Retrograde urethrography in children: a decade of experience at a children’s hospital

Abstract

Background

Retrograde urethrography (RUG) is a radiologic procedure that optimizes imaging evaluation of the urethra, particularly in settings of difficulty with micturition or urethral injury.

Objective

To review our experience with RUG at a large pediatric radiology practice.

Materials and methods

We conducted a retrospective review of medical records and fluoroscopic images of RUGs performed from January 2010 to December 2020.

Results

We identified 180 RUG exams (median frequency 17 exams per year), all in male children (median age 13 years). The most common indications were stricture (42%; n=76), postsurgical evaluation (34%; n=62) and trauma (16%; n=29). The most commonly used catheter was Foley (40%; n=72), with a median catheter size of 5 French (Fr) for infants younger than 1 year, 7 Fr for children ages 1–5 years and 8 Fr for children older than 5 years. About a third of the children (57; 32%) had combined voiding cystourethrography (VCUG)–RUG exams. Water-soluble contrast agent, either 17% or 43% Cysto-Conray, was used. Most RUG exams were normal (46%; n=83). The most common urethral pathology was stricture (30%; n=54), commonly involving a bulbar urethra (n=26). Urethral trauma was seen in 11 children (6%), 10 bulbar and 1 membranous. Most children with stricture were surgically treated (n=40; 74%), whereas most children with trauma were conservatively treated (n=8; 73%). The remaining diagnoses included diverticula, polyps, valves, fistulas and duplications, constituting <17% of our sample; most of these were surgically treated. Four exams (2%) were non-diagnostic.

RUG showed 89% sensitivity and 97% specificity compared to cystourethroscopy/VCUG findings. Technical difficulties occurred in 14 (8%) children (e.g., pain or inappropriate catheter seal).

Conclusion

Our experience indicates that when catheterization techniques are properly tailored, RUG provides a useful and successful radiologic method of evaluating the pediatric male urethra.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00247-023-05589-7.

Introduction

Although relatively uncommon in children, urethral abnormalities can lead to clinical manifestations that significantly impair the quality of life of those affected. Fluoroscopic imaging plays a vital role in the diagnosis, treatment planning, and follow-up of a wide range of urethral diseases in children and adults. Voiding cystourethrography (VCUG) and retrograde urethrography (RUG) are standard imaging modalities for assessing urethral pathologies [1].

The efficacy and reproducibility of VCUG and RUG have been evaluated in adults. At present, most of the radiologic literature addressing pediatric RUG focuses on the general guidelines and the techniques of the exam or its use for specific indications (e.g., urethral stricture or injury). However, to the best of our knowledge, none has described the overall institutional experience of RUG use in children and its role in guiding patient management. Information on pediatric urethral pathologies and their treatment strategies is therefore often extrapolated from the adult literature. The primary objectives of this study were to describe the indications, technique, imaging findings, diagnostic accuracy and complications of RUG in the pediatric population at a large quaternary academic pediatric radiology department, and to determine the role of RUG in directing urologic management of these children.

Materials and methods

Subject selection

This single-center study was approved by our institutional review board and complied with the Health Insurance Portability and Accountability Act. The requirement for patient informed consent was waived. We reviewed the medical records and fluoroscopic images of patients ages 0 to 18 years who underwent RUG exams at our institution over an 11-year period from January 2010 to December 2020. Children who did not have images associated with RUG reports (n=2) or had incomplete medical records (n=5) were excluded from our cohort.

