eMedicine Specialties > Radiology > Pediatrics
Posterior Urethral Valve: Imaging
Updated: Feb 21, 2010
Radiography
Findings
Plain radiographs do not add to the actual diagnosis of posterior urethral valves; however, chest radiography may be useful in the evaluation of pulmonary hypoplasia, and images of the kidneys, ureters, and bladder (KUB images) may show the ground-glass appearance of urinary ascites, if present.
VCUG (represented in the images below) is considered the diagnostic study of choice for the evaluation of posterior urethral valves. The bladder is typically thickened with trabeculae and may exhibit vesicoureteral reflux or, less commonly, diverticula. The bladder neck is typically hypertrophic, leading to a lucent ring or collar. On voiding, the posterior urethra is dilated (ie, shield shaped), and valve leaflets may be seen as lucencies, giving the appearance of a spinning top. If leaflets are not visible, a commonly associated finding of posterior urethral bulging distally over the bulbar urethra may be noted. The anterior urethra is typically underfilled, and voiding is incomplete.
Anteroposterior view of the abdomen during a voiding cystourethrographic study. This image demonstrates a dilated bladder with trabeculation, diverticula, and bilateral massive reflux.
Anteroposterior view of the abdomen during a voiding cystourethrographic study. This image demonstrates bilateral grade 4 vesicoureteral reflux. No intrarenal reflux is noted.
Sagittal voiding image of the bladder and urethra that was obtained from a voiding cystourethrographic study before catheter removal. This image demonstrates a trabeculated, hypertrophied bladder. The bladder neck is hypertrophied and well demarcated between the body of the bladder and the dilated posterior urethra, the latter of which has the classic spinnaker-sail appearance.
Late anteroposterior image from a voiding cystourethrographic study. This image demonstrates a small, trabeculated bladder with bilateral diverticula. The posterior urethra is dilated.
Lateral view of a voiding cystourethrographic study during voiding after catheter removal. The dilated posterior urethra is highly suggestive of a posterior urethral valve, which is seen as the nonopacified line that separates the dilated posterior urethra from the normal-caliber distal urethra. The absence of the urethral catheter may be critical to demonstrate the valve, as good urethral distention is mandatory.
IVP is not routinely used in children because the contrast agent is poorly concentrated and visualized in newborn kidneys, particularly if renal function is diminished. Elevated serum creatinine levels may preclude the use of intravenous (IV) contrast material. IVP can show an absent kidney in the case of renal dysplasia or delayed renal function with persistent high intraluminal pressures. Hydroureteronephrosis may be seen. Delayed images may show bladder or urethral pathology, but the lower urinary tract is better visualized with VCUG.
Degree of Confidence
Again, VCUG is the criterion standard diagnostic test for posterior urethral valves. The constellation of bladder and urethral abnormalities with or without valve identification typically confirms the presence of valves. Cystourethroscopy with the patient under general anesthesia may be required to formally confirm the presence of posterior urethral valves at the time of intervention.
False Positives/Negatives
Regarding false-positive findings, any of the obstructive etiologies listed in the Differentials section above may show bladder and upper-tract changes that are typical of posterior urethral valves. However, most of the listed conditions have significant differences in imaging that separate them from posterior valves, such as the location of involvement (anterior valves, syringocele), associated anomalies (prune-belly syndrome), and degree of impairment (plicae colliculi). False-positive results should not be seen with functional disorders because the posterior urethra should not be dilated, except potentially in detrusor sphincter dyssynergy/dyssynergia.
False-negative results are rarely noted in cases of posterior urethral valve that have minimal anatomic obstruction and, thus, limited functional impairment and upper-tract changes. In boys with these findings, VCUG may not show valve leaflets. However, in a boy with the clinical stigmata of a posterior valve in whom definitive visualization of the valve is lacking, cystourethroscopy may be indicated to rule out urethral pathology. It is important to obtain voiding images in the lateral view with—and, ideally, without—the catheter in situ, because the images with the catheter removed optimally demonstrate the valves. It has long been believed that leaving the urethral catheter in place may hold the valves open and prevent proper visualization, but that does not happen in practice if good urethral distention is achieved.
