Findings: Ultrasound demonstrates bilateral hydronephosis and hydroureter down to the level of the uterovesical junctions. The renal parenchyma is diffusely echogenic bilaterally with loss of the corticomedullary junction. A VCUG reveals a distended and trabeculated bladder with marked bilateral vesicoureteral reflux. There is dilatation of the posterior urethra consistent with posterior urethral valves.

Diagnosis: Obstructive bilateral hydronephrosis secondary to posterior urethral valves (PUV).

Discussion: As in this patient, hydronephrosis is often diagnosed in utero. Severe hydronephrosis warrants further work-up with VCUG and ultrasound. In the neonatal period, posterior urethral valves accounts for about 20% of obstructive hydronephrosis seen in infancy and occurs in 1:5,000-8,000 boys. Other obstructive types of hydronephrosis include UPJ obstruction, UVJ obstruction and ectopic ureterocele. PUV is associated with the more fatal form of Prune-Belly Syndrome.

What are posterior urethral valves? Just distal to the verumontanum, the interior urethral crest terminates into several plicae or folds. If these folds become to prominent, they act as membranous valves which obstruct antegrade outflow of urine. There are several proposed types of posterior urethral valves:

TYPES OF POSTERIOR URETHRAL VALVES

1. Type I valves are attached but primarily below the verumontanum (most common).
2. Type II valves are above the verumontanum.
3. Type III valves is a diaphragm with a central aperture located below and sometimes well distal to the verumontanum.

Patients may present with a distended bladder (abdominal mass), difficulty voiding or urinary tract infection. Prenatal ultrasound may demonstrate not only hydronephrosis but oligohydramnios. As a consequence of oligohydramnios, neonates may present with pulmonary hypoplasia.

VCUG is the imaging exam of choice to diagnosis posterior urethral valves. In addition to the characteristic findings of a dilated posterior urethra – bladder tracbeculation, vesicoureteral reflux and urinary ascites may also be seen.

Treatment: Surgical ablation of the valves.

References:

1. Blickman H. Pediatric Radiology: The Requisites, 2nd Edition, 1988.
2. Danhert W. Radiology Review Manual, 2nd Edition, 1993.