Hindbrain morphometry and choroid plexus position in differential diagnosis of posterior fossa cystic malformations

'Choroid bar': easy-to-seek marker of normal posterior fossa at 12-14 weeks' gestation

OBJECTIVES

Our objectives were: (1) to assess the visualization rate of the choroid bar in a consecutive series of 306 first-trimester scans; (2) to verify, in this cohort of fetuses, the normality of the posterior fossa later in pregnancy; and (3) to confirm the non-visualization of the choroid bar in a retrospective series of fetuses with posterior fossa malformations.

METHODS

This study included a prospective and a retrospective series. The former comprised 306 fetuses undergoing routine obstetric ultrasound at our unit in both the first and second trimesters over a 6-month period, while the latter comprised 12 cases of posterior fossa malformations. In the prospective study, the presence of the choroid bar, which is defined as a visually continuous, homogeneously hyperechogenic, thick structure bridging the cisterna magna from side to side, was evaluated at the end of the first-trimester nuchal translucency scan. In the retrospective study, previously acquired three-dimensional volume datasets were processed in order to assess whether the choroid bar could be visualized in cases of open spinal dysraphisms and vermian cystic anomalies. In the prospective study, confirmation of a normal posterior fossa was based on the sonographic features of this anatomical region at the time of the second-trimester anomaly scan at 19-21 weeks' gestation, while, in the retrospective study, it was based on autopsy results, when available, or further direct imaging of the defect later in pregnancy.

RESULTS

In the prospective study, the choroid bar could be visualized in all 306 fetuses, on transabdominal ultrasound in 287 (93.8%) cases and on transvaginal ultrasound in 19 (6.2%) cases. The choroid bar was displayed with a ventral/dorsal approach in 67 (21.9%) cases, with a lateral approach in 56 (18.3%) cases and with both in 183 (59.8%) cases. All 306 cases were confirmed to have a sonographically normal posterior fossa at 19-21 weeks. On the other hand, in the retrospective study, it was not possible to visualize the choroid bar in any of the fetuses with posterior fossa malformations.

CONCLUSIONS

We have described a new sign, the choroid bar, consistent with a normal posterior fossa at 12-14 weeks' gestation. The choroid bar provides the option of screening for major abnormalities of the posterior fossa, since its absence raises suspicion of both open spinal dysraphisms and posterior fossa cystic malformations. At the same time, it is easy to visualize, as it can be seen with all lines of insonation. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

ChOP-CT: quantitative morphometrical analysis of the Hindbrain Choroid Plexus by X-ray micro-computed tomography

The Hindbrain Choroid Plexus is a complex, cerebrospinal fluid-secreting tissue that projects into the 4th vertebrate brain ventricle. Despite its irreplaceability in the development and homeostasis of the entire central nervous system, the research of Hindbrain Choroid Plexus and other Choroid Plexuses has been neglected by neuroscientists for decades. One of the obstacles is the lack of tools that describe the complex shape of the Hindbrain Choroid Plexus in the context of brain ventricles. Here we introduce an effective tool, termed ChOP-CT, for the noninvasive, X-ray micro-computed tomography-based, three-dimensional visualization and subsequent quantitative spatial morphological analysis of developing mouse Hindbrain Choroid Plexus. ChOP-CT can reliably quantify Hindbrain Choroid Plexus volume, surface area, length, outgrowth angle, the proportion of the ventricular space occupied, asymmetries and general shape alterations in mouse embryos from embryonic day 13.5 onwards. We provide evidence that ChOP-CT is suitable for the unbiased evaluation and detection of the Hindbrain Choroid Plexus alterations within various mutant embryos. We believe, that thanks to its versatility, quantitative nature and the possibility of automation, ChOP-CT will facilitate the analysis of the Hindbrain Choroid Plexus in the mouse models. This will ultimately accelerate the screening of the candidate genes and mechanisms involved in the onset of various Hindbrain Choroid Plexus-related diseases.

Impact of choroid plexus size in prenatal diagnosis of normal and abnormal closure of fourth ventricle

OBJECTIVE

To assess the role of the choroid plexus (CP) of the fourth ventricle (4V) in fetuses with an open 4V and a normal cerebellar vermis.

