Magnetic resonance imaging of the intrauterine fetal genitourinary tract: normal anatomy and pathology.

Although ultrasonography (US) remains the most widely used diagnostic imaging modality for routine evaluation of the fetus, magnetic resonance (MR) imaging has become an invaluable complement to US in all cases in which additional information is desirable. While the ability of US to detect fetal abnormalities is limited in cases such as maternal obesity, oligohydramnios, and in certain fetal positions, MR using fast and ultrafast pulse sequences enables high-quality fetal images to be acquired regardless of the mother's physical condition or fetal position. Fetal genitourinary disorders are the most common intrauterine abnormalities detected by US, accounting for approximately 30% of all antenatally detected anomalies. Although they usually occur in isolation, these defects can form part of more complex syndromes or chromosomopathies, and MR is indicated to rule out associated abnormalities. In some severe genitourinary disorders, there is a severe deficit of amniotic fluid; these cases are associated with other fetal anomalies such as pulmonary hypoplasia and very poor prognosis. In other cases, the amniotic fluid is not compromised, yet the further detection, localization, and characterization of prenatal disorders will have an impact on postnatal follow-up. This article reviews the role of fetal MR in urogenital tract disorders.