Fetal MRI assessment of posterior fossa anomalies: A review

Abstract

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.

Prenatal magnetic resonance imaging of cerebellar dysplasia or malformations and coexistent malformations: A retrospective study in a single institution

“…Blake's pouch cysts (Fig. 6) are occasionally di cult to differentiate from Dandy-Walker malformations (previously known as Dandy-Walker variants) to some extent because the presence of inferior vermis is rarely de ned [9,11]. The different point of our ndings from the reported literature was that the obstructive hydrocephalus sign was not seen in any diagnosed Blake's cyst cases.…”

“…This condition is easily confused and encountered in foetuses at early gestational age. Miller E et al thought that the diagnosis of vermian dysplasia should be made very cautiously on MR in the early second trimester, and follow-up studies were helpful to thoroughly evaluate the growth of the vermis [9]. We agreed with this view given that in foetuses with GA between 20 and 24 gestational weeks, the morphology of the vermis may change variably.…”

“…The different point of our ndings from the reported literature was that the obstructive hydrocephalus sign was not seen in any diagnosed Blake's cyst cases. It has been reported that isolated Blake's pouch cyst has a good prognosis given a high probability of intrauterine resolution and normal growth in almost all cases [9]. Tethered cord syndrome is another common nervous system malformation that often involves intracranial compartments (tonsil hernia or hydrocephaly) [21].…”

“…As early as approximately 5-6 gestational weeks, the cerebellum and brainstem start to develop from the mesencephalon and rhombencephalon, which can be observed on US from the tenth gestational week [9].…”

“…For non-CNS anomalies, US had the similar diagnostic performance compared to MRI and for all anomalies, three-dimensional US had the highest speci city [4]. Regardless of both foetal and maternal body position, high soft tissue resolution and arbitrary scanning planes are the main characteristics of MR that are superior to US [8,9]. The major disadvantages of MR scans include requirements for trained dedicated radiologists and technicians, high examination fees and limited availability (currently, only most tertiary centres are equipped).…”