A multimodality review of male urethral imaging: pearls and pitfalls with an update on urethral stricture treatment

Optimum radiological assessment of the male urethra requires knowledge of the normal urethral anatomy and ideal imaging techniques based on the specific clinical scenario. Retrograde urethrography is the workhorse examination for male urethral imaging, usually utilized as the initial, and often solitary, modality of choice not only in the setting of trauma, but also in the pre- and post-operative evaluation of urethral strictures. There is, however, growing interest in utilization of ultrasound and magnetic resonance for evaluation of the male urethra owing to lack of ionizing radiation and improved delineation of the adjacent tissue. We review the various modalities utilized for imaging of the male urethra for a variety of known or suspected disorders, and provide an update on current treatments of urethral strictures. Additionally, we detail the key information needed by urologists to guide management of urethral strictures. We conclude with a brief discussion of neophallus urethral diseases following female-to-male sexual confirmation surgery.

Introduction

Imaging of the male urethra has grown considerably since the inception of retrograde urethrography (RUG) and voiding cystourethrography (VCUG). Ultrasound, MRI, and CT can all serve a role in urethral assessment, depending on the specific patient scenario. Radiologists must assess the urethra for a wide array of pathologies, ranging from acute traumatic urethral injury to post-radiation urethral stricture. Regardless of the pathology, understanding the normal urethral anatomy is necessary for accurate radiologic evaluation. By providing precise anatomic information, radiologists aid urologists in making critical clinical decisions, including the best approach to patient treatment. Additionally, knowledge of the limitations of imaging modalities allows radiologists to better assist referring providers in choosing the optimum radiologic examination to answer their clinical question(s).

Our review serves to update radiologists on the current imaging options available for the male urethra in the setting of trauma, infection, neoplasm, and strictures. Imaging protocols, pearls, and pitfalls are also interwoven throughout to provide additional educational value. An update on urethral stricture management and the perspective of urologists on the required information in a radiology report are also discussed. We will conclude with a brief discussion of the neophallus urethra following female-to-male sexual confirmation surgery.

Male urethra normal anatomy

The male urethra extends from the bladder to the external urethral meatus, spans approximately 18–20 cm in length, and is divided into the anterior and posterior urethra. The anterior urethra includes the fossa navicularis, as well as the penile and bulbar segments. The posterior urethra includes the membranous and prostatic segments. Additional details regarding the normal urethra anatomy are discussed in Table 1. Normal outpouchings exist along the course of the urethra, and some possess glandular functionality (Table 2).

Table 1.

Normal urethra anatomy

	Urethra segment	Urethra segment features	Urethra segment outpouchings	Illustration of normal urethra anatomy. Fossa navicularis (a), penile (b), bulbar, (c) membranous (d), and prostatic (e) segments
Anterior urethra	Penile	Extends from the meatus to the suspensory ligament	Glands of Littre
	Fossa navicularis (part of the penile urethra segment)	1–1.5 cm in length, beginning at the meatus
	Bulbar	Extends from suspensory ligament to the urogenital diaphragm	Cowper’s Glands open into the bulbar urethra
Posterior urethra	Membranous	Traverses through the urogenital diaphragm/ membrane, measure approximately 1 cm	Cowper’s glands themselves flank the membranous segment	Retrograde urethrogram (RUG) demonstrates the fossa navicularis (a), penile (b), bulbar (c), membranous (d), and prostatic (e) segments. The subtle gentle undulation of the anterior urethra represents the suspensory ligament that demarks the transition from the penile urethra to the bulbar urethra. The bulbar urethra may demonstrate a circumferential or anterior impression related to the normal compressor nudae muscle

RUG, retrograde urethrogram.

Table 2.

Urethra glands and ducts

	Urethra segment	Urethra segment outpouchings	Illustrated coronal cross-section of the penis from the bladder neck to the glans demonstrating the orifices of the urethral ducts. (a) Periurethral Littre glands along the anterior urethra; (b) Cowper’s glands; (c) ejaculatory ducts are formed by the union of the vas deferens and seminal vesicles with the orifice abutting the verumontanum; (d) prostate ducts surround the urethra at the level of the prostate
				Anterior urethra	Penile	Glands of Littre	Littre glands on RUG
								Bulbar	Cowper’s Glands open into the bulbar urethra	Cowper’s glands on RUG
											Posterior urethra	Membranous	Cowper’s glands themselves flank the membranous segment
					Prostatic	The ejaculatory ducts open into the prostatic urethra, which is distal and lateral to the utricle	Ejaculatory ducts and seminal vesicles on RUG
								The prostate ducts (or sinuses) drain along the prostatic course of the urethra	Prostatic ducts on RUG

RUG, retrograde urethrogram.

Imaging techniques

Fluoroscopic evaluation of the urethra with RUG and VCUG remains the mainstay for urethral imaging. Although ultrasound, CT, and MRI offer additional benefits in selected patients, they require appropriate radiologist and technologist expertise. Ultimately, the choice of the best imaging technique depends on the clinical indication, and the radiologist’s experience (Table 3).

Table 3.

Various available imaging modalities for evaluation of the male urethra

	Fluoroscopy: RUG	Fluoroscopy: VCUG	Ultrasound	Computed tomography	Magnetic resonance imaging
Indication	Trauma, stricture, fistula, urinary retention	Best for posterior urethra evaluation (injury, stricture, etc.)	Infertility, erectile dysfunction, stricture	Trauma	Trauma, fistula, prosthesis complication, tumor
Contraindication	Active infection, allergy to iodinated contrast	Active infection, allergy to iodinated contrast	Active infection	Active infection, allergy to iodinated contrast	Claustrophobia and some medical devices
Advantages	Low cost, readily available	Low cost, readily available	Low cost, non-ionizing radiation	Fast, readily available	Global pelvic evaluation, non-ionizing radiation
Disadvantages	Radiation, operator-dependent	Radiation, operator-dependent, requires patient co-operation	Operator- dependent, greater technical skill to perform	Radiation, greater technical skill to perform (creation of protocol)	Not readily available, requires greater technical skill (creation of protocol)

RUG, retrograde urethrography; VCUG, voiding cystourethrography.

