endoscopic and radiographic appearances of the stricture. Moreover, no information is available about the extent of periurethral fibrosis [1]. In the last decade, sonourethrography and magnetic resonance imaging (MRI) were provided as modern tools for evaluating male urethral pathologies with the advantage of lack of exposure to gonads [1], [2]. Ultrasound with high-frequency probes has a high spatial resolution and has proved to be sensitive, specific, and accurate in diagnosis of anterior urethral pathologies such as strictures [3]. Nevertheless, it showed a small field of view and has difficulty demonstrating the urethral lumen. In contrast, owing to multiplanar capability and excellent soft tissue contrast, MRI can provide anatomic details about both the urethra and periurethral tissue with orientation of the lesion in three dimensions [2]. Although many studies have compared conventional radiographic urethrogram and sonographic urethrography in the evaluation of urethral strictures [4], [5], no similar studies have compared them with MR urethrography. The aim of this work is to judge the clinical relevance of MRI in the evaluation of male urethral stricture in comparison to conventional urethrography. 2. Materials and methods Over a 4-mo period from January 2004 to April 2004, 20 men were referred to our institute for management of clinically suspected urethral stricture. Sixteen patients were referred because of postinflammatory urethral strictures, two with previous iatrogenic injury, and two for posttraumatic strictures. Six patients presented with an indwelling suprapubic tube and the others had obstructive lower urinary tract symptoms. All patients underwent dynamic retrograde urethrography (RUG) and MR urethrogram prior to the intervention and results were interpreted by the same radiologist. RUG was done with the patient placed in a 45° oblique position, with the dependent hip acutely flexed and the penis extended along the soft tissue of the thigh and as parallel to the tibia as possible. The entire length of urethra was assessed for any narrowing or abnormal fistulous communications. In cases of posterior urethral distraction defect (PUDD), RUG was combined with a micturition study to measure the defect. Measuring of urethral stricture length at ascending urethrography was done using the Magic View Picture Archiving and Communicating System (PACS; General Electric, Milwaukee, WI) after measurement calibration. The MR technique includes injection of sterile gel into the urethra, then application of a soft clamp to the penile tip to keep the urethra distended. Then, sagittal high-resolution T2 imaging of the penis and urinary bladder was performed with the following parameters: TR=4000–6000mscc, TE=80–120mscc, slice thickness=2mm, interslice gap=0mm. The reformatted images at different axial, coronal, and sagittal oblique planes were obtained to delineate the entire length of the urethra, characterize the surrounding soft tissue with depth and density of periurethral fibrosis, and define stricture length. Processing of the images was done at a separate work station (Advantage window 4.1; General Electric). In both methods, the total stricture length was measured including the tapered segments on either side of the tight stricture. Strictures with length <1.5cm were defined as “short strictures,” whereas longer strictures were defined as “long strictures.” All patients were examined by urethroscopy under anesthesia with intention for endoscopic treatment. Failure of endoscopic management was followed by open reconstructive procedures in another operative setting. The radiologic data reported by both techniques were compared with endoscopic and operative findings in all patients. Accuracy of both techniques was defined as the sum of true positive and true negative cases divided by the total number of patients examined. The mean stricture length as measured by both techniques was calculated and the difference was computed by the Mann-Whitney U test, with p<0.05 considered significant. 3. Results RUG showed a normal urethrogram in a single patient, short segment strictures in 12, long segment stricture (>1.5cm) in 2, short segment stricture associated with pathology (stone, urethral diverticulum, and poorly defined urethrorectal fistula) in 3, and PUDD in the last 2 patients (without delineation of proximal urethra in one). On the other hand, MR urethrography was interpreted as normal urethrogram in one patient, short segment stricture in 13, short segment stricture associated with pathology (urethral tumor, associated bladder tumor, stone and well-defined urethra-rectal fistula) in 3, long segment stricture (>1.5cm) in one (mainly due to extensive severe spongiofibrosis rather than lumen reduction) and