Retrograde urethrography technique

Retrograde urethrography was performed with the child lying in a supine oblique position where one leg was partially flexed, with the other leg stretched above it over the table (Fig. 1). Children who could void were instructed to empty their bladder prior to the exam. A scout radiograph of the pelvis was taken prior to contrast instillation to assess bony structures and any calcified urinary tract pathology. Under sterile techniques, the tip of a Foley catheter was then inserted through the urethral meatus, the balloon was inflated with 1–2 mL of saline and secured in the fossa navicularis, and a small amount of contrast agent (~ 10–15 mL) was injected under fluoroscopy (Fig. 1). Lidocaine anesthetic gel was not routinely used to facilitate catheter insertion in our patients unless the child developed significant discomfort with prior attempts. The penis could be stretched to elongate the urethra and the glans could be pressed tightly around the catheter during injection to prevent contrast leakage through the urethral meatus. When age-appropriate, children were instructed to keep their pelvic floor muscles relaxed during injection. Static oblique fluoroscopic spot views that included the entire urethra were captured in most exams. Cine series were obtained in certain pathologies, e.g., suspected urethral injury or urethrocutaneous fistula, for better visualization and documentation of contrast agent leak. At our institution, RUG exams were mainly performed by radiologists, sometimes in collaboration with urologists if a urethral injury was suspected such as in children with trauma or post surgery.

Fig. 1.

Illustration of retrograde urethrography (RUG) and voiding cystourethrography (VCUG) exam. a–e Sketch illustrates patient position during RUG exam (a), conventional RUG technique (b), VCUG technique through urethral catheter (c), VCUG technique through suprapubic catheter (d) and peri-catheter RUG technique (e). Ang. = Angiocatheter; Cath. = Indwelling Foley catheter

In some children, VCUG was combined with RUG for further assessment of the posterior urethra and the urinary bladder. VCUG technique varied depending on whether the child had a vesicostomy and suprapubic catheter at the time of RUG exam [2]. In children who did not have a vesicostomy or suprapubic catheter, after injection of the contrast agent for the RUG exam the balloon was deflated and the urethral catheter was advanced to the bladder, where contrast agent was instilled via gravity drip under intermittent fluoroscopic observation (Fig. 1). Children with suprapubic catheters had their urethral catheter removed, and contrast agent was injected through the suprapubic catheter into the bladder (Fig. 1) [3].

Catheters other than Foley were used in certain circumstances. In some children who had urethroplasty, pericatheter RUG exams were performed to assess for contrast leakage by inserting smaller-caliber tubes (feeding tube/angiocatheter) alongside the indwelling post-procedural Foley catheter (Fig. 1) [4]. These small-caliber catheters were also used in children who were evaluated for urethral duplication. In these cases, the small catheter was introduced through the accessory meatus while a Foley catheter was inserted through the dominant meatus [5]. Latex-free material were used in all cases [6].

Data collection

We evaluated each RUG exam and report for the following parameters: indications, procedures, exam findings and technical difficulties. For procedures, we recorded the type and size of catheter used, presence of indwelling or suprapubic catheter prior to the exam, type and concentration of the contrast agent used and whether a VCUG was performed in conjunction with the original RUG exam. For exam reports indicating stricture, we reviewed the fluoroscopic images and recorded the stricture site, number, length and diameter; presence of reflux into urethral glands; false tracts; and any filling defects. We determined stricture length and diameter by direct measurement on the image, and we applied calibration to account for image magnification. Urethral trauma grading was based on location (Goldman’s classification [7]) and severity (American Association for the Surgery of Trauma (AAST) classification [8]). Urethral duplications were classified according to the Effman classification [9]. We compared RUG findings with intraoperative/cystourethroscopy or VCUG findings as the gold standard, if available. We recorded all technical difficulties and adverse events for each exam, as well as relevant clinical history including chief complaints, other urologic exams performed within 3 weeks of the RUG, and patient management following RUG exams.

Statistical analysis

We used descriptive statistics to report counts and frequencies (in percentages) for categorical variables, as well as mean, median, standard deviation, interquartile ranges and range for continuous variables. We also calculated sensitivity, specificity and accuracy of RUG exams relative to cystourethroscopy findings (or VCUG findings if cystourethroscopy was not available). All data analyses were computed using SPSS Statistics (v. 25.0; IBM, Armonk, NY).

Results

Patient characteristics

We identified 180 RUG exams (all male; median age 13 years, interquartile range [IQR]: 7–16 years). At our institution, RUG exams were performed less frequently (median: 17/year) than other urethral imaging and diagnostic procedures (Fig. 2).

Fig. 2.

