(Radiographics. 2001;21:1169-1185.)
© RSNA, 2001
MR Imaging of the Male and Female Urethra1
Jeong-ah Ryu, MD and
Bohyun Kim, MD
1 From the Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul 135-710, Korea. Recipient of a Certificate of Merit award for an education exhibit at the 2000 RSNA scientific assembly. Received March 19, 2001; revision requested April 6 and received May 18; accepted May 18. Address correspondence to B.K. (e-mail: bhkim@smc.samsung.co.kr).
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Abstract
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Conventional radiographic contrast material–enhanced studies (eg, retrograde urethrography [RUG], voiding cystourethrography [VCUG], double-balloon catheter urethrography) and ultrasonography are useful in evaluating the anatomy of the urethra but are limited in demonstrating anatomic derangement of adjacent structures. Since the anatomic details of both the urethra and periurethral tissues can be evaluated noninvasively with magnetic resonance (MR) imaging, this modality can be used as an adjunctive tool for evaluation of urethral abnormalities. In patients with congenital anomalies, MR imaging is reserved for cases of intersex anomalies or complex genitourinary anomalies, in which evaluation of internal organs is essential. MR imaging may demonstrate diverticula that are not seen on radiographic contrast-enhanced studies, including VCUG, RUG, or double-balloon catheter study. In cases of inflammation, MR imaging can demonstrate not only inflammatory infiltration around the urethra but also the presence of a periurethral abscess or sinus tract. In cases of trauma, MR imaging is helpful in assessing the presence and extent of anterior or posterior urethral injury and predicting the occurrence of complications. At MR imaging, a fistula can be seen as a direct communicating channel with an adjacent organ. In patients with urethral tumors, the major role of MR imaging is in local staging.
Index Terms: Fistula, genitourinary system, 84.2459, 851.2459 • Genitourinary system, infection, 84.20, 84.21, 851.20, 851.21 • Genitourinary system, injuries, 84.41, 851.41 • Urethra, abnormalities, 84.14, 851.14 • Urethra, diverticula, 84.1491, 851.1491 • Urethra, neoplasms, 84.30, 851.30
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Discuss the basic principles, advantages, and disadvantages of MR imaging of the urethra.
- Recognize a variety of pathologic conditions of the urethra on MR images.
- Describe effective MR imaging techniques for evaluation of the urethra.
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Introduction
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Clinical evaluation of the male and female urethra is often difficult. Conventional imaging studies including retrograde urethrography (RUG), voiding cystourethrography (VCUG), double-balloon catheter urethrography, and ultrasonography (US) may be helpful in demonstrating urethral abnormalities. However, radiographic contrast material–enhanced studies are invasive and do not provide information regarding the periurethral tissues. US has a small field of view and has difficulty demonstrating the urethral lumen. In contrast, owing to multiplanar capability and excellent tissue contrast, magnetic resonance (MR) imaging can provide anatomic details about both the urethra and periurethral tissues and the orientation of the lesion in three dimensions.
This article presents various pathologic conditions that affect the urethra or periurethral tissues and their appearances at MR imaging. Specific topics discussed are normal anatomy at MR imaging, MR imaging techniques, congenital anomalies, diverticulum, inflammation, trauma, fistula, tumors, and miscellaneous conditions.
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Normal Anatomy at MR Imaging
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Male Urethra
The male urethra is approximately 18–20 cm long and runs from the bladder to the external urethral meatus. It is divided into posterior and anterior portions. The posterior urethra extends from the bladder neck distally to the inferior urogenital diaphragm, and the anterior urethra extends distally to the external meatus. The posterior urethra consists of a prostatic segment and a membranous segment. The prostatic urethra is surrounded by the prostate gland. On axial images, it is seen in the central portion of the posterior prostate (Fig 1). The verumontanum, a prominence of smooth muscle, is located in theposterior wall of the prostatic urethra. The proximal portion of the prostatic urethra is rarely visualized on MR images unless a Foley catheter is placed (1). The membranous urethra is approximately 1 cm long and traverses the urogenital diaphragm. The urogenital diaphragm contains the external urethral sphincter and a Cowper gland in each side. The membranous urethra can be seen on axial T2-weighted images as a low-signal-intensity ring surrounding the high-signal-intensity epithelial surface.
