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Helping the Urologist |
1 Department of Urology, Washington University School of Medicine, St Louis, Missouri
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Although the use of MR imaging to evaluate benign masses is intriguing, I have usually employed Doppler US, which is typically more readily available, quicker, less expensive, and less technically demanding than MR imaging. In my practice, I have routinely used US to evaluate Cowper duct syringocele (1), cavernosal thrombosis, and Peyronie disease. From a practical standpoint, if the patient is interested in a surgical correction (plication or incision and grafting) of his penile curvature, I routinely obtain a color duplex US scan before any surgery. Color duplex US after intracavernous injection of a vasodilator helps define vascular function and collateral circulation. Gall et al (2) have shown a good correlation between the Doppler study and arteriographic findings. Treatment for Peyronie disease is dependent on the degree of penile curvature and penile erection function. MR imaging appears to provide little additional practical information over that yielded by US. Recently, we also used MR imaging to diagnose a neurofibroma of the proximal part of the penis in a patient with known neurofibromatosis.
As to penile trauma, penile fracture is, with few exceptions, a diagnosis made at clinical presentation. The typical history and physical findings rarely warrant further radiologic inquiry to achieve the diagnosis. The use of cavernosography and US has also been advocated for fracture evaluation. Regardless, the diagnosis and site of injury are usually apparent at physical examination, and in such circumstances cavernosography or MR imaging are an unnecessary expense and consume too much time, particularly since the treatment is prompt surgical repair. MR imaging may have a role if the physical examination is difficult and diagnosis uncertain.
I have also found MR imaging to be particularly helpful in the surgical planning of posterior urethroplasty for prostatomembranous disruption injury from pelvic fracture. MR imaging is typically most useful when the combined retrograde urethrography and voiding cystourethrography do not adequately show the length and extent of intervening stricture. Furthermore, if the bladder neck does not relax, stricture length can be grossly overestimated. MR imaging can accurately show the displacement of the prostatic apex and thus stricture length, as well as help explain posttraumatic impotence by documenting cavernosal avulsion from the ischium. The degree of distraction determines the surgical plan, such as the need for corporal cavernosal body separation, inferior pubectomy, or urethral rerouting under the crus. A combined transpubic and retropubic approach is rarely, if ever, needed today. Typically, it is reserved for the most severe defects, usually greater than 6 cm with extensive superolateral displacement, or orthopedic deformities that preclude perineal access.
In its practical role, MR imaging of the penis and urethra is a promising and evolving imaging modality.
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Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
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In the penis or in any organ, it is not the role of diagnostic imaging to obviate biopsy, as the diagnosis of malignancy is always made histologically. Although some penile malignancies may be correctly staged by means of clinical examination, most are staged with the guidance of an imaging study. US has traditionally filled this role for penile malignancies, but the superior resolution and soft-tissue contrast of MR imaging give it several natural advantages in this application. A "skip" metastasis such as that seen in Figure 7 would be a difficult finding at physical examination or directed US examination, and pelvic lymphadenopathy is surely much more easily evaluated with MR imaging.
Evaluation of penile trauma can also benefit from prompt MR imaging. Again, although the nature and extent of injury may be apparent from history and physical examination in some cases, most patients will undergo imaging in some fashion. Cavernosography is rarely performed, and the "on-call" radiologist may have little or no experience in performing such a procedure. Penile US is also a rare examination in many institutions, and few sonographers or radiologists have a wealth of experience in imaging the traumatized penis. MR imaging, however, is a straightforward examination, and it has the great advantage of high contrast between the T2-weighted hyperintense corporal bodies and the T2-weighted hypointense tunica albuginea. The entire organ can be imaged noninvasively in a few minutes, and disruption of the hypointense tunica, if present, is readily visualized.
Although MR imaging has many advantages over other modalities for imaging the penis, we do not advocate it for all cases. Many questions can be answered with US, particularly when it is performed by experienced personnel. It was once the case, though, that radiologists had little to offer if US examination failed to answer questions about penile pathologic conditions. We feel this is no longer true.
Related Article
RadioGraphics 2001 21: S283-S298.
This article has been cited by other articles:
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  D. J. Sung, Y. H. Kim, S. B. Cho, Y. W. Oh, N. J. Lee, J. H. Kim, K. B. Chung, D. G. Moon, and J. J. Kim Obliterative Urethral Stricture: MR Urethrography versus Conventional Retrograde Urethrography with Voiding Cystourethrography Radiology, September 1, 2006; 240(3): 842 - 848. [Abstract] [Full Text] [PDF]
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