Fluoroscopy

Fluoroscopy is typically the first radiologic examination used to assess the urethra in cases of trauma, and in known or suspected urethral fistula and/or stricture evaluation.¹ RUG best evaluates the anterior urethra, whereas VCUG better demonstrates the posterior urethra (Figure 1). There are no absolute contraindications to these examinations; however, relative contraindications include active infection and a known allergy to iodinated contrast.²

Figure 1.

Normal RUG and VCUG. (A) RUG demonstrates fossa navicularis (a), penile urethral segment (b), bulbar urethral segment (c), membranous urethral segment (d), and prostatic segment (e). (B) VCUG demonstrates improved visualization of the posterior urethra compared to RUG due to greater distention of the posterior segment (d and e). RUG, retrograde urethrogram; VCUG, voiding cystourethrogram.

Technique

Appropriate positioning of the pelvis and the penis is important for fluoroscopic evaluation of the urethra. The patient should be in the supine oblique (45°) position, facing the radiologist. The obturator foramen of the hemipelvis not touching the table should appear rounded on fluoroscopy. The penis should be draped horizontally over the thigh that is contacting the table. For both RUG and VCUG, the external urethral meatus should be prepared in a sterile manner.

Retrograde urethrography (RUG)

A balloon catheter (10F) is the more commonly used device for RUG, although a Christmas tree adapter or clamp can be used as well.^3,4 The catheter should be connected to a syringe containing 60 ml of non-diluted, water-soluble iodinated contrast. The tip of the catheter is placed in the meatus/fossa navicularis. One must ensure that the meatus is occluded to prevent leakage of contrast and to allow adequate urethral opacification. Urethral occlusion can be accomplished via gentle manual pressure at the urethral meatus, or if a balloon catheter is being used the balloon can be inflated. Moderate traction should also be applied to the penis, either with the operator’s hand or with a 4 × 4 inch gauze pad folded lengthwise and wrapped around the glans.^1,5 Contrast should be injected slowly and gently to prevent spasm of the external sphincter and intravasation of contrast into the periurethral soft tissues (Figure 2).²

Figure 2.

Urethral contrast intravasation. When injecting urethral contrast, use gentle continuous pressure. Excessive pressure will cause contrast to intravasate into urethral and periurethral tissues, which could be mistaken for urethral disruption as shown in this outpatient/non-trauma patient being evaluated for possible urethral stricture. Penile veins (a) and corpus spongiosum (b) were opacified due to excessive injection pressure in this case of an otherwise normal RUG. RUG, retrograde urethrography.

A pericatheter RUG may be requested in cases of trauma where a urethral injury was not initially suspected and a catheter was therefore placed by the managing clinical/surgical team. In these instances, the urinary catheter is left in place and a RUG is performed by injecting contrast along the indwelling catheter in a similar manner as the above-described non-pericatheter RUG.^6,7 If a balloon catheter is utilized for a pericatheter RUG, it should be a small sized/pediatric catheter (4–6F), and balloon inflation may be required to ensure sufficient urethral opacification.⁶

Voiding cystourethrography (VCUG)

Water-soluble iodinated contrast is administered via a catheter to distend the bladder. The patient voids, distending and opacifying the posterior urethra and improving visualization and assessment of the posterior urethra (Figure 1B).

Non-fluoroscopic imaging modalities

MRI and ultrasound have been shown to better delineate the extent of periurethral fibrosis in cases of pre-operative urethral stricture assessment.^8,9 CT may be useful in trauma (CT voiding cystourethrogram) if the patient is already being imaged, thus limiting the need for additional transport and setup. The indications and techniques for each aforementioned modality may vary by practice/institution.

Magnetic resonance imaging

MRI may be employed in cases of urethral fistula, infection, and tumor evaluation to determine the extent of soft-tissue infiltration.¹⁰ MR urethrography can be performed to better delineate sites of stricturing by injection of saline or sterile lubricating jelly into the urethra.⁸ The patient should be supine and the penis should be in anatomic position, midline without rotation along its long axis, and the glans directed towards the patient’s head.¹¹

T  ₂ weighted (T  ₂W) sequences provide the best anatomic overview, and should be obtained in multiple planes (axial, coronal, sagittal, and oblique planes) using thin slices (3–5 mm) and a small field of view (FOV), while including the entire region of interest. The urethral mucosa is T2 hyperintense, and the enveloping fascia (tunica albuginea and Buck’s fascia) encircling the corpus spongiosum and cavernosa is T2 hypointense (Figure 3). T  ₁ weighted (T  ₁W) pre-contrast images are useful for the assessment of hemorrhage and vascular thrombosis, while the T  ₁W post-contrast images are useful in evaluation of masses.¹² Diffusion-weighted imaging (DWI) can assist in depiction of a urethral mass by showing restricted diffusion within the mass.¹² Short-tau inversion recovery (STIR) images are useful to assess for inflammation.¹² A detailed recommended protocol is provided in Table 4.

Figure 3.

MRI of normal urethral in coronal (A) and sagittal (B) planes. (a) Urethral mucosa is T2 hyperintense. (b) Enveloping fascia connecting to the corpus spongiosum is T2 hypointense. (c) Corpus spongiosum is T2 hyperintense. Sagittal image demonstrates the T2 hypointense urogenital diaphragm (d).

