(Radiographics. 2001;21:S283-S298.)
© RSNA, 2001
MR Imaging of the Penis1
E. Scott Pretorius, MD,
Evan S. Siegelman, MD,
Parvati Ramchandani, MD and
Marc P. Banner, MD
1 From the Department of Radiology, University of Pennsylvania Medical Center, 1 Silverstein, 3400 Spruce St, Philadelphia, PA 19104. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received January 10, 2001; revision requested April 11 and received May 7; accepted May 15. Address correspondence to E.S.P. (e-mail: pretoriu@rad.upenn.edu).
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Abstract
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The signal intensity of the corpora cavernosa of the penis at magnetic resonance (MR) imaging may vary from that of the corpus spongiosum; this difference is dependent on the rate of blood flow within the cavernous spaces that constitute the corporal bodies. Also visible at MR imaging are the layers of fibrous tissue that envelop the corporal bodies, the deep arteries and veins, subcutaneous connective tissue, tunica dartos, epidermis, and urethra. While the iliac, pudendal, perineal, and common penile arteries can be evaluated with three-dimensional MR angiography, the smaller end arteries of the penis have not yet been reliably demonstrated. MR imaging may be used to detect and stage penile and urethral cancers, identify and characterize benign penile masses, evaluate arteriogenic impotence, identify penile fractures, evaluate penile prostheses, localize periurethral abscesses, and identify plaques of Peyronie disease. With its direct multiplanar imaging capabilities, superb soft-tissue contrast, and excellent spatial resolution, high-field surface coil MR imaging can show the soft-tissue and vascular anatomy of the penis, as well as the appearance of many penile diseases.
Index Terms: Penis, diseases, 847.211, 847.29 • Penis, injuries, 847.41 • Penis, MR, 847.12141 • Penis, neoplasms, 847.32
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Introduction
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Although ultrasonography (US) has been the primary modality for cross-sectional imaging of the penis, the superior soft-tissue contrast and spatial resolution afforded by magnetic resonance (MR) imaging provide an opportunity to advance imaging evaluation of this organ. Clinical questions that remain unresolved after US examination can often be answered with penile MR imaging.
This article reviews the anatomy of the penis as shown with surface-coil MR imaging performed at 1.5 T. Strategies for optimal MR imaging of the penis are discussed, including organ and surface coil positioning, pulse sequence selection, vasodilator injection, and gadolinium administration. Among the conditions presented are primary and metastatic penile malignancies, periurethral abscess, venous thrombosis, Peyronie disease, and penile fracture. The MR imaging appearance of the postsurgical penis and of penile prostheses is also demonstrated.
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Anatomy and Physiology
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The penis is composed of three cylindrical bodies of endothelium-lined cavernous spaces: the paired dorsolateral corpora cavernosa, and the single, ventral, and midline corpus spongiosum (Fig 1).
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Figure 1a. (a) Axial illustration of penile anatomy. (b) Sagittal illustration of penile anatomy. (Fig 1a and 1b courtesy of Frank M. Corl, MS, Johns Hopkins Medical Institutions, Baltimore, Md.)
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Figure 1b. (a) Axial illustration of penile anatomy. (b) Sagittal illustration of penile anatomy. (Fig 1a and 1b courtesy of Frank M. Corl, MS, Johns Hopkins Medical Institutions, Baltimore, Md.)
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The variable MR signal intensity of these structures is dependent on the rate of blood flow within the cavernous spaces that constitute the corporal bodies. In general, the three corpora are of intermediate T1-weighted and high T2-weighted signal intensity. The corpora cavernosa are isointense relative to one another, as they are connected via fenestrations in their septum and therefore have similar flow. The corpus spongiosum is a separate space and may normally have flow and signal intensity characteristics different from those of the cavernosa. The posterior portions of the corpora cavernosa are known as the crura, which flare laterally to attach to the ischiopubic rami. The corpus spongiosum arises within the perineum from the bulbous spongiosum and extends anteriorly to form the glans penis (Fig 2a).
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Figure 2a. Normal penile anatomy in a 20-year-old man. (a) Axial T2-weighted MR image shows the normal attachment of the posterior aspects of the corpora cavernosa, the crura (curved arrows), and to the ischial rami (thin arrows). At T2-weighted imaging, signal intensity in the penile bulb (open straight arrow), which is the base of the corpus spongiosum, is different from that in the corpora cavernosa (thick solid arrows). This finding is normal. (b) Axial T2-weighted image (5,000/96 [repetition time msec/echo time msec]) shows the paired corpora cavernosa surrounded by the Buck fascia and the tunica albuginea, which at MR imaging appear as a single hypointense border to the cavernosa (small straight black arrow). The central arteries of the corpora cavernosa (large curved black arrows) and the septum (thin arrow) that divides the corpora cavernosa are also seen. The flattened, nondistended urethra is seen within the unpaired ventral corpus spongiosum (small curved black arrow). The hypointense tunica dartos (straight white solid arrow) is present, just deep to the skin. Midline within the connective tissue, deep to the tunica dartos, lies the dorsal vein of the penis (curved white arrow). The epidermis is hyperintense relative to the dartos at T2 weighting and is the most external layer (open arrow). (c) T1-weighted MR image (433/10) provides less anatomic detail than does the corresponding T2-weighted image. The corpus spongiosum is surrounded by a thin, hypointense layer of tunica albuginea (white arrow). The tunica albuginea is thicker around the corpora cavernosa (black arrow), where it is fused with the Buck fascia. (d) Parasagittal T2-weighted image (3,500/96) obtained after intracavernosal injection of prostaglandin E1 shows normal high signal intensity within the corpus cavernosum (curved arrow) and corpus spongiosum (open arrow) surrounded by the low-signal-intensity tunica albuginea (black arrows). The penis has been dorsiflexed and taped against the lower abdomen.