PUDD in the last 2 patients. Notably, the proximal part of the urethra was well delineated in the last two cases. The patients ranged in age from 17 to 77 yr, with a mean age of 55±19 yr. Among these 20 patients, 4 patients did not show a real narrowing of the urethral lumen on endoscopy. Two showed just a short segment of tight urethra, related to previous urethral surgery, and were managed by urethral dilatation under anesthesia. The other two had normal urethroscopic findings. Reduction of the lumen up to complete obliteration was observed in the remaining 16 patients. Ten patients were successfully managed by visual internal urethrotomy (VIU) and four patients required open urethral reconstructive procedures. Radical cystectomy and cutaneous diversion were offered in two because of associated transitional cell carcinoma (TCC) of the bladder in one and primary TCC of the urethra in the second. The mean stricture length as measured by RUG was 1.5±1.3 and by MR urethrography, 1.2±0.9, with no statistically significant difference between the modalities (p=0.25). Similarly, the crude overall accuracy for diagnosis of urethral strictures was identical with both modalities (85%). Regarding characterization of the urethral stricture and defining associated radiologic findings, both modalities provided similar radiologic data in 13 cases (11 short segment strictures, 1 normal, and 1 with PUDD). In cases of short urethral strictures, nine proved to have a clinically short stricture segment that was managed by VIU, and two showed false radiologic diagnosis with no real narrowing of the lumen (one was managed by dilatation under anesthesia due to tight short segment and the other showed a normal urethra). The case with normal urethrogram and that with PUDD were confirmed clinically. In the last case, both modalities could delineate the proximal urethra with a distraction defect of 4cm in both images. MR urethrography provided extra clinically valuable data in the remaining seven patients (35%) in a way that affected the intervention plan. It was superior to RUG in judging the urethral stricture length in two patients. In two of them, at RUG (Fig. 1A) there was a false increase in the length of stricture (>1.5cm) due to inadequate opacification of proximal tapered segment in comparison with MR urethrography (Fig. 1B) that showed shorter length (<1.5cm). These patients were proved to have a short segment stricture and were managed endoscopically. In the third patient, both modalities showed a short segment of lumen reduction, but MR imaging showed an associated severe spongiofibrosis extending for >3cm. Endoscopic management failed in the latter patient, who was then successfully treated by pedicle flap urethroplasty. MR urethrography diagnosed a primary urethral tumor in one patient, which was interpreted as short stricture with proximal urethral diverticulum by RUG, and detected an accidentally discovered bladder tumor associated with the urethral stricture that was completely missed by the conventional radiography (Fig. 2A and B). In a patient, who was presented as a case of urethral stricture with an indwelling suprapubic tube following a complicated transurethral resection of the prostate, proper characterization of the site of urethra-rectal fistula could be obtained from the MR urethrography images that judged the operative approach. Lastly, accurate delineation of the proximal urethra in a patient with PUDD was achieved by the MR urethrography despite no opacification of that segment in the conventional combined study (Fig. 3A and B). Table 1 summarizes the radiologic findings and urethral stricture lengths as judged by RUG and MR urethrography as well as definitive operative management in all patients.  Fig. 1. (A) RUG showing long segment stricture (>1.5cm) of the anterior urethra. (B) MR urethrography for the same patient showing evidence of short segment stricture (<1.5cm).  Fig. 2. (A) RUG showing stricture bulbous urethra with the curved arrow pointing toward the filling defect of a stone in a dilated posterior urethra. (B) MR urethrography for the same patient with the curved white arrow pointing toward the stone and the curved black arrow pointing toward associated bladder tumor.  Fig. 3. (A) RUG combined with cystogram for a patient with PUDD without delineation of the proximal urethra. (B) MR urethrography for the same patient with well-delineated malaligned proximal urethra.
