The role of the transcerebellar view in the detection of fetal central nervous system anomaly

Prenatal diagnosis of rhombencephalosynapsis: neuroimaging features and severity of vermian anomaly

OBJECTIVES

To describe the prenatal neuroimaging spectrum of rhombencephalosynapsis (RES) and criteria for its classification according to the severity of vermian anomaly.

METHODS

In this multicenter retrospective study of fetuses with RES between 2002 and 2020, the medical records and brain ultrasound and magnetic resonance images were evaluated comprehensively to determine the severity of the vermian anomaly and the presence of associated brain findings. RES was classified, according to the pattern of vermian agenesis and the extent of the fusion of the hemispheres, as complete RES (complete absence of the vermis) or partial RES (further classified according to the part of the vermis that was missing and, consequently, the region of hemispheric fusion, as anterior, posterior, severe or mixed RES). Findings were compared between cases with complete and those with partial RES.

RESULTS

Included in the study were 62 fetuses with a gestational age ranging between 12 and 37 weeks. Most had complete absence of the vermis (complete RES, 77.4% of cases), a 'round-shaped' cerebellum on axial views (72.6%) and a transverse cerebellar diameter (TCD) < 3^rd centile (87.1%). Among the 22.6% of cases with partial RES, 6.5% were classified as severe partial, 6.5% as partial anterior, 8.1% as partial mixed and 1.6% as partial posterior. Half of these cases presented with normal or nearly normal cerebellar morphology and 28.5% had a TCD within the normal limits. Infratentorially, the fourth ventricle was abnormal in 88.7% of cases overall, and anomalies of the midbrain and pons were frequent (93.5% and 77.4%, respectively). Ventriculomegaly was observed in 80.6% of all cases, being more severe in cases with complete RES than in those with partial RES, with high rates of parenchymal and septal disruption.

CONCLUSIONS

This study provides prenatal neuroimaging criteria for the diagnosis and classification of RES, and identification of related features, using ultrasound and magnetic resonance imaging. According to our findings, a diagnosis of RES should be considered in fetuses with a small TCD (severe cerebellar hypoplasia) and/or a round-shaped cerebellum on axial views, during the second or third trimester, especially when associated with ventriculomegaly. Partial RES is more common than previously thought, but presents an extreme diagnostic challenge, especially in cases with normal or nearly-normal cerebellar morphobiometric features. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Nomogram of the cerebellar vermis height at birth in small-for-gestational-age neonates

AIM

To establish a nomogram of the height of the cerebellar vermis at birth in small-for-gestational-age neonates.

METHODS

Eighty-five consecutively born healthy singletons who were small for gestational age were enrolled in a cross-sectional observational study. The height of the cerebellar vermis was measured by ultrasonography in the midsagittal plane. Reference intervals for the vermian height at 5th, 50th and 95th centiles were estimated at any week of gestational age using a mean and standard deviation model based on least squares polynomial regression.

RESULTS

All attempts at obtaining neonatal vermian height were successful. Mean (standard deviation) maternal age was 29.6 (4.7) years; median parity was 1 (range, 1-3). No difference was found between males and females for the vermian height (mean difference [95% confidence interval], -0.03 [-0.16; 0.10] cm). Mean vermian height (in cm) against gestational age (in weeks) was suitably modelled by a quadratic-cubic polynomial (r2= 0.790, p < 0.0001) as 0.712 + 0.00129 x gestational age2- 0.0000053 x gestational age3 (SD =-1.009 + 0.0504 x gestational age -0.000014 x gestational age3).

CONCLUSION

A nomogram of the height of the cerebellar vermis at birth against gestational age was established for use in small-for-gestational-age neonates.

Height of the cerebellar vermis and gestational age at birth

OBJECTIVES

The objective of this study was to construct reference ranges of the neonatal cerebellar vermis height with respect to the gestational age at birth.

METHODS

This observational study assessed 434 neonates born at 25-42 weeks' gestation. The neonates were singleton and appropriate in size for gestational age, and did not exhibit any abnormalities or neonatal disease. Gestational age was based on the date of the last menstrual period and confirmed by ultrasound examination performed within the 12(th) week of pregnancy. Sonographic measurements of the height of the cerebellar vermis in the mid-sagittal plane were performed within 24 h of birth by the same neonatal sonographer. Reference ranges (5(th), 50(th) and 95(th) centiles) were estimated by a mean and SD model based on least-squares polynomial regression.

RESULTS

Neonatal sonographic measurements were obtained in all cases. Mean (SD) maternal age was 30.2 (4.3) years. Mean cerebellar vermis height adjusted for gestational age did not differ between males and females, the mean adjusted difference being 0.012 (95% CI, - 0.009 to 0.033) cm. Mean cerebellar vermis height (cm) against gestational age (weeks) was suitably modeled by a linear-cubic polynomial as - 1.784 + 0.137 x GA - 0.000019 x GA(3) (SD = - 0.147 + 0.008 x GA), where GA = gestational age.