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Figure 2b. Normal penile anatomy in a 20-year-old man. (a) Axial T2-weighted MR image shows the normal attachment of the posterior aspects of the corpora cavernosa, the crura (curved arrows), and to the ischial rami (thin arrows). At T2-weighted imaging, signal intensity in the penile bulb (open straight arrow), which is the base of the corpus spongiosum, is different from that in the corpora cavernosa (thick solid arrows). This finding is normal. (b) Axial T2-weighted image (5,000/96 [repetition time msec/echo time msec]) shows the paired corpora cavernosa surrounded by the Buck fascia and the tunica albuginea, which at MR imaging appear as a single hypointense border to the cavernosa (small straight black arrow). The central arteries of the corpora cavernosa (large curved black arrows) and the septum (thin arrow) that divides the corpora cavernosa are also seen. The flattened, nondistended urethra is seen within the unpaired ventral corpus spongiosum (small curved black arrow). The hypointense tunica dartos (straight white solid arrow) is present, just deep to the skin. Midline within the connective tissue, deep to the tunica dartos, lies the dorsal vein of the penis (curved white arrow). The epidermis is hyperintense relative to the dartos at T2 weighting and is the most external layer (open arrow). (c) T1-weighted MR image (433/10) provides less anatomic detail than does the corresponding T2-weighted image. The corpus spongiosum is surrounded by a thin, hypointense layer of tunica albuginea (white arrow). The tunica albuginea is thicker around the corpora cavernosa (black arrow), where it is fused with the Buck fascia. (d) Parasagittal T2-weighted image (3,500/96) obtained after intracavernosal injection of prostaglandin E1 shows normal high signal intensity within the corpus cavernosum (curved arrow) and corpus spongiosum (open arrow) surrounded by the low-signal-intensity tunica albuginea (black arrows). The penis has been dorsiflexed and taped against the lower abdomen.
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Figure 2c. Normal penile anatomy in a 20-year-old man. (a) Axial T2-weighted MR image shows the normal attachment of the posterior aspects of the corpora cavernosa, the crura (curved arrows), and to the ischial rami (thin arrows). At T2-weighted imaging, signal intensity in the penile bulb (open straight arrow), which is the base of the corpus spongiosum, is different from that in the corpora cavernosa (thick solid arrows). This finding is normal. (b) Axial T2-weighted image (5,000/96 [repetition time msec/echo time msec]) shows the paired corpora cavernosa surrounded by the Buck fascia and the tunica albuginea, which at MR imaging appear as a single hypointense border to the cavernosa (small straight black arrow). The central arteries of the corpora cavernosa (large curved black arrows) and the septum (thin arrow) that divides the corpora cavernosa are also seen. The flattened, nondistended urethra is seen within the unpaired ventral corpus spongiosum (small curved black arrow). The hypointense tunica dartos (straight white solid arrow) is present, just deep to the skin. Midline within the connective tissue, deep to the tunica dartos, lies the dorsal vein of the penis (curved white arrow). The epidermis is hyperintense relative to the dartos at T2 weighting and is the most external layer (open arrow). (c) T1-weighted MR image (433/10) provides less anatomic detail than does the corresponding T2-weighted image. The corpus spongiosum is surrounded by a thin, hypointense layer of tunica albuginea (white arrow). The tunica albuginea is thicker around the corpora cavernosa (black arrow), where it is fused with the Buck fascia. (d) Parasagittal T2-weighted image (3,500/96) obtained after intracavernosal injection of prostaglandin E1 shows normal high signal intensity within the corpus cavernosum (curved arrow) and corpus spongiosum (open arrow) surrounded by the low-signal-intensity tunica albuginea (black arrows). The penis has been dorsiflexed and taped against the lower abdomen.
