Lower urinary tract obstruction: fetal intervention based on prenatal staging

Abstract

The authors present an overview of lower urinary tract obstruction (LUTO) in the fetus with a particular focus on the insult to the developing renal system. Diagnostic criteria along with the challenges in estimating long-term prognosis are reviewed. A proposed prenatal LUTO disease severity classification to guide management decisions with fetal intervention to maintain or salvage in utero and neonatal pulmonary and renal function is also discussed. Stage I LUTO (mild form) is characterized by normal amniotic fluid index after 18 weeks, normal kidney echogenicity, no renal cortical cysts, no evidence of renal dysplasia, and favorable urinary biochemistries when sampled between 18 and 30 weeks; prenatal surveillance is recommended. Stage II LUTO is characterized by oligohydramnios/anhydramnios, hyperechogenic kidneys but absent renal cortical cysts or apparent signs of renal dysplasia and favorable fetal urinary biochemistry; fetal vesicoamniotic shunting (VAS) or fetal cystoscopy is indicated to prevent pulmonary hypoplasia and renal failure. Stage III LUTO is oligohydramnios/anhydramnios, hyperechogenic kidneys with cortical cysts and renal dysplasia and unfavorable fetal urinary biochemistry after serial evaluation; fetal vesicoamniotic shunt may prevent severe pulmonary hypoplasia but not renal failure. Stage IV is characterized by intrauterine fetal renal failure, defined by anhydramnios and ultrasound (US) findings suggestive of severe renal dysplasia, and is associated with death in 24 h of life or end-stage renal disease (ESRD) within the first week of life; fetal vesicoamniotic shunt and fetal cystoscopy are not indicated.

Prediction model of postnatal renal function in fetuses with lower urinary tract obstruction (LUTO)—Development and internal validation

“…A recently published classification system with selection criteria for eligibility for fetal intervention by Ruano et al, approaches the fetus on an individual basis to provide the current best management. This classification system uses fetal renal ultrasound parameters, amniotic fluid volume, and fetal urinalysis separately . However, an individualized estimate of the postnatal renal function is not attempted.…”

Prenatal regenerative fetoscopic interventions for congenital anomalies

“…Conversely, a retrospective study of 72 fetuses with megacystis showed a statistically significant correlation between fetal urinary electrolytes and postnatal renal outcomes 132. The use of fetal urinary biochemistry to evaluate fetal renal function should, therefore, take into account three main considerations: (1) the available evidence is mostly based on studies that evaluated fetal urinary biochemistry during the second trimester; (2) fetal urinary biochemistry is only a “snapshot picture” of fetal renal function, which means that many other factors could influence renal function prenatally and postnatally; and (3) fetal urinary biochemistry is only a part of comprehensive fetal evaluation and should be interpreted along with fetal renal imaging for appropriate staging of disease severity 112133134135136137…”

“…To this end, standardized prenatal LUTO diagnosis using prenatal ultrasound, fetal urine biochemistry, and clinical parameters has been proposed to improve LUTO prognostication 138139140141. A retrospective study133134138 described a prenatal LUTO staging system that correlates with postnatal survival and also proposed fetal intervention according to disease severity (table 2).…”

“…Fetal cystoscopy involves direct visualization of the urinary outflow tract (with a fetoscope) for etiological diagnosis and specific treatment of LUTO113133134135136137144145146147148 (fig 3B). The fetoscope is placed into the bladder outlet (under ultrasound guidance) and pediatric posterior urethral valve (PUV), the commonest etiology of LUTO, can be treated with laser fulguration of occluding membranes 114…”

“…Serial amnioinfusion, which involves repeated infusion of sterile warm saline or lactated Ringer’s solution to restore amniotic fluid, is indicated for stage IV LUTO (intrauterine fetal renal failure) that occurs spontaneously or after fetal VAS (in stage III LUTO), according to our protocol (ClinicalTrials.gov Identifiers: NCT03723564, NCT03101891133134138). It aims to prevent severe pulmonary hypoplasia and perinatal demise, working as a bridge to postnatal dialysis and renal transplantation 150151.…”