Table 4.

MRI penile protocol

Sequence	FOV and planes	Slice thickness (gap) in mm	Purpose
Scout/localizers	Whole pelvis - axial, coronal, and sagittal	10 (5)	Scan planning
T  2W FSE	Whole pelvis - axial and coronal	5 (1)	Assess full pelvis and penis for injuries, adenopathy, or other disease processes
T  2W FSE	Small FOV (centered around the penis) - axial	4 (0.5)	Higher spatial resolution evaluation of the penis for injuries, masses, or other disease processes
T  2W with fat saturation FSE, or STIR	Small FOV (centered around the penis) - axial	4 (0.5)	Higher spatial resolution evaluation of the penis for injuries, masses, or other disease processes
Axial diffusion-weighted imaging (b values of 50, 400, and 800)	Whole pelvis - axial	8 (2)	Evaluate penile masses
Pre-contrast T  1W spoiled gradient-echo (in-phase and out-of-phase)	Whole pelvis - axial	5 (1)	Evaluate fluid collections for features of blood products
Pre-contrast T  1W 3D fat saturated spoiled-gradient- echo	Small FOV (centered around the penis) - axial	3 (0)	Baseline for comparing post-contrast sequences
1 min post-contrast T  1W 3D fat saturated spoiled-gradient- echo	Small FOV (centered around the penis) - axial	3 (0)	Evaluate masses, fluid collections, vascular malformations, scarring, and inflammation
2 min post-contrast T  1W 3D fat saturated spoiled-gradient- echo	Small FOV (centered around the penis) - axial	3 (0)	Evaluate masses, fluid collections, vascular malformations, scarring, and inflammation
Post-contrast T  1W 3D fat saturated spoiled-gradient echo	Small FOV (centered around the penis) – Coronal and sagittal	3 (0)	Evaluate masses, fluid collections, vascular malformations, scarring, and inflammation

3D, three-dimensional; FOV, field of view; FSE, fast spin echo; STIR, short-tau inversion recovery.

Sonourethrography

In cases of stricturing, sonourethrography (SUG) can be used to determine the extent of periurethral fibrosis which may extend beyond the site of urethral narrowing. Thus, compared to RUG, SUG has a higher correlation with intraoperative findings of anterior urethral strictures.⁹

A high-frequency linear transducer is used, and the patient should be positioned supine. Sterile normal saline or sterile lubrication jelly is injected into the urethra, and ultrasound images are obtained. Strictures will be seen as sites of urethral narrowing, which should be measured for caliber and length (Figure 4). Periurethral fibrosis will be seen as hyperechogenic tissue that typically abuts the location of stricturing. SUG is not useful in the assessment of acute traumatic urethral injury.^13,14

Figure 4.

Sonourethrogram. Patient with anterior urethral stricture. (A) Sagittal plane demonstrates anterior urethral stricture measuring 2.5 cm in length (calipers). (B) Multiple sites of narrowing (strictures) with smallest caliber measuring 3–4 mm (calipers).

Computed tomography

CT is the most frequently used modality in the setting of trauma. Posterior urethral injuries can be suspected indirectly, such as with a high-riding prostate (superior displacement of the prostatic apex). Alternatively, urethral injuries can be directly observed with CT voiding urethrography,¹⁵ which is obtained 10–15 min after the acquisition of the initial intravenous contrast-enhanced trauma CT following adequate bladder distention. Alternatively, if a bladder catheter has already been placed by the managing clinical or surgical service, the bladder can be filled via gravity drip with an iodinated contrast sterile saline mixture (50 ml of iso-osmolar iodinated intravenous contrast mixed with 500 ml of sterile saline). Ideally, a minimum of 300 ml solution should be introduced into the bladder; however, less can be utilized if the patient reports discomfort. A pelvic CT is then acquired while the patient is voiding. This technique combined with curved-reformatted images of the urethra can often demonstrate urethral abnormalities (Figure 5).¹⁶ A detailed recommended protocol is provided in Table 5.

Figure 5.

Computed tomography voiding cystourethrography with membranous urethral injury. Patient fell from a horse with blood noted at the penile meatus on physical examination. Initial trauma CT (not shown) demonstrated pubic symphysis diastasis, as well as pelvic soft-tissue hematoma along the urogenital diaphragm. (A) RUG demonstrates elongation of the prostatic and membranous urethra, but no clear contrast extravasation is seen (arrow). (B) Follow-up CT voiding urethrogram axial image revealed a small left-sided membranous urethral tear (large arrow) with the contrast leak tracking along the left aspect of the urethra (small arrow). The left-sided wall of the urethra is clearly visualized, as indicated by the arrowhead. (C) Three-dimensional reformat image of the pelvis demonstrates the site of contrast leakage along the left aspect of the urethra (arrow). RUG, retrograde urethrography.

Table 5.

CT voiding cystourethrogram protocol

Plane	Kernel	Slice thickness
Scout/topogram	-	-
Axial	Soft tissue	2 mm, as well as a series of thin slices (1 mm or less) to be used for post-processing (i.e. off axis multiplanar reconstruction, curved multiplanar reconstruction, and/or 3D rendering)
Coronal	Soft tissue	2 mm
Sagittal	Soft tissue	2 mm

3D, three-dimensional.

Typically, the scan is acquired from the L4 vertebral body to below the ischial tuberosities, ensuring to also scan the entire penis. Contrast solution: 50 ml of iso-osmolar iodinated intravenous contrast mixed with 500 ml of sterile saline. A minimum of 300 ml should be administered; however, less can be utilized if the patient reports discomfort. Scan while the patient is actively voiding. Automatic exposure control should be used to reduce the patient’s radiation dose. If metallic hardware or foreign bodies are present, metallic artifact reduction algorithms should also be employed.