Line graph shows frequency of retrograde urethrography (RUG) exams (median: 17/year) performed at our institution spanning a period of 10 years (2010–2019) compared to other urethral diagnostic procedures such as contrast-enhanced voiding urosonography (ceVUS; median: 70/year), cystourethroscopy (median: 104/year) and voiding cystourethrography (VCUG; median: 511/year). We excluded from analysis the frequency of exams in 2020 because of the disruption of the service caused by the coronavirus disease 2019 (COVID-19) outbreak. Breaks (≈) within the graph indicate a shift in the values displayed on the y-axis so that both large and small values could be well demonstrated

The most common exam indications were evaluation of urethral stricture (e.g., idiopathic or postsurgical; 42%; n=76), postsurgical evaluation (e.g., urethroplasty, hypospadias repair; 34%; n=62) and recent trauma (16%; n=29). Most of the children were treated conservatively (e.g., medications, uroflowmetry; 41%; n=74) but some underwent endoscopic or operative interventions (36%; n=65) and some had no treatment (23%; n=41).

The most common presenting symptoms were weak urinary stream (46%; n=82) and dysuria with recurrent urinary tract infections (UTIs; 13%; n=23), especially among children evaluated for stricture. Gross hematuria (14%; n=25) was a common symptom among children evaluated for trauma, but two children were referred for hematuria at the end of voiding (i.e. urethrorrhagia). Forty-nine (27%) children were asymptomatic and, in most cases, were undergoing an RUG exam for postoperative follow-up.

6 (3.3)Additional imaging and urologic exams including VCUG, cystourethroscopy, scrotal US and pelvic US were performed depending on the RUG indication or finding. A VCUG (36%; n=64) was the most common exam performed either alone (n=7) or in conjunction with RUG (n=57) to evaluate for posterior urethral or urinary bladder abnormalities. Cystourethroscopy exams (31%; n=55) were performed either to manage abnormal RUG findings (n=50) or to rule out pathology when RUG exams were normal (n=3) or non-diagnostic (n=2). Most scrotal US with Doppler exams (8/10) were performed in children being evaluated for urethral trauma to assess for coexistent testicular injury. Most abdominal-pelvic US exams (17/22) were performed in children being evaluated for stricture to assess the post-void residual urine volume and to exclude other causes of urinary tract obstruction. The characteristics of our cohort are summarized in Table 1.

Table 1.

Patient characteristics

Characteristic	n (%) or n (range)
Total number of exams, n	180
Median age (IQR)	13 years (7–16)
Gender (male)	100%
RUG Indication
- Urethral stricture (e.g., congenital, idiopathic or post-surgical)	76 (42.2)
- Postoperative follow-up (e.g., urethroplasty, hypospadias repair)	62 (34.4)
- Urethral trauma	29 (16.1)
- Urethral duplication	7 (3.9)
- Others (e.g., meningocele, Foley catheter break, urethrorrhagia)	6 (3.3)
Chief complaintsa
- Diminished urinary stream, straining, hesitancy, post-voidal dribbling	82 (45.6)
- Dysuria ± recurrent UTI	23 (12.8)
- Gross hematuria/urethrorrhagia	25 (13.9)
- Penile pain/swelling	15 (8.3)
- Erectile dysfunction	6 (3.3)
- Nocturnal enuresis	2 (1.1)
- Asymptomatic	49 (27.2)
- Others (e.g., extra meatus, double stream, meningocele, scrotal mass)	16 (8.9)
RUG diagnosis (exam findings)b
- Stricture	54 (30)
- Trauma	11 (6.1)
- Duplication	6 (3.3)
- Posterior urethral valve	5 (2.8)
- Anterior urethral valve	2 (1.1)
- Diverticulum	5 (2.8)
- Meatal stenosis	4 (2.2)
- Detrusor sphincter dyssynergia	2 (1.1)
- Cowper’s duct cyst (Syringocele)	1 (0.6)
- Urethro-cutaneous fistula	2 (1.1)
- Urethral polyp	2 (1.1)
- Urethral calculus	1 (0.6)
- Normal	83 (46.1)
- Non-diagnostic	4 (2.2)
Other exams within 3-week time interval of RUG
- Combined RUG and VCUG	57 (31.6)
✓ Through suprapubic catheter	22 (11.9)
✓ Through urethral catheter	35 (19.5)
- VCUG	7 (3.8)
✓ Through suprapubic catheter	3 (1.6)
✓ Through urethral catheter	4 (2.2)
- Cystourethroscopy	55 (30.5)
- Scrotal US with Doppler	10 (5.4)
- Abdominal US	22 (11.9)
Management
- Reassurance ± follow-up	41 (22.8)
- Conservative (e.g., biofeedback, medications as antibiotics, α1 blockers)	74 (41.1)
- Surgical (e.g., urethroplasty, meatotomy)	65 (36.1)

