SPR Unknown # 55-- FINAL
Publication Date: 2011-07-29
History of oligohydramnios. Prenatal MRI performed at 31 gestational weeks.
Within the abdomen, visceral situs solitus is present. Renal size is appropriate and the renal parenchyma bilaterally appears normal. However, there is bilateral hydronephrosis with mild calyceal dilatation and partly extra-renal pelves on both sides. Bilateral tortuous, moderate hydroureters are also seen all the way down to the level of the bladder. There is trace fluid in the perirenal space on the right but no significant fetal ascites.
The urinary bladder is moderately filled, and considering the degree of filling, the wall of the urinary bladder appears slightly prominent and hypointense, suggestive of bladder wall thickening. A keyhole appearance noted, on both sagittal and coronal views, as there is dilatation of the posterior urethra. The fetal gender is male.
Posterior urethral valves (PUVs) are abnormal membranes congenitally present in 1/8000 male infants, in the posterior urethra near the verumontanum, analogous to the female hymen. They arise during embryogenesis, and can show variable degree of development. Their presence will result in bladder outlet obstruction. Milder cases will be diagnosed later, possibly even post-natally. Larger valves will result in earlier and more severe obstructive uropathy, and have the potential of resulting in early renal failure as well as pulmonary hypoplasia or even Potter’s sequence if there is accompanying severe oligohydramnios/anhydramnios antenatally. Approximately 50% of these boys also have vesicoureteric reflux. In certain instances, the hydroureteronephrosis associated with the bladder outlet obstruction is significant enough and occurs early enough to result in chronic significant abdominal distension and lead to thinned, malformed abdominal wall muscles – a condition known as Prune Belly Syndrome, which is difficult to diagnosis antenatally but is usually evident after birth.
Outcome in cases of PUVs appears to be related to whether renal parenchyma (and therefore function) is preserved. Partly extra-renal pelves are a favorable anatomic variant in this respect, since some of the pressure build-up is taken by the expanding extra-renal pelvis, sparing the renal parenchyma from the deleterious effects of chronic increased intracapsular pressure which leads to parenchymal loss.
Treatment consists primarily of post-natal urethral valve ablation, with or without prior vesicostomy or pyelostomy. In certain centers, fetal therapies offered include amnioinfusion to prevent the pulmonary hypoplasia and Potter sequence, and vesicoamniotic shunts to relieve the obstruction and preserve renal function.