CONCLUSIONS

Reference ranges for the height of the cerebellar vermis at birth with respect to gestational age at birth have been constructed in appropriate-for-gestational-age neonates.

Nomograms of the axial fetal cerebellar hemisphere circumference and area throughout gestation

OBJECTIVE

The widely applied transcerebellar diameter (TCD) obtained at axial cranial imaging, measures the distance between the lateral aspects of the cerebellum and incorporates the width of the cerebellar vermis. Our objective was to create reference ranges of axial fetal cerebellar hemisphere circumference (CHC) and area (CHA), independent of the cerebellar vermis, throughout gestation.

METHODS

This cross-sectional study involved pregnant patients between 14 and 41 weeks of gestation. Inclusion criteria consisted of well-established dates (confirmed by early ultrasound), non-anomalous singleton fetuses and intact amniotic membranes. Sonographic measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL), TCD, and estimated fetal weight (EFW). Values of axial fetal CHC and CHA were each calculated as the mean of three separate measurements. The 5th, 50th and 95th centiles were estimated at each week of gestational age (GA) by least-squares regression for the mean and standard deviation (SD) of the CHC and CHA as functions of GA. r2 and associated P-values for the relationships of CHC and CHA with other sonographic biometric measurements were calculated.

RESULTS

The study included 651 consecutive patients. All attempts at obtaining axial fetal CHC and CHA were successful. Mean maternal age was 27.3+/-6.7 years, median gravidity was 1 (range 1-16), and median parity was 1 (range 0-6). Mean CHC (cm) throughout gestation was modeled as -2.091+0.2563xGA (weeks) (SD=-0.075+0.0164xGA), and mean CHA (cm2) was modeled as 0.245-0.0765xGA+0.00506xGA2 (SD=1.167-0.1565xGA+0.006785xGA(2)-0.00008028xGA3). Fetal axial CHC and CHA correlated significantly and strongly with BPD, HC, AC, HL, FL, TCD and EFW (all R2 values were >or=0.95, and all P-values were <0.001).

CONCLUSION

Nomograms of axial fetal cerebellar hemisphere circumference and area throughout gestation, independent of the cerebellar vermis, have been provided.

Diagnosis, outcome, and management of fetal abnormalities: fetal hydrocephalus

INTRODUCTION

It has been recognized that the morphological fetal CNS findings detected in early development are not always the final features: occasionally they may not be determined in diagnosis and may change developmentally or chronologically during the fetal life in utero.

DISCUSSION

Certain factors of the fetal chronology of CNS anomalies can cause irreversible changes during fetal life. These include: significant delay in the neuronal maturation process in fetal hydrocephalus developed in clinico-embryological stage II of the Perspective Classification of Congenital Hydrocephalus (PCCH), secondary neural injury in the intactly developing spinal cord above the neural placode in fetuses with spina bifida aperta (myeloschisis), histological "evolution" of tumors or dysgenetic CNS, and deformity of the normally developed intracranial or intraspinal CNS structures. Considering the current status of fetal surgery in general and technical advances promising improved outcomes, fetal neurosurgery can also be applied to the above-mentioned progressive pathology or pathophysiology in the fetal CNS. However, since the failure of the first trial of fetal neurosurgery in the 1980s, the prerequisites have still not been clarified. In order to use advanced neurosurgery techniques in the management of fetal CNS anomalies, these prerequisites have to be established.

Fetal cerebellum: US appearance with advancing gestational age

PURPOSE

To evaluate the change in ultrasonographic (US) appearance of the fetal cerebellum with advancing gestation.

MATERIALS AND METHODS

A total of 291 normal fetuses of uncomplicated pregnancies were evaluated at gestational ages (GAs) between 15 and 41 weeks with a 3.75-MHz transabdominal curvilinear probe. After the transcerebellar view was obtained, the transverse cerebellar diameter (TCD) was measured and the images were stored. On hard-copy US images, cerebella were assigned three grades of appearance. These grades were analyzed in relation to GA and TCD. Inter- and intraobserver variations were assessed in 91 randomly selected cases.

RESULTS

Cerebella in 137 (47.1%), 71 (24.4%), and 83 (28.5%) of 291 subjects were classified as grade I (hypoechoic, "eyeglass" shape), grade II (intermediate echogenicity, "dumbbell" outline), and grade III (hyperechoic, "fan" shape), respectively. With advancing gestation, the dominant grade changed from I to III gradually and progressively. The median GA and TCD, respectively, were 22 weeks and 22 mm for grade I, 29 weeks and 35 mm for grade II, and 36 weeks and 46 mm for grade III. These differences were statistically significant (P <.001). The agreements within inter- and intraobserver estimations were 96% (87 of 91) and 95% (86 of 91), respectively.