IQR interquartile range, RUG retrograde urethrography, SD standard deviation, US ultrasound, UTI urinary tract infection, VCUG voiding cystourethrography

^aSome children had more than one complaint

^bTwo children had both urethral strictures and trauma

Technical aspects of retrograde urethrography exam

The Foley catheter was used most commonly (n=72; 40%). Median catheter size varied with patient age: 5 French (Fr) for children younger than 1 year, 7 Fr for children 1–5 years age and 8 Fr for children older than 5 years (Fig. 3). Twenty-eight (16%) children had suprapubic catheters at the time of exam; 22 of these children underwent combined RUG–VCUG exams and 3 underwent VCUG exams alone at a later date.

Fig. 3.

Box and whisker plot shows median, interquartile range (IQR) and outliers of catheter size for children of various age groups: <1 year, 1–5 years and >5 years

Water soluble contrast agent, either 17% or 43% Cysto-Conray (Guerbet, Villepinte, France), was used at the discretion of the radiologist performing the exam, but 34 of the 57 combined RUG–VCUG exams used both contrast concentrations to provide some differentiation in contrast density between the retrograde and the voiding stream. During RUG, the contrast agent reached the posterior urethra in 139 (77%) as well as the bladder in 106 (59%) examinations. Contrast refluxed in urethral glands in 13 (7%) children, 11 with strictures and 2 with normal RUG exams. Contrast leakage occurred in nine children, seven of whom had urethral trauma and two of whom had postoperative urethra-cutaneous fistulas. Penile vascular intravasation occurred in two children with trauma.

Technical difficulties were reported in 14 children (8%): inadequate catheter seal with suboptimal urethral distention in 9 and significant pain in 5. No contrast-related adverse events were reported in any RUG exam. Technical aspects of RUG exams are presented in Table 2.

Table 2.

Procedures of retrograde urethrography (RUG) exams

Variable	Results n (%)
a) Catheters
Types of catheter
- Foley catheter	72 (40)
- Feeding tube	18 (10)
- Angiocatheter	4 (2.2)
- Not available	86 (47.8)
Vesicostomy and suprapubic catheter at time of exam	28 (15.1)
Indwelling transurethral catheter at the time of exam	19 (10.3)
b) Contrast agent
Contrast concentration
- 17% Cysto-Conray	48 (26.7)
- 43% Cysto-Conray	93 (51.7)
- 43% Cysto-Conray for RUG and 17% Cysto-Conray for VCUG	34 (18.9)
- Not available	5 (2.8)
Contrast opacification
- Anterior urethra only	41 (22.8)
- Posterior and anterior urethras	33 (18.3)
- Urinary bladder, posterior and anterior urethras	106 (58.9)
Contrast reflux in glandsa	13 (7.2)
- Cowper gland duct	11 (6.1)
- Prostatic gland duct	2 (1.1)
- Ejaculatory duct	1 (0.5)
Contrast leakage	9 (5)
- Anterior urethra	8 (4.4)
- Posterior urethra	1 (0.5)
Contrast penile vascular intravasation	2 (1.1)
c) Technical difficulties	14 (7.7)
- Suboptimal urethral distention and inadequate catheter seal	9 (5)
- Significant pain	5 (2.8)

VCUG voiding cystourethrography

^aOne child had reflux both in Cowper and prostatic gland ducts

Retrograde urethrography exam findings and patient management

Details about RUG findings and patient management relative to these findings are presented in Online Supplementary Material 1.

