Fetal MR imaging in urogenital system anomalies

Abstract

Fetal magnetic resonance imaging (MRI) is an important adjunct to ultrasound in evaluation of fetal urogenital system. While, ultrasound remains the primary modality, MRI helps in more complicated cases or where ultrasound is limited due to technical factors such as poor acoustic window. The goal of this article is to review the common fetal urogenital anomalies and their imaging manifestations on ultrasound and MRI, and discuss how MRI adds diagnostic value.

The use of fetal MRI for renal and urogenital tract anomalies

“…MRI with its superior tissue contrast and large field of view facilitates visualization of the kidneys . On T2W sequences, fetal kidneys are identified as oval structures of intermediate signal intensity on both sides of the spine.…”

“…On T2W sequences, fetal kidneys are identified as oval structures of intermediate signal intensity on both sides of the spine. A long‐T2 rim surrounds the kidney, caused by the peri‐renal fat . The renal cortex has a slightly lower T2 signal when compared to the medulla.…”

“…Normally, the fetal kidney shows restricted diffusion similar to that of the mother's kidneys. Conversely, a functionally impaired kidney demonstrates higher signal on ADC . When DWI is performed with low diffusion sensitization in capillarized tissue, the measured signal attenuation has a second component caused by the microcirculation within the capillary network (intra‐voxel incoherent motion) .…”

“…Multi‐compartment models such as used in adult and pediatric populations are also suitable for fetal applications, but to the best of our knowledge have not yet been attempted. DWI can also be a helpful adjunct to US to confirm an ectopic kidney, in the differential diagnosis of renal agenesis . Lack of a normal DWI bright signal in the renal fossae without evident renal signal elsewhere is consistent with renal agenesis rather than ectopic kidneys .…”

“…DWI can also be a helpful adjunct to US to confirm an ectopic kidney, in the differential diagnosis of renal agenesis . Lack of a normal DWI bright signal in the renal fossae without evident renal signal elsewhere is consistent with renal agenesis rather than ectopic kidneys . It has also been suggested that DWI with ADC determination is useful for predicting renal function in the presence of posterior urethral valves …”