2006-08-07-10 Posterior urethral valves © Werner www.thefetus.net/
Posterior urethral valves
Heron Werner, MD
Clinica de Diagnostico por Imagem (CDPI) & Instituto Fernandes Figueira (FF), Rio de Janeiro, Brazil The urinary tract anomalies represent some of the most common anomalies seen in fetal and neonatal life. The bladder-outlet obstruction has the potential to affect the development of the whole urinary tract as well as the lungs. In males, the most common cause is posterior urethral valves and in females is urethral atresia.
Posterior urethral valves are thought to be embryologically derived from mullerian duct remnants or remnants of the cloacal membrane dating back to between the 7th and 11th week of gestation. The urethral membrane acts as valve, resulting in bladder outlet obstruction. The incidence of posterior urethral valves has been reported to be between 0.25-0.5:10,000 births. It accounts for 10% of all urological anomalies detected by prenatal ultrasound. The overall mortality is 25– 50%. Renal insufficiency develops in up to 45% of survivors.
The severity ranges from mild to severe. At the better end of the spectrum the fetus may have obstructive uropathy with preservation of amniotic fluid volume, minimal changes in the bladder and ureters, and no dysplastic changes in the kidneys. At the severe end of the spectrum. there are fetuses with severe oligohydramnios, distended bladder, and ureters with cystic dysplastic changes in the kidneys. Fetuses with obstructive uropathy can also have other associated anomalies, like chromosomal abnormalities (especially trisomies 13, 18 and 21), and some deformations related to the oligohydramnios.
The sonographic and MRI findings are:
- persistent dilatation of the urinary bladder with a thickened, often trabeculated, bladder wall (> 2 mm)
- the posterior urethra is dilated in urethral obstruction due to posterior urethral valves
- the dilated proximal urethra resembles a keyhole, extending from the bladder toward the fetal perineum
- the dilated bladder can become quite large, filling both pelvis and abdomen
- ureterectasis and caliectasis due to vesicoureteral reflux induced by high intravesical pressure
In high-grade obstruction the urinary bladder may spontaneously decompress through rupture of the urinary tract, resulting in fetal urinary ascites. Oligohydramnios is indicative of high-grade obstruction and, if long-standing may result in deformations including Potter facies and club feet.
Fetal urinary ascites (28 weeks) in a case of posterior urethral valves and the 3d reconstruction
Left image: 3D view of the liver (black arrow) and urinary ascites (white arrow). Right image: 3D view of the high-grade bladder obstruction (black arrow) and urinary ascites (white arrow). Note the dysplastic changes in the right kidney (blue arrow).
3D reconstruction of the dysplastic kidney (28 weeks)
Left image: Dysplastic modifications of the kidneys (coronal view). Note echogenic kidneys with collecting system dilatation. This represents a poor prognosis sign for renal function, suggesting renal dysplasia. Right image: Urinary ascites (axial view). Note the liver (blue arrow).
Dilated bladder, urinary ascites (28 weeks) and displastic kidneys
The dilated proximal urethra resembles a keyhole (blue arrow).
Dilated bladder with a thickened wall and trabeculations and dilated posterior urethra.
Sagittal T2 view showing the dysplastic right kidney (blue arrow) and urinary ascites (red arrow). Note the oligohydramnios.
Sagittal T2 view showing a dilated bladder (blue arrow) and proximal urethra (red arrow).
Figure 21: Coronal T2 view showing ascites and dilated bladder.
Axial T2 view showing ascites (blue arrow).
Axial T2 view showing a dilated bladder (blue arrow)
Sagittal T1 view showing a dilated bladder (blue arrow) and proximal urethra (red arrow).
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• Werner H, Brandão A, Daltro P.: Ressonância magnética em ginecologia e obstetrícia. Revinter 2001.