Normal retrograde urethrography exams

Retrograde urethrography exams were normal in 83 cases (46%) (Fig. 4). Most of these children underwent RUG to evaluate for stricture because of difficulty with voiding (n=34) or prior urethral procedures where RUG was performed for postoperative follow-up (n=26).

Fig. 4.

Normal retrograde urethrography (RUG) findings. Fluoroscopic image in a 16-year-old boy shows a normal RUG exam. ① penile urethra, ② bulbar urethra, ③ membranous urethra. Note Foley balloon (arrow)

The majority of these children either received no treatment (n=32) or were treated conservatively (n=49), depending on their case (e.g., uroflowmetry to assess for dynamic obstruction, medication to relieve pain). Two children eventually received surgical treatment because cystourethroscopy, performed later on, demonstrated the RUG findings to be false negatives (discussed later).

Retrograde urethrography findings of stricture and injury

Retrograde urethrography showed abnormal findings of urethral stricture in 52 cases (29%), injury in 9 cases (5%) and both stricture and injury in 2 cases (1%). Table 3 summarizes RUG findings and management for children with stricture and injury.

Table 3.

Retrograde urethrography exam findings of stricture and trauma

Variable	Results
a) Stricture	54 children
Total number of strictures in all childrena	60
Median number of strictures per child (range)	1 (1–3)
Mean stricture length (mm) ± standard deviation (SD)
- Total	9.3 ± 10.8
- DIVU	4.3 ± 3.6
- EPA	10.1 ± 4.2
- Buccal mucosal graft urethroplasty	26.3 ± 6.5
Location
- Penile urethra	3
- Bulbar urethra	26
- Membranous urethra	20
- Neourethra	4
- Junction of anterior and posterior urethra	5
- Pan-urethral (both anterior and posterior urethras)	2
Contrast crossing stricture n (%)	45 children (83.3)
b) Trauma	11 children
Grade (Goldman classification) of trauma patients based on location
- I (elongation of the otherwise intact posterior urethra)	0
- II (injury above urogenital diaphragm)	0
- III (membranous urethra injury extending to proximal bulbous urethra)	1
- IV (bladder neck injury extending into the proximal urethra)	0
- V (isolated anterior urethral injury)	10
Type (AAST classification) of trauma patients based on severity
- 1 (contusion)	1
- 2 (elongation with no contrast leakage)	1
- 3 (partial disruption with contrast leakage)	7
- 4 (complete disruption with < 2 cm separation with contrast leakage)	2
- 5 (complete disruption with > 2 cm separation with contrast leakage)	0
Contrast leakage n (%)	7 children (63.6)
Penile intravasation n (%)	2 children (18.1)

AAST American Association for the Surgery of Trauma, DIVU direct vision internal urethrotomy, EPA excision and primary end-to-end urethroplasty, RUG retrograde urethrography

^aSome children had more than one stricture

Among the 54 stricture cases, most children had only one stricture, but 5 had multiple strictures (up to 3). Strictures were most commonly located in the bulbar urethra (n=26) (Fig. 5), followed by the membranous urethra (n=20) (Fig. 6). Contrast agent was not able to cross the stricture in 15 children. Mean stricture length was 9 mm.

Fig. 5.

Bulbar urethral stricture in a 12-year-old boy who had complaints of weak urinary stream. Fluoroscopic image shows a bulbar urethral stricture (arrowheads), likely idiopathic given the absence of a history of urethral trauma, infection or surgery. The stricture was treated with direct vision internal urethrotomy

Fig. 6.

Membranous urethral stricture in a 14-year-old boy who had complaints of straining during micturition and incomplete bladder emptying. Fluoroscopy shows membranous urethral stricture (arrowheads), likely idiopathic given the absence of a history of urethral trauma, infection or surgery. The stricture was treated with excision and primary end-to-end urethroplasty

In 11 children with RUG findings of recent urethral injury, 10 were isolated to the bulbar urethra (grade V Goldman classification) and one extended to involve the membranous urethra and was associated with pelvic fracture (grade III). Contrast leakage was seen in seven children (Fig. 7) and venous intravasation in two (Fig. 8).

Fig. 7.