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Figure 1a. Normal MR imaging anatomy of the male urethra in a 59-year-old man. (a) Axial T2-weighted image obtained through the midprostate shows the prostatic urethra (P) in the posterior prostate as a small round structure of high signal intensity. (b) Axial T2-weighted image obtained through the root of the penis shows the bulbous urethra (B) traversing the midline within the corpus spongiosum. (c) Midline sagittal T2-weighted image shows the course of the urethra from the bladder neck to the proximal bulbous urethra (B). The anterior penile urethra is not well seen. M = membranous urethra, P = prostatic urethra.
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Figure 1b. Normal MR imaging anatomy of the male urethra in a 59-year-old man. (a) Axial T2-weighted image obtained through the midprostate shows the prostatic urethra (P) in the posterior prostate as a small round structure of high signal intensity. (b) Axial T2-weighted image obtained through the root of the penis shows the bulbous urethra (B) traversing the midline within the corpus spongiosum. (c) Midline sagittal T2-weighted image shows the course of the urethra from the bladder neck to the proximal bulbous urethra (B). The anterior penile urethra is not well seen. M = membranous urethra, P = prostatic urethra.
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Figure 1c. Normal MR imaging anatomy of the male urethra in a 59-year-old man. (a) Axial T2-weighted image obtained through the midprostate shows the prostatic urethra (P) in the posterior prostate as a small round structure of high signal intensity. (b) Axial T2-weighted image obtained through the root of the penis shows the bulbous urethra (B) traversing the midline within the corpus spongiosum. (c) Midline sagittal T2-weighted image shows the course of the urethra from the bladder neck to the proximal bulbous urethra (B). The anterior penile urethra is not well seen. M = membranous urethra, P = prostatic urethra.
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The anterior urethra consists of a bulbous segment and a penile or pendulous segment. The bulbous urethra is located between the inferior margin of the urogenital diaphragm and the penoscrotal junction, and the penile urethra extends from the penoscrotal junction to the external meatus. The bulbous urethra courses within the root of the penis and is seen as a lower-signal-intensity tubular structure in the midline within the bulb of the corpus spongiosum. Sagittal and coronal T2-weighted images may show the course of the anterior and posterior urethra. The distal penile urethra is often not seen on MR images if a Foley catheter is not inserted (1). Gadolinium-enhanced MR imaging can be helpful in selected cases such as extensive tumors and inflammation involving the urethra and periurethral tissues. However, further studies are needed to determine the role of contrast media in MR imaging of the urethra (2).
Female Urethra
The female urethra is approximately 4 cm long. It extends from the internal urethral meatus at the bladder neck through the urogenital diaphragm to the external urethral meatus anterior to the vaginal opening. It courses obliquely downward and forward; it is slightly curved with the concavity directed forward. Multiple tiny urethral glands, called the paraurethral glands of Skene, open into the urethral orifice (3–5).
On axial T2-weighted images or gadolinium-enhanced T1-weighted images, the normal urethra has a characteristic targetlike appearance. On axial T2-weighted images, the urethra is seen as four concentric rings of different signal intensities: an outer ring of low signal intensity, a middle layer of higher signal intensity, an inner ring of low signal intensity, and finally a high-signal-intensity zone in the center (Fig 2a) (6,7). These layers at MR imaging can be correlated with the known histologic features of the female urethra (8). According to Hricak et al (7), the outer ring corresponds to the outer striated muscle, the middle layer corresponds to the smooth muscle and submucosa, and the central portion corresponds to the mucosa lined by the stratified epithelium. Similar zonal anatomy can also be seen on sagittal images (9) (Fig 2b).
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Figure 2a. Normal MR imaging anatomy of the female urethra in a 54-year-old woman. (a) Axial T2-weighted image shows that the urethra has a characteristic targetlike appearance with four concentric rings: an outer ring of low signal intensity (O), a middle layer of higher signal intensity (M), an inner ring of low signal intensity (I), and a high-signal-intensity zone in the center (C). (b) Sagittal T2-weighted image shows similar zonal anatomy. C = center zone, I = inner ring, M = middle layer, O = outer ring.
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Figure 2b. Normal MR imaging anatomy of the female urethra in a 54-year-old woman. (a) Axial T2-weighted image shows that the urethra has a characteristic targetlike appearance with four concentric rings: an outer ring of low signal intensity (O), a middle layer of higher signal intensity (M), an inner ring of low signal intensity (I), and a high-signal-intensity zone in the center (C). (b) Sagittal T2-weighted image shows similar zonal anatomy. C = center zone, I = inner ring, M = middle layer, O = outer ring.
