Date Published: December 13, 2019
Publisher: Springer US
Author(s): Subramaniyan Ramanathan, Vineetha Raghu, Parvati Ramchandani.
To discuss the imaging appearances of various pathologies affecting adult male urethra and to review the role of imaging in the assessment of artificial urinary sphincters and penile prostheses. Diagnosis of common male urethral diseases heavily depends on two conventional fluoroscopic techniques namely retrograde urethrography and voiding cystourethrography. These are useful in evaluating common urethral diseases like traumatic injury, infections, and strictures. Cross-sectional imaging can be useful in evaluating periurethral pathologies. Artificial urinary sphincters, slings, and periurethral bulking agents are used in the management of urinary incontinence and imaging can be utilized to detect complications in these devices. Cross-sectional imaging especially MRI plays a significant role in evaluating the different types of penile prostheses and their malfunctioning.
Evaluation of the urethra is indicated in trauma, inflammatory pathologies, strictures due to any cause, and for post-operative assessment. Retrograde urethrography (RUG) and voiding cystourethrography (VCUG) are the two common fluoroscopic contrast techniques used currently to assess the anterior and posterior urethra, respectively, for the many indications mentioned above. Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) are necessary for the evaluation of periurethral structures. MRI is the gold standard for evaluation of urethral diverticula and urethral tumors.
The male urethra measures 17 to 20 cm in length and is divided into anterior and posterior segments. The anterior urethra is further subdivided into the penile and bulbar parts, and the posterior urethra into the membranous and prostatic segments. The prostatic urethra courses through the prostate gland and has two specific landmarks. The verumontanum is an ovoid mound of tissue on the posterior wall, housing the utricle and ejaculatory duct openings. The membranous urethra is the shortest and least distensible segment of the urethra, narrowest only second to the meatus. The bulbo-membranous junction is located at the inferior margin of the urogenital diaphragm, and corresponds to the “cone” seen on fluoroscopic contrast studies. The penile urethra measures about 20 cm in length, and ends at the external urethral meatus. The distal end of the penile urethra located in the glans penis is dilated to form the ‘fossa navicularis’ and is approximately 1.5 cm long. Surrounding the urethra are lubricating glands: the pea-sized paired Cowper glands located within the urogenital diaphragm which drain into the bulbar urethra, and the periurethral glands of Littre, most abundant in the dorsal penile urethra and the bulbous urethral sump [1, 2].
The RUG remains an invaluable technique for assessing the anterior urethra. A scout film (KUB radiograph) is initially performed to look for bony abnormalities or calcification and should ideally extend to at least a few centimeters below the pubic symphysis. A 14 to 18F Foley catheter is inserted through the external meatus with aseptic technique. A smaller (8F or 10F) can be used in patients with meatal stenosis to avoid iatrogenic trauma. The catheter must be flushed before insertion to get rid of air bubbles which may be mistaken for filling defects within the urethra. The balloon of the catheter is placed in the fossa navicularis and inflated with 1.5 ml fluid, either contrast or saline; air should not be used to inflate the balloon as it is more compressible than fluid and inadvertent balloon withdrawal can occur during the study. It is best not to lubricate the catheter prior to placement to prevent slippage of the catheter from the glans. The patient is positioned supine with a 45° oblique tilt, and dependent hip flexed. The penis is placed sideways over the thigh with moderate traction; oblique positioning of the patient and penile traction are necessary to straighten the urethra, particularly at the penoscrotal junction. 20–30 ml of iodinated contrast is injected under fluoroscopic guidance.
VCUG is a method to delineate the anatomy and pathology of the posterior urethra. In this technique, the bladder is filled with contrast through a Foley catheter, suprapubic catheter or performed at the end of excretory urogram (the latter produces less dense contrast and may not result in optimal visualization of the urethra). The volume of contrast depends on the individual’s bladder capacity, which can vary from 300 to 800 ml, but it is necessary to fill until the patient reports a strong urge to void. Voiding is performed under fluoroscopic control in upright 45° oblique position or supine oblique position on a horizontal table in patients unable to stand [1, 4].
Although conventional urethrographic techniques help in excellent evaluation of the luminal pathologies, cross-sectional modalities such as US, CT, and MRI are indicated in certain cases of periurethral abnormalities and enable comprehensive evaluation of the male urethra.
The male urethra may be injured by blunt or penetrating trauma. Clinically, there may be blood at the meatus (approximately 50% of cases), and this should prompt a RUG prior to attempted urethral catheterization, in order to prevent exacerbation of an injury. Urethral injuries may lead to strictures, fistulae (usually due to iatrogenic injuries, often as a complication of radiation therapy or surgery), incontinence (if the external sphincter is involved), and impotence with severe posterior urethral injuries in association with pelvic fractures .