Trauma with contrast leakage. Fluoroscopic image in a 15-year-old boy who presented with penile pain and hematuria following a straddle injury shows bulbar urethral trauma (grade V) with contrast leakage (arrow)

Fig. 8.

Trauma with vascular intravasation. Fluoroscopic image in a 12-year-old boy who had a history of bulbar urethral trauma following a dog bite shows penile and pelvic vascular intravasation (arrow)

Most of the children with isolated stricture (40/52) were surgically treated (e.g., by direct vision internal urethrotomy [DIVU] or excision primary anastomosis urethroplasty [EPA]). Conversely, most of the children with isolated urethral injury (8/9) were either managed conservatively (e.g., by catheter placement) or received no treatment. For the two cases with combined urethral stricture and injury, one underwent surgical management (DIVU) and the other was catheterized.

Other abnormal retrograde urethrography findings

The remaining diagnoses constituted less than 17% of our sample. Six (3.3%) children with urethral duplication were identified; 5/6 had incomplete duplication (type IA): 2 were surgically treated because of recurrent episodes of purulent secretions and 3 received no treatment because they were asymptomatic. One child with complete urethral duplication (type IIA₂) (Fig. 9) and a double urinary stream was treated surgically.

Fig. 9.

Urethral duplication. Fluoroscopic image in a 4-year-old boy who presented with double urinary stream shows complete (type IIA2) urethral duplication (arrowheads). The urethral duplication was surgically repaired

Five (2.8%) children underwent RUG for a urethral diverticulum (Fig. 10): three were treated surgically, one received antibiotics and one received no treatment. Detrusor sphincter dyssynergia (DSD) was suspected in two children and was confirmed by electromyography. One child had urinary tract calculi, which were managed conservatively through adequate hydration and urine straining (Fig. 11). The majority of the remaining cases (10%; n=16) (Figs. 12, 13 and 14) — including polyps, valves, fistulas, syringocele (also referred to as Cowper duct cyst) and meatal stenosis — were surgically treated except one child with meatal stenosis, who declined procedural intervention. Four (2.2%) RUG exams were non-diagnostic.

Fig. 10.

Urethral diverticulum. Fluoroscopic image in an 8-year-old boy who had surgical history of urethroplasty shows a urethral diverticulum (asterisk). The boy had obstructive symptoms, so the diverticulum was excised

Fig. 11.

Urethral stones. Fluoroscopic image in a 10-year-old boy who had pain during micturition and hematuria shows urethral stones (arrow). The case was treated conservatively by generous hydration, diet adjustment and patient instructions to strain during micturition

Fig. 12.

Urethrocutaneous fistula in a 2-year-old boy who had undergone surgical repair for hypospadius. Fluoroscopic image shows urethrocutaneous fistula (arrow). Contrast agent is leaking from the ventral aspect of the penile shaft. The fistula was surgically treated

Fig. 13.

Urethral polyp. Fluoroscopic image in a 15-year-old boy who presented with diminished urinary stream shows urethral polyp (arrow) arising from bulbar urethra. The polyp was excised

Fig. 14.

Dilated posterior urethra and posterior urethral valve (PUV). Fluoroscopic images of a 14-month-old boy who underwent combined retrograde urethrography (RUG) and voiding cystourethrography (VCUG) because of a history of antenatal hydronephrosis. a RUG shows abrupt termination of contrast agent at the proximal bulbar urethra (arrow). b Following cystoscopic catheter insertion, VCUG shows dilated posterior urethra (asterisk) and PUV (arrow) during voiding. The boy was surgically treated

Retrograde urethrography exam accuracy

In 100 children, cystourethroscopy and/or VCUG were performed in conjunction with RUG and were used as gold standard references. Cystourethroscopy/VCUG showed pathology in 34 children and was normal in 66 children. Compared to these findings, RUG showed 89% (32/36) sensitivity, 97% (62/64) specificity and 94% (94/100) accuracy. All false RUG findings (n=6) were confined to posterior urethral pathologies.

Two children had a false-positive RUG findings of membranous strictures; one was shown to be normal on VCUG and received no treatment, and one was found to have posterior urethral valve (PUV) at cystourethroscopy and was surgically treated.