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MR Imaging Techniques
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Both T1- and T2-weighted imaging are often needed to evaluate the male and female urethra. The urethra can be evaluated in orthogonal planes (axial, sagittal, and coronal) or imaged obliquely along its course. In male patients, the membranous urethra is best evaluated in the axial plane and the relation between the membranous and bulbous urethra (particularly in cases of trauma) is best evaluated in the coronal or sagittal plane (1,9). For imaging of the anterior urethra, the penis should be positioned anteriorly in the supine position and taped to the abdominal wall beneath the surface coil (10). In female patients, axial images are essential (9). For evaluation of a urethral diverticulum or spread of urethral cancer, a combination of axial and sagittal or coronal imaging may be helpful.
A thin section thickness (3–5 mm) and a small intersection gap (1–2 mm) are desirable for imaging the urethra (11). The signal-to-noise ratio can be improved by using surface coils or endovaginal or endorectal coils (12–15). Although endocavitary coils may improve the spatial resolution, the small field of view may limit the area of imaging and the high signal intensity in the near field may degrade image quality. Since evaluation of adjacent organs is often essential for diagnosis of urethral disease, we prefer using pelvic or torso phased-array coils.
Use of intravenous contrast media can be beneficial in selected cases, particularly in patients with extensive tumors or inflammation. Although a few studies have found that the normal urethra or urethral lesions can be better demonstrated on contrast-enhanced images than on T2-weighted images, they included only a small number of cases and thus lack statistical analysis (6,7,10).
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Congenital Anomalies
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Congenital anomalies of the urethra include anomalies of number (duplication) and form (posterior urethral valves, congenital stricture, congenital polyp, congenital diverticulum) and malformations of the urethral groove (epispadias, hypospadias). Most of these defects are readily detected with inspection or radiographic contrast-enhanced studies (such as RUG). MR imaging is reserved for patients with intersex anomalies or complex genitourinary anomalies, in whom evaluation of internal organs is essential. MR imaging can be helpful in determining the presence or absence of urogenital organs or demonstrating abnormal communications with these organs (16).
Male Urethra
Epispadias is a rare congenital anomaly that is almost always associated with exstrophy of the bladder. The roof of the urethra is absent, and the urethra opens anywhere between the base and the glans of the penis. Hypospadias is a congenital defect of the anterior urethra, which opens anywhere along the ventral aspect of the penile shaft. The presence of hypospadias is thought by some to be a form of intersex. Although VCUG or RUG can demonstrate the urethra per se, the anatomy of the urethra and adjacent structures can be better evaluated with MR imaging (Fig 3).
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Figure 3a. Hypospadias in a 28-year-old man with Turner syndrome who demonstrated penoscrotal transposition and a hypoplastic penis and prostate at MR imaging. (a) Axial T2-weighted image of the root of the penis shows a small, hypoplastic penis in the posterior aspect of the scrotum. The distal urethra is seen in the ventral aspect of the corpus spongiosum (arrow). (b) Axial T2-weighted image of the lower pelvis shows a hypoplastic prostate (arrowhead) surrounding the prostatic urethra (U). (c) Sagittal T2-weighted image shows a high-signal-intensity tubular structure between the urethra and the rectum, which may represent a urogenital sinus (UG). The distal urethra opens into the perineum in the ventral aspect of the corpus spongiosum (arrow). P = prostatic urethra, UT = utricle. (d) RUG image shows the anatomic relationships between the prostatic urethra (P), urogenital sinus (UG), and utricle (UT), which correlate well with the MR imaging findings.
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Figure 3b. Hypospadias in a 28-year-old man with Turner syndrome who demonstrated penoscrotal transposition and a hypoplastic penis and prostate at MR imaging. (a) Axial T2-weighted image of the root of the penis shows a small, hypoplastic penis in the posterior aspect of the scrotum. The distal urethra is seen in the ventral aspect of the corpus spongiosum (arrow). (b) Axial T2-weighted image of the lower pelvis shows a hypoplastic prostate (arrowhead) surrounding the prostatic urethra (U). (c) Sagittal T2-weighted image shows a high-signal-intensity tubular structure between the urethra and the rectum, which may represent a urogenital sinus (UG). The distal urethra opens into the perineum in the ventral aspect of the corpus spongiosum (arrow). P = prostatic urethra, UT = utricle. (d) RUG image shows the anatomic relationships between the prostatic urethra (P), urogenital sinus (UG), and utricle (UT), which correlate well with the MR imaging findings.