RUG: retrograde urethrography; MRU: magnetic resonance urethrography; VIU: visual internal urethrotomy; PUDD: posterior urethral distraction defect. 4. DiscussionObstructive conditions of the urethra are generally defined as urethral strictures. Anterior urethral strictures result from trauma or inflammation and are usually associated with scarring in the surrounding corpus spongiosum (spongiofibrosis). In contrast, the mechanism of posterior urethral strictures is complete or partial disruption of the lumen continuity secondary to pelvic trauma resulting in displacement of the urethral axis and urethral obliteration from intervening fibrosis. Urethral strictures rarely involve both anterior and posterior segments simultaneously [6]. Being popularized in 1910 by Cunningham [7], RUG remained as the gold standard imaging study for diagnosing urethral strictures for nearly a century. RUG is a straightforward, readily available, cost-effective technique consisting of simply a plain radiograph during retrograde instillation of dilute contrast [6]. Nevertheless, limitations of RUG, concerning the technique and clinical interpretation, were reported frequently. Technically, variations in patient positioning and penile traction during imaging can greatly alter the radiographic appearance of the stenotic areas [8], and forceful injection of contrast may lead to a false diagnosis of urethral stricture due to reflex contraction of the pelvic muscles or anaphylaxis and systemic sepsis due to rupture of mucosal barriers [9]. Even with technique standardization, stricture length might be inaccurately estimated [5], [10], no information is obtained regarding spongiofibrosis [11], and effective antegrade imaging may not be feasible in cases of posttraumatic stricture [12]. In this study, we standardized the method as described by Schulam et al [13]. Moreover, we measured the stricture length using computed radiography with aid of the PACS to get the most accurate measurements possible. To overcome the shortcomings of RUG, sonourethrography was first introduced by McAninch in 1988 [14]. Although it was met initially with a high degree of enthusiasm because of the initial promising results as it provides information not only on the urethral lumen but also on the corpus spongiosum [1], it has not been widely used because of smaller field of view and the poor compliance of urologists [3]. Moreover, the results of urethral ultrasound need to be interpreted by an experienced investigator because excessive pressure must be avoided to prevent urethral compression and faulty positive diagnosis [1]. Recently, it was suggested that RUG and sonourethrography be combined to achieve full assessment for patients with urethral strictures [5]. In this investigation, we tried to provide evidence that merits of both methods could be combined in one imaging modality. Although evaluation of the male urethra using MRI was suggested more than a decade ago [15], it is not yet routinely included in the armamentarium of urethral investigations. In 2003, Pavlica et al, in their review of male urethra imaging, judged MRI to be not widely used for examination of male urethral pathologies because it was somewhat complex and offered little extra information [3]. However, we believe that MRI is an evolving radiographic modality and is widely replacing the conventional radiographic modalities despite its relative high cost. In our institute, MRI was used as a single radiographic modality in evaluating potential kidney donors, replacing the conventional modalities [16]. In this study, we elected to inject the sterile gel into the urethra to allow easier and more stable distention of the urethra compared with saline, as previously described [3]. Accurate assessment of urethral stricture length is crucial for appropriate choice of treatment. Endoscopic treatment is usually curative for strictures <1.5cm involving the epithelium or superficial spongiosum, but for longer or full-thickness scars, open reconstructive surgery is usually indicated [17]. Despite this fact, inaccurate measurement of stricture length with RUG either in the form of magnification [5] or underestimation [10] is frequently reported. On the contrary, assessment of bulbar urethral stricture by sonourethrography is much more accurate than radiography [1], [3], [5]. In this study, MR urethrography was an efficient tool for accurate judgment of urethral stricture length. The data obtained from the MR images matched the operative findings in all the examined patients including the three cases with radiographic magnification or underestimation (Fig. 4).  