Fetal MRI assessment of posterior fossa anomalies: A review.

Prenatal ultrasound (US) is the first prenatal imaging tool for screening and evaluation of posterior fossa malformations since it is noninvasive, widely available, and safe for both mother and child. Fetal MRI is a widely used secondary technique to confirm, correct, or complement questionable US findings and plays an essential role in evaluating fetuses with suspected US findings and /or positive family history. The main sequences of fetal MRI consist of T2-weighted (T2w) ultrafast, single-shot sequences. Axial, coronal, and sagittal images are typically acquired allowing for a detailed evaluation of the posterior fossa contents. Also, various complimentary sequences, such as T1w, T2*w gradient sequences, or advanced techniques, including diffusion-weighted imaging, diffusion tensor imaging, and magnetic resonance spectroscopy, may provide additional information based on the studied malformation. Inclusion of these techniques should be done with careful risk-benefit analysis. The use of fetal MRI also aims to evaluate for associated anomalies. In addition, prenatal diagnosis of posterior fossa malformations is still a challenge but advances in knowledge in human developmental anatomy, genetic, and imaging recognition patterns have enabled us to shed some light on prognostic information that will help with the counseling of families. Finally, high-resolution late third trimester fetal MRI offers a safe alternative to early postnatal MR imaging, basically taking advantage of the uterine environment as a kind of "maternal incubator." Our goal is to discuss the spectrum of prenatal posterior fossa pathologies that can be studied by fetal MRI and their key neuroimaging features.