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Figure 2d. Normal penile anatomy in a 20-year-old man. (a) Axial T2-weighted MR image shows the normal attachment of the posterior aspects of the corpora cavernosa, the crura (curved arrows), and to the ischial rami (thin arrows). At T2-weighted imaging, signal intensity in the penile bulb (open straight arrow), which is the base of the corpus spongiosum, is different from that in the corpora cavernosa (thick solid arrows). This finding is normal. (b) Axial T2-weighted image (5,000/96 [repetition time msec/echo time msec]) shows the paired corpora cavernosa surrounded by the Buck fascia and the tunica albuginea, which at MR imaging appear as a single hypointense border to the cavernosa (small straight black arrow). The central arteries of the corpora cavernosa (large curved black arrows) and the septum (thin arrow) that divides the corpora cavernosa are also seen. The flattened, nondistended urethra is seen within the unpaired ventral corpus spongiosum (small curved black arrow). The hypointense tunica dartos (straight white solid arrow) is present, just deep to the skin. Midline within the connective tissue, deep to the tunica dartos, lies the dorsal vein of the penis (curved white arrow). The epidermis is hyperintense relative to the dartos at T2 weighting and is the most external layer (open arrow). (c) T1-weighted MR image (433/10) provides less anatomic detail than does the corresponding T2-weighted image. The corpus spongiosum is surrounded by a thin, hypointense layer of tunica albuginea (white arrow). The tunica albuginea is thicker around the corpora cavernosa (black arrow), where it is fused with the Buck fascia. (d) Parasagittal T2-weighted image (3,500/96) obtained after intracavernosal injection of prostaglandin E1 shows normal high signal intensity within the corpus cavernosum (curved arrow) and corpus spongiosum (open arrow) surrounded by the low-signal-intensity tunica albuginea (black arrows). The penis has been dorsiflexed and taped against the lower abdomen.
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On axial T2-weighted images, the deep arteries of the corpora cavernosa are depicted as small, round areas of hypointensity (due to faster flow) within the medial, dorsal portions of the cavernosa (Fig 2b). A layer of fibrous tissue, the tunica albuginea, surrounds both the corpora cavernosa and the corpus spongiosum, but the layer is thicker around the cavernosa (1) (Fig 2b, 2c). A second fibrous layer, the Buck fascia, surrounds the corpora cavernosa and separates them from the corpus spongiosum. Composed of mature fibrous tissue, both the tunica albuginea and Buck fascia are imaged as low T1-weighted and low T2-weighted signal-intensity bands that surround the corporal bodies. The individual layers of enveloping fibrous tissue are not currently distinguishable with MR imaging, and they are most often depicted as a single thick rim that is hypointense relative to the erectile tissues.
External to the Buck fascia is a loose layer of subcutaneous connective tissue, which appears hyperintense relative to the fascia at T2 weighting (Fig 2b). The deep dorsal vein of the penis lies in the midline within this layer (Fig 2b). The tunica dartos, another T2-hypointense fascial layer, envelops the subcutaneous connective tissue and separates it from the relatively T2-hyperintense skin epidermis (Fig 2b).
The posterior urethra consists of the prostatic and membranous portions. The latter traverses the urogenital diaphragm. The anterior urethra, which begins at the urogenital diaphragm, consists of the bulbous and pendulous portions of the urethra, both of which are surrounded by the corpus spongiosum. If not dilated or distended, the anterior urethra is difficult to see at MR imaging. On heavily T2-weighted images, the collapsed muscular walls of the urethra are revealed as a band of relative hypointensity compared with the bright cavernous spaces of the corpus spongiosum (2) (Fig 2b).
Vascular Anatomy
The arterial supply to the penis originates from the right and left internal pudendal arteries, which, in turn, arise from the anterior division of the internal iliac arteries (Fig 3). Each internal pudendal artery gives rise to the perineal and common penile arteries. The branches of the common penile artery are variable but classically consist of three: the bulbourethral artery, the dorsal artery of the penis, and the cavernosal artery. While the iliac, pudendal, perineal, and common penile arteries can be evaluated with three-dimensional MR angiography, the smaller end arteries of the penis have not yet been reliably demonstrable with MR angiography (3).
The bulbourethral artery supplies the penile bulb, the bulbourethral (Cowper) glands, and the posterior aspect of the corpus spongiosum. It gives rise to the urethral artery, which parallels the course of the urethra within the corpus spongiosum.
The paired deep dorsal arteries lie external to the tunica albuginea within the hypodermal connective tissue and course lateral to the deep dorsal vein. They supply the penile skin and the glans penis.
The cavernosal arteries are easily visible on axial MR images of the penis within the dorsal, medial third of the corpora cavernosa. They give rise to multiple helicine arteries, which supply the sinusoids of the corpora cavernosa. After the administration of gadopentetate dimeglumine, enhancement of the cavernosa proceeds centrifugally, extending from the region surrounding the cavernosal arteries to the periphery of the corporal bodies and from the proximal part of the cavernosa to the distal (4).
The cavernosa are drained through the emissary veins of the wall of the corpora. Distally, these veins drain into the unpaired deep dorsal vein of the penis. Proximally, they drain into the cavernous veins, which join with the bulbar vein to form the internal pudendal veins.
Physiology of Erection
Vascular resistance in the flaccid penis is high due to the normally contracted state of the helicine arteries and of the smooth muscle of the sinusoids. After stimulation, parasympathetic nerves promote the release of molecules that dilate the helicine arteries and relax sinusoidal smooth muscle, thereby increasing flow of blood in the cavernosal arteries. As the cavernous spaces fill with blood and expand, they compress the emissary veins against the nonexpandable tunica albuginea, thereby decreasing venous outflow and maintaining penile erection.