Fig. 4. (A) RUG showing short segment stricture bulbous urethra (<1.5cm). (B) MR urethrography for the same patient with short segment stricture bulbous urethra (<1.5cm) that is surrounded by significant hypointense area of spongiofibrosis as encircled by the interrupted line. Spongiofibrosis is a critical determinant of appropriate therapy and ultimate prognosis. Jordan and Devine [18] outlined treatment selections according to the degree of spongiofibrosis with open urethroplasty provided for those with full-thickness fibrosis of the spongy tissues. This concept was never popularized because the traditional clinical evaluation was not able to assess the extent of disease beneath the urethral surface. Spongiosography [11] was even suggested to assess this pathology. Nevertheless, this technique was never clinically accepted because it was invasive and not reproducible. The great advantage of MRI over RUG is the assessment of the periurethral changes with accurate detection of fibrosis with actual depth and location (Fig. 4). Using T1 sequences, the latter provide high-contrast resolution with good visualization of the tunica albuginea (hypointense) and spongiosum tissue (hyperintense). Contrast medium is injected to evaluate the degree of activity in inflammatory lesions where fibrotic alterations of the corpus spongiosum can be seen clearly on T1- and T2-weighted images because hypointense areas easily distinguishable from normal spongy tissue [3]. Although sonourethrography was reported to provide sufficient data about the degree of fibrosis [1], we believe that the wider field of MRI as well as the contrast enhancement data could provide an extra advantage. Notably, the degree of spongiofibrosis affected the treatment plan in one of our examined patients. Another advantage of MRI is diagnosis of associated lesions. In this study, we could diagnose two cases of associated malignancy. Undoubtedly, sufficient data about local staging was available. Radiographically, tumors associated with existing strictures show narrowing and irregular margins of the stricture. In these cases, the changes could be indicative of a tumor but never diagnostic [3]. We could also accurately characterize the site and extent of the urethrorectal fistula in one case, which helped the surgeon judge his approach. The rate of detection of various fistulae with MRI has been reported to be fairly high [19]. Finally, the traditional approach to evaluate patients with PUDD includes retrograde urethrography and simultaneous cystography. This technique often does not provide an accurate determination of the defect length because of poor prostatic urethral filling. This study agrees with the experiences of others that the degree of dislocation can be clearly identified by combined MRI views, particularly with coronal and sagittal reconstruction [15], [20]. In this small series of patients, MRI proved to be a promising technique for evaluating male urethral pathologies. It combined the advantages of RUG as well as sonourethrography and gained compliance and acceptance by urologists. Limitations of this imaging modality include cost effectiveness as well as a longer learning curve for radiologists. Restriction of MR urethrography to more extensive strictures would reduce the cost and limit its use to patients who might truly benefit. Future studies are invited to individualize patients with urethral stricture who can get maximum benefit from this new approach. Currently, we are conducting a new study comparing both RUG and sonourethrography versus MR urethrography on a larger group of patients to specify its clinical implications. 5. Conclusion MR urethrography is a promising tool for defining anterior and posterior male urethral strictures as an alternative to traditional radiographic methods. With the advantage of avoiding radiation to the testes, MR urethrography could accurately measure the stricture length, judge the extent of spongiofibrosis, and aid in the diagnosis of any associated pathologies. This modality can provide extra guidance for treatment planning that cannot be obtained with RUG. Editorial Comment Luigi Cormio, University of Foggia, Italy This email address is being protected from spam bots, you need Javascript enabled to view it Magnetic resonance imaging (MRI) of the urethra is an interesting issue and should become part of the urologists diagnostic armamentarium. The present study showed that MRI and retrograde urethrography (RUG) had the same (85%) crude overall accuracy in diagnosing urethral strictures, but MRI provided further information in 35% (7 of 20) of the cases. However, it is likely that adding urethral ultrasound (US) to RUG would have provided the same information as MRI, for example, in the two cases of short stricture diagnosed as long by RUG, in the case of short stricture with extensive spongiofibrosis, and in the case of urethral tumor. Also the case with associated bladder tumor should have been diagnosed by bladder US which, in my opinion, is mandatory in the assessment of patients with urethral strictures. On the other hand, MRI certainly provided additional information, probably affecting treatment strategy, in the two patients with lesions of posterior urethra (rectourethral fistula and posterior urethral disruption). It would have been interesting to explore the diagnostic value of transrectal US in such cases. Thus, coming back to the present study, it would have been of greater value to compare MRI with RUG+US, to determine whether MRI can provide more information and consequently replace these two techniques. Such a study would also provide information on another interesting issue, that is, determining which diagnostic modality performs better according to the portion of the urethra. In my opinion, US is probably better that MRI for the pendulous urethra, because this portion is easy to explore with US and, on the other hand, penile mobility can make difficult having adequate urethral alignment in MRI sections. Conversely, the posterior urethra is likely to be explored better with MRI than with US, although it would be interesting to compare MRI with transrectal US. As for the bulbar urethra, it would be interesting to see whether MRI, with or without contrast medium, provides more information on spongiofibrosis than US. Urethral strictures are not easy to deal with, and refinements in diagnostic tools, which could turn into better treatment outcome, are extremely welcome. I look forward to seeing studies comparing MRI with RUG and US (uretrhal, perineal, and transrectal) aiming to address the above-mentioned issues, because such information would certainly be of great value for the urologic community. References1. Heidenreich A, Derschum W, Bonfig R, Wilbert D. Ultrasound in the evaluation of urethral stricture disease: a prospective study in 175 patients. Br J Urol. 1994;74:93–98.2. Ryu J, Kim B. MR imaging of the male and female urethra. Radiographics. 2001;21:1169–1185. 3. Pavlica P, Menchi I, Barozzi L. New imaging of the anterior male urethra. Abdom Imaging. 2003;28:180–186. 4. Gupta S, Majumdar B, Tiwari A, Gupta R, Kumar A, Gujral R. Sonourethrography in the evaluation of anterior urethral strictures: correlation with radiographic urethrography. J Clin Ultrasound. 1993;21:231–239. 5. Babnik Peskar D, Visnar Perovic A. Comparison of radiographic and sonographic urethrography for assessing urethral strictures. Eur Radiol. 2004;14:137–144. 6. Gallentine M, Morey A. Imaging of the male urethra for stricture disease. Urol Clin North Am. 2002;29:361–372. 7. Cunningham J. The diagnosis of stricture of the urethra by Roentgen rays. Trans Am Assoc Genitourin Surg. 1910;5:369–371. 8. Rosen M, McAninch J. Preoperative staging of the anterior urethral stricture. In: McAninch JW editors. Traumatic reconstructive urology. Philadelphia: Saunders; 1996;p. 551–564. 9. Mullin E, Peterson L, Paulson D. Retrograde urethrogram: diagnostic aid and hazard. J Urol. 1973;110:464–466. 10. Skati D. Ultrasonographic evaluation of the urethral stricture disease. Urology. 1992;40:237–242. 11. Beckert R, Gilbert P, Kreutzig T. Spongiosography: a valuable adjunct to the diagnosis of urethral strictures. J Urol. 1991;146:993–996. 12. Morey A, McAninch J. Ultrasound evaluation of the male urethra for assessment of urethral stricture. J Clin Ultrasound. 1996;24:473–479. 13. Schulam P, Kawashima A, Sandler C, Barron B, Lamki L, Goldman S. Urinary tract imaging: basic principles. In: Walsh P, Retik A, et al. editor. Campbell's urology. 8th ed.. Philadelphia: Saunders; 2002;p. 122–167. 14. McAninch J, Laing F, Jeffrey B. Sonourethrography in the evaluation of urethral strictures: a preliminary report. J Urol. 1988;139:294–297. 15. Narumi Y, Hricak H, Armenakas N, Dixon C, McAninch J. MR imaging of traumatic posterior urethral injury. Radiology. 1993;188:439–443. 16. El-Diasty T, El-Ghar M, Shokeir A, et al.. Magnetic resonance imaging as a sole method for the morphological and functional evaluation of live kidney donors. BJU Int. 2005;96:111–116. 17. Devine C, Jordan G, Schlossberg S, Vaughan E. Surgery of the penis and urethra. In: Walsh P, Retik A, et al. editor. Campbell's urology. 8th ed.. Philadelphia: Saunders; 2002;p. 3886–3954. 18. Jordan G, Devine P. Management of urethral stricture disease. Clin Plast Surg. 1988;15:493–505. 19. Semelka R, Hricak H, Kim B, et al.. Pelvic fistulas: appearance on MR images. Abdom Imaging. 1997;22:91–95. 20. Dixon C, Hricak H, McAninch J. Magnetic resonance imaging of traumatic posterior urethral defects and pelvic crush injuries. J Urol. 1992;148:1162–1165. Yasser Osmana, Mohamed Abou El-Gharb, Osama Mansourb, Huda Refaieb, Tarek El-Diastyb a Urology Department, Urology & Nephrology Center, Mansoura University, Mansoura, Egypt b Radiology Department, Urology & Nephrology Center, Mansoura University, Mansoura, Egypt Accepted 10 January 2006 published online 23 January 2006. doi:10.1016/j.eururo.2006.01.015
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