In the postoperative setting after valve ablation, some posterior urethral dilatation usually persists, with secondary bladder changes. However, if incomplete valve ablation is suspected, then repeating cystourethroscopy rather than VCUG is recommended.
Computed Tomography
Findings
Rarely necessary in neonates, CT scans with IV contrast enhancement may reveal dysplastic and/or dilated kidneys with delayed renal function and excretion, hydroureter, dilated bladder with wall thickening, trabeculation, and diverticula. A dilated posterior urethra might be seen, although leaflets may be easily missed. Elevated serum creatinine levels generally preclude use of IV contrast material.
Degree of Confidence
CT scans cannot reliably depict valves, although they should reveal the sequelae of bladder outlet obstruction.
False Positives/Negatives
False findings are identical to those for radiography. An exception is that plicae colliculi, which might be seen on VCUG studies, should not be noted on CT scans.
Magnetic Resonance Imaging
Findings
MRI findings are similar to those of CT scanning except that enhancement with IV gadolinium-based contrast agents may allow functional as well as anatomic assessment.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Degree of Confidence
The degree of confidence is similar to that with CT scanning.
False Positives/Negatives
False findings are similar to those observed with CT scanning.
Ultrasonography
Findings
A proper ultrasonographic study to evaluate the urinary tract must include images of both kidneys, the ureters, and the bladder. Hydroureteronephrosis (seen in the first 5 images below) with or without cortical thinning, a thick-walled bladder with trabeculation and diverticula, and a dilated posterior urethra with a hypertrophic bladder neck are usually seen. In the setting of renal dysplasia, the renal parenchyma is typically hyperechogenic with visible small cysts (<10 mm), but in the most mildly affected cases, renal ultrasonographic findings may be normal. Echogenic lines that are the actual valve leaflets might be seen. The combination of the dilated, thick-walled bladder and dilated posterior urethra has been described as a keyhole appearance (as demonstrated in the sixth image below).
Longitudinal sonogram of the right kidney in a 1-day-old male infant. This image demonstrates grade 4 hydronephrosis, with thinning of the renal parenchyma.
Longitudinal sonogram of the right kidney (same patient as in the image above). This image shows that the hypoechoic areas interconnect, a finding that is consistent with hydronephrosis rather than multiple distinct renal cysts, which do not interconnect.
Renal sonogram (same patient as in the images above). This image shows grade 4 hydronephrosis of the left kidney.
Renal sonogram (same patient as in the images above). This image shows grade 4 hydronephrosis of the left kidney.
Renal sonogram (same patient as in the images above). This image shows grade 4 hydronephrosis of the left kidney.
Longitudinal sonogram of the bladder. This image demonstrates a distended bladder, with the classic keyhole appearance of the posterior urethra seen distally (on the right).
The bladder may be of large or small volume, but it is invariably thick-walled. Urinary ascites or perinephric collections due to urinomas may also be seen, most commonly soon after birth, and are caused by rupture of the urinary tract, typically at the level of the calyces. A suggestive prenatal sonogram reveals a male fetus with bilateral hydroureteronephrosis; a dilated and thickened bladder with poor emptying; and, possibly, oligohydramnios (features seen in the images below). After the diagnosis has been established and initial management has begun, ultrasonography is useful to follow up on the degree of hydronephrosis and parenchymal integrity after treatment, as well as the adequacy of bladder evacuation with voiding and the resolution of any urinomas.
Prenatal longitudinal sonogram of the right kidney. This image demonstrates significant hydronephrosis with possible renal cortical thinning. The kidney is larger than expected for the patient's gestational age.
Prenatal longitudinal sonogram of the left kidney. This image demonstrates significant hydronephrosis with possible renal cortical thinning. As is the case with the right kidney, the left kidney is longer than expected for the patient's gestational age (same patient as in the above image).
Prenatal axial sonogram of the abdomen. This image demonstrates bilateral hydronephrosis. (The spine is the echogenic ring near the top of the image.)
Prenatal sonogram almost in the coronal plane. A distended urinary bladder is depicted throughout this image as well as previous prenatal ultrasonographic studies. The bladder wall may be thickened.
Prenatal sonogram almost in the coronal plane (same patient as in the image directly above). A distended urinary bladder is depicted throughout this image as well as previous prenatal ultrasonographic studies. The bladder wall may be thickened.
An initial prenatal sonogram. This image demonstrates a distended urinary bladder and oligohydramnios.
A first prenatal sonogram. This image demonstrates a cystic area in the region of the left renal fossa. This cystic area appears to be separate from the left kidney, which is located just to the left of the fluid collection on the image. The fluid collection was thought to represent a urinoma.
Sonogram. This image demonstrates mild pelvocaliectasis that involves the right kidney (same patient as in the 5 images below).
A second prenatal sonogram. This image demonstrates interval resolution of the fluid collection in the left renal fossa and a left kidney with pelvocaliectasis.
A second prenatal sonogram. This image also demonstrates pelvocaliectasis that involves the right kidney.
A second prenatal sonogram, transverse view. This image of the abdomen demonstrates bilateral pelvocaliectasis.
Postnatal sonogram on the first day of life. This sagittal image of the bladder demonstrates bladder wall thickening and prominence of the distal left ureter.
Transverse sonogram of the bladder. Bladder wall thickening is again demonstrated.
Degree of Confidence
The sum of the ultrasonographic findings with clinical correlates, combined with the rarity of other obstructive lesions, is highly indicative of posterior urethral valves. The valves typically cannot be seen on sonograms, and VCUG is required to make the definitive diagnosis.
False Positives/Negatives
False-positive results may be seen with other obstructive and functional disorders of bladder emptying. The ultrasonographic findings are the final common signs of most of the conditions in the differential diagnosis (see Differentials). False-negative results may be seen in mild cases without upper-tract abnormality and an essentially normal bladder. In a study by Williams et al, the reported sensitivity of renal and bladder ultrasonography for valves was 87% in patients younger than 4 years and 98% for those age 4 years or older.7
Nuclear Imaging
Findings
Nuclear cystography has no role in the diagnosis of posterior urethral valves because of the poor anatomic detail, but this modality can depict the presence of vesicoureteral reflux. However, grading of such reflux is not as accurate as with contrast VCUG.
Nuclear renography may be used to assess upper-tract consequences of bladder outlet obstruction. A urethral catheter must be placed before the study to eliminate the effect of a distended, high-pressure bladder on renal function and drainage. An absent or dysplastic kidney is seen as a photopenic area in the renal fossa. Delayed visualization of a renal unit with a slow rise to peak activity suggests altered renal function. Differential renal function is important to estimate relative renal impairment and is based on activity at 1-2 minutes after injection of a tracer. Hydronephrosis with ureteral dilatation can represent ureterovesical obstruction or chronic nonobstructive changes of posterior urethral valves; the latter should demonstrate washout after furosemide administration, if renal function is adequate. Renal scanning studies are shown below.
Excretory images obtained from renal scanning that was performed with diethylenetriaminepentaacetic acid. This study demonstrates radiotracer accumulation within the dilated renal collecting systems and dilated ureters. The bladder remains empty because of catheter drainage.
Renal scanning images performed with diethylenetriaminepentaacetic acid. This study demonstrates accumulation of radiotracer within the renal collecting systems bilaterally; within the dilated ureters bilaterally; and within a small, irregular-appearing bladder. Renograms (top right and bottom left) demonstrate poor clearance of contrast material from the renal collecting systems. The relatively poorer function in the left kidney reflects congenital renal dysplasia.
