Pictorial essay: Congenital anomalies of male urethra in children

Abstract Congenital anomalies of the male urogenital tract are common. Some lesions like posterior urethral valve or anterior urethral diverticulum tend to present early in infancy and are often easily diagnosed on conventional contrast voiding cystourethrograms. Other conditions like posterior urethral diverticulum or utricle can be relatively asymptomatic and therefore present late in childhood. We present the spectrum of imaging findings of common and uncommon anomalies involving the male urethra. Since the pediatric radiologist is often the first to make the diagnosis, he or she should be well aware of these conditions.


Introduction
Congenital anomalies of the urogenital tract are among the commonest anomalies found in the fetus, neonate, and infant. [1] Most of these anomalies can be easily diagnosed by conventional contrast voiding cystourethrogram (VCUG), retrograde urethrogram (RGU), intravenous urography (IVU), or nuclear imaging, and can be successfully treated with a good outcome. Hence, the radiologist should be aware of not just the common but also the uncommon congenital anomalies and their imaging correlates; this requires a good knowledge of the anatomy and embryology of the genitourinary tract.
Of the congenital anomalies of the urogenital tract, many involve the male urethra [ Table 1], sometimes with associated anomalies of the external genitalia or anorectal malformations. This article attempts to give a pictorial overview of the congenital anomalies of the male urethra in children.
The male urethra can be divided into a proximal pelvic urethra and a distal phallic urethra. The pelvic urethra (prostatic and membranous urethra) develops from the urogenital sinus. The phallic urethra (bulbar and penile part) develops from the degeneration of the urethral plate and ventral fusion of the urethral folds between the 8th and 12 th week of gestation. [2]

Congenital Conditions
Hypospadias Hypospadias is the most common congenital urethral anomaly. It is sometimes associated with other urogenital abnormalities. The urethral meatus is located on the ventral surface, anywhere from the penile shaft to the penoscrotal region, and is associated with a dorsal chordee [ Figure 1].

Epispadias
Epispadias can be isolated or seen as part of the exstrophyepispadias complex. The urethral meatus is located dorsally on the penile shaft [ Figure 2]. In severe forms associated with exstrophy, there is a deficient lower anterior abdominal wall and anterior urinary bladder wall, a small phallus, and widely divergent pubic bones [ Figure 3]. The ureters take an abnormal lateral and upward curvature at the terminal part to give a hooked or "Hurley-stick appearance." [3]

Congenital urethral duplication
Urethral duplication can be divided into the following types: [4,5] type I, blind and incomplete; type IIA, complete patent duplication, with two meati; type IIB, complete patent duplication, with both the urethrae joining distally and opening through a single meatus; and type III, urethral duplication occurring as part of a very rare anomaly termed complete caudal duplication. [6] In complete caudal duplication, the bladder is usually completely divided in the sagittal plane, each half receiving one (ipsilateral) ureter and having a separate urethra [ Figure 4 A-B]. Rarely, there may be a single urethra leading to outlet obstruction of one of the bladders. [7,8] Urethral duplication commonly occurs in the sagittal plane, though rare cases of duplication in the coronal plane have also been reported. [9] Duplication of the urethra could be partial [ Figure 5] or complete [ Figure 6] and either hypospadiac or epispadiac [ Figure 7], depending on the relation of the accessory channel with the orthotopic urethra. In the rare epispadiac type, there is a dorsal accessory urethral opening and the child is usually incontinent.

H-or N-type recto-or anoprostatic urethral fistula
This is an extremely rare type of anorectal malformation. There is a fistulous communication between the prostatic urethra and the anterior wall of the rectum or anus. Typically, the urethra distal to the site of the fistula is narrow and stenotic, resulting in a poor urinary stream. [10] Some    studies suggest that the ventral urethra is usually functional in all cases of hypospadiac urethral duplication, whereas in congenital urethroperineal fistula the dominant urinary stream is through the dorsal orthotopic channel. [11]

Rectourethral fistula associated with anorectal malformation
Congenital rectourethral fistula is usually associated with the high and intermediate type of anorectal malformations. A contrast study, either through the colostomy or via retrograde urethrography, demonstrates the fistulous tract in most patients. The fistulous communication is between the blind-ending rectum and either the bulbar urethra [ Figures 8 and 9] or, more commonly, the prostatic urethra. [10,12]