Four children had false-negative RUG findings. Two had normal RUG exams, but cystourethroscopy demonstrated the presence of membranous stricture in one child, which was treated with DIVU, and PUV in the other child, which was resected. The remaining 2/4 cases had vesicostomies where RUG exams were non-diagnostic but VCUG showed membranous urethral strictures, and were maintained with indwelling suprapubic catheters. Cases with false RUG findings are outlined in Online Supplementary Material 1.

Discussion

Although a decade of review has indicated that RUG is infrequently performed at our institution, RUG has shown very high accuracy and could be regarded as an optimal imaging technique for evaluating specific pathologies, such as stricture or trauma, affecting the male anterior urethra. RUG plays no role in assessing the female urethra and has limited capability of displaying the posterior urethra in the vast majority of indications; therefore, VCUG remains the gold standard in the overall evaluation of the urethra for both sexes [1]. To that end, some radiologists might rely solely on VCUG for evaluating all urethral, bladder and reflux abnormalities without performing RUG, which might justify the low annual frequency of RUG observed in our cohort. However, radiologists should be aware that VCUG alone might not accurately demonstrate certain abnormalities of the male anterior urethra because the urethra is not fully distended to the degree seen on RUG [1]. Another possible reason for the low RUG frequency is the growing trend of radiologists to use contrast-enhanced voiding urosonography (ceVUS) as an alternative urethral imaging procedure for both VCUG and RUG to limit exposure of pediatric patients to ionizing radiation [10, 11].

Stricture was the most common abnormal finding on RUG in our cohort. The most common causes of pediatric urethral strictures in developed countries are iatrogenic and congenital (idiopathic) [12]. At RUG, the affected segment often appears to be narrowed, elongated, asymmetrical, irregular or even completely absent if the contrast agent does not cross through the stricture [1]. Although retrograde reflux of contrast agent into the Cowper duct, prostate gland or seminal vesicle ducts can be seen in association with a urethral stricture, it is also occasionally seen in normal RUG exams [1]. Careful consideration must be taken when evaluating membranous urethra in RUG because it often appears as an opacified thin wisp of contrast agent at the apex of the prostatic urethra in normal exams and can be misinterpreted as a urethral stricture [13]. Such a false-positive finding was seen in one of our cases, initially interpreted as a membranous urethral stricture but later excluded by VCUG performed in the same session.

Management of urethral strictures in pediatric patients varies with stricture length, number, severity and location [14]. All penile, posterior or pan-urethral strictures were treated with urethroplasty regardless of their cause and length. For bulbar or junctional strictures, DIVU was performed for short strictures (<1 cm), EPA for medium strictures (<2 cm) and buccal mucosal graft urethroplasty for long strictures (>2 cm) [15]. Postoperative strictures (e.g., post-urethroplasty or post-hypospadias) were managed with repeated urethroplasties, urinary diversion by suprapubic cystostomies, or nonsurgical alternatives such as intermittent catheterization or medical therapy if the children were not candidates for surgery or if they declined operative repair [16].

Pediatric urethral trauma is relatively uncommon: only 3–5% of children admitted for trauma are reported to have urethral injuries [17]. In our sample, most of the trauma patients had bulbar urethral injuries (grade V), which is the most common site injured in children [17], as a result of straddle (e.g., blow to the penis) or iatrogenic (e.g., urethroplasty) causes. Urethral injuries are rarely life-threatening in the absence of major bladder trauma; therefore, an urgent urethral repair can be deferred while maintaining urethral integrity and functionality by urinary or suprapubic catheterization until more urgent pelvic injuries are appropriately managed [8]. Strictures can occur in up to 50% of patients with traumatic injuries, particularly those with complete disruption of the bulbar urethra (i.e. AAST injuries type 4 and 5) and might require urgent surgical treatment to avoid significant morbidities [18]. Contrast intravasation is a very rare incident that occurs in less than 1% of RUG exams where penile and pelvic venous tributaries are visualized on fluoroscopy. It is particularly common in patients with predisposing urethral tear, and can lead to unusual complications, e.g., anaphylaxis or embolism [19]. All children in our series with urethral trauma who had transient complaints (e.g., transient hematuria or pain) but normal RUG exams were either symptomatically treated with conservative measures or not treated at all.

