Obstructive Uropathy
Fetal Surgery for Obstructive Uropathy
Prenatal Treatment of Fetal Obstructive Uropathy | References | Contact Us / Request an Appointment
Experience has demonstrated the usefulness of shunting procedures in some fetal conditions, but the limitations of these catheters have also become apparent.
In addition to their problems with obstruction, dislodgment, and short functional life span, shunting procedures are not adequate for many conditions. The experience with open fetal surgery in the 1960s for the treatment of erythroblastosis fetalis was discouraging, and it was soon abandoned with the introduction of percutaneous techniques of fetal transfusion.
Harrison and colleagues introduced open fetal surgery for the treatment of obstructive uropathy in 1982. Although the procedure (bilateral ureterostomy) was technically successful, the fetus made no urine, oligohydramnios persisted, and the infant died of pulmonary hypoplasia.
Despite this initial unsuccessful result, a new era in fetal therapy was opened. Soon, successful open surgical procedures were reported in the treatment of:
An appreciation of the fetal natural history of these conditions and the success of Harrison's group at the University of California at San Francisco encouraged groups in Philadelphia, Boston, Denver, Memphis and Cincinnati in the United States as well as Seoul, Korea, Melbourne, Australia and Paris, France, to undertake open fetal surgery. Clinical experience is still quite limited, however, with fewer than an estimated 400 cases of open fetal surgery performed worldwide.
Posterior urethral valves (PUVs) are the leading cause of antenatally diagnosed lower urinary tract obstruction and are the structural genitourinary anomaly amenable to fetal therapy. PUVs are found only in the male population and have an incidence of 1 in 5000 births. The mortality rate in these patients has been reported to be as high as 63%, especially when it is associated with severe oligohydramnios owing to pulmonary hypoplasia.
The natural history and outcome of antenatally diagnosed obstructive uropathy differ significantly from those of postnatally diagnosed obstruction. Reports of PUVs diagnosed at birth reveal a significant mortality associated with respiratory and renal insufficiency.
Oligohydramnios occurring before 24 weeks of gestation profoundly affects the fetal lung development during the critical transition from the canalicular to the alveolar phase of lung development. Profound oligohydramnios owing to PUV is also associated with clubfoot and Potter facies, and there is a 9% incidence of chromosomal anomalies in obstructive uropathy.
The major diagnostic tool in obstructive uropathy remains antenatal ultrasonography. With current techniques, fetal ultrasonography may detect urinary tract anomalies as early as 12 to 13 weeks of gestation.
The prenatal diagnosis of obstructive uropathy requires an understanding of physiologic and pathologic dilatation of the urinary tract. Hydronephrosis is the most common pathologic finding on prenatal ultrasonography in cases of fetal obstructive uropathy.
The discovery of echogenic kidneys with pronounced cystic dysplasia is an ominous finding, universally associated with a poor overall prognosis. However, with less severe pathology, distinguishing pathologic dilatation of the renal pelvis (pelviectasis) from physiologic dilatation is difficult, especially early in pregnancy.
Transient dilatation of the fetal urinary tract is a relatively common finding, occurring in 1 out of every 100 pregnancies. This frequency is far more common than that of pathologic obstruction, as found on postnatal evaluation and autopsies.
Measurements of the anteroposterior (AP) pelvic diameter and its ratio to the overall AP renal diameter have been proposed as criteria for discriminating between normal and abnormal pelvic dilatation. In fetuses younger than 20 weeks' gestation, the parameters of abnormal pelvic distention have not been defined.
A recent prospective study correlating screening ultrasonography in patients 16 to 23 weeks' gestation with postnatal outcome revealed that a pelvic diameter greater than 4 mm was 76% sensitive in identifying a pathologic obstruction.
Furthermore, fetuses with a urinary tract obstruction demonstrated a more rapid increase in this dilatation over the remainder of gestation than did fetuses without obstruction.
For fetuses older than 23 weeks gestation, threshold values associated with pathologic fetal hydronephrosis are an AP pelvic diameter greater than 10 mm and an AP pelvic–to–AP renal diameter ratio greater than 0.5. The additional finding of caliectasis provides even stronger support to a pathologic etiology.