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Figure 3c. Hypospadias in a 28-year-old man with Turner syndrome who demonstrated penoscrotal transposition and a hypoplastic penis and prostate at MR imaging. (a) Axial T2-weighted image of the root of the penis shows a small, hypoplastic penis in the posterior aspect of the scrotum. The distal urethra is seen in the ventral aspect of the corpus spongiosum (arrow). (b) Axial T2-weighted image of the lower pelvis shows a hypoplastic prostate (arrowhead) surrounding the prostatic urethra (U). (c) Sagittal T2-weighted image shows a high-signal-intensity tubular structure between the urethra and the rectum, which may represent a urogenital sinus (UG). The distal urethra opens into the perineum in the ventral aspect of the corpus spongiosum (arrow). P = prostatic urethra, UT = utricle. (d) RUG image shows the anatomic relationships between the prostatic urethra (P), urogenital sinus (UG), and utricle (UT), which correlate well with the MR imaging findings.
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Figure 3d. Hypospadias in a 28-year-old man with Turner syndrome who demonstrated penoscrotal transposition and a hypoplastic penis and prostate at MR imaging. (a) Axial T2-weighted image of the root of the penis shows a small, hypoplastic penis in the posterior aspect of the scrotum. The distal urethra is seen in the ventral aspect of the corpus spongiosum (arrow). (b) Axial T2-weighted image of the lower pelvis shows a hypoplastic prostate (arrowhead) surrounding the prostatic urethra (U). (c) Sagittal T2-weighted image shows a high-signal-intensity tubular structure between the urethra and the rectum, which may represent a urogenital sinus (UG). The distal urethra opens into the perineum in the ventral aspect of the corpus spongiosum (arrow). P = prostatic urethra, UT = utricle. (d) RUG image shows the anatomic relationships between the prostatic urethra (P), urogenital sinus (UG), and utricle (UT), which correlate well with the MR imaging findings.
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Female Urethra
Urethral duplication can occur in female patients. Congenital urethral polyp and diverticulum occur most commonly in male patients and are rare in female patients. An ectopic ureteral orifice is commonly associated with ureteral duplication. It is more common in female patients. In about 15% of cases, the ectopic ureter opens caudal to the normal orifice, anywhere in the posterior wall of the urethra, in a urethral diverticulum, or in the urethrovaginal septum (16). In female patients, the urethra and vestibule are the most common sites. At MR imaging, the course of the dilated ureter can be traced to the ectopic orifice, although demonstration of the exact site of insertion is not always possible (Fig 4).
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Figure 4a. Ectopic ureter in a 35-year-old woman. (a) Axial T2-weighted image shows a dilated right distal ureter (UR) located between the vagina (V) and urethra (arrowhead), a position that is lower than normal. Insertion of the right distal ureter into the urethra is not well demonstrated on this view. (b, c) Consecutive sagittal T2-weighted images show that the dilated ureter (UR) is tortuous and inserts into the midurethra (arrow). (d) Radiograph shows a dilated right duplex ureter, which inserts into the bladder in a lower than normal position (arrow).
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Figure 4b. Ectopic ureter in a 35-year-old woman. (a) Axial T2-weighted image shows a dilated right distal ureter (UR) located between the vagina (V) and urethra (arrowhead), a position that is lower than normal. Insertion of the right distal ureter into the urethra is not well demonstrated on this view. (b, c) Consecutive sagittal T2-weighted images show that the dilated ureter (UR) is tortuous and inserts into the midurethra (arrow). (d) Radiograph shows a dilated right duplex ureter, which inserts into the bladder in a lower than normal position (arrow).
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Figure 4c. Ectopic ureter in a 35-year-old woman. (a) Axial T2-weighted image shows a dilated right distal ureter (UR) located between the vagina (V) and urethra (arrowhead), a position that is lower than normal. Insertion of the right distal ureter into the urethra is not well demonstrated on this view. (b, c) Consecutive sagittal T2-weighted images show that the dilated ureter (UR) is tortuous and inserts into the midurethra (arrow). (d) Radiograph shows a dilated right duplex ureter, which inserts into the bladder in a lower than normal position (arrow).