Urethrocutaneous fistulas in children most commonly occur as a postoperative complication after hypospadias repair, with a reported rate of 4–25% [20]. Findings on RUG show contrast leakage through an abnormal ventral communication at the distal part of the neourethra, which is the most susceptible site for tissue ischemia and where epithelial devitalization occurs [21, 22]. Urethrocutaneous fistulas are often surgically treated [23]. Differentiation of urethral fistulas from urethral duplication by RUG is important because the management approach for these entities can differ [21].

Urethral duplication, an uncommon developmental anomaly with fewer than 500 cases reported, was rarely evaluated at our institution at RUG [24]. Management of duplication depends on the presence of symptoms and type of anomaly [9, 25]. Non-communicating urethral duplications, such as type 1A, are often asymptomatic and therefore require no treatment. Occasionally, the blind accessory urethral pouches are a nidus for infections, causing episodes of purulent secretions, and need to be surgically excised [26]. Communicating urethral duplications, such as type IIA2 where the accessory channel connects with the membranous portion of the dominant urethra, are often associated with urinary symptoms such as bifid stream or urinary incontinence, and require surgical repair [27]. One child in our sample underwent RUG to evaluate for urethral duplication. RUG ruled this out, and meatotomy was performed to cut a septum separating the two meatal orifices.

As previously mentioned, RUG is much less useful than VCUG in evaluating posterior urethral lesions [28]. PUV is occasionally seen on RUG, often appearing as a shelf-like filling defect within membranous urethra with a marked caliber change between the proximal and distal urethra. However, PUV is easily missed on RUG exams, leading to false-negative results, as was the case in one of our patients. All children with suspected findings of PUV at RUG in our sample also underwent a VCUG exam to confirm pathology and all were treated with cystoscopic valve ablation [29]. RUG alone can also fail to diagnose bladder voiding disorders, particularly those with DSD. Two children in our series with history of multiple sclerosis and suspected DSD [30] had combined RUG and VCUG; the studies showed marked distention of the bladder, distension of the posterior urethra with concomitant narrowing of the membranous urethra at the area of external urethral sphincter consistent with DSD that was later confirmed with electromyography [30].

Several anterior urethral lesions including anterior urethral valves (AUVs), diverticula, polyps and syringoceles can be very well distinguished on RUG. At RUG, the proximal part of an AUV forms an obtuse angle with the ventral floor of the urethra, whereas the proximal lip of a diverticulum forms an acute angle [31]. During contrast filling, the urethral diverticulum becomes distended with contrast agent, whereas syringocele, particularly the imperforate subtype, appears as an external non-opacified mass with smooth margins indenting the floor of bulbar urethra [31, 32]. A fibrovascular polyp appears as a smooth filling defect connected by a stalk to the urethral wall [1, 33]. In treatment, AUVs are often ablated, polyps are excised and syringoceles are deroofed because of their obstructive symptoms [34, 35]. Diverticula can be surgically excised in children presenting with obstructive symptoms, conservatively treated with antibiotics in those with recurrent UTI, or left untreated in asymptomatic patients [36].

There is an important limitation in our study. Not all children underwent cystourethroscopy and VCUG during follow-up because sometimes this was not clinically indicated, especially if RUG was normal. Therefore, the true accuracy of RUG in our sample remains unknown because there was no gold standard exam available for all cases with which to compare RUG findings.

Conclusion

This study describes our experience using RUG in children for a wide variety of urethral pathologies. Although infrequently performed when compared to conventional fluoroscopic VCUG, our experience indicates that when catheter selection and catheterization techniques are properly tailored according to patient size and age, RUG provides a useful, safe and often successful radiologic method of evaluating the pediatric male urethra, particularly in the settings of anterior urethral stricture, prior urethral surgery, and trauma. RUG is best implemented in fluoroscopic cystography protocols when more detailed assessment of the anterior urethra is required; however, VCUG remains the gold standard for evaluating the posterior urethra.

Supplementary Information

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Declarations

Conflicts of interest

None