METHODS

Two groups of patients were recruited in two fetal medicine referral centers. The prospectively collected control group included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome, recruited in the period between 2019 and 2022. The study group was selected retrospectively by searching our databases to identify all cases with an isolated open 4V and normal anatomy and size of the cerebellar vermis. The inclusion criteria of the study group were: (1) gestational age between 20 and 22 weeks; (2) a brainstem-vermis angle ≥ 18° in the midsagittal plane with an otherwise normal cerebellum and vermis; (3) 4V-CP visible and seen separately from the vermis; (4) absence of other intra- and extracranial anomalies; and (5) available prenatal and/or postnatal magnetic resonance imaging (MRI) data.

RESULTS

In 169 cases of the control group, the 4V-CP was seen separately from the cerebellar vermis and was noticed to progressively fill the space caudal to the 4V, between the vermis and brainstem. From 12 to 22 weeks, the surface areas of the vermis and medial portion of the 4V-CP increased progressively with advancing gestation (P < 0.0001). Intra- and interobserver correlation analysis showed good reproducibility for the measurements. Among the cases with an open 4V and a normal vermis, it was retrospectively feasible to visualize the 4V-CP separately from the inferior part of the vermis in 41 fetuses. In five of these cases, the open 4V was due to a small CP. In all 41 fetuses, the diagnosis on MRI was isolated upward rotation of the cerebellar vermis, and no additional anomaly was found.

CONCLUSIONS

Closure of the 4V is dependent on the 4V-CP and not only the cerebellar vermis. In fact, a small CP may represent another cause of an open 4V. Therefore, separate visualization of the 4V-CP and cerebellar vermis is crucial to improve discrimination between the different causes of an open 4V at the anomaly scan and its clinical implications. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Second trimester fetal MRI of the brain: Through the ground glass

Fetal MRI is an important tool for the prenatal diagnosis of brain malformations and is often requested after second-trimester ultrasonography reveals a possible abnormality. Despite the immature state of the fetal brain at this early stage, early suggestive signs of the presence of brain malformations can be recognized. To differentiate between the normal dynamics of the growing brain and the developing pathological conditions can be challenging and requires extensive knowledge of normal central nervous system developmental stages and their neuroradiological counterparts at those different stages. This article reviews the second-trimester appearances of some commonly encountered brain malformations, focusing on helpful tricks and subtle signs to aid in the diagnosis of such conditions as rhombencephalosynapsis, various causes of vermian rotation, molar tooth spectrum anomalies, diencephalic-mesencephalic junction dysplasia, ganglionic eminence anomalies, and the most common malformations of cortical development.

A myriad of posterior fossa cysts: A single center experience

Antenatal posterior fossa cystic lesions are intimidating due to overlapping imaging features of benign and severe malformations. Sonographic assessment of the posterior fossa with good resolution median sagittal and axial views, either primary or secondarily reconstructed, plays the lead role in antenatal evaluation, further enhanced when sequential assessments are added. We present 10 cases of fetal posterior fossa cystic lesions diagnosed in the first and second trimesters that were sequentially analyzed and followed up till delivery or termination. The ultrasound imaging appearance, evolution, and morphometry have been presented in this article.

Refining the Neuroimaging Definition of the Dandy-Walker Phenotype

BACKGROUND AND PURPOSE

The traditionally described Dandy-Walker malformation comprises a range of cerebellar and posterior fossa abnormalities with variable clinical severity. We aimed to establish updated imaging criteria for Dandy-Walker malformation on the basis of cerebellar development.

MATERIALS AND METHODS

In this multicenter study, retrospective MR imaging examinations from fetuses and children previously diagnosed with Dandy-Walker malformation or vermian hypoplasia were re-evaluated, using the choroid plexus/tela choroidea location and the fastigial recess shape to differentiate Dandy-Walker malformation from vermian hypoplasia. Multiple additional measures of the posterior fossa and cerebellum were also obtained and compared between Dandy-Walker malformation and other diagnoses.

RESULTS

Four hundred forty-six examinations were analyzed (174 fetal and 272 postnatal). The most common diagnoses were Dandy-Walker malformation (78%), vermian hypoplasia (14%), vermian hypoplasia with Blake pouch cyst (9%), and Blake pouch cyst (4%). Most measures were significant differentiators of Dandy-Walker malformation from non-Dandy-Walker malformation both pre- and postnatally (P < .01); the tegmentovermian and fastigial recess angles were the most significant quantitative measures. Posterior fossa perimeter and vascular injury evidence were not significant differentiators pre- or postnatally (P > .3). The superior posterior fossa angle, torcular location, and vermian height differentiated groups postnatally (P < .01), but not prenatally (P > .07).