Male urethral trauma

Traumatic injury to the urethra can be divided into three subtypes: blunt, penetrating, and injury secondary to penile fracture. While blunt trauma can cause injury to either the anterior or posterior urethra, penetrating trauma or traumatic penile fracture will most often result in injury to the anterior urethra. Failure to diagnose and treat urethral trauma can result in strictures, fistulae, and long-term incontinence and impotence.⁶

The most widely accepted classification system of urethral injuries was originally described by Colapinto and McCallum,¹⁷ which was later revised by Goldman et al.¹⁸ In the Goldman classification scheme, there are five types of urethral injuries defined by the location of the injury.^6,18 Posterior urethral injuries (types I–IV) are characterized by their location relative to the urogenital diaphragm, as well as the presence or absence of bladder involvement; isolated anterior urethral injuries are given their own classification (Type V) (Table 6). The type of injury guides decision to manage the patient conservatively vs surgically. Surgical management of urethral injuries may be performed immediately or delayed, based on the type and extent of the injury.

Table 6.

Goldman urethral injury classification¹⁸

Goldman type	Injury description	Case example
I	Posterior urethral stretch injury	Goldman I. RUG demonstrating an elongated posterior urethra (arrow), and bulbar urethral injury (arrowhead).
II	Posterior urethral disruption above the urogenital diaphragm	Goldman II. RUG demonstrating urethral contrast column cutoff at the urogenital diaphragm (arrow), and contrast extravasation at the level of the membranous urethra (arrowhead).
III	Membranous urethral disruption below the urogenital diaphragm, involving the anterior urethra (most common type of injury)	Goldman III. RUG demonstrates abrupt urethral caliper transition at bulbomembranous urethra (arrow), as well as extensive contrast extravasation along the anterior urethra (arrowhead).
IV	Bladder neck injury extending to the proximal urethral	Goldman IV. RUG demonstrates extraperitoneal contrast extravasation at the bladder neck (arrow).
IVa	Bladder base injury simulating a Type IV injury	---
V	Isolated anterior urethral injury	Goldman V. RUG demonstrates an isolated bulbar urethra injury (arrow).

RUG, retrograde urethrography; VCUG, voiding cystourethrography.

Blunt trauma

Blunt trauma can result in injury to both the anterior and posterior urethra. Posterior urethral injury occurs most often secondary to pelvic crushing trauma, which is reported to occur in up to 25% of patients with pelvic fracture.⁶ Anterior urethral injury is most often secondary to straddle injury, where the urethra is compressed against the pubis.⁶ Indications for RUG in these settings include the presence of penile meatus blood, gross hematuria, a high-riding prostate, inability to void, perineal/penile hematoma, or a combination of these injuries.^6,19 Ideally, a RUG should be performed before transurethral catheter placement is attempted to avoid worsening of a urethral tear.⁶ If urethral transection is demonstrated on a RUG, the location and length of transection should be reported. Additionally, concomitantly performing a VCUG should be considered if posterior urethral or bladder injury is suspected.⁶ It is important to remember that incomplete opacification of the posterior urethra during RUG can mimic urethral injury. To circumvent this potential pitfall, the appropriate amount of contrast injection pressure should be used, and VCUG can be performed to improve posterior urethral visualization.

Penetrating trauma

Up to 50% of penile penetrating injuries involve the anterior urethra.¹⁹ Ballistic injuries may need urethral grafting due to tissue loss, while knife wounds can often undergo primary repair.¹⁹ Usually, imaging of penetrating trauma is not needed as urgent surgical exploration is required.²⁰

Penile fracture

Penile fracture is a rare urologic emergency that may occur during intercourse, and requires immediate diagnosis as surgical repair is often necessary. The sudden increase of intracorporal pressure by an external force causes tearing of the tunica albuginea, and there is often rupture of one of the corpus cavernosa^21,22 (Figure 6). Penile fracturing is associated with anterior urethral injury in up to 38% of cases^19,22; therefore, RUG may be performed in these cases (Figure 7). Whereas ultrasound and MR have roles in evaluating penile fractures, their roles in the assessment of acute urethral injury have yet to be established, to our knowledge.^13,14

Figure 6.

Penile fracture on magnetic resonance imaging. Patient with penile swelling and discoloration after hearing and feeling a “pop” during sexual intercourse. No tunica albuginea disruption was identified on ultrasound. Sagittal T  ₂ weight MR image of the penis revealed focal irregular morphology of the tunica albuginea along the ventral aspect of the corpus spongiosum consistent with a penile fracture (arrow). The associated hypointense signal within the corpus spongiosum was consistent with a hematoma (arrowhead).

Figure 7.

Combined penile fracture with anterior urethral injury. Patient heard “pop” during sexual intercourse, and meatal blood was noted on physical examination. RUG demonstrates contrast opacifying the corpora cavernosa (arrow) from the fossa navicularis (arrowhead), indicating disruption of both structures. RUG, retrograde urethrography.

Male urethral infection and inflammation

Infectious urethritis

In the United States, infectious urethritis affects approximately 2.8 million males per year.²³  Neisseria gonorrhea remains the most common infectious organism, accounting for >50% of cases.²³ Amongst “non-gonococcal” infections, Chlamydia trachomatis is the most common organism.²³ Less common non-gonococcal infections include tuberculosis and human papilloma virus.^19,23,24

Symptoms of acute urethritis range in severity from purulent discharge (most common) to a malodorous urinary scent (least common).²³ The diagnosis of acute urethritis is usually established clinically, and imaging is not generally employed. An estimated 15% of patients with previous gonococcal urethritis develop urethral stricturing 2–30 years post-infection.¹⁹ On RUG, post-gonococcal strictures are long, and have irregular luminal morphology.