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Figure 4d. Ectopic ureter in a 35-year-old woman. (a) Axial T2-weighted image shows a dilated right distal ureter (UR) located between the vagina (V) and urethra (arrowhead), a position that is lower than normal. Insertion of the right distal ureter into the urethra is not well demonstrated on this view. (b, c) Consecutive sagittal T2-weighted images show that the dilated ureter (UR) is tortuous and inserts into the midurethra (arrow). (d) Radiograph shows a dilated right duplex ureter, which inserts into the bladder in a lower than normal position (arrow).
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Diverticulum
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Acquired urethral diverticulum occurs more frequently in female patients and is rare in male patients. Most commonly, it occurs in the midurethra and on the posterolateral wall rather than on the anterior wall. It is thought to result from inflammation and trauma of the periurethral Skene glands and ducts, leading to local glandular dilatation and subsequent rupture into the urethra (17). It may arise in association with a congenital anomaly, such as cloacal epithelium or a wolffian or müllerian duct remnant.
At MR imaging, a diverticulum is seen as a multiseptated cystic lesion surrounding the urethra (Figs 5, 6). MR imaging may demonstrate diverticular sacs that are not seen on radiographic contrast-enhanced studies, including VCUG, RUG, or double-balloon catheter study (18) (Fig 5). MR imaging has been reported to have a higher sensitivity for detection of urethral diverticulum than VCUG or cystoscopy (6). It allows direct visualization of the diverticulum and evaluation of the anatomic relationship to the urethra or adjacent structures such as the vagina and the base of the bladder. It has also been reported to be useful in diagnosing inflammation and tumor of the diverticulum (18,19) (Fig 7). The content of an inflamed diverticulum may have heterogeneous signal intensity higher than that of urine on T1-weighted images and intense high signal intensity on T2-weighted images. It may also demonstrate fluid-fluid levels on T2-weighted images (Fig 7).
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Figure 5a. Urethral diverticula in a 36-year-old woman. (a, b) Axial (a) and sagittal (b) T2-weighted images of the pelvis show diverticular sacs (arrows) as multiple cystic lesions surrounding the urethra (U). (c) VCUG image shows only one diverticulum (arrowhead) out of the more than two demonstrated at MR imaging.
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Figure 5b. Urethral diverticula in a 36-year-old woman. (a, b) Axial (a) and sagittal (b) T2-weighted images of the pelvis show diverticular sacs (arrows) as multiple cystic lesions surrounding the urethra (U). (c) VCUG image shows only one diverticulum (arrowhead) out of the more than two demonstrated at MR imaging.
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Figure 5c. Urethral diverticula in a 36-year-old woman. (a, b) Axial (a) and sagittal (b) T2-weighted images of the pelvis show diverticular sacs (arrows) as multiple cystic lesions surrounding the urethra (U). (c) VCUG image shows only one diverticulum (arrowhead) out of the more than two demonstrated at MR imaging.
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Figure 6. Multiseptated urethral diverticula in a 50-year-old woman. Sagittal T2-weighted image clearly shows multiple septated diverticula (arrows). Note that the bladder neck is elevated (arrowhead).
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Figure 7a. Infected urethral diverticulum in a 38-year-old woman. (a) Axial T2-weighted image shows a fluid-fluid level (arrow) in a diverticular sac. (b) Contrast-enhanced axial T1-weighted image shows debris along the thickened wall of the diverticulum (arrows).
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Figure 7b. Infected urethral diverticulum in a 38-year-old woman. (a) Axial T2-weighted image shows a fluid-fluid level (arrow) in a diverticular sac. (b) Contrast-enhanced axial T1-weighted image shows debris along the thickened wall of the diverticulum (arrows).
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Since MR imaging is noninvasive and can better demonstrate anatomic details of adjacent structures, it can serve as an adjunctive diagnostic tool, particularly when urethroscopic or urethrographic findings are equivocal (6).
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Inflammation
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Although imaging studies do not play a major role in evaluation of urethral or periurethral inflammation, MR imaging can demonstrate severe urethral inflammation and its complications. In women, urethral inflammation often occurs in combination with cystitis and vaginitis or may follow radiation therapy (Fig 8). Urethral diverticulum, periurethral inflammation, and sinus tracts are thought to result from inflammation of the Skene glands. In men, sexually transmitted urethral infection including gonococcal disease used to be the most common cause of urethral stricture (20). However, postinfectious urethral stricture is now less common than posttraumatic stenosis (21).