CONCLUSIONS

As confirmed by objective measures, the modern Dandy-Walker malformation phenotype is best defined by inferior predominant vermian hypoplasia, an enlarged tegmentovermian angle, inferolateral displacement of the tela choroidea/choroid plexus, an obtuse fastigial recess, and an unpaired caudal lobule. Posterior fossa size and torcular location should be eliminated from the diagnostic criteria. This refined phenotype may help guide future study of the numerous etiologies and varied clinical outcomes.

Regulation of choroid plexus development and its functions

The choroid plexus (ChP) is an extensively vascularized tissue that protrudes into the brain ventricular system of all vertebrates. This highly specialized structure, consisting of the polarized epithelial sheet and underlying stroma, serves a spectrum of functions within the central nervous system (CNS), most notably the production of cerebrospinal fluid (CSF). The epithelial cells of the ChP have the competence to tightly modulate the biomolecule composition of CSF, which acts as a milieu functionally connecting ChP with other brain structures. This review aims to eloquently summarize the current knowledge about the development of ChP. We describe the mechanisms that control its early specification from roof plate followed by the formation of proliferative regions-cortical hem and rhombic lips-feeding later development of ChP. Next, we summarized the current knowledge on the maturation of ChP and mechanisms that control its morphological and cellular diversity. Furthermore, we attempted to review the currently available battery of molecular markers and mouse strains available for the research of ChP, and identified some technological shortcomings that must be overcome to accelerate the ChP research field. Overall, the central principle of this review is to highlight ChP as an intriguing and surprisingly poorly known structure that is vital for the development and function of the whole CNS. We believe that our summary will increase the interest in further studies of ChP that aim to describe the molecular and cellular principles guiding the development and function of this tissue.

Position of the choroid plexus of the fourth ventricle in first- and second-trimester fetuses: a novel approach to early diagnosis of cystic posterior fossa anomalies

OBJECTIVE

To describe the sonographic appearance and position of the choroid plexus of the fourth ventricle (4V-CP) between 12 and 21 weeks' gestation in normal fetuses and in fetuses with Dandy-Walker malformation (DWM) or Blake's pouch cyst (BPC).

METHODS

The study population comprised 90 prospectively recruited normal singleton pregnancies and 41 pregnancies identified retrospectively from our institutional database that had a suspected posterior fossa anomaly at 12-13 weeks' gestation based on the ultrasound finding of abnormal hindbrain spaces. In all cases the final diagnosis was confirmed by prenatal and/or postnatal magnetic resonance imaging or postmortem examination. All pregnancies underwent a detailed ultrasound assessment, including a dedicated examination of the posterior fossa, at 12-13 weeks, 15-16 weeks and 20-21 weeks of gestation. Two-dimensional ultrasound images of the midsagittal and coronal views of the brain through the posterior fontanelle and three-dimensional volume datasets were obtained. Multiplanar orthogonal image correlation with volume contrast imaging was used as the reference visualization mode. Two independent operators, blinded to the fetal outcome, were asked to classify the 4V-CP as visible or not visible in both normal and abnormal cases, and to assess if the 4V-CP was positioned inside or outside the cyst in fetuses with DWM and BPC.

RESULTS

Of the 41 fetuses with apparently isolated cystic posterior fossa anomaly in the first trimester, eight were diagnosed with DWM, 29 were diagnosed with BPC and four were found to be normal in the second trimester. The position of the 4V-CP differed between DWM, BPC and normal cases in the first- and second-trimester ultrasound examinations. In particular, in normal fetuses, no cyst was present and, in the midsagittal and coronal planes of the posterior fossa, the 4V-CP appeared as an echogenic oval-shaped structure located inside the 4V apparently attached to the cerebellar vermis. In fetuses with DWM, the 4V-CP was not visible in the midsagittal view because it was displaced inferolaterally by the cyst. In contrast, in the coronal view of the posterior brain, the 4V-CP was visualized in all cases with DWM at 12-13 weeks, with a moderate decrease in the visualization rate at 15-16 weeks (87.5%) and at 20-21 weeks (75%). In the coronal view, the 4V-CP was classified as being outside the cyst in all DWM cases at 12-13 weeks and in 87.5% and 75% of cases at 15-16 and 20-21 weeks, respectively. In fetuses with BPC, the 4V-CP was visualized in all cases in both the midsagittal and coronal views at 12-13 weeks and in 100% and 96.6% of cases, respectively, at 15-16 weeks. In the coronal view, the 4V-CP was classified as being inside the cyst in 28 (96.6%), 27 (93.1%) and 25 (86.2%) cases at 12-13, 15-16 and 20-21 weeks, respectively. The medial segment of the 4V-CP was visualized near the inferior part of the vermis.