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Imaging Techniques
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MR imaging of the penis is facilitated by appropriate positioning of the patient. With the patient supine, a folded towel is placed between the patient’s legs inferior to the perineum, to elevate the scrotum and penis. The penis is then dorsiflexed against the lower abdomen in the midline and taped in position to reduce motion of the organ during the examination (Fig 2d). A 3-inch or 5-inch surface coil is employed to maximize signal-to-noise ratio at small fields of view.
If imaging of the penis in the erect state is required, prostaglandin E1 (alprostadil, 10 µg) is injected into one of the corpora. After injection, the patient is asked to massage the injection site and to manually stimulate the penis until it is erect. Intracavernosal injection of prostaglandin E1 is contraindicated in men who have conditions that predispose them to priapism, such as sickle cell anemia, sickle cell trait, multiple myeloma, leukemia, cavernosal thrombosis, and tumors that are known to invade the cavernosa. Use of prostaglandin E1 is also contraindicated in men with penile prostheses. Anatomic abnormalities of the penis are a relative contraindication to prostaglandin injection. For this reason, we do not routinely inject prostaglandin E1 before MR imaging of the abnormal penis but reserve its use for select cases in which imaging of the flaccid penis fails to answer the clinical question. After injection of prostaglandin E1, the increased size of the erect penis allows for easier positioning of the organ and acquisition of a greater number of sections and larger fields of view (Fig 4).
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Figure 4a. Palpable penile abnormality in a 39-year-old uncircumcised man. (a) Sagittal T2-weighted MR image (5,500/144) shows a focus of low signal intensity (arrow) on the ventral aspect of the penis. (b) Sagittal half-Fourier T2-weighted MR image (20,614/94) obtained after intracavernosal injection of prostaglandin E1 more clearly shows the mass of low T2-weighted signal intensity (arrows), which represented a squamous cell carcinoma.
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Figure 4b. Palpable penile abnormality in a 39-year-old uncircumcised man. (a) Sagittal T2-weighted MR image (5,500/144) shows a focus of low signal intensity (arrow) on the ventral aspect of the penis. (b) Sagittal half-Fourier T2-weighted MR image (20,614/94) obtained after intracavernosal injection of prostaglandin E1 more clearly shows the mass of low T2-weighted signal intensity (arrows), which represented a squamous cell carcinoma.
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Imaging protocols are customized to address the clinical question. In general, though, we acquire axial (short-axis) spin-echo T1-weighted and axial, sagittal, and fat-saturated coronal fast spin-echo T2-weighted images.
If gadolinium is administered, we employ either a two- or three-dimensional fat-saturated T1-weighted gradient-echo pulse sequence before, during, and after the dynamic administration of intravenous gadolinium chelate. If the entire pelvis also needs evaluation, such as in the case of penile malignancy, we obtain body coil axial T1-weighted spin-echo pelvic images to look for inguinal or obturator lymphadenopathy. In patients who undergo evaluation for arteriogenic impotence, pelvic MR angiography is performed with a three-dimensional T1-weighted gradient-echo pulse sequence and an approximately 36-cm field of view to obtain images from the distal aorta to the distal pudendal arteries.
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Penile Malignancies
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Squamous Cell Carcinoma of the Penis
Most primary penile malignancies are squamous cell carcinomas and occur most often during the 6th and 7th decades of life. Although it is one of the most commonly diagnosed malignancies of men in Asia and Africa (5), the disease is rare in the United States, with only about 200 cases recorded in 1999 (6). Uncircumcised men are more often affected, probably because of the chronic irritative effect of smegma (7). An association between human papilloma viruses 16 and 18 and squamous cell carcinoma has also been reported (8). In the United States, African-American men are affected at twice the rate of Caucasians (9).
Squamous cell carcinomas of the penis usually begin on the glans as a focal epithelial thickening with or without ulceration. The lesions are generally not painful, and affected patients often delay seeking medical attention. After penectomy with 2-cm margins, patients with tumors that have not invaded the corpora cavernosa have a greater than 95% 3-year survival rate. Survival decreases markedly with cavernosal invasion or with spread to regional lymph nodes.
At MR imaging, squamous cell carcinomas are usually hypointense relative to the corpora on both T1- and T2-weighted images. At contrast-enhanced imaging, these lesions do increase in signal intensity but less so than the normal corporal bodies (Figs 4, 5).
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Figure 5a. Penile squamous cell carcinoma in a 37-year-old man. (a) Axial T2-weighted MR image (4,300/135) shows a heterogeneous high-signal-intensity mass (black arrow), a squamous cell carcinoma, replacing the majority of the base of the penis. The penile bulb can be identified (white arrow). (b) Sagittal T2-weighted MR image shows the extent of the mass (black arrows). A transperineal catheter is also apparent (white arrows).