Posterior urethral valve
Posterior urethral valves (PUVs) are the commonest cause of bladder outlet obstruction in a male child. [2] This condition may be diagnosed antenatally, in the neonatal period, or later, with the age at presentation depending on the degree of obstruction. Though earlier divided into three types, [13] currently only one type (formerly called type I) is recognized. PUVs can only be diagnosed with a VCUG and not with retrograde urethrography. VCUG shows a disproportionately dilated posterior urethra, with an abrupt transition into a narrow anterior urethra, bladder neck hypertrophy, and trabeculation/sacculation of the bladder [ Figures 10 and 11], usually with a small capacity; also, there may or may not be associated vesicoureteric reflux. In highgrade obstruction, a neonate may present with perirenal urinoma, dysplastic kidneys, or urinary ascites. [14,15] Nowadays, the entity is termed congenital obstructive posterior urethral membrane (COPUM).

Posterior urethral polyp
Posterior urethral polyp, a rare cause of intermittent urethral obstruction, [16] is an elongated pedunculated polypoid lesion attached to the verumontanum. On VCUG, the lesion appears as a lucent filling defect that moves downwards during micturition.

Prostatic utricle
The prostatic utricle is a small, blind-ending midline pouch arising from the prostatic urethra at the level of the verumontanum [ Figure 12]. It represents the remnant of the caudal end of the fused Müllerian ducts. [17] A large prostatic utricle may be associated with urinary retention, stasis, and infection. It can be associated with hypospadias or the prune belly syndrome. [18] Posterior urethral diverticulum Most posterior urethral diverticulae are acquired in origin and lined with columnar epithelium or granulation tissue. A congenital posterior urethral diverticulum is a rare entity [ Figure 13]. A large diverticulum may be complicated by urinary stasis, infection, and calculi formation.

Anterior urethral diverticulum
An anterior urethral diverticulum is a saccular outpouching arising from the ventral surface of the anterior urethra. Two types are described. Most commonly it arises from the ventral surface of the bulbar urethra [ Figures 14 and 15]. The other rarer type is found located near the penile tip     [ Figure 16] and has a short neck. The former usually presents with obstruction [19][20][21] to the urinary stream, while the latter is more prone to calculus formation.

Anterior urethral valve
An anterior urethral valve is a posteriorly directed semilunar fold arising from the floor of the anterior urethra and causing urethral obstruction during micturition. On imaging, it can mimic an anterior urethral diverticulum, but the posterior lip is absent in a valve.

Congenital megalourethra
This is a rare congenital anomaly resulting from the faulty development of the corpora cavernosa and corpus spongiosum. Two types are described. The milder and commoner form, scaphoid megalourethra, results from a localized underdevelopment or deficiency of the corpus  An oblique VCUG image (B) reveals an elongated, dilated, and patulous posterior urethra, with tapered transition into a normal anterior urethra (arrow). Note the grossly dilated ureters and the vesicoureteric reflux (curved arrow). It is the tapered transition of the posterior urethra that helps differentiate this condition from PUV, in which there is an abrupt transition. There is bilateral grade V vesicoureteric reflux (arrow) and grossly tortuous laterally placed ureters (C), in this frontal VCUG image the corpus spongiosum, [22,24] resulting in diffuse dilatation of the penile urethra [ Figure 18].

Prune belly syndrome
This refers to a constellation of anomalies, including lax abdominal wall musculature, cryptorchidism, and various lower urinary tract anomalies. [25][26][27] The posterior urethra is typically dilated, high-placed, and tapered distally; the appearance may mimic a posterior urethral valve [ Figure 19 A-C].

Congenital meatal stenosis
Congenital meatal stenosis is most frequently associated with hypospadias. On VCUG, the entire urethra up to the meatus is dilated [ Figure 1].

Conclusion
A number of congenital conditions can affect the male urethra, and the diagnosis is predominantly based on VCUG, RGU, and USG. Congenital causes of urethral obstruction like PUV can be diagnosed on antenatal USG or MRI. Though VCUG may be essential for diagnosis, radiation issues should be taken into consideration when performing the investigation in a newborn or an infant. Jana, et al.: Congenital urethral anomaly spongiosum [ Figure 17], [22,23] with intact corpora cavernosa. Fusiform megalourethra is the rarer, more severe, form in which there is deficiency of the corpora cavernosa as well as