Megacystis in the first trimester of pregnancy: Prognostic factors and perinatal outcomes

Pearls and Pitfalls of First-Trimester US Screening and Prenatal Testing: A Pictorial Review

First-trimester US is imperative in evaluation of early pregnancy to confirm pregnancy location and number and gestational age. The 2024 Society of Radiologists in Ultrasound consensus conference established a first-trimester lexicon to highlight the importance of clear and concise language, which is incorporated and featured by the authors. With improved technologies and understanding of fetal development, first-trimester anatomic studies, between 11 weeks and 13 weeks 6 days gestation, are becoming more frequently used. While not a replacement for the second-trimester anatomic study, systematic evaluation of fetal anatomy at this early gestational age allows detection of 40%-70% of anomalies, whether structural or related to aneuploidy. All patients, regardless of age or baseline risk, should be offered screening and diagnostic testing for chromosomal abnormalities. A variety of prenatal screening approaches are available, each with strengths and limitations. Noninvasive prenatal testing with detection of fetal cell-free DNA can be performed in the first trimester and is the most sensitive and specific screening for the common fetal aneuploidies, but is not equivalent to diagnostic testing. Alternatively, serum analytes for maternal biomarkers in conjunction with nuchal translucency (NT) measurement can be used to calculate a risk estimate for common trisomies. Increased NT is the most common abnormality seen in the first trimester. Positive screening results, increased NT, or other anomaly at US should prompt genetic counseling and be confirmed with diagnostic testing (chorionic villus sampling or amniocentesis). Early detection of aneuploidy and structural anomalies allows counseling and informs decisions for pregnancy management. ©RSNA, 2025 Supplemental material is available for this article.

Intermediate outcomes of children (4-10 years) with postnatally preserved renal function after vesico-amniotic shunt insertion for lower urinary tract obstruction (LUTO)

PURPOSE

The purpose of this retrospective study was to examine the intermediate outcomes and renal development of children (four to ten years) who had undergone prenatal vesico-amniotic shunt insertion (VAS) for lower urinary tract obstruction (LUTO), and later demonstrated preserved kidney function as neonates.

PATIENTS & METHODS

Of 63 fetuses that underwent VAS for LUTO, 47 survived both the pregnancy and the neonatal period. Twenty-four of them were born with preserved renal function as defined by normal laboratory values for creatine, urea, and/or GFR. Twenty of them (83.3 %) were available for our study. We analyzed their pediatric general, surgical, urological, and radiological medical records with a particular emphasize on renal function.

RESULTS

All children of the cohort are still alive. None of the pediatric study subjects have required renal replacement therapy after four to ten years of follow-up. In 90 % of the cases, renal function as defined by laboratory values for creatine, urea, and/or GFR remained preserved. Only two children (10 %) demonstrated impaired renal function.

CONCLUSION

The findings of our retrospective study suggest that when normal laboratory values for creatine, urea, and/or GFR are observed in the neonatal period following prenatal VAS for LUTO, these parameters will likely remain normal in most patients for the first four to ten years of their life. Confirming our previously published novel management strategy, the highest preservation rates can be achieved when after early detection of LUTO, VAS can be performed prior to the completion of 16 weeks of gestation.

Obstructive or non-obstructive megacystis: a prenatal dilemma

Introduction

Diagnosis of prenatal megacystis has a significant impact on the pregnancy, as it can have severe adverse effects on fetal and neonatal survival and renal and pulmonary function. The study aims to investigate the natural history of fetal megacystis, to try to differentiate in utero congenital lower urinary tract obstruction (LUTO) from non-obstructive megacystis, and, possibly, to predict postnatal outcome.

Materials and methods

A retrospective single-center observational study was conducted from July 2015 to November 2023. The inclusion criteria were a longitudinal bladder diameter (LBD) >7 mm in the first trimester or an overdistended/thickened-walled bladder failing to empty in the second and third trimesters. Close ultrasound follow-up, multidisciplinary prenatal counseling, and invasive and non-invasive genetic tests were offered. Informed consent for fetal autopsy was obtained in cases of termination of pregnancy or intrauterine fetal demise (IUFD). Following birth, neonates were followed up at the same center. Patients were stratified based on diagnosis: LUTO (G1), urogenital anomalies other than LUTO ("non-LUTO") (G2), and normal urinary tract (G3).

Results

This study included 27 fetuses, of whom 26 were males. Megacystis was diagnosed during the second and third trimesters in 92% of the fetuses. Of the 27 fetuses, 3 (11.1%) underwent an abortion, and 1 had IUFD. Twenty-three newborns were live births (85%) at a mean gestational age (GA) of 34 ± 2 weeks. Two patients (neonates) died postnatally due to severe associated malformations. Several prenatal parameters were evaluated to differentiate patients with LUTO from those with non-LUTO, including the severity of upper tract dilatation, keyhole sign, oligohydramnios, LBD, and GA at diagnosis. However, none proved predictive of the postnatal diagnosis. Similarly, none of the prenatal parameters evaluated were predictive of postnatal renal function.

Discussion

The diagnosis of megacystis in the second and third trimesters was associated with live births in up to 85% of cases, with LUTO identified as the main cause of fetal megacystis. This potentially more favorable outcome, compared to the majority reported in literature, should be taken into account in prenatal counseling. Megacystis is an often misinterpreted antennal sign that may hide a wide range of diagnoses with different prognoses, beyond an increased risk of adverse renal and respiratory outcomes.

Single-center outcome analysis of 46 fetuses with megacystis after intrauterine vesico-amniotic shunting with the Somatex®intrauterine shunt

OBJECTIVES

To assess the spectrum of underlying pathologies, the intrauterine course and postnatal outcome of 46 fetuses with megacystis that underwent intrauterine vesico-amniotic shunting (VAS) with the Somatex® shunt in a single center.