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Figure 8a. Radiation-induced urethritis in a 42-year-old woman with uterine cervical carcinoma. F = Foley catheter. (a) Axial T2-weighted image shows diffuse thickening of the urethra (arrows) and periurethral tissues with intermediate signal intensity. (b) Sagittal T2-weighted image shows that the entire urethra (arrows) is enlarged and has high signal intensity.
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Figure 8b. Radiation-induced urethritis in a 42-year-old woman with uterine cervical carcinoma. F = Foley catheter. (a) Axial T2-weighted image shows diffuse thickening of the urethra (arrows) and periurethral tissues with intermediate signal intensity. (b) Sagittal T2-weighted image shows that the entire urethra (arrows) is enlarged and has high signal intensity.
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MR imaging can demonstrate not only inflammatory infiltration around the urethra but also the presence of a periurethral abscess or sinus tract. At MR imaging, urethral and periurethral inflammation is seen as diffuse thickening of the urethra and periurethral tissues with intermediate signal intensity on T2-weighted images (Figs 8, 9). A periurethral abscess is seen as a cavitary lesion along the course of the urethra (Fig 9). A periurethral sinus tract may have similar MR imaging findings but may demonstrate an opening to the perineum (Fig 10). Occasionally, periurethral abscess and sinus tract are indistinguishable from a urethral diverticulum located in the distal urethra at MR imaging.
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Figure 9. Urethral and periurethral inflammation with microabscesses of the Skene glands in a 27-year-old woman. Coronal T2-weighted image shows periurethral infiltration with loss of surrounding fat planes (arrows). F = Foley catheter, M = microabscesses.
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Figure 10a. Periurethral sinus tract in a 49-year-old woman. Axial (a) and coronal (b) T2-weighted images show an elongated, crescentic cystic lesion (arrow) along the right posterolateral aspect of the urethra. The lesion resembles a urethral diverticulum. At physical examination, an opening was found near the external urethral meatus.
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Figure 10b. Periurethral sinus tract in a 49-year-old woman. Axial (a) and coronal (b) T2-weighted images show an elongated, crescentic cystic lesion (arrow) along the right posterolateral aspect of the urethra. The lesion resembles a urethral diverticulum. At physical examination, an opening was found near the external urethral meatus.
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Trauma
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Urethral injury occurs as a result of blunt or penetrating trauma or iatrogenic injury. Because of the mobility and short length of the female urethra, injuries to it are extremely rare. MR imaging has been reported to be helpful in assessing the presence and extent of anterior or posterior urethral injury and predicting the occurrence of complications (2,6).
Injury of Anterior Urethra
Anterior urethral injury commonly occurs in the bulbous urethra, often as a result of straddle injury. It may result in rupture of the bulbous urethra (Fig 11) or may be associated with penile fracture. MR imaging can demonstrate disruption of the involved urethra with resultant surrounding hematoma (Fig 11). Since major urethral injury requires surgical intervention and is associated with a higher rate of complications, accurate assessment of the presence and extent of the injury is essential for treatment planning (2).
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Figure 11. Posttraumatic rupture of the bulbous urethra following a traffic accident in a 64-year-old man. Sagittal T2-weighted image shows a fluid-filled cystic lesion (F) surrounding a Foley catheter (arrow) in the bulbous urethra. The lesion may represent a urinoma or hematoma about the ruptured urethra (U). A = scrotal abscess.
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Injury of Posterior Urethra
Most often, posterior urethral injury is initially managed with cystostomy and suprapubic urinary diversion (22). Standard evaluation before urethroplasty includes combined cystography and RUG to determine the length of the urethral defect. However, these studies provide only two-dimensional information and offer little information about adjacent structures, such as the displacement of the prostatic apex and the presence of hematoma or fibrosis (Fig 12). MR imaging can be very helpful in evaluating the anatomic derangement of a posterior urethral injury. It has been reported to be accurate for estimating the length of the urethral injury and the displacement of the prostatic apex (23,24) (Fig 12). MR imaging can demonstrate anatomic details even when distal urethral stenosis hampers evaluation of the more proximal urethra (25) (Fig 13). It can also be helpful in identifying the organic components of posttraumatic impotence and in selecting effective, cause-specific therapy (26).