If any of these criteria are met, the patient should undergo further sonographic assessment and a full prognostic profile, including sequential taps of the fetal bladder for urinary electrolyte determination if oligohydramnios develops in a case of suspected bladder outlet obstruction.
Lower urinary tract obstruction must be distinguished from the other pathologic causes of fetal hydronephrosis. The presence of megacystis, thickened bladder wall, posterior urethral dilatation, bilateral hydronephrosis and ureterectasis characterizes the changes associated with PUV and urethral atresia in contrast to the more common ureteropelvic junction obstruction, ureterovesical obstruction or vesicoureteral reflux.
These cases of lower urinary tract obstruction lead to oligohydramnios, as urinary output is the major component of amniotic fluid after 16 weeks' gestation.
In contrast, a unilateral obstruction, such as a ureteropelvic junction obstruction, does not lead to oligohydramnios, and it carries a universally favorable prognosis provided that the other kidney functions normally.
Among cases of fetal urinary tract obstruction, a fetus with preserved renal function produces more hypotonic urine, whereas one with advanced renal dysfunction is a "salt waster," producing less hypotonic urine.
The usefulness of assessing urine chemistry in fetal obstructive uropathy lies in the separation of fetuses into "good" or "poor" prognostic categories based on preservation of renal function reflected by the tonicity of the fetal urine.
In one study, urine samples taken from fetuses who subsequently had a good outcome revealed levels of Na+ less than 100 mEq/L, Cl less than 90 mEq/L, and osmolarity less than 210 mOsm/L.19 These values were chosen because they were two standard deviations from the mean values of fetuses with a good prognosis.
Fetuses with urine chemistries beyond these values had irreversible renal damage and suffered from severe oligohydramnios and pulmonary insufficiency. The efficacy of these proposed criteria were subsequently confirmed to reflect postnatal outcome and appropriately select fetuses for intervention.
In a separate study, this approach was modified to include three sequential vesicocentesis at 24-hour intervals. This regimen permits a comparative analysis of stagnant urine (first sample) with fresh urine (third sample). Fresh urine samples more accurately reflect fetal renal function, and this approach increases the predictive value of fetal urinary electrolytes.
Urinary b2-microglobulin levels have become an important adjunct in predicting the severity of renal damage. In one study, b2-microglobulin levels below 2 mg/L were found to have as good a predictive value as urinary sodium levels below 70 mEq/L.165.
Furthermore, urinary b2-microglobulin levels may have greater value in predicting the outcome of fetal obstructive uropathy in the absence of oligohydramnios. In one study, b2-microglobulin levels from fetuses with evidence of obstructive uropathy but without oligohydramnios were significantly higher in those who eventually developed renal insufficiency at 1 year of age.
This distinguishing feature may enable the selective antenatal treatment of fetuses with a good prognostic profile who, despite normal amniotic fluid volume, are still at risk for ongoing renal damage.
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The two goals of prenatal intervention in fetal obstructive uropathy are decompression of the obstructed fetal urinary bladder and restoration of amniotic fluid dynamics. Percutaneous vesicoamniotic shunting has been the most common technique used to accomplish these goals with minimal maternal morbidity in patients with isolated lower urinary tract obstruction and a good prognostic profile.
Because of the lack of a prospective, randomized trial, the most difficult question to address in the treatment of fetal obstructive uropathy is the efficacy of prenatal decompression. The only series that attempted to address this question, albeit in a retrospective analysis, was reported by Timothy Crombleholme, MD, FACS, FAAP, and coworkers.
In fetuses predicted to have either good or poor prognoses by fetal urine electrolyte and ultrasound criteria, the survival rate was greater among those decompressed in utero, as opposed to those who were not decompressed. In the group of fetuses predicted to have a poor prognosis by selection criteria, 10 fetuses were treated.
Three of those fetuses were electively terminated, four neonates died from pulmonary hypoplasia or renal dysplasia, and three neonates survived. All three survivors had restoration of normal amniotic fluid levels and no pulmonary complications, but two subsequently developed renal failure and underwent renal transplantation.
Among the 14 patients with no intervention, there were no survivors (11 terminations and three neonatal deaths from pulmonary hypoplasia).
