Fetal Ultrasound and Fetal MRI in Diagnosing CAKUT

Research study background

Congenital anomalies of the kidney and urinary tract (CAKUT) are one of the most commonly identified anomalies in the prenatal period. CAKUT encompasses a spectrum of disorders — some of which can have significant implications for a child's health. Early and accurate prenatal diagnosis of these anomalies is critical to ensure expectant parents receive sufficient counseling, including discussion of prenatal and postnatal strategies aimed at improving outcomes.

Fetal ultrasound, the gold standard for prenatal diagnosis of CAKUT, is capable of visualizing kidney and bladder findings suggestive of CAKUT on second trimester anatomy scans but cannot determine the specific diagnosis. Fetal magnetic resonance imaging (MRI), with its enhanced imaging capabilities, is increasingly utilized for complex anomalies in conjunction with fetal ultrasounds. However, its diagnostic accuracy for CAKUT is unknown.

A multidisciplinary team of pediatric urology and radiology experts from Children’s Hospital Colorado compared the two imaging modalities for prenatal diagnosis of CAKUT. They retrospectively reviewed data from pregnant patients referred to the Colorado Fetal Care Center for potential CAKUT between 2012 and 2020. Thirty-three fetuses met the study criteria and were included in the analysis. The team categorized prenatal imaging and postnatal diagnoses into kidney, ureteral and/or bladder anomalies and evaluated diagnostic accuracy for identifying postnatal anomalies.

They found fetal MRI was significantly less likely to produce incomplete results than ultrasound (6.7% vs. 12.1%). Fetal MRI had greater sensitivity and negative predictive value for detecting anomalies across all anatomic categories, but overall specificity and positive predictive value was slightly lower compared to ultrasound. Results for ureteral anomalies were the same. In the kidney, the diagnostic accuracy of MRI was higher, except for specificity, which was equivalent to ultrasound. In the bladder, the diagnostic accuracy was the same for both modalities. However, the sample size was too small to reach statistical significance for any of the comparisons between measures of diagnostic accuracy.

Clinical implications

This study demonstrates that fetal MRI could enhance early and accurate diagnosis and supports more routine use as a complementary imaging modality, particularly for kidney and ureteral anomalies. An abstract of these results was presented at the 2024 annual meeting of the American Urology Association, and the team is working to validate their findings with a larger cohort.