CONCLUSIONS

Our study shows that longitudinal ultrasound assessment of the 4V-CP and its temporal changes from 12 to 21 weeks is feasible. The 4V-CP is located inside the cyst, just below the vermis, in BPC and outside the cyst, inferolaterally displaced and distant from the vermian margin, in DWM, consistent with the pathogenesis of the two conditions. The position of the 4V-CP is a useful sonographic marker that can help differentiate between DWM and BPC as early as in the first trimester of pregnancy. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Taenia-tela choroidea complex and choroid plexus location help distinguish Dandy-Walker malformation and Blake pouch cysts

BACKGROUND

Dandy-Walker malformation and Blake pouch cysts can have overlapping imaging features. The choroid plexus and associated taenia-tela choroidea complex are displaced inferolaterally in Dandy-Walker malformation and below the vermis in Blake pouch cysts.

OBJECTIVE

To determine the normal fetal and postnatal MR appearance of the choroid plexus and taenia-tela choroidea complex, and whether their location can help distinguish Dandy-Walker malformation from Blake pouch cysts.

MATERIALS AND METHODS

In this retrospective study, we evaluated brain MR exams from normal-appearing fetuses (gestational age 19-38 weeks) and infants, fetal and postnatal exams in Blake pouch cysts and Dandy-Walker malformation, and ambiguous cases equivocal for mild Dandy-Walker malformation and Blake pouch cysts. We documented choroid plexus and the taenia-tela choroidea complex location and axial and sagittal angles in each case. Then we contrasted and compared the original and updated fetal diagnoses based on taenia-tela choroidea complex and choroid plexus positions.

RESULTS

The choroid plexus location and the taenia-tela choroidea complex location and angles varied significantly among normal exams, Blake pouch cyst exams and Dandy-Walker malformation exams (P<0.01). Dandy-Walker malformation showed inferolateral displacement of the taenia-tela choroidea complex and choroid plexus distant from the vermis. Adding the taenia-tela choroidea complex and choroid plexus into the assessment improved diagnostic accuracy, especially in ambiguous cases.

CONCLUSION

The location of the taenia-tela choroidea complex and choroid plexus provided additional diagnostic neuroimaging clues that could be used in conjunction with other conventional findings to distinguish Dandy-Walker malformation and Blake pouch cysts. Normal, Blake pouch cyst, and Dandy-Walker malformation cases differed with regard to taenia-tela choroidea complex and choroid plexus position. Inferolateral taenia-tela choroidea complex displacement distant from the vermian margin was characteristic of Dandy-Walker malformation.

Isolated Upward Rotation of the Fetal Cerebellar Vermis (Blake's Pouch Cyst) Is a Normal Variant: An Analysis of 111 Cases

INTRODUCTION

The objective of the study was to provide more detailed data about fetal isolated upward rotation of the cerebellar vermis rotation (Blake's pouch cyst) in particular regarding pregnancy outcome.

METHODS

This is a retrospective study of all cases of fetal isolated upward rotation of the cerebellar vermis (URCV) diagnosed in 3 referral centers in Italy from January 2009 to November 2019. Whenever possible, prenatal magnetic resonance imaging (MRI) was performed and a fetal karyotype was obtained. A detailed follow-up was obtained by consultation of medical records, interview with the parents, and the pediatricians.

RESULTS

Our study population included 111 patients with a prenatal diagnosis of isolated URCV made at a median gestational age of 21 weeks +3 days (interquartile range (IQR) 21 + 0-22 + 2). The median brain stem-vermis (BV) angle was 27° (IQR 24-29°). In 37.9% of the cases, a regression of the finding with restoration of normal anatomy was noted at a follow-up scan or at postnatal checks. A BV angle of 25° or less predicted regression with a probability in excess of 90%. MRI was performed in utero or at birth in 101 patients and always confirmed sonographic diagnosis. Fetal CGH array and/or karyotype was available in 97 cases and was always normal, but in 1 case. A postnatal follow-up was available in 102 infants (mean 7 months, range 0-10 years of age) and documented a normal neurologic development in all the cases.

CONCLUSIONS

Isolated URCV is most likely a normal variant of fetal anatomy without clinical consequences, at least at an early follow-up. A BV angle of 25° or less predicts intrauterine regression of the finding, but the outcome is good in all the cases. When a confident sonographic diagnosis is made, MRI is not mandatory. The risk of a chromosomal anomaly in these cases is probably low.