In the group of fetuses predicted to have a good prognosis by selection criteria, nine fetuses were treated, with one elective termination (after the development of procedure-related chorioamnionitis), no deaths, and eight neonatal survivors. Of the seven patients in the good prognosis group who were not treated, five survived and two died after birth. Two of the survivors later developed renal failure.
When oligohydramnios develops during the canalicular stage of lung development (16 to 24 weeks), the fetus usually has pulmonary hypoplasia that precludes survival. When in utero intervention for obstructive uropathy associated with oligohydramnios restores amniotic fluid volume, neonatal demise from pulmonary hypoplasia is clearly averted.
In the group of fetuses reported by Timothy Crombleholme, MD, and coworkers, there was a preponderance of oligohydramnios in the poor prognosis group (23 of 24) compared with the good prognosis group (7 of 16). Despite this, fetuses from the good prognosis group seemed to survive as a direct result of fetal treatment.
In the good prognosis group, six of the seven fetuses with oligohydramnios had intervention, and all six survived with normal renal function. However, the patient with oligohydramnios who was not treated died at birth of pulmonary hypoplasia. In the entire series, uncorrected oligohydramnios was associated with a 100% neonatal mortality rate. Normal or restored amniotic fluid volume was associated with a 94% survival rate.
Although in utero decompression appears to prevent neonatal death from pulmonary hypoplasia, the effect of in utero decompression on renal function is less clear.
The maternal morbidity of vesicoamniotic shunting has been reported to be minimal, but there has been a high incidence (14%) of associated chorioamnionitis. These cases of chorioamnionitis occurred before routine use of prophylactic antibiotics and during a period when long-term (four to 16 hours) bladder catheterization, rather than aspiration, was used for fetal urine sampling.
In addition, there have been reports of shunt-induced abdominal wall defects with herniation of bowel through trocar stab wounds and maternal ascites from leakage of amniotic fluid into the maternal peritoneal cavity.
The usefulness of vesicoamniotic shunts is limited by brief duration of decompression, risk of infection, catheter obstruction or dislodgment, fetal injury during placement, and potentially inadequate decompression of the fetal urinary tract. These factors make vesicoamniotic shunts less appealing for long-term decompression of the urinary tract early in gestation.
In addition, there is a growing appreciation that the longterm outcome of children following vesicoamniotic shunting may be complicated by renal insufficiency, bladder dysfunction, and growth problems. Freedman et al reported outcomes in 14 patients who survived beyond 2 years of age. Renal function was normal in only 6 (43%).
Of the remaining 8 patients, 5 had renal failure requiring kidney transplantation and 3 have chronic renal insufficiency. In 3 of the 4 whose obstructive uropathy was due to posterior urethral valves have required bladder augmentation.
In addition, growth has been a problem with 86% below the 25th percentile and 50% below the 5th percentile. The postnatal problems following vesicoamniotic shunting, including renal failure and bladder dysfunction, have been a catalyst for the development of alternative open fetal surgical or fetoscopic techniques to treat obstructive uropathy in utero.
Dissatisfaction with catheter decompression first led Harrison and colleagues to perform a small series of open fetal procedures for PUVs, initially bilateral ureterostomies, and, subsequently, open vesicostomy.
Open vesicostomy is certainly the most definitive compression of the urinary tract. However, there are increased maternal risks with this approach. These issues have led some investigators to pursue percutaneous fetal cystoscopy and fulguration or laser ablation of PUVs. Although this technique appears to be technically feasible and my have theoretical advantages over shunting, there have been no survivors in the initial experience.
Currently, once the diagnosis and favorable prognostic profile are confirmed, we recommend percutaneous vesicoamniotic shunting for fetal lower urinary tract obstruction.
Fetoscopic cystoscopy is offered as an alternative which be performed to assess the posterior urethra to determine if the fetus is a candidate for laser ablation of valves. Those who are not candidates for laser ablation have a vesicoamniotic shunt placed.
Vesicostomy is rarely employed but might be considered if vesicoamniotic shunting fails to decompress the bladder and restore amniotic fluid dynamics. Experienced ultrasound guidance is essential in vesicoamniotic shunt placement. Furthermore, serial sonography is critical to confirm sustained shunt function, good bladder drainage, decompression of the upper urinary tracts, and normalization of amniotic fluid volume.
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