Prenatal sonographic diagnosis of vermal agenesis

Reference Charts for Fetal Cerebellar Vermis Height: A Prospective Cross-Sectional Study of 10605 Fetuses

OBJECTIVE

To establish reference charts for fetal cerebellar vermis height in an unselected population.

METHODS

A prospective cross-sectional study between September 2009 and December 2014 was carried out at ALTAMEDICA Fetal-Maternal Medical Centre, Rome, Italy. Of 25203 fetal biometric measurements, 12167 (48%) measurements of the cerebellar vermis were available. After excluding 1562 (12.8%) measurements, a total of 10605 (87.2%) fetuses were considered and analyzed once only. Parametric and nonparametric quantile regression models were used for the statistical analysis. In order to evaluate the robustness of the proposed reference charts regarding various distributional assumptions on the ultrasound measurements at hand, we compared the gestational age-specific reference curves we produced through the statistical methods used. Normal mean height based on parametric and nonparametric methods were defined for each week of gestation and the regression equation expressing the height of the cerebellar vermis as a function of gestational age was calculated. Finally the correlation between dimension/gestation was measured.

RESULTS

The mean height of the cerebellar vermis was 12.7mm (SD, 1.6mm; 95% confidence interval, 12.7-12.8mm). The regression equation expressing the height of the CV as a function of the gestational age was: height (mm) = -4.85+0.78 x gestational age. The correlation between dimension/gestation was expressed by the coefficient r = 0.87.

CONCLUSION

This is the first prospective cross-sectional study on fetal cerebellar vermis biometry with such a large sample size reported in literature. It is a detailed statistical survey and contains new centile-based reference charts for fetal height of cerebellar vermis measurements.

Rhombencephalosynapsis: prenatal imaging and autopsy findings

OBJECTIVES

Rhombencephalosynapsis is a rare, but increasingly recognized, brain malformation characterized by congenital fusion of the cerebellar hemispheres and absence of the vermis. Rhombencephalosynapsis is associated with significant developmental delay, seizures and involuntary head movements. We report four cases, with correlation of prenatal and postnatal imaging and autopsy findings.

METHODS

Over a 2-year period, four cases of rhombencephalosynapsis were diagnosed in the perinatal period, three in one center and one in another center. The clinical cases were reviewed, and correlation was made between the prenatal and postnatal imaging and autopsy findings where available.

RESULTS

All cases presented initially with ventriculomegaly on prenatal ultrasound examination. Subsequent magnetic resonance imaging (MRI) established the diagnosis in two cases and postnatal MRI established the diagnosis in a further two cases. Autopsy was available and confirmed the diagnosis in two cases. In one case the pregnancy was terminated, two infants died in the neonatal period and one died in infancy.

CONCLUSIONS

The cases in this perinatal series of rhombencephalosynapsis showed a very poor prognosis. The presence of ventriculomegaly on prenatal ultrasound imaging should alert the physician to consider rhombencephalosynapsis in the differential diagnosis. MRI appears to be the imaging modality of choice in establishing the diagnosis.

The Fetal Cerebellar Vermis

Fetal magnetic resonance provides a new tool in the imaging of the posterior fossa and is proving useful in cases that are difficult to assess sonographically by allowing further assessment of the fourth ventricle, cisterna magna, and vermian growth and development. We describe various criteria with which to evaluate vermian growth, including vermian biometry and the relationship between the superior and inferior lobes. We demonstrate 2 markers of normal vermian development: the primary fissure and fastigial point. We illustrate the tegmento-vermian angle, "closure" of the fourth ventricle, and communication of the fourth ventricle with the basal cisterns during development and in several disorders. We correlate those features with the expected embryological course of development and illustrate identification of these features and associated abnormalities of the posterior fossa, brain stem, and central nervous system in mid-trimester scans of fetuses with abnormal development. Correlation with contemporaneous ultrasound examinations is demonstrated.

Rotation of the vermis as a cause of enlarged cisterna magna on prenatal imaging

OBJECTIVES

Dandy-Walker complex is a continuum of developmental anomalies of the posterior fossa which includes vermian rotation. However, vermian rotation alone may be benign. The aim of this study was to describe our experience with sagittal-plane prenatal ultrasound in the diagnosis of rotation of the vermis in cases of suspected enlarged cisterna magna on routine antenatal imaging, and to describe the follow-up of these patients.

METHODS

Seven women, who were referred to our ultrasound unit for evaluation of an enlarged fetal cisterna magna and suspected agenesis of the vermis on axial-plane imaging, underwent further multiplanar studies of the posterior fossa and measurements of the vermis.

RESULTS

The mean maternal age was 27 (range, 20-33) years and the mean gestational age at diagnosis was 19.5 (range, 18-31) weeks. The standard axial plane image showed a 'direct communication' between the cisterna magna and the fourth ventricle. In the mid-sagittal plane, the vermis was clearly delineated, with posterosuperior rotation. Vermis size was within normal limits for gestational age in all cases. Findings were confirmed by prenatal magnetic resonance imaging (MRI) in two cases and postