Neurofetal Counseling for Cerebellar and Posterior Fossa Malformations—Where Do We Stand Today?

Abstract

In this article, Garel et al discuss the main steps of cerebellar development, describe the normal imaging pattern of the fetal cerebellum (by ultrasonography [US] and magnetic resonance imaging [MRI]), and present the main pathologies of the fetal cerebellum as may be diagnosed by fetal imaging—all in an attempt to create a unified terminology for practical aspects of neurofetal counseling. Neurofetal counseling is becoming an important part of the practice of the pediatric neurologist, neurosurgeon, geneticist, and neonatologist. It is truly an issue that has to be addressed by a multidisciplinary task force to combine understanding of neurofetal imaging, laboratory results, postnatal neurodevelopment, and treatment options of certain pathologies—all to facilitate a practical tool for appropriate decision making when a fetal brain abnormality is suspected by fetal ultrasound. Termination of pregnancy is only one aspect of neurofetal counseling; even if abortion is not a valid option in some countries or traditions, counseling is still important, as understanding the precise pathology in a fetus may shed light on a misdiagnosed familial/genetic pathology and may have a practical impact on future pregnancies in the same family. Moreover, neurofetal counseling deals with timing and mode of delivery, to be decided together with the perinatologist, and includes recommendations about further fetal follow-up until expected delivery. For example, progressive ventriculomegaly with increased head circumference and biparietal diameter may dictate elective cesarean section as soon as maturity of the lungs is expected. One of the most important issues for the family is the postnatal prognosis; and in some countries where abortion is allowed, termination of pregnancy may be relevant even in very late stages of gestation if the anticipated prognosis is bad. Thus, a multidisciplinary approach with a common language between the gynecologist/perinatologist, radiologist, and practitioners in all other disciplines is a critical tool for appropriate management. Several factors have changed modern neurofetal counseling: improved ultrasonography including three-dimensional images, the introduction of fetal MRI during the late 1990s, genetic information that is accumulated constantly, and our ability to use late-outcome data regarding neurodevelopment of fetuses suspected to have brain abnormalities. Our treatment options have also improved: preimplantation genetic diagnosis, fetal treatment mainly by fetal surgeries (eg, in fetal meningomyelocele), and major progress in postnatal-surgical options in some fetal pathologies (eg, obstructive hydrocephalus and intracranial cysts, introducing neuroendoscopy into the armamentarium of the pediatric neurosurgeon). Still, the main issue in fetal neurocounseling is to provide a reliable prognosis to an abnormal appearance of a fetal brain. For this to occur, two preconditions are mandatory: (1) better understanding of the ultrasonographic images and (2) accurate interpretation of such images by using a common language among different consultants from several disciplines. One of the main fields with pitfalls in diagnosis and prognostication is the fetal posterior fossa, including the abnormalities of the fetal cerebellum. Magnetic resonance imaging has dramatically changed our understanding of the developing fetal cerebellum and our ability to demonstrate not only anatomy but also processes. A fascinating example is the demonstration of secondary chiari 2 malformation in fetuses with a meningomyelocele that is resolving after fetal surgery. However, issues such as the timing of MRI to demonstrate the posterior fossa and indications for fetal brain MRI are not fully resolved. Thus, even with better quality magnetic resonance images that depict anatomy more accurately, final diagnosis is not always possible. The importance of the cerebellum in normal neurodevelopment is well acknowledged, thanks to several recent reports regarding the association between abnormal child development and anatomical damage to a potentially normal cerebellum in a developing brain (eg, in premature babies with cerebellar hemorrhage). The strong association between abnormal findings