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Figure 5b. Penile squamous cell carcinoma in a 37-year-old man. (a) Axial T2-weighted MR image (4,300/135) shows a heterogeneous high-signal-intensity mass (black arrow), a squamous cell carcinoma, replacing the majority of the base of the penis. The penile bulb can be identified (white arrow). (b) Sagittal T2-weighted MR image shows the extent of the mass (black arrows). A transperineal catheter is also apparent (white arrows).
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Although neither MR nor other imaging is generally needed for diagnosis (the tumor is usually visible at physical examination), MR imaging may be performed for staging purposes. In the commonly used Jackson staging system, stage I lesions are confined to the glans or prepuce, stage II lesions involve the penile shaft, stage III extend to inguinal nodes, and stage IV involve deep pelvic nodes or distant metastases. Both computed tomography (CT) and MR imaging depict pelvic lymphadenopathy, but MR imaging is superior for evaluation of the primary lesion (10).
Anterior Urethral Carcinoma
Carcinomas of the male urethra occur most often in the bulbous and membranous portions of the urethra, followed by the fossa navicularis (7). The anatomy of the urothelium changes along the course of the male urethra, with transitional cells lining the prostatic and membranous segments, stratified and pseudostratified columnar epithelium in the bulbous and pendulous parts, and squamous cells in the fossa navicularis and urethral meatus. Squamous cell carcinomas, followed by transitional cell carcinomas and adenocarcinomas, are the most common anterior urethral carcinomas (11).
At MR imaging, urethral carcinomas are usually hypointense relative to the normal cavernosa on both T1- and T2-weighted images (1) (Fig 6). Suspected etiologic factors include chronic inflammation and chronic urethral stricture disease. Surgical treatment consists of partial penectomy for lesions that involve the glans penis or distal part of the shaft and radical or total penectomy with or without cystoprostatectomy for lesions that involve the proximal part of the shaft or the posterior part of the urethra.
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Figure 6a. Adenocarcinoma of the urethra in a 72-year-old man. (a) Axial T2-weighted MR image (5,233/147) shows a low-signal-intensity mass (arrow) invading the corpus spongiosum. The corpora cavernosa were not involved by tumor. (b) Coronal T2-weighted MR image (3,900/90) shows a similar finding (arrow). This tumor was a primary adenocarcinoma of the urethra.
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Figure 6b. Adenocarcinoma of the urethra in a 72-year-old man. (a) Axial T2-weighted MR image (5,233/147) shows a low-signal-intensity mass (arrow) invading the corpus spongiosum. The corpora cavernosa were not involved by tumor. (b) Coronal T2-weighted MR image (3,900/90) shows a similar finding (arrow). This tumor was a primary adenocarcinoma of the urethra.
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Penile Sarcoma
Primary sarcomas can also occur in the penis. These include epithelioid sarcoma, Kaposi sarcoma, leiomyosarcoma, and rhabdomyosarcoma. All these lesions are rare and together represent less than 5% of all penile malignancies (12).
The MR imaging findings of epithelioid sarcoma are nonspecific. A recently reported case was isointense relative to the corpora on T1-weighted images, was hypointense relative to the corpora on T2-weighted images, and enhanced less than the normal corpora after administration of contrast material (13). At clinical examination, epithelioid sarcoma may manifest as focal induration (14,15) and mimic Peyronie disease.
Leiomyosarcomas of the penis may arise from either the smooth muscle of the glans or thecorpora cavernosa (Fig 7). Those that arise in the latter tend to metastasize early because of their proximity to the vascular structures of the penis (16).
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Figure 7. Palpable penile mass in a 38-year-old man. Sagittal T2-weighted MR image shows a heterogeneous mass within the distal part of the penile shaft (black arrow) that is invading the corpora cavernosa. This mass was a leiomyosarcoma. A second metastasis is seen within the more proximal aspect of the corpora cavernosa (white arrow).
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Rhabdomyosarcoma is the most common malignancy of the lower genitourinary tract in the first 2 decades of life. At MR imaging, rhabdomyosarcoma generally is isointense relative to skeletal muscle on T1-weighted images, is hyperintense relative to muscle on T2-weighted images, and enhances heterogeneously after administration of contrast material (17). Because it arises from primitive cells, rhabdomyosarcoma may originate in any organ, although its tendency for aggressive local invasion may make identification of the primary organ of origin difficult. The imaging findings of rhabdomyosarcoma are nonspecific, and the diagnosis suspected at imaging studies is based on its aggressive appearance and patient age (Fig 8).
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Figure 8. Large perineal mass in a 23-year-old man. Sagittal T2-weighted image (4,000/105) shows a heterogeneous perineal mass invading the base of the penis (arrow), sparing only the penile bulb. This mass represented a rhabdomyosarcoma.
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Metastases to the Penis
Metastases to the penis are rare and may manifest with malignant priapism (18). In approximately 70% of cases, penile metastases arise from other primary malignancies of portions of the genitourinary tract such as the prostate (19) or urinary bladder (20) (Fig 9). Metastases from the colon, stomach, esophagus, and pancreas have been reported less often (21). Metastatic spread of malignancy to the penis represents an advanced stage of disease, and prognosis is generally poor.