Periurethral abscesses and fistulae are rare complications of urethritis (Figure 8). Abscesses are often encountered in patients with urethral strictures related to prior gonococcal infection resulting in Littre gland obstruction. The abscess can progress to a fistula and potentially Fournier gangrene. The terms “watering can perineum” or “watering can penis” describe urethral fistulae that extends to the perineum or scrotum associated with various infectious entities including tuberculosis.^25,26

Figure 8.

Periurethral abscess and fistula. (A) Patient with pelvic pain and pyuria underwent an i.v. contrast-enhanced CT of the abdomen and pelvis that demonstrated a peripherally enhancing 2 cm periurethral fluid collection (arrow). (B) Subsequent RUG revealed diffusely abnormal urethral contour with mucosal outpouchings diagnostic of fistulae and abscesses (arrows). Large inguinal hernia containing bowel loops was also noted (B, arrowhead). RUG, retrograde urethrography.

Inflammatory urethritis

Non-infectious/inflammatory urethritis has multiple etiologies, both iatrogenic and non-iatrogenic. Iatrogenic etiologies include unsupported Foley catheters (i.e. not taped/connected to the patient’s abdomen or leg) that can induce urethral pressure necrosis. Prostate-related procedures including transurethral resection of the prostate for treatment of benign prostatic hypertrophy, as well as radiation and/or prostatectomy, can induce urethritis as well. Urethral strictures can occur in up to 32% of patients who have previously received radiation therapy.^27–30

Urethral calculi are a less common cause of urethritis. The calculi more commonly descend from the bladder, but may also form within the urethra due to diverticula and strictures.¹⁹

Urethral malignancy

Urethral malignancies account for fewer than one percent of urinary tract malignancies.^19,31 Patients are usually ≥50-years-old, and clinical symptoms include a palpable abnormality along the distribution of the urethra, urinary obstruction, hematuria, and perineal pain, as well as perineal infection/inflammation.^19,32 Radiologic examinations are unlikely to permit differentiation of a malignant from a benign tumor. Rather, imaging helps confirm the presence of a mass, and in cases of malignancy it can also provide local staging and be used to assess for metastatic disease.³³ Primary urethral carcinomas are histopathologically classified as urothelial, squamous, adenocarcinoma, or undifferentiated.^34,35 The most common urethral malignancy is squamous cell carcinoma, and the most common locations for urethral malignancy are the bulbar and membranous urethral segments.¹⁹ Conditions that predispose to malignancy development include chronic urethritis and urethral strictures.³⁶ Although rare, and beyond the scope of this manuscript, metastatic disease to the urethra has been reported in cases of bladder, prostate, and colorectal cancer (Figure 9).³⁷ Imaging cannot reliably be used to differentiate between primary and secondary urethral malignancies, and biopsy is ultimately required.^19,37

Figure 9.

Bladder urothelial carcinoma metastasis to the urethra on magnetic resonance imaging. 67-year-old male with a history of primary bladder urothelial carcinoma complaining of difficulty urinating and palpable masses along the penis. Sagittal T  ₁ weighted dynamic contrast enhancement of the penis (A, earliest acquisition; B, second acquisition; C, third acquisition) revealed progressive increased conspicuity of masses located along the corpus spongiosum and eroding into the urethra (large arrow). Notice how the surrounding corpus spongiosum (small arrow) normally enhances, as does the corpora cavernosa (arrowhead).

RUG and VCUG are limited for local tumor staging, but may demonstrate a tumor as a filling defect (Figure 10A), irregular luminal narrowing, and/or a tumor fistula tract.¹⁹ MR imaging offers high soft-tissue contrast that can aid in both malignancy detection and local staging, although small tumors may be difficult to identify.³² On MR, squamous cell carcinoma is usually hypointense on T  ₁W, hypo- or intermediate signal intensity on T  ₂W imaging when compared to the corpora cavernosa, and tends to progressively enhance following intravenous gadolinium administration.^32,38 MR can also be used to assess for the presence of pelvic lymphadenopathy, which has substantial impact on the patient’s prognosis; unilateral metastatic lymphadenopathy can have a threefold increase in 5-year survival compared to bilateral lymphadenopathy.^32,36,39 CT and ¹⁸F-fludeoxyglucose-positron emission tomography/CT are used to evaluate for metastatic disease, but are not generally recommended for local tumor staging due to their inability to help differentiate tumor from superimposed infection/inflammation.³⁸

Figure 10.

Urethral tumor and tumor mimics. (A) Patient with difficulty urinating underwent RUG to assess for possible stricture, which revealed a bulbar urethral mass (arrow) that was subsequently proven squamous cell carcinoma. (B) RUG in second patient that is post-fall, which demonstrates small air bubble at the penile urethra that is completely surrounded by contrast (arrow). Additionally, there are multiple bulbar urethral strictures (arrowhead). (C) Third patient with bulbar urethra injury (arrow) with associated intraluminal clot (arrowhead). Urethral clots in the setting of trauma are relatively common, but the recommendation for follow-up at a later time is helpful to ensure an underlying urethral neoplasm is not present. RUG, retrograde urethrography.