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Figure 12a. Posterior urethral injury in a 32-year-old man with a remote history of a traffic accident. (a) Sagittal T2-weighted image shows that the prostatic apex (P) is displaced upward. Displaced proximal (small arrows) and distal (large arrows) urethral ends with intervening extensive retropubic fibrosis (arrowheads) are well demonstrated. (b) Image from combined cystography and RUG shows only a two-dimensional view of the area; the urethra is not visualized. S = urethral sound introduced through the cystostomy opening.
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Figure 12b. Posterior urethral injury in a 32-year-old man with a remote history of a traffic accident. (a) Sagittal T2-weighted image shows that the prostatic apex (P) is displaced upward. Displaced proximal (small arrows) and distal (large arrows) urethral ends with intervening extensive retropubic fibrosis (arrowheads) are well demonstrated. (b) Image from combined cystography and RUG shows only a two-dimensional view of the area; the urethra is not visualized. S = urethral sound introduced through the cystostomy opening.
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Figure 13a. Posterior urethral injury in a 38-year-old man. (a) Sagittal T2-weighted image clearly shows a dilated bulbous urethra (B) and the actual length of a defect in the membranous urethra (between arrows). (b) Image from a combined radiographic study does not show the dilated bulbous urethra due to distal urethral stenosis (U).
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Figure 13b. Posterior urethral injury in a 38-year-old man. (a) Sagittal T2-weighted image clearly shows a dilated bulbous urethra (B) and the actual length of a defect in the membranous urethra (between arrows). (b) Image from a combined radiographic study does not show the dilated bulbous urethra due to distal urethral stenosis (U).
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Fistula
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Urethral fistulas may communicate with the perineum, vagina, rectum, and seminal vesicles and the skin of the thigh and gluteal muscles. Urethrovaginal fistulas most commonly occur following pelvic surgery. Radiation, vaginal delivery, and inflammation may also result in fistulas (14). Rectourethral fistulas are rare and are reported to occur from developmental causes, usually in association with complex anorectal abnormalities (14). At MR imaging, a fistula can be seen as a direct communicating channel with an adjacent organ (Fig 14). However, direct visualization of the fistula is not always possible and only the secondary signs including focal enhancement with loss of intervening fat planes may be seen. The rate of detection of various fistulas with MR imaging has been reported to be fairly high (27).
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Figure 14. Urethrovaginal fistula in a 74-year-old woman with a history of delivery trauma. Sagittal T2-weighted image shows a fistulous communication (arrows) between the urethra (U) and vagina (V).
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Tumors
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Primary Tumors
Benign urethral tumors are rare (28). Benign mesenchymal tumors such as fibrous polyp, leiomyoma, and hemangioma can be encountered. Ninety-five percent of malignant urethral tumors are epithelial in origin, and urethral cancer is much more common in women than in men, although it accounts for less than 0.02% of all malignancies occurring in women (29–31). Squamous cell carcinoma is the most common histologic type in both male and female patients (male patients, 80% of cases; female patients, 60%), followed by transitional cell carcinoma (male patients, 15%; female patients, 20%) and adenocarcinoma (male patients, 5%; female patients, 10%) (29). In male patients, about 60% of urethral tumors occur in the bulbomembranous area, 30% occur in the penile urethra, and 10% occur in the prostatic urethra (28,32). Although squamous cell carcinoma is the most common histologic type of penile or bulbomembranous urethral cancer, transitional cell carcinoma is most common in the prostatic urethra. In female patients, urethral cancer is classified as anterior or entire. Anterior tumors are located exclusively in the distal third of the urethra and account for 46% of urethral tumors. In general, anterior urethral tumors are low grade and less extensive (33,34).
The penile urethra in men and the distal urethra in women drain into the superficial and deep inguinal lymph nodes. The bulbous, membranous, and prostatic urethra in men and the proximal urethra in women drain into the obturator, external iliac, and internal iliac lymph nodes (28).
The major role of MR imaging in patients with urethral tumors is for local staging. MR imaging has been reported to be useful in evaluating the local extent of the tumor and in treatment planning (35–39).
In male patients, urethral tumors have signal intensity similar to or lower than that of the surrounding corpus on T1-weighted images and intermediate to low signal intensity on T2-weighted images. At contrast-enhanced MR imaging, the tumor usually shows mild enhancement (Fig 15). Sometimes, it has very high signal intensity on T2-weighted images due to associated inflammation (1). For tumors that invade the root of the penis, physical examination is often limited and MR imaging can play a major role. Tumor extension into the tunica albuginea or septa of the corpus cavernosum can be readily demonstrated on T2-weighted images. A tumor arising from the Cowper gland can be readily detected with MR imaging due to its typical location (Fig 16).