The Role of Fetal MRI for Suspected Anomalies of the Posterior Fossa

BACKGROUND

Posterior fossa anomalies can be diagnostic dilemmas during the fetal period. The prognosis for different diagnoses of the posterior fossa varies widely. We investigated whether fetal magnetic resonance imaging (MRI) and prenatal neurology consultation led to an alternate prognosis for fetuses referred due to concern for a fetal posterior fossa anomaly and concordance between pre- and postnatal diagnoses.

METHODS

This is a retrospective study of cases referred to the Prenatal Pediatrics Institute at Children's National Hospital from January 2012 to June 2018 due to concern for posterior fossa anomaly. Each encounter was scored for change in prognosis based upon clinical and fetal MRI report. Postnatal imaging was compared with prenatal imaging when available.

RESULTS

In total, 180 cases were referred for fetal posterior fossa anomalies based on outside obstetric ultrasound and had both fetal MRI and a neurology consultation. Fetal MRI and neurology consultation resulted in a change in fetal prognosis in 70% of cases. The most common referral diagnosis in our cohort was Dandy-Walker continuum, but it was not often confirmed by fetal MRI. In complex cases, posterior fossa diagnosis and prognosis determined by fetal MRI impacted choices regarding pregnancy management. Postnatal imaging was obtained in 57 (47%) live-born infants. Fetal and postnatal prognoses were similar in 60%.

CONCLUSIONS

Fetal diagnosis affects pregnancy management decisions. The fetal-postnatal imaging agreement of 60% highlights the conundrum of balancing the timing of fetal MRI to provide the most accurate diagnosis of the posterior fossa abnormalities in time to make pregnancy management decisions.

Brain views that benefit from three-dimensional ultrasound

PURPOSE OF REVIEW

Fetal central nervous system malformations are among the most common congenital anomalies. Whereas simple axial views are sufficient for basic fetal brain examination, other important views are essential for a more detailed examination, which are sometimes challenging to obtain. Three-dimensional ultrasound can be helpful in obtaining standardized and reproducible images of many difficult fetal brain views. The aim of the present review is to explore the most recent evidence on the utility and technique of three-dimensional ultrasound in the examination of the fetal brain, with particular emphasis on the brain views that benefit from three-dimensional ultrasound.

RECENT FINDINGS

The article describes the various techniques of acquisition and analyses of three-dimensional ultrasound volumes of the fetal brain and their usefulness in the assessment of normal and abnormal fetal brain anatomy. Three-dimensional ultrasound has also permitted the application of many new technologies, such as artificial intelligence and deep machine learning. Recently, thanks to high-quality three-dimensional ultrasound, fetal cortical development can be assessed quantitatively and reliably.

SUMMARY

Three dimensional ultrasound can help as a complementary tool to two-dimensional ultrasound in the assessment of the fetal brain development and malformations. In addition, it paves the way for the application of promising technologies in the evaluation of fetal brain.

VIDEO ABSTRACT

A video summarizing the findings of the article. The video illustrates the various approaches and techniques applied for the examination of the fetal brain using three-dimensional ultrasound. Furthermore, the advantages and future perspectives of the application of three-dimensional ultrasound in the examination of the fetal brain are discussed, http://links.lww.com/COOG/A74.

Prenatal visualisation of the torcular herophili by means of a Doppler technology highly sensitive for low-velocity flow in the expert assessment of the posterior fossa: a prospective study

OBJECTIVE

To evaluate the usefulness of a Doppler technology highly sensitive for low-velocity flow in the antenatal imaging of the torcular herophili (TH) in the second trimester of pregnancy.

DESIGN

Prospective study.

SETTING

Referral Fetal Medicine Unit.

POPULATION

Non-consecutive series of singleton pregnancies submitted to antenatal neurosonogram between 20 and 28 weeks of gestation.

METHODS

A midsagittal section of the fetal brain was obtained by insonating through the anterior fontanelle, then the MV-Flow™ and LumiFlow™ presets were selected to visualise the TH as the posterior confluence of the superior sagittal sinus and the straight sinus.

MAIN OUTCOME MEASURES

Evaluation of the anatomic relationship of the TH with the 'transpalatal line' joining the upper bony palate to the fetal skull.