Urethral malignancy treatments and imaging follow-up

Penile cancer treatment has changed in recent years, as the goal is now to avoid total penectomy if possible, and instead utilize penile-preserving procedures (partial penectomy and partial urethrectomy), which can improve a patient’s psychological health and quality of life.³⁹ In cases of stage T1 urethral cancer, transurethral resection of the tumor can be performed, followed by intraurethral chemotherapy and/or Bacillus Calmette-Guerin treatment.³⁹ Distal urethral cancers involving the penile segment may qualify for penile-preserving surgery with neoadjuvant chemotherapy or chemoradiation. Total penectomy is performed in tumors involving the bulbar segment or posterior segments.³⁹ Rates of disease recurrence are reportedly higher following penile-preserving surgery when compared to total penectomy, at 27.7 vs 5.3%.⁴⁰ Penile-preserving techniques have demonstrated comparable outcomes when compared to total penectomy, but require close patient follow-up due to the higher rates of recurrence, and may include a combination of chemotherapy, radiation, and possible eventual total penectomy.³⁹

Following primary treatment, urethroscopy and cystoscopy are routinely performed to monitor for local recurrence. Depending on the patient’s final staging, surveillance for metastatic disease may be performed solely as pelvic CT or MR with contrast (low-risk T1). In more advanced stages, radiologic surveillance may be performed with an i.v. contrast-enhanced chest CT, and either an i.v. contrast-enhanced CT or MR of the abdomen and pelvis. A defined frequency of imaging surveillance for male urethral carcinoma has yet to be established, to our knowledge, due to the rarity of this diagnosis. Currently, it is suggested to tailor imaging surveillance to the patient’s individual risk for recurrence.⁴¹

Urethral tumor mimics

Differentiating non-neoplastic urethral filling defects from malignancy is difficult on fluoroscopy, and patients may ultimately need further assessment with MR or urethroscopy. Detailed history for prior trauma, surgery, and infection could help provide a differential that includes non-malignant etiologies. A commonly encountered intraluminal pseudomass is an air bubble related to poor catheter preparation (Figure 10B and C). Air bubbles are usually rounded, well-circumscribed, and may be surrounded by contrast. More importantly, the air bubbles move freely within the urethral lumen and should not persist if the urethral contrast is evacuated, and the procedure is repeated. Periurethral cysts and abscesses can exert mass effect on the urethra, which fluoroscopically could mimic a broad-based urethral mass.³²

MR may be obtained for follow-up of a urethral mass seen on RUG, or as the initial radiologic assessment of a palpable mass. Infected urethral diverticula, periurethral abscesses, and urethral bulking agents may mimic a neoplasm. Obtaining detailed history regarding the patient’s symptoms and prior procedures can help with the differential diagnostic considerations. An inflamed and/or infected urethral diverticulum may contain complex intermediate T  ₂W signal intensity with possible heterogeneous wall enhancement, compared to a non-inflamed diverticulum that typically demonstrates water signal and little if any wall enhancement.³² Urethral bulking agents may be made of collagen or microbeads, neither of which should demonstrate enhancement.³² Collagen agents will appear hyperintense on T  ₂W imaging if recently administered, and eventually becomes hypointense on T  ₂W imaging. Microbeads will appear hypointense on T  ₂W imaging regardless of the time of administration.³²

Congenital urethral pathologies

The breadth of male urethral embryology and congenital abnormalities encountered in childhood is beyond the scope of this review. Instead, we will focus on more commonly known entities that may persist into adulthood, as well as congenital pathologies that mimic acute urethral injuries.

Hypospadias

Hypospadias affects approximately 1 in 300 children, and results from incomplete urethral fold fusion along the ventral penis such that the urethral meatus can be located anywhere from the penile glands to the perineum.⁴² Up to a third of treated patients present in adolescence or adulthood with late complications of surgical repair, including strictures, urethral-cutaneous fistula (UCF), difficulty voiding, recurrent urinary tract infection, sexual dysfunction, and cosmetic deformity.⁴³

In the surgically naïve hypospadias patients, pre-operative imaging is performed with RUG and VCUG to assess for urethral stricturing and other urogenital abnormalities that may require simultaneous correction at the time of hypospadias repair (i.e. prostatic utricle cyst).

In cases of prior hypospadias repair with creation of a neourethra, RUG and VCUG may be obtained to assess for urethral strictures, urethral dilation, and the presence of post-surgical UCF.⁴⁴ Neourethral strictures can occur anywhere, although commonly occur near the anastomoses.⁴⁴ Neourethral dilation can occur due to the inherent weakness of the neourethral walls, which can promote infection due to urinary stasis.⁴⁴

Due to the overlapping appearance, a post-operative UCF would be difficult to radiologically differentiate from a congenital urethroperineal fistula; the latter will be briefly discussed in the subsequent section. Fluoroscopically, a post-operative UCF tract extends from the urethra to any cutaneous surface. MR can provide better anatomic detail of the fistula tract with regards to course and involvement of additional pelvic structures such as musculature, which aids in surgical planning.⁴⁵

Congenital urethral pathologies that can mimic urethral trauma

Two rare congenital male urethral pathologies that can mimic traumatic or chronic infectious etiologies include urethral duplication and congenital urethroperineal fistula. Urethral duplication has multiple variants ranging from partial to complete duplication, and is subtyped based on the Effman classification.⁴⁶ In congenital urethroperineal fistula, there is both an orthotopic urethra and a secondary urinary channel arising from the prostatic urethra that emanates at the perineum and could potentially mimic a post-infectious or inflammatory tract. If urethral duplication is unknown, and RUG is performed for urethral trauma assessment, the duplicated lumen could be mistaken for a site of urethral injury.

Urethral stricture classification and treatment

Urethral stricture classification

In order to standardize reporting of anterior urethral strictures, the Trauma and Urological Reconstruction Network of Surgeons developed a classification system based on the stricture length (L), segment (S), and etiology (E) (LSE classification; Table 7).⁴⁷ This information ultimately guides the patient’s treatment.⁴⁸

Table 7.

