Prenatal diagnosis of congenital uropathies

Predictive accuracy of prenatal ultrasound findings for lower urinary tract obstruction: A systematic review and Bayesian meta-analysis

BACKGROUND

Lower urinary tract obstruction (LUTO) is a rare but critical fetal diagnosis. Different ultrasound markers have been reported with varying sensitivity and specificity.

AIMS

The objective of this systematic review and meta-analysis was to identify the diagnostic accuracy of ultrasound markers for LUTO.

MATERIALS AND METHODS

We performed a systematic literature review of studies reporting on fetuses with hydronephrosis or a prenatally suspected and/or postnatally confirmed diagnosis of LUTO. Bayesian bivariate random effects meta-analytic models were fitted, and we calculated posterior means and 95% credible intervals for the pooled diagnostic odds ratio (DOR).

RESULTS

A total of 36,189 studies were identified; 636 studies were available for full text review and a total of 42 studies were included in the Bayesian meta-analysis. Among the ultrasound signs assessed, megacystis (DOR 49.15, [15.28, 177.44]), bilateral hydroureteronephrosis (DOR 41.33, [13.36,164.83]), bladder thickening (DOR 13.73, [1.23, 115.20]), bilateral hydronephrosis (DOR 8.36 [3.17, 21.91]), male sex (DOR 8.08 [3.05, 22.82]), oligo- or anhydramnios (DOR 7.75 [4.23, 14.46]), and urinoma (DOR 7.47 [1.14, 33.18]) were found to be predictive of LUTO (Table 1). The predictive sensitivities and specificities however are low and wide study heterogeneity existed.

DISCUSSION

Classically, LUTO is suspected in the presence of prenatally detected megacystis with a dilated posterior urethra (i.e., the keyhole sign), and bilateral hydroureteronephrosis. However, keyhole sign has been found to have modest diagnostic performance in predicting the presence of LUTO in the literature which we confirmed in our analysis. The surprisingly low specificity may be influenced by several factors, including the degree of obstruction, and the diligence of the sonographer at searching for and documenting it during the scan. As a result, providers should consider this when establishing the differential for a fetus with hydronephrosis as the presence or absence of keyhole sign does not reliably rule in or rule out LUTO.

CONCLUSIONS

Megacystis, bilateral hydroureteronephrosis and bladder wall thickening are the most accurate predictors of LUTO. Given the significant consequences of a missed LUTO diagnosis, clinicians providing counselling for prenatal hydronephrosis should maintain a low threshold for considering LUTO as part of the differential diagnosis.

Critical and distinct roles for key RET tyrosine docking sites in renal development

Molecular mechanisms that lead to congenital anomalies of kidneys and the lower urinary tract (CAKUT) are poorly understood. To elucidate the molecular basis for signaling specificity of GDNF-mediated RET signaling in kidney development, we characterized mice that exclusively express either the human RET9 or RET51 isoform, or express these isoforms with individual mutations in docking tyrosines for PTB and SH2-domain-containing adaptors Src (Y981), PLCgamma (Y1015), and Shc (Y1062). Our results provide evidence for differential and isoform-specific roles of these docking sites in murine kidney development. Homozygous Ret(RET9) and Ret(RET51) mice were viable and show normally developed kidneys, indicating redundant roles of human RET isoforms in murine kidney development. In the context of the RET51 isoform, only mutation of the docking Tyr 1015 (Y1015F) resulted in severe renal anomalies. These included bilateral megaureters and multicystic kidneys that were caused by supernumerary ureteric buds that fail to separate from the wolffian duct as well as decreased branching morphogenesis. Similar kidney and ureter defects were observed in RET9(Y1015F) mice that contain the Y1015F mutation in the RET9 isoform. Interestingly, loss of RET9(Y1062)-mediated AKT/MAPK activation resulted in renal agenesis or kidney rudiments, whereas mutation of this residue in RET51 had no obvious effect on AKT/MAPK activity and renal development. These results reveal novel roles of key RET-dependent signaling pathways in embryonic kidney development and provide murine models and new insights into the molecular basis for CAKUT.