CONCLUSION

A gradual change in US appearance of the fetal cerebellum is seen with advancing gestation.

Intrauterine high-resolution magnetic resonance imaging in fetal hydrocephalus and prenatal estimation of postnatal outcomes with "perspective classification"

OBJECT

It is possible to diagnose hydrocephalus prenatally based on the morphological appearance of the fetus on neurodiagnostic images; however, the prognosis of this disease shows wide variation. The authors previously proposed a classification system for the prediction of postnatal outcome based on progression of hydrocephalus and affected brain development, known as the "Perspective Classification of Congenital Hydrocephalus (PCCH)." In this study the authors have used their classification system to analyze long-term follow-up results obtained in each clinicoembryological stage of fetal hydrocephalus.

METHODS

Sixty-one fetuses with hydrocephalus were examined to predict postnatal outcome by using this newly developed classification. The authors' recently developed method of using heavily T2-weighted imaging with a superconducting magnet clearly delineated the cerebrospinal fluid (CSF) space and the malformed brain and spinal cord. Imaging was achieved in less than 1 second per slice and required no sedation of the fetus. The technique appears to be simple and good at delineating intrauterine anatomy. Hydrocephalus was diagnosed in two fetuses at PCCH embryological Stage I (8-21 gestational weeks), in 28 fetuses at Stage II (22-31 weeks), and in 31 fetuses at Stage III (32-40 weeks). Among these 61 fetuses, clinicopathological typing showed that 19 had primary hydrocephalus (nine in Stage II and 10 in Stage III), 34 had dysgenetic hydrocephalus (two in Stage I, 16 in Stage II, and 16 in Stage III), and eight had secondary hydrocephalus (three in Stage II and five in Stage III). When the hydrocephalic state developed during PCCH Stage I or II, the prognosis was very poor, and only one of 18 fetuses with dysgenetic hydrocephalus and none of three fetuses with secondary hydrocephalus had an acceptable postnatal outcome. Even within the same category or subtype of fetal hydrocephalus, such as primary hydrocephalus in its simple form, or hydrocephalus with spina bifida aperta (myeloschisis), the postnatal outcomes differed depending on the time of onset of hydrocephalus. When the diagnosis of hydrocephalus was made during PCCH Stage II, the fetuses had a poorer postnatal outcome compared with those at Stage III (p < 0.05).

CONCLUSIONS

It is emphasized that postnatal prognosis is not simply a function of the form of the diagnosis but is also dependent on the progression of hydrocephalus and the degree to which that process affects neuronal development. Early decompressive procedures, conventionally performed after but, hopefully, performed before birth, are indicated to obtain the optimal postnatal prognosis of fetuses with hydrocephalus diagnosed at PCCH Stage II.

Prenatal diagnosis of central nervous system abnormalities

Fetal anomalies have been the subject of innumerable publications both in the prenatal and neonatal literature. This has significantly increased in the last 10 years, mainly because of the advent of high-resolution ultrasound equipment and improvement of scanning techniques. In addition, guidelines issued by professional organizations involved in prenatal diagnosis have encouraged a more universal approach to the imaging and documentation of prenatal findings. The fetal central nervous system is the most frequently investigated organ system, mainly because of its easy accessibility and prominence even in the early stages of embryologic development. The biparietal diameter was the first fetal measurement to be widely used in determining gestational age. As investigators gained more experience, the appearance of ultrasound images achieved the resolution that allows direct comparisons with gross specimens and more recent sophisticated techniques of computed tomography and magnetic resonance imaging. Now endovaginal ultrasound can document early first trimester development and compare it to known embryologic landmarks. Interest in demonstrating the ultrasound counterpart of central nervous system structures in the early stages of development has resulted in a plethora of articles proving the unique ability of ultrasound in imaging the developing fetus. In view of all these developments, the beginning ultrasound specialist is faced with the challenge and responsibility not only of being familiar with the literature but also of the mastery of scanning techniques that allow accurate prenatal diagnosis. It is therefore helpful to review key developmental milestones in embryologic life and correlate them with the corresponding prenatal ultrasound appearance. In addition, the changing appearance of the developing fetus has created a need for a systematic approach in the evaluation of structures so routine protocols can be established. This has been the subject of other publications that allow the novice to draw from the cumulative experience of different centers around the world. It is important to pay attention to the specifics described in the literature when duplicating results in one's laboratory. The frustration of not being able to reproduce results is common, especially when technical limitations prevent imaging under ideal conditions. This is especially true in patients who are first seen in the later third trimester with no prior prenatal care.(ABSTRACT TRUNCATED AT 400 WORDS)