Gonococcal urethritis is a sexually transmitted disease caused by Neisseria gonorrhoeae. It commonly presents with purulent discharge. It often leads to complications like strictures which can be severe.
Fibrous strictures of the urethra are pathologically characterized by spongial fibrosis, which refers to scarring of the periurethral corpus spongiosum . Clinically, the patient may present with decreased urinary stream, hesitancy, and incomplete evacuation.
Various congenital abnormalities that can found in the urethra include prostatic utricle, posterior and anterior urethral valves, anterior urethral diverticulum, anorectal malformations with associated urethral fistula, meatal stenosis, hypospadiasis and epispadiasis and urethral duplication. Among these, congential urethral anomaly that can be seen in adults include prostatic utricle and mullerian duct cysts.
These are usually calculi that have been expelled from the bladder (migrant calculi) and lodge at points of narrowing (such as the membranous urethra, external urethral meatus, or proximal to a urethral stricture). Rarely, urethral calculi may form in diverticula or proximal to a stricture (Figs. 14 and 15).Fig. 14Urethral calculus. a Plain abdominal radiograph demonstrates a urethral calculus close to pubic symphysis (arrow). b Retrograde urethrogram depicts the urethral calculus as a rounded filling defect (long arrow) within the urethra proximal to a stricture (short arrow)Fig. 15Calculus in Cowper’s duct syringocele. a, b Frontal and oblique plain radiograph shows radio opaque focus just below pubic symphysis along urethral course (arrows). c, d Retrograde urethrogram shows the calculus along the ventral aspect of proximal bulbar urethra (arrow) with extrinsic indentation. On further opacification (d), it is masked by the dense contrast in the dilated Cowper’s duct suggesting syringocele (short arrow)
Urethrography (RUG and VCUG) are not without complications. A temporary burning sensation and difficulty passing urine may be reported by the patient which usually resolves with time and reassurance. Infection (urethritis) as a complication is rare. Traumatic instrumentation with contrast extravasation has also been described specially in cases of difficult catheterization or underlying stricture. Venous intravasation due to urethral mucosal disruption by the inflated Foley balloon in the glans or the pressure of contrast injection especially in the presence of strictures may occur, can lead to opacification of the corpus spongiosum and draining pelvic veins. As with any contrast study, allergic reaction to contrast may occur due to systemic absorption [3, 21].
Gas bubbles inserted through the catheter can mimic filling defects or polyps.Short pseudo strictures may result from urethral kinking due to inadequate penile traction or insufficient oblique position.False estimation of stricture length may result if RUG or VCUG are used in isolation. It is good practice to combine RUG and VCUG for assessing the length of strictures.External urethral sphincter contraction and bulbocavernous (constrictor nudae) spasm may mimic stricture. These are usually overcome by gentle steady pressure of injection.Opacification of the prostatic ducts, Cowper ducts, and periurethral glands of Littre may be mistaken for extravasation.High pressure injections may lead to contrast intravasation into the spongiosal plexus, and may mimic contrast leak.Fig. 16Pitfalls of retrograde urethrogram. a Bulbocavernous spasm (arrow) may mimic stricture, and is usually overcome by gentle and firm pressure of injection. b Pseudo stricture (arrow) may result from inadequate traction. c Air bubbles (thick arrow) injected into the urethra mimicking polypsFig. 17Normal structures in retrograde urethrogram mimicking urethral contrast extravasation. a Opacification of the Cowper ducts (arrow). b Periurethral glands of Littre (arrow). c High pressure injections may lead to contrast intravasation into the corpus spongiosa (long arrow) and venous plexus (short arrow)
Penile prostheses (PP) are the third line therapy for erectile dysfunction after the failure of pharmacotherapy and vacuum devices. It gives high degree of patient satisfaction rate albeit an expensive and complex surgical procedure .
Urinary incontinence is a relatively common symptom in the aging male population, with the prevalence of daily urinary incontinence in older men reported to range from 2 to 11% with increasing prevalence reported with increasing age . Prostate surgery, including radical prostatectomy and transurethral resection of the prostate (TURP), is the most common cause of stress urinary incontinence .
In spite of widespread usage of cross-sectional modalities in genitourinary imaging, urethrography still holds an important place. It is the imaging modality of choice in suspected urethral trauma and urethral strictures and also useful in surgical planning and evaluating post-operative complications. Radiologists must be aware of the anatomy, imaging appearances of various urethral pathologies, and pitfalls in image interpretation. A clinically oriented approach to imaging and reporting is helpful for the treating urologist.