METHODS

Retrospective analysis of 46 fetuses with megacystis that underwent VAS either up to 14 + 0 weeks (early VAS), between 14 + 1 and 17 + 0 weeks (intermediate VAS) or after 17 + 0 weeks of gestation (late VAS) in a single tertiary referral center. Intrauterine course, underlying pathology and postnatal outcome were assessed and correlated with the underlying pathology and gestational age at first VAS.

RESULTS

46 fetuses underwent VAS, 41 (89%) were male and 5 (11%) were female. 28 (61%) fetuses had isolated and 18 (39%) had complex megacystis with either aneuploidy (n = 1), anorectal malformations (n = 6), cloacal malformations (n = 3), congenital anomalies overlapping with VACTER association (n = 6) or Megacystis-Microcolon Intestinal-Hypoperistalsis Syndrome (MMIHS) (n = 2). The sonographic 'keyhole sign' significantly predicted isolated megacystis (p < 0.001). 7 pregnancies were terminated, 4 babies died in the neonatal period, 1 baby died at the age of 2.5 months and 34 (74%) infants survived until last follow-up. After exclusion of the terminated pregnancies, intention-to-treat survival rate was 87%. Mean follow-up period was 24 months (range 1-72). The underlying pathology was highly variable and included posterior urethral valve (46%), hypoplastic or atretic urethra (35%), MMIHS or prune belly syndrome (10%) and primary vesico-ureteral reflux (2%). In 7% no pathology could be detected postnatally. No sonographic marker was identified to predict the underlying pathology prenatally. 14 fetuses underwent early, 24 intermediate and 8 late VAS. In the early VAS subgroup, amnion infusion prior to VAS was significantly less often necessary (7%), shunt complications were significantly less common (29%) and immediate kidney replacement therapy postnatally became less often necessary (0%). In contrast, preterm delivery ≤ 32 + 0 weeks was more common (30%) and survival rate was lower (70%) after early VAS compared to intermediate or late VAS. Overall, 90% of liveborn babies had sufficient kidney function without need for kidney replacement therapy until last follow-up, and 95% had sufficient pulmonary function without need for mechanical respiratory support. 18% of babies with complex megacystis suffered from additional health restrictions due to their major concomitant malformations.

CONCLUSIONS

Our data suggest that VAS is feasible from the first trimester onward. Early intervention has the potential to preserve neonatal kidney function in the majority of cases and enables neonatal survival in up to 87% of cases. Despite successful fetal intervention, parents should be aware of the potential of mid- or long-term kidney failure and of additional health impairments due to concomitant extra-renal anomalies that cannot be excluded at time of intervention.

Troubleshooting Tips for Diagnosing Complex Fetal Genitourinary Malformations

Fetal genitourinary anomalies can present a diagnostic challenge for the radiologist. The absence of a normally located kidney may represent agenesis or be secondary to a fusion or migration abnormality. A dilated renal pelvis should prompt evaluation for a specific cause, including ureteropelvic junction obstruction, reflux, or an obstructed duplicated system. Cystic parenchymal changes are characteristic of a multicystic dysplastic kidney but may also be seen in obstructive cystic dysplasia. There are numerous causes of megacystis including chromosomal (trisomy 18 syndrome), obstruction (posterior urethral valves, urethral atresia), or muscular dysfunction (prune belly syndrome, megacystis microcolon intestinal hypoperistalsis syndrome). Important mimics of a large bladder include hydrocolpos and urogenital sinus or cloacal malformation. Complications of genitourinary malformations are common and include oligohydramnios, urinary ascites, and urinoma. Making an accurate diagnosis often requires additional US views beyond those obtained in the standard fetal survey and occasionally performing fetal MRI. The appropriate use of orthogonal T2-weighted sequences, in conjunction with diffusion-weighted images for evaluation of the kidneys and gradient-recalled-echo sequences for evaluation of T1-hyperintense meconium in the colon, can play an integral role in diagnosis. Accurate diagnosis of fetal genitourinary malformations is vital to direct patient counseling and pregnancy management as outcomes are highly variable. Some conditions can be surgically corrected quite simply, some require multiple complex procedures, and some are lethal. The authors offer troubleshooting tips to narrow the differential diagnosis for four observations: unilateral absent kidney, dilated renal pelvis, cystic renal parenchyma, and megacystis and its mimics. ©RSNA, 2023 Test Your Knowledge questions are available in the Online Learning Center.

Fetal Megacystis: Associated Structural Abnormalities and Obstetric Outcomes

Purpose: We evaluated the obstetrical outcomes, ultrasonographic characteristics, and final diagnosis in pregnancies with fetal megacystis (FM). Methods: We evaluated the obstetrical outcomes and associated structural abnormalities of fetuses with FM detected between FM between 2000 and 2021. Results: 17 FM were diagnosed, 16 had follow up. 16 were early megacystis. 14/16 (87.5%) of pregnancies were terminated, 1/16 (6.25%) resulted in intrauterine death, and 1/16 (6.25%) survived. FM was associated with 13 other abnormal sonographic findings in 12/16 (75%) pregnancies. The most common associated ultrasound abnormality was umbilical cord cyst in 3/16 (18.75%). Recognized etiologies included posterior urethral valves (2), trisomy 18 (2), trisomy 13 (1), Prune Belly syndrome (1), and Megacystis-Microcolon-Hypoperistalsis syndrome (1). Conclusion: Most FM are detected in the 2nd trimester, most are electively terminated, are associated with other ultrasonic abnormalities in 75%, most commonly umbilical cord cyst, and have an identifiable cause in 44%.