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Figure 15. Extensive transitional cell carcinoma involving almost the entire urethra in a 75-year-old man. Contrast-enhanced T1-weighted image shows a poorly enhancing tumor (arrowheads) expanding the urethral lumen and invading the periurethral tissues.
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Figure 16a. Adenocarcinoma arising from the Cowper gland in a 59-year-old man. (a) Axial T2-weighted image shows a multilobulated soft-tissue mass of intermediate signal intensity (arrows) in the left side of the membranous urethra within the urogenital diaphragm. An enlarged left inguinal lymph node (N) is also seen. (b) Coronal T2-weighted image shows that the distal prostatic urethra (U) is displaced by the tumor (arrows).
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Figure 16b. Adenocarcinoma arising from the Cowper gland in a 59-year-old man. (a) Axial T2-weighted image shows a multilobulated soft-tissue mass of intermediate signal intensity (arrows) in the left side of the membranous urethra within the urogenital diaphragm. An enlarged left inguinal lymph node (N) is also seen. (b) Coronal T2-weighted image shows that the distal prostatic urethra (U) is displaced by the tumor (arrows).
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In female patients, urethral tumors have low signal intensity on T1-weighted images and relatively high signal intensity on T2-weighted images (Figs 17, 18). The extent of the tumor is best evaluated on sagittal T2-weighted images. Tumors in the distal urethra may extend into the adjacent perineum, and the targetlike appearance of the normal urethra on axial T2-weighted images may be disrupted (Fig 19). MR imaging is helpful in evaluating the size, location, and local extension of urethral tumors (Figs 18, 19). Its accuracy in evaluation of local tumor extension has been reported to be 90% (7).
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Figure 17. Squamous cell carcinoma of the distal urethra in a 62-year-old woman. Coronal T2-weighted image shows a soft-tissue mass of intermediate signal intensity (arrows) about the distal urethra. The mass extends into adjacent structures at the level of the urogenital diaphragm.
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Figure 18. Clear cell adenocarcinoma of the upper two-thirds of the urethra in a 63-year-old woman. Sagittal T2-weighted image shows a tumor of heterogeneous high signal intensity (T) that involves nearly the entire length of the urethra and the base of the bladder.
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Figure 19. Malignant melanoma in a 64-year-old woman. Axial T2-weighted image shows an ill-defined mass of intermediate signal intensity (arrows) in the distal urethra. The mass infiltrates into adjacent periurethral soft tissues.
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Secondary Tumors
Urethral involvement by extraurethral malignancy most commonly occurs by contiguous extension from adjacent organs such as the bladder, cervix (Fig 20), and vagina. Hematogenous spread from the prostate, kidney, ureter, and testis has been reported in the literature (40–42).Lymphatic or venous extension may occur. Priapism, hematuria, obstruction, pain, urethral induration, and nodularity are frequent signs and symptoms (43). At MR imaging, secondary tumors are seen within the urethral lumen with or without extension into surrounding tissues (Figs 21, 22) or in the periurethral tissues, surrounding the urethra (Fig 20).
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Figure 20a. Urethral and periurethral invasion from recurrent cervical cancer in a 75-year-old woman. (a) Axial T2-weighted image shows an irregular soft-tissue mass of intermediate signal intensity (arrows) surrounding the urethra (U). The outer ring of the urethra is disrupted in the left anterolateral portion (arrowhead), suggesting invasion of the outer muscle layer. (b) Sagittal T2-weighted image shows that the uterine cervix is shrunken and the vagina is diffusely thickened, probably due to post-radiation therapy changes. Residual tumor (arrow) is seen in the upper anterior aspect of the thickened urethra (U) at the bladder base.
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Figure 20b. Urethral and periurethral invasion from recurrent cervical cancer in a 75-year-old woman. (a) Axial T2-weighted image shows an irregular soft-tissue mass of intermediate signal intensity (arrows) surrounding the urethra (U). The outer ring of the urethra is disrupted in the left anterolateral portion (arrowhead), suggesting invasion of the outer muscle layer. (b) Sagittal T2-weighted image show | |
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Abstract
LEARNING OBJECTIVES
