A peek into the uterus: MRI of the fetal CNS

Abstract

The purpose of this article is to provide an overview of MR imaging of the fetal central nervous system, and to briefly discuss recent advances. Fetal MRI has been commonly used throughout the world for over 20 years. Compared to US it has better contrast resolution, allows direct visualization of both hemispheres and the additional limitations of sonography do not affect the quality of MRI. There are no known adverse short-term or long-term side effects of MRI in children, who were imaged in the fetal period. The standard protocol for fetal MRI consists of single-shot rapid acquisition T2 weighted sequences in three planes, fast spoiled gradient recalled T1 weighted sequence, T2 gradient echo sequence and diffusion weighted sequence in the axial plane. The clinical applications of advanced MRI techniques are still limited. Fetal MRI is performed to confirm abnormalities detected on US, and to exclude additional pathology. Interpreting fetal MRI images requires understanding of normal fetal CNS development and one should also evaluate other fetal structures, the umbilical cord and placenta. The most common indication for MR imaging of the fetal CNS is mild ventriculomegaly. Other common indications, that are also discussed in the article, include commissural abnormalities, infratentorial abnormalities, cortical malformations, spinal pathology and complications of monochorionic twin pregnancy. 

Conclusion: Fetal MRI provides important information in prenatal counseling, therefore familiarity with the applications and limitations of fetal MRI, and multidisciplinary collaboration remain essential for the radiologist involved in prenatal imaging.