Degree of Confidence
Nuclear medicine study is poor for the specific diagnosis of posterior urethral valves, but it is excellent for assessment of the upper-tract consequences (see Nuclear Medicine, Findings).
False Positives/Negatives
False-positive findings can result when a urethral catheter is not used. High bladder storage pressure or vesicoureteral reflux can prevent drainage from the kidney and ureter. Distal ureteral obstruction by ureterovesical junction obstruction or a ureterocele can mimic the changes of valves. False-negative findings can be seen in cases in which there is normal renal function and drainage.
More on Posterior Urethral Valve |
| Overview: Posterior Urethral Valve |
 Imaging: Posterior Urethral Valve |
| Follow-up: Posterior Urethral Valve |
| Multimedia: Posterior Urethral Valve |
| References |
| Further Reading |
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References
Young HH, Frontz WA, Baldwin JC. Congenital obstruction of the posterior urethra. J Urol, 3: 289-365, 1919. J Urol. Jan 2002;167(1):265-7; discussion 268. [Medline].
Heikkilä J, Rintala R, Taskinen S. Vesicoureteral reflux in conjunction with posterior urethral valves. J Urol. Oct 2009;182(4):1555-60. [Medline].
Otukesh H, Sharifiaghdas F, Hoseini R, et al. Long-term upper and lower urinary tract functions in children with posterior urethral valves. J Pediatr Urol. Aug 11 2009;[Medline].
Youssif M, Dawood W, Shabaan S, et al. Early valve ablation can decrease the incidence of bladder dysfunction in boys with posterior urethral valves. J Urol. Oct 2009;182(4 Suppl):1765-8. [Medline].
Sarhan O, El-Dahshan K, Sarhan M. Prognostic value of serum creatinine levels in children with posterior urethral valves treated by primary valve ablation. J Pediatr Urol. Feb 2010;6(1):11-14. [Medline].
Imaji R, Dewan PA. The clinical and radiological findings in boys with endoscopically severe congenital posterior urethral obstruction. BJU Int. Aug 2001;88(3):263-7. [Medline]. [Full Text].
Williams CR, Pérez LM, Joseph DB. Accuracy of renal-bladder ultrasonography as a screening method to suggest posterior urethral valves. J Urol. Jun 2001;165(6 pt 2):2245-7. [Medline].
Soliman SM. Primary ablation of posterior urethral valves in low birth weight neonates by a visually guided fogarty embolectomy catheter. J Urol. May 2009;181(5):2284-9; discussion 2289-90. [Medline].
Bani Hani O, Prelog K, Smith GH. A method to assess posterior urethral valve ablation. J Urol. Jul 2006;176(1):303-5. [Medline].
Glassberg KI, Horowitz M. Urethral valve and other anomalies of the male urethra. In: Belman AB, King LR, Kramer SA, eds. Clinical Pediatric Urology. 4th ed. London, UK: Martin Dunitz Ltd; 2002:899-946.
Krishnan A, de Souza A, Konijeti R, Baskin LS. The anatomy and embryology of posterior urethral valves. J Urol. Apr 2006;175(4):1214-20. [Medline].
Salam MA. Posterior urethral valve: outcome of antenatal intervention. Int J Urol. Oct 2006;13(10):1317-22. [Medline].
Further Reading
Clinical guidelines:
Daytime lower urinary tract conditions. In: Guidelines on paediatric urology. European Association of Urology - Medical Specialty Society
European Society for Paediatric Urology - Medical Specialty Society. 2008 Mar (revised 2009 Mar). 4 pages. NGC:007221
Posterior urethral valves. In: Guidelines on paediatric urology. European Association of Urology - Medical Specialty Society
European Society for Paediatric Urology - Medical Specialty Society. 2008 Mar (republished 2009 Mar). 6 pages. NGC:006514
Keywords
posterior urethral valve, hydronephrosis, hydronephrosis kidney, PUV, urethral dilation, posterior urethral, posterior urethral valves, voiding dysfunction, renal hydronephrosis, bladder outlet obstruction
