Diagnosis of urethral obstruction with prenatal magnetic resonance imaging

Ultrasonography is the primary modality used in the prenatal diagnosis of fetal malformations. Most urinary tract abnormalities can be visualized at 18 to 20 weeks of gestation.(1,2) Decreasing amniotic fluid volume can be seen in the second trimester, which is when most urological anomalies are detected. While ultrasonography is cost-effective and readily available, diagnosis of uropathological conditions can be difficult in the presence of oligohydramnios, a common finding in fetal genitourinary abnormalities.(3) Other modalities that can improve prenatal detection of fetal malformations include 3-dimensional (D) ultrasonography and magnetic resonance imaging (MRI) with or without amnio-infusion.(4,5) Amnio-infusion is invasive and is associated with increased risk of chorioamnionitis, premature rupture of the membranes and premature labor. The availability and quality of the examination as well as the skill of the examiner can limit 3-D ultrasound evaluation.(6) 3-D ultrasonography is further impaired by oligohydramnios as in standard 2-D ultrasound evaluation. MRI using ultrafast sequences is useful in late pregnancy, provides excellent soft tissue characterization and can detect fetal abnormalities even in the presence of oligohydramnios.(7) We report the prenatal diagnosis of urethral obstruction with MRI.