TURNS LSE anterior urethral stricture classification system TURNS. Adapted and reproduced with permission from⁴⁷

L – Length (Total length of disease urethra, an M modifier can be used if there are two L variable values being listed)
1	≤2 cm
2	2–7 cm
3	>7 cm
S – Urethral segment (If multiple strictures are present but are going to be managed with a single technique, classify the stricture as a single stricture. However, if the strictures are going to be managed separately, an M modifier can be used to allow description of each)
1	Bulbar urethra
1a	Bulbar urethra stricture WITHOUT distal bulbar involvement
1b	Bulbar urethra stricture WITH distal bulbar involvement
2	Penile urethra
2a	Stricture involving BOTH the bulbar and penile urethral segments WITHOUT involvement of the fossa navicularis and/or urethral meatus
2b	Stricture ISOLATED to the PENILE URETHRA WITHOUT fossa navicularis or meatal involvement
2c	Stricture ISOLATED to the PENILE URETHRA WITH fossa navicularis or meatal involvement
2d	Stricture ISOLATED to fossa navicularis or meatal involvement
3	Pan-anterior urethral stricture, i.e. involves the meatus/fossa, penile, and bulbar urethra segments
E – Etiology (If multiple etiologies are suspected/known, stage with the highest numbered etiology)
1	External trauma (i.e. known straddle injury)
2	Idiopathic/unknown etiology
3	Iatrogenic
3a	Internal trauma (i.e. TURP or TURBT)
3b	Recurrent urethral stricture in the setting or prior urethroplasty; excluding hypospadias repair
3c	Radiation induced urethral stricture
4	Infectious/inflammatory (i.e. post-gonococcal)
5	Prior hypospadias repair
6	Lichen sclerosis

LSE, length, segment, and etiology; TURBT, trans urethral resection of bladder tumour; TURNS, Trauma and Urological Reconstruction Network of Surgeons; TURP, transurethral resection of the prostate.

Urethral stricture treatment

The goal of stricture treatment is return of urinary function with minimal morbidity. The aforementioned factors set the framework urologists require to provide the best treatment possible for patients.⁴⁸

Patient with urethral strictures may present in one of two ways. The first is in the emergency setting with acute urinary retention and lower abdominal pain.⁴⁹ The urologic work-up usually begins with a bladder ultrasound to measure the pre-void bladder volume, followed by immediate bladder drainage via a transurethral catheter allowing for simultaneous stricture dilation, or placement of a suprapubic catheter.⁴⁹

The second clinical scenario is in the outpatient/non-emergent setting with patient complaining of abnormal voiding symptoms that have progressed indolently. The typical work-up includes obtaining a detailed history of prior instrumentation or sexually transmitted infections; calculating post-void bladder residual volume with ultrasound; and if possible uroflowmetry to measure urine flow velocity/volume.⁴⁹ When there is concern for a urethral stricture, the patient is referred for RUG, cystoscopy, and/or other imaging modalities such as ultrasound or MRI. If the patient is able to void with low post-void residuals, catheter placement may not be necessary at the initial visit.⁴⁹ If catheter placement is performed before imaging is obtained, the stricture may be partially reduced and incompletely characterized, thus potentially altering the patient’s treatment.

Following the diagnosis of a urethral stricture, a urethral catheter may be placed and left for a short period of time to allow the urethra to heal and potentially reform. The catheter can subsequently be removed if the patient can void after removal. Some urologists advocate for “urethral rest”, whereby a suprapubic catheter is left in place for 4–12 weeks prior to urethroplasty.⁵⁰

Endoscopic management of urethral strictures (Dilation and direct vision internal urethrotomy)

Strictures located in the bulbar urethra, fossa navicularis, or meatus can initially be managed endoscopically via urethral dilation (Figure 11) or direct vision internal urethrotomy.⁴⁸ The initial success rates for these procedures varies, but can be as low as 9%, with higher success in bulbar strictures that measure <1 cm.^48,51 In cases of repeated endoscopic stricture treatment, procedural failure rates approach 100%.^51,52 Post-direct vision internal urethrotomy complications occur in 11–14% of patients, and include hematuria, infection, stricture recurrence, and worsening stricture.⁵³

Figure 11.

Pre- and post-endoscopic urethral dilation. Patient complaining of slow urinary stream, as well as chronic sense of bladder fullness. (A) RUG obtained prior to endoscopic urethral dilation demonstrates a long-segment penile urethral stricture (arrow). (B) RUG obtained after endoscopic urethral dilation demonstrates restoration of normal urethral contour (arrow). Patient reported improved symptoms following treatment. RUG, retrograde urethrography.

Urethroplasty

There are two types of urethroplasty: excision with primary anastomosis, and graft/flap substitution, with both having a reported success rate of 80–95%.⁴⁸ Excision with primary anastomosis is typically used for bulbar strictures, ideally <2 cm in length (short strictures) (Figure 12).^54,55 Graft substitution urethroplasty is usually performed in cases of long strictures (>2 cm), and in cases of penile segment strictures, complex strictures, and strictures related to prior surgery (hypospadias) or lichen sclerosis (Figure 13).⁴⁸ The preferred harvest site for grafts is from the buccal mucosa.⁴⁸ Sexual side-effects are practically absent with oral graft urethroplasty.^52,56 A urethral catheter is left in place for 2–4 weeks, with many urologic practices obtaining a post-operative RUG and VCUG at the time of catheter removal.⁵⁷ VCUG may be preferred due to its physiologic urethral pressurization, whereas RUG might excessively pressurize the urethra mimicking neo-urethral anastomotic disruption.⁵⁷ Post-operative neourethral anastomotic disruption is associated with a 74% rate of stricture recurrence, vs 13% without disruption.⁵⁸ If disruption is present, the urethral catheter can be replaced and a repeat RUG and/or VCUG is performed several weeks later.⁵⁸ Noting the degree of contrast extravasation is important, as some studies report an association with stricture recurrence.⁵⁹

Figure 12.

