Fetal Surgery for Urinary Tract Obstruction

Updated: Dec 18, 2017
  • Author: S Christopher Derderian, MD; Chief Editor: Hanmin Lee, MD  more...
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Overview

Background

Urinary tract obstructions are a common antenatal diagnosis, and outcomes range from clinically insignificant to in-utero fetal demise (IUFD). Many of these patients survive to birth but develop end-stage renal failure, requiring renal replacement therapy and, ultimately, kidney transplantation.

A role for fetal intervention was originally suggested in the 1980s when Harrison’s group demonstrated that urinary diversion could hinder the progression of renal parenchymal damage. [1]  However, determining which patients would benefit from urine diversion has proved challenging and requires an extensive antenatal evaluation.

Vesicoamniotic shunts can be a temporizing measure and provide a survival advantage in a select cohort of fetuses with urinary tract obstruction. In addition, various groups are investigating approaches to treat obstruction of the lower urinary tract via fetal cystoscopy. [2, 3]

This article reviews the diagnosis, evaluation, and treatment strategies for fetal urinary tract obstruction.

Clinically significant urinary tract obstructions occur with a frequency of 1 in 500 live births and are associated with high morbidity and mortality. [4]  With antenatal ultrasonography, urinary tract anomalies can be detected as early as 12-14 weeks’ gestation. These anomalies can be stratified into upper urinary tract obstruction and lower urinary tract obstruction (LUTO).

Common causes of upper urinary tract obstruction include ureteropelvic junction (UPJ) obstruction, ureterovesical junction obstruction, collecting system duplications, multicystic dysplastic kidney, ureterocele/ectopic ureter, and pelvic tumors. Because upper urinary tract obstruction is not currently amenable to fetal intervention, the remainder of this article focuses on LUTO.

Posterior urethral valves (PUVs) account for 9% of all urinary tract obstructions and more than 50% of LUTOs. [5] Other causes of LUTO include urethral atresia (the second most common cause), anterior urethral valves, meatal stenosis, epispadias, and hypospadias. [6]  LUTOs are far more common in males; when identified in females,they  should raise suspicion for cloacal malformations.

LUTO is often diagnosed with antenatal ultrasonography during the first or second trimester. Findings frequently include megacystis, bilateral hydronephrosis, pyelocaliectasis, and oligohydramnios/anhydramnios. The hallmark sonographic finding of PUV is the "keyhole sign," which results from bladder and urethral distention proximal to the valve (see the image below). The presence of a normal volume of amniotic fluid suggests a partial obstruction.

Classic keyhole sign seen in patients with posteri Classic keyhole sign seen in patients with posterior urethra valves

Urinary obstructions can lead to cystic renal dysplasia and impairment of the glomerular and tubular apparatus. In severe cases, oligohydramnios or anhydramnios may ensue, predisposing the fetus to limb abnormalities and pulmonary hypoplasia. Oligohydramnios/anhydramnios associated with urethral obstruction carries a grim prognosis, and when it is identified in the early to middle stages of gestation, mortality approaches 95%. [7] Prognostic indicators such as bladder aspiration, evaluation of refill time, sonographic findings of renal parenchyma, and amniotic fluid volume have proved unreliable. [8, 9, 10]

A retrospective study reviewing different prognostic markers between “poor functioning” kidneys and “good functioning” kidneys on the basis of autopsy or biopsy pathology found that “poor functioning” kidneys had decreased amniotic fluid volume, urine output of less than 2 mL/hr, a urine sodium concentration of more than 100 mEq/L, urine chloride levels of greater than 90 mEq/L, and a urine osmolality level greater than 210 mOsm/L. [11]

Further studies identified calcium, β2 -microglobulin, and total protein as being of prognostic importance. [4]  Repeated fetal urine aspirations, trending osmolarity, and sodium and chloride levels may be of use in deciding which fetuses would benefit from in-utero intervention (see Laboratory Medicine).