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Figure 9a. Ulcerated metastasis near the glans penis in a 67-year-old man who had undergone resection of transitional cell carcinoma of the bladder 4 years previously. (a) Sagittal T2-weighted MR image (4,000/144) shows a low-signal-intensity mass (arrow) occupying the central part of the glans penis. (b) Coronal postgadolinium T1-weighted gradient-echo MR image (200/1.9) shows that the tumor (arrow) enhances less than the remainder of the glans. This tumor was a metastatic focus of transitional cell carcinoma.
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Figure 9b. Ulcerated metastasis near the glans penis in a 67-year-old man who had undergone resection of transitional cell carcinoma of the bladder 4 years previously. (a) Sagittal T2-weighted MR image (4,000/144) shows a low-signal-intensity mass (arrow) occupying the central part of the glans penis. (b) Coronal postgadolinium T1-weighted gradient-echo MR image (200/1.9) shows that the tumor (arrow) enhances less than the remainder of the glans. This tumor was a metastatic focus of transitional cell carcinoma.
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Benign Masses
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MR imaging can be used to evaluate a number of benign entities that manifest as palpable penile masses, the nature of which may not be apparent at clinical evaluation.
Cowper Duct Syringocele
Cowper duct syringocele represents cystic dilatation of the main duct of the bulbourethral (Cowper) glands. Affected patients may present with postvoid dribbling, urinary frequency, weak stream, or hematuria (22). At MR imaging, Cowper duct syringocele appears as a midline oval structure at the penile base adjacent to the ventral aspect of the proximal bulbous urethra and is of high T2 signal intensity (Fig 10). Treatment by means of surgical incision of the obstructed duct is generally curative.
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Figure 10a. Palpable abnormality at the base of the penis in a 43-year-old man. (a) Axial T2-weighted MR image (3,000/85) shows a high-signal-intensity midline structure (arrow) near the penile bulb that represents a Cowper duct syringocele. (b) Sagittal postgadolinium T1-weighted spin-echo MR image (400/13) obtained after urinary voiding shows no enhancement within the syringocele (arrow) and no filling of the structure after voiding.
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Figure 10b. Palpable abnormality at the base of the penis in a 43-year-old man. (a) Axial T2-weighted MR image (3,000/85) shows a high-signal-intensity midline structure (arrow) near the penile bulb that represents a Cowper duct syringocele. (b) Sagittal postgadolinium T1-weighted spin-echo MR image (400/13) obtained after urinary voiding shows no enhancement within the syringocele (arrow) and no filling of the structure after voiding.
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Periurethral Abscess
Uncomplicated cases of lower genitourinary tract infection or inflammation do not require imaging. Cases in which abscess is suspected may benefit from imaging evaluation, and the inherently high soft-tissue contrast afforded by MR imaging makes it an excellent modality for this purpose (Fig 11). MR imaging can show the relationship of the inflammatory mass to the corporal bodies and urethra.
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Figure 11a. Pain, inflammation, and palpable penile abnormality in a 44-year-old man. (a) Sagittal fast spin-echo T2-weighted image (400/96) shows a high-signal-intensity periurethral structure (arrow) in the subcutaneous soft tissues of the base of the penis. The abnormality was a periurethral abscess. (b) Axial T1-weighted (701/11) MR image shows the abscess with heterogeneous high to intermediate signal intensity.
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Figure 11b. Pain, inflammation, and palpable penile abnormality in a 44-year-old man. (a) Sagittal fast spin-echo T2-weighted image (400/96) shows a high-signal-intensity periurethral structure (arrow) in the subcutaneous soft tissues of the base of the penis. The abnormality was a periurethral abscess. (b) Axial T1-weighted (701/11) MR image shows the abscess with heterogeneous high to intermediate signal intensity.
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Partial Cavernosal Thrombosis
Several cases of the MR imaging appearance of segmental thrombosis of the corpora cavernosa have been reported (23,24). Partial priapism, or induration of a portion of one of the corpora cavernosa, is the most common presenting finding. At MR imaging, the affected cavernosal segment is distended with thrombotic blood and may compress the contralateral corpus cavernosum (Fig 12). The signal intensity of the affected segment is dependent on the age of the thrombus. Generally, it is hyperintense relative to the normal cavernosum on T1-weighted images and hypointense on T2-weighted images.
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Figure 12a. Firm mass at the base of the penis in an 18-year-old bicyclist. (a) Axial T1-weighted MR image (500/10) shows high signal intensity within an expanded left corpus cavernosum (arrow). (b) Corresponding T2-weighted MR image (2,200/80) shows the region to be hypointense relative to the other corpus cavernosum (arrow). This finding represented segmental thrombosis of the corpus cavernosum.
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Figure 12b. Firm mass at the base of the penis in an 18-year-old bicyclist. (a) Axial T1-weighted MR image (500/10) shows high signal intensity within an expanded left corpus cavernosum (arrow). (b) Corresponding T2-weighted MR image (2,200/80) shows the region to be hypointense relative to the other corpus cavernosum (arrow). This finding represented segmental thrombosis of the corpus cavernosum.