Pre- and post-urethral stricture EPA. Patient with remote history of prior urethral injury presents with slow urinary stream, as well a sense of incomplete bladder emptying. (A) RUG demonstrates a short-segment bulbar urethral stricture (arrow). (B) Intraoperative image of the ventral aspect of the penis demonstrating the site of excised bulbar urethra (bracket) before the urethral ends (stars) are approximated and anastomosed. (C) Follow-up RUG demonstrates resolved posterior urethral dilation (arrow). EPA, excision with primary anastomosis; RUG, retrograde urethrography.

Figure 13.

Graft substitution urethroplasty techniques. Ventral onlay procedure. (A) RUG with long-segment bulbar urethral stricture. (B, C) Intraoperative images of a ventral onlay buccal graft substitution urethroplasty. Initially, the case was planned as an urethral stricture excision with primary anastomosis; however, due to insufficient tissue for closure a subsequent ventral only procedure was required. (B) Ventral view of the urethra after the site of stricturing had been excised (bracket indicates the ventral urethral defect requiring onlay graft for closure; arrow indicates the site of suturing that was performed during the initially planned excision with primary anastomosis). (C) Ventral view of the urethra after placement of ventral buccal graft (arrowhead) before complete closure. An intraoperatively placed urethral stent is present (star). (D) Illustration demonstrating location of the ventral urethral incision (gap indicates the location of excision; red curved line indicates the graft to be placed). Dorsal onlay procedure. (E) RUG demonstrating long-segment penile urethral stricture (arrow). (F, G) Intraoperative images of a dorsal onlay buccal graft substitution urethroplasty. (F) The urethra was exposed through a ventral incision of the penis. Sutures were used to rotate the urethra (curved arrow) to allow access to the dorsum of the urethra. The dorsal aspect of the urethra was then incised at the location of stricturing (bracket). (G) A buccal graft was then placed at the dorsal aspect of the urethra (arrow). (H) Illustration demonstrating location of dorsal onlay urethral incision (gap indicates the location of excision; red curved line indicates the graft to be placed). RUG, retrograde urethrography.

EPA complications include neuropraxia, flaccid glans, infection, stricture recurrence, and erectile dysfunction.⁵⁴ Graft/flap substitution urethroplasty complications are similar to EPA, with the addition of urethral diverticula and fistula formation (Figure 14).^52,56

Figure 14.

Post-graft substitution (dorsal onlay) complication, anterior urethra leak. (A) Patient with post-traumatic long-segment bulbar urethral stricture (arrow) underwent dorsal onlay urethroplasty. (B) Post-operative RUG, there is improved caliber of the bulbar urethra (arrow); however, patient developed a small penile urethra leak (arrowhead) that was managed conservatively with a longer duration of catheter. RUG, retrograde urethrography.

Perineal urethrostomy

Perineal urethrostomy can be used to bypass the anterior urethra, creating a connection between the bulbar urethra and the perineum by using flaps.⁴⁸ Indications include complex severe urethral or pan-urethral strictures, elderly patients with co-morbidities that would preclude definitive urethroplasty, failed prior urethroplasty, lichen sclerosis, and patient preference.^48,60 Success rates have been reported at 70%, with 97% patient satisfaction, and no statistically significant difference in 2-year failure rates or outcomes compared to urethroplasty.^61,62

Gender confirmation neophallus urethra

When patients undergo female-to-male gender-confirmation/gender-affirmation surgery, they may elect for a surgically created neo-phallus that can be performed as a total phalloplasty (volume similar to genetic males) or metoidioplasty. The goal of both procedures is an end result neophallus which is capable of achieving an erection, as well as allow the patient to urinate while standing.⁶³ Whereas total phalloplasty requires multiple surgeries, metoidioplasty can typically be performed in a single-stage procedure. In addition to clitoral lengthening and straightening, a combination of buccal grafting, labia minora flaps, and anterior vaginal wall flaps may be utilized to create the neo-urethra.^63,64 Minor urethral complications that require no surgical intervention include post-operative hematoma, local cutaneous infection, urinary tract infection, and urinary dribbling or spraying during voiding.⁶³ A major complication that would require surgical intervention is a urethral fistula, which has a wide range of occurrence in the literature: 2–75% of cases.^63,65 RUG can be performed, and knowledge of sites of anastomoses is necessary as these locations can have mild narrowing that is not pathological.⁶⁵ VCUG may be more helpful for identifying locations of urinary flow limitation.⁶⁵

Conclusion

The breadth of information regarding the radiologic assessment of the male urethra continues to grow due to our ever-expanding imaging capabilities beyond the once singleton RUG examination. As such, radiologists should have a familiarity with the indications and protocols for each examination in order to inform urologists of the ideal imaging modality that will both answer their clinical question and lead to the best patient outcome.

Acknowledgment

Dr Alana Brown for medical illustration contributions.

Disclosures:

J.W.R., J.S.W., J.R.F., M.A.G., W.M.T, D.K.: Nothing to disclose.

S.S.W.: Activities related to the present article: No relevant relationships. Activities not related to the present article: receives publication royalties from Amirsys.

M.M: Activities related to the present article: No relevant relationships. Activities not related to the present article: Editor of the RSNA Case Collection