Effect of prenatal diagnosis on epidemiologic studies of birth defects

Prenatal diagnostic technology makes it possible to offer women the option of electively terminating pregnancies affected by birth defects. Excluding these pregnancies from epidemiologic studies may affect study results. We explored this effect using examples from the literature. We calculated the bias in the odds ratio caused by excluding prenatally diagnosed pregnancies when the exposure of interest is not correlated with the likelihood of terminating an affected pregnancy and when it is correlated with an increase or decrease in this likelihood. We assumed that control infants did not have birth defects. When the exposure is not associated with the likelihood of a pregnancy termination, studies excluding terminations suffer a loss of precision. When the exposure is associated with an increase or decrease in this likelihood, the odds ratios are biased toward or away from the null, respectively. The magnitude of the bias will vary according to characteristics of the study population such as the prevalence of the exposure and the frequency with which prenatal diagnosis and elective termination are used. Whenever possible, pregnancies terminated after prenatal diagnosis must be included in epidemiologic studies.

Fetal hydrolaparoscopy and endoscopic cystotomy in complicated cases of lower urinary tract obstruction

OBJECTIVE

Vesicoamniotic shunting may be difficult or impossible in selected cases of fetal lower obstructive uropathy. The purpose of this article is to describe the performance of fetal hydrolaparoscopy and endoscopic fetal cystotomy in two fetuses with complicated lower obstructive uropathy.

STUDY DESIGN

Fetal hydrolaparoscopy-endoscopic fetal cystotomy was performed in a patient with a markedly thickened bladder that could not be entered percutaneously. A peritoneoamniotic (bridge) shunt was also placed. Fetal hydrolaparoscopy-endoscopic fetal cystotomy was performed in a second patient with a collapsed bladder from a previous vesicocentesis, because vesicoinfusion resulted in further ascites. Fetal cystoscopy was performed after endoscopic fetal cystotomy, and posterior urethral valves were ablated with neodymium:yttrium-aluminum-garnet laser energy. A vesicoamniotic shunt was left in place.

RESULTS

Adequate bladder drainage was obtained in both cases. The first baby required bilateral nephrotomy and a permanent cystotomy at birth and is scheduled for a bladder expansion procedure at the age of year. The second patient had premature rupture of membranes and fetal death from treatment of this complication 5 days after the original procedure.

CONCLUSION

Fetal hydrolaparoscopy-endoscopic fetal cystotomy can be performed in complicated cases of lower obstructive uropathy. The procedure involves the creation of a defect in the bladder dome under direct endoscopic visualization within a spontaneous or intentional hydroperitoneum. Peritoneoamniotic shunting, vesicoamniotic shunting, or ablation of posterior urethral valves may then be performed. Fetal hydrolaparoscopy-endoscopic fetal cystotomy should be reserved only for complicated cases of lower obstructive uropathy in which conventional vesicoamniotic shunting is not safely possible. Further experience with fetal hydrolaparoscopy-endoscopic fetal cystotomy is necessary to establish its risks and benefits.

In-utero percutaneous cystoscopy in the management of fetal lower obstructive uropathy

In fetuses with lower obstructive uropathy, sonography cannot establish the cause of obstruction. We assessed whether percutaneous fetal cystoscopy could be useful in the evaluation and treatment of obstructive defects in utero. We inserted a fibreoptic endoscope through the lumen of the needle or trocar into the fetal bladder at the time of vesicocentesis or vesicoamniotic-shunt placement and looked at the the urethra, bladder neck, and ureteral orifices. Urethral vesicoamniotic shunting was considered in suitable cases; otherwise a percutaneous shunt was inserted. Fetal cystoscopy was possible in 11 of 13 patients referred. The bladder mucosa appeared haemorrhagic or oedematous in three. The ureteral orifices were seen in 9/11 fetuses, dilation was seen in five, but was only suspected in two by ultrasound. Ureteral webs were noted in two other fetuses. Two of seven fetuses underwent urethral vesicoamniotic shunting; urethral patency was achieved with urethral probing alone in one fetus. The remaining four fetuses were shunted with a standard technique. Fetal cystoscopy helps define the underlying conditions responsible for sonographic findings of lower obstructive uropathy, and allows the introduction of new treatments.

Percutaneous fetal cystoscopy and endoscopic fulguration of posterior urethral valves

Percutaneous fetal cystoscopy was performed in a male fetus with ultrasonographic evidence of lower urinary tract obstruction at 19 weeks of gestation. The diagnosis of posterior urethral valves was confirmed. Percutaneous endoscopic fulguration of the valves was successfully performed at 22 weeks of gestation, and urethral patency was established. This case illustrates the feasibility of performing diagnostic and therapeutic endoscopic procedures within the human fetus for the management of a congenital anomaly. While we believe that fetal cystoscopy may improve our diagnostic, prognostic, and therapeutic capabilities in the management of fetuses with lower obstructive uropathy, studies are needed to establish the actual value, risks, and limitations of this new approach in fetal medicine.