The first successful fetal decompression operation for hydronephrosis was an open procedure performed in 1981. [12]  Since then, advances in fetoscopy have eliminated the need for open operations. Current management of LUTO involves ultrasound-guided vesicoamniotic shunt placement under local anesthesia. Amnioinfusion may be required, in that oligohydramnios tends to limit visualization. In addition, various groups have begun to investigate the role of fetoscopic cystoscopy. [3, 2]

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Indications

It has been a challenge to determine which patients would benefit from fetal intervention. Animal models suggest a therapeutic role for in utero intervention. [1, 13]

The relevant role of fetal surgery for LUTO was established after experiments using the fetal lamb, which suggested that resolution of LUTOs improved oligohydramnios and decreased the risk of developing pulmonary hypoplasia. [13] This work demonstrated that obstructing a single ureter (bilateral obstruction led to fetal demise) resulted in impaired renal function and histologic changes as compared with an unobstructed kidney. Furthermore, obstructed fetal kidneys had a decreased glomerular filtration rate (GFR) and increased loss of sodium and chloride. [14] Decompression by end ureterostomy led to improved renal function and fewer histologic changes. [13]

Fetuses with favorable urine electrolyte levels and no indication of renal dysplasia are considered for vesicoamniotic shunting or fetal cystoscopy.

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Contraindications

Contraindications for fetal intervention can be either maternal or fetal.

Maternal contraindications include the following:

  • Frequent contractions
  • Membrane rupture
  • Short cervix
  • Uncontrolled comorbidities that may predispose the patient to preeclampsia or HELLP syndrome

Fetal contraindications include the following:

  • Multiple fetal anomalies
  • Chromosomal abnormalities
  • Anatomic restrictions, including an anterior-lying placenta, which may prohibit safe access
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Technical Considerations

Best practices

Currently, fetal intervention has no role for upper urinary tract obstruction. The algorithm for managing patients with LUTOs is illustrated in the image below. Because the role of fetoscopic cystoscopy is not yet well defined, it is not included. 

Treatment algorithm for fetal lower urinary tract Treatment algorithm for fetal lower urinary tract obstructions. From The Unborn Patient: The Art and Science of Fetal Therapy (p. 272), by Johnson MP, Philadelphia: W.B. Saunders Company. 2001. Adapted with permission.

Antenatal ultrasonography should first be performed to screen for associated anomalies. If no other anomalies are present, fetal karyotyping is recommended. If the patient has a normal male karyotype, the next step is to obtain serial fetal urine samples. If serial electrolyte and β2-microglobulin levels and the total protein profile are favorable, vesicoamniotic shunt placement is recommended.

Deviation from this pathway portends a poor prognosis, and counseling regarding expectations is currently the best practice.

In 2017, Ruano et al proposed a staging system to guide best practice. Stage I is characterized by a normal amniotic fluid index, without renal echogenicity or cortical cysts and with a favorable urinary biochemical profile, and warrants antenatal surveillance. Stage IV is suggested by in-utero renal failure, as defined by anhydramnios and renal dysplasia, and is not survivable. Stage II and III fall between these extremes and are the stages in which vesicoamniotic shunt placement plays a role. [15] Further validation studies are needed, but this proposed staging system offers an opportunity for standardization. 

Procedural planning

Antenatal ultrasonography is an essential component of the LUTO algorithm; anhydramnios poses a challenge to vesicoamniotic shunt deployment, in that the catheter requires a fluid pocket for coiling. Therefore, amnioinfusion is frequently required in severe cases.

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Outcomes

The mortality associated with LUTO ranges from 33% to 75%, depending on coexisting anomalies and the severity of oligohydramnios. [16] The presence of early oligohydramnios carries a mortality ranging from 45% to 80%, [17, 18] likely resulting from pulmonary hypoplasia. Outcome analysis suggests that 25-30% of patients diagnosed with LUTOs required dialysis or renal transplantation. [18, 19]  There appears to be a perinatal advantage to in-utero vesicoamniotic shunt placement in select patients, but more studies are needed to determine the long-term benefit. [20]  

To date, no randomized control trials have compared the success rates of antenatal and postnatal therapy for LUTO. In 1997, a retrospective analysis of 169 successful percutaneous vesicoamniotic shunts placed over a 14-year period calculated the overall survival to be 47%, and 40% of survivors developed end-stage renal disease. [21]

When vesicoamniotic shunts are compared with fetal cystoscopy, reported survival rates are 40% and 75%, respectively. Ruano found that postnatal normal renal function was evident in 50% of those who previously underwent vesicoamniotic shunt placement versus 65% who underwent fetal cystoscopy. [22]  An additional benefit of fetal cystoscopy is that it is an accurate tool for diagnosing the underlying etiology of LUTO. [23]

Although fetal cystoscopy does appear to result in more favorable outcomes than vesicoamniotic shunt placement, only 60 cases have been reported in the literature, and further studies are needed for validation.

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