RESULTS

A total of 99 pregnant women were recruited, including one fetus with open spina bifida, one with Dandy-Walker malformation (DWM) and two with Blake's pouch cysts. In normal fetuses, the TH appeared to lie on or just below the 'transpalatal line'. In the cases of Blake's pouch cyst, the position of the TH appeared normal if compared with controls, whereas in DWM a supra-elevated position of the TH in respect of the transpalatal line was demonstrated. Finally, in the fetus with Chiari II malformation the TH was identified below the 'transpalatal plane'.

CONCLUSIONS

Prenatal ultrasound visualisation of the TH by means of newly developed Doppler technologies characterised by high sensitivity for low-velocity flow is feasible and allows the indirect evaluation of the insertion of cerebellar tentorium in the second trimester.

TWEETABLE ABSTRACT

Prenatal imaging of the torcular herophili using a Doppler technology highly sensitive for low-velocity flow.

Quantitative fetal magnetic resonance imaging assessment of cystic posterior fossa malformations

OBJECTIVE

Normal cognitive development usually requires a structurally intact and complete cerebellar vermis. The aim of this study was to evaluate whether quantification by fetal magnetic resonance imaging (MRI) of vermis- and brainstem-specific imaging markers improves the definition of cystic posterior fossa malformations (cPFM).

METHODS

Fetuses diagnosed with cPFM that had an available midsagittal plane on T2-weighted MRI were identified retrospectively and compared with gestational-age (GA) matched brain-normal controls. Fetuses with cPFM were assigned to three groups, according to standard criteria (vermian size and brainstem-vermis (BV) angle): normal vermian area and BV angle < 25° (Group 1); reduced vermian area and/or BV angle of 25-45° (Group 2); and reduced vermian area and BV angle > 45° (Group 3; Dandy-Walker malformation (DWM) group). The number of differentiable vermian lobules and the areas of the vermis, mesencephalon, pons and medulla oblongata were quantified, correlated with and controlled for GA, and compared between the study groups.

RESULTS

In total, 142 cases of cPFM were included, with a mean GA of 25.20 ± 5.11 weeks. Cases comprised Blake's pouch cyst (n = 46), arachnoid cyst (n = 12), inferior vermian hypoplasia (n = 5), megacisterna magna (n = 35) and classic DWM (n = 44). In the control group, 148 fetuses were included, with a mean GA of 25.26 ± 4.12 weeks. All quantified areas and the number of differentiable vermian lobules had a significant positive correlation with GA. The number of vermian lobules and the areas of all quantified regions, except for that of the medulla oblongata, differed significantly between the study groups (P ≤ 0.015 for all). The control group had the highest number of differentiable vermian lobules and the DWM group had the lowest (P < 0.01).

CONCLUSIONS

Prenatal MRI assessment of vermian lobules is a useful addition to standard neuroradiological and neurosonographic techniques. The quantification of vermian lobules using fetal MRI allows further differentiation of cPFM into subgroups and thereby improves the classification of hindbrain malformations. © 2019 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Blake's Pouch Cysts and Differential Diagnoses in Prenatal and Postnatal MRI : A Pictorial Review

PURPOSE

The clinical variability of Blake's pouch cysts (BPC) may range from asymptomatic via ataxia to sequelae of decompensated hydrocephalus. On the other hand, Dandy-Walker malformation (DWM) and cerebellar vermis hypoplasia generally correlate with less favorable neurologic development. The aim was to illustrate the potential of prenatal and postnatal neuroimaging to distinguish a BPC or persistent BP from other posterior fossa malformations.

METHODS

This pictorial review addresses the inconsistent nomenclature, clinical features, and magnetic resonance imaging (MRI) patterns of BPC and five differential diagnoses. The MRI findings of 11 patients, acquired at up to 3 T in 3 institutions, are demonstrated. Furthermore, the literature was searched for recent improvements in genetic and embryological background knowledge.

RESULTS

Posterior fossa malformations often resemble each other and may even be imitated by sequelae of hemorrhagic, ischemic or infectious disruptions, i.e. congenital anomalies of morphology despite normal developmental potential. Hydrocephalus is a typical, albeit not always congenital finding in BPC. It is frequently associated with cerebellar disruptions and DWM; however, it is also a rare complication of posterior fossa arachnoid cysts. A moderately elevated vermis needs follow-up to confirm persistent BP versus vermian hypoplasia or DWM. The fetal cerebellar tail, previously assumed to be specific for DWM, may be imitated in cases of persistent BP.

CONCLUSION

The accurate diagnosis of isolated BPC is not always straightforward, which is especially critical in the context of fetomaternal medicine. A detailed description of posterior fossa malformations is to be preferred over unspecific terminology.