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Peyronie Disease
Chronic inflammation that leads to fibrosis and focal thickening of the tunica albuginea is termed Peyronie disease. The indurated area, which may be painful, results in varying degrees of penile deformity with erection. If severe, this deformity may interfere with sexual intercourse. Peyronie plaques may or may not calcify. If calcified, the plaque may be visible at radiography, CT, and US. At MR imaging, Peyronie disease is seen as focal thickening of the tunica albuginea and is best seen on T2-weighted images (Fig 13). After intravenous administration of gadolinium, enhancement of the plaque has been shown to correlate with the presence of active inflammation (25).
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Figure 13a. Peyronie disease in a 28-year-old man. (a) Axial T1-weighted MR image (550/9) of the dorsiflexed penis shows focal thickening of the dorsal part of the tunica albuginea (short arrow) and of the intercavernosal septum (long arrow). (b) Axial T2-weighted image (6,600/139) shows similar findings (arrows). The calcified plaques are hypointense relative to normal soft tissues on both T1- and T2-weighted images.
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Figure 13b. Peyronie disease in a 28-year-old man. (a) Axial T1-weighted MR image (550/9) of the dorsiflexed penis shows focal thickening of the dorsal part of the tunica albuginea (short arrow) and of the intercavernosal septum (long arrow). (b) Axial T2-weighted image (6,600/139) shows similar findings (arrows). The calcified plaques are hypointense relative to normal soft tissues on both T1- and T2-weighted images.
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Other Benign Penile Lesions
The MR imaging appearance of penile hemangiomas (26,27) and of penile root neurofibroma (28) have been reported.
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Trauma
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Although not often performed in the acute setting, MR imaging can play an important role in the evaluation of penile or urethral trauma.
MR imaging is highly accurate in the identification of penile fractures and tears of the tunica albuginea (29). Fracture generally occurs secondary to an unusual external force applied to the erect penis. Most cases result from vigorous sexual intercourse. MR imaging examination reveals discontinuity of the hypointense tunica albuginea, with or without associated hematoma (Fig 14). MR imaging detection of disruption of the tunica and associated anterior urethral tear has also been reported (30).
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Figure 14. Pain and palpable penile abnormality in a 32-year-old man after vigorous sexual intercourse. Coronal T1-weighted MR image shows interruption of the low-signal-intensity tunica albuginea, indicating fracture of the corpus cavernosum (straight arrow). There is an associated hematoma (curved arrow).
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Pelvic trauma complicated by posterior urethral injury can also be evaluated with MR imaging (Fig 15). Prior to surgical repair of urethral structures, simultaneous retrograde urethrography and voiding cystourethrography are usually performed. However, MR imaging can provide similar as well as additional information such as the degree and direction of prostate dislocation and the presence of cavernosal avulsion from the ischium, pelvic hematomas, and osseous fractures (31). Identification of displacement of the prostatic apex alters the surgical approach. In cases without displacement, a transperineal approach is utilized for posterior urethral repair. In cases with superior or lateral displacement, a combined transperineal and transpubic approach is employed (32).
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Figure 15a. Posterior urethral injury in a 34-year-old man involved in a severe motor vehicle accident. (a) Simultaneous voiding cystourethrogram via a suprapubic bladder catheter and retrograde urethrogram demonstrate traumatic disruption of the membranous portion and proximal part of the bulbous portion of the urethra (arrows). (b) Sagittal T2-weighted MR image (4,000/102) shows truncation of the membranous urethra (arrow). The anterior urethra is not visualized without distention.
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Figure 15b. Posterior urethral injury in a 34-year-old man involved in a severe motor vehicle accident. (a) Simultaneous voiding cystourethrogram via a suprapubic bladder catheter and retrograde urethrogram demonstrate traumatic disruption of the membranous portion and proximal part of the bulbous portion of the urethra (arrows). (b) Sagittal T2-weighted MR image (4,000/102) shows truncation of the membranous urethra (arrow). The anterior urethra is not visualized without distention.
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Arteriogenic Impotence
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Although catheter angiography and Doppler US have long been used for imaging of the penile vasculature (33), MR imaging may be a useful alternative in the evaluation of arteriogenic impotence (34). Arteriogenic impotence may be secondary to aortoiliac occlusive disease or to small vessel disease. Dynamic gadolinium-enhanced MR angiography can be used reliably to evaluate the aorta, internal iliac arteries, and internal pudendal arteries (Fig 16).
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Figure 16a. Arteriogenic impotence after pelvic trauma in a 34-year-old man with reduced flow in the right cavernosal artery at Doppler US examination. (a) Left parasagittal maximum intensity projection reformatted MR image from a dynamic gadolinium-enhanced three-dimensional T1-weighted gradient-echo acquisition shows a normal left internal pudendal artery (arrows). (b) Right parasagittal maximum intensity projection reformatted MR image shows an abrupt cutoff to the right internal pudendal artery (arrow).
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Figure 16b. Arteriogenic impotence after pelvic trauma in a 34-year-old man with reduced flow in the right cavernosal artery at Doppler US examination. (a) Left parasagittal maximum intensity projection reformatted MR image from a dynamic gadolinium-enhanced three-dimensional T1-weighted gradient-echo acquisition shows a normal left internal pudendal artery (arrows). (b) Right parasagittal maximum intensity projection reformatted MR image shows an abrupt cutoff to the right internal pudendal artery (arrow).
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MR Imaging of the Penis after Surgery
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As mentioned previously, surgical treatment of carcinoma of the penis consists of either partial or total penectomy. Follow-up physical examination to look for local recurrence is limited in allowing the detection of pelvic lymphadenopathy and deep recurrence; therefore, cross-sectional imaging is often performed (Fig 17). In addition to identification of sites of tumor recurrence, MR imaging can be helpful in the identification of normal postsurgical findings (Fig 18). Complications of surgery of the lower urinary tract can also be well shown with MR imaging (Fig 19).
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Figure 17a. Examination in a 51-year-old man after total penectomy for squamous cell carcinoma. (a) Sagittal T2-weighted MR image shows a normal postpenectomy appearance. The difference in signal intensity between the corpus cavernosum (thick arrow) and the corpus spongiosum (thin arrow) is probably related to a difference in blood flow. (b) Axial T1-weighted image (500/10) shows a large inguinal lymph node (arrow), which represents recurrence of squamous cell carcinoma.
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Figure 17b. Examination in a 51-year-old man after total penectomy for squamous cell carcinoma. (a) Sagittal T2-weighted MR image shows a normal postpenectomy appearance. The difference in signal intensity between the corpus cavernosum (thick arrow) and the corpus spongiosum (thin arrow) is probably related to a difference in blood flow. (b) Axial T1-weighted image (500/10) shows a large inguinal lymph node (arrow), which represents recurrence of squamous cell carcinoma.
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Figure 18a. Examination in a 38-year-old man after total penectomy for squamous cell carcinoma. (a) Axial CT image obtained after penectomy shows a soft-tissue mass (arrows) that was interpreted as recurrent squamous cell carcinoma. (b) Axial T2-weighted MR image (4,500/102) shows that the "mass" seen at CT is the patient’s testicles (arrows), which were placed within the perineum after penectomy.
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Figure 18b. Examination in a 38-year-old man after total penectomy for squamous cell carcinoma. (a) Axial CT image obtained after penectomy shows a soft-tissue mass (arrows) that was interpreted as recurrent squamous cell carcinoma. (b) Axial T2-weighted MR image (4,500/102) shows that the "mass" seen at CT is the patient’s testicles (arrows), which were placed within the perineum after penectomy.
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Figure 19a. Lump in the penis after a corporal spongiosal shunt was surgically created to treat post-radical prostatectomy priapism in a 55-year-old man. (a) Sagittal T2-weighted MR image (4,000/140) shows an elongated collection (arrow) that is hyperintense relative to the adjacent corpus cavernosum. (b) Retrograde urethrogram shows a urethrocavernosal fistula (arrow) and intracavernosal collection secondary to the prior surgical shunt procedure.
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Figure 19b. Lump in the penis after a corporal spongiosal shunt was surgically created to treat post-radical prostatectomy priapism in a 55-year-old man. (a) Sagittal T2-weighted MR image (4,000/140) shows an elongated collection (arrow) that is hyperintense relative to the adjacent corpus cavernosum. (b) Retrograde urethrogram shows a urethrocavernosal fistula (arrow) and intracavernosal collection secondary to the prior surgical shunt procedure.
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Penile Prostheses
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A variety of MR imaging–compatible inflatable penile prostheses are available for treatment of impotence. Most of these consist of cylinders implanted in the paired corpora cavernosa, the degree of distension of which defines the state of penile flaccidity or erection. As both the paired cavernosal cylinders and the intraabdominal reservoirs used to fill the cylinders contain fluid, they are of high signal intensity on T2-weighted images and readily identified. MR imaging also can be used to examine for complications of penile prostheses (Fig 20).
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Figure 20a. Penile prosthesis and postimplantation infection in a 40-year-old man. (a) Coronal T2-weighted MR image (4,000/90) shows both the intraabdominal fluid reservoir (black arrow) and corporal cylinders (white arrow) filled with high-signal-intensity fluid. (b) Sagittal T2-weighted MR image (4,000/90) shows an infected fistulous track to the skin (arrows). No discrete fluid collection was present.
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Figure 20b. Penile prosthesis and postimplantation infection in a 40-year-old man. (a) Coronal T2-weighted MR image (4,000/90) shows both the intraabdominal fluid reservoir (black arrow) and corporal cylinders (white arrow) filled with high-signal-intensity fluid. (b) Sagittal T2-weighted MR image (4,000/90) shows an infected fistulous track to the skin (arrows). No discrete fluid collection was present.
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Footnotes
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See the commentary by Brandes
following this article.
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Abstract
Introduction
