MRI for the assessment of the malformed fetus.

Ultrafast MRI sequences have changed the use of MRI for evaluating fetal abnormalities. Currently, the best application is the demonstration of normal fetal brain development and the further definition of suspected brain abnormalities found on ultrasound. MRI differentiates well the various types of fetal ventriculomegaly. Superior posterior fossa visualization allows differentiation of Dandy Walker malformation from a large cisterna magna. Anomalies of the corpus callosum and some disorders of neuronal migration can be seen. MRI is also valuable in the evaluation of fetal giant neck masses for planning delivery of the baby and surgery for life threatening airway obstruction. In the chest, MRI differentiates masses such as diaphragmatic hernia, cystic adenomatoid malformation and sequestration, and aids in planning fetal surgery because MRI directly visualizes the position of the lung, liver and bowel. MRI defines abnormalities of the urinary tract by demonstrating dysplastic pathology in the renal cortex and dilation of the collecting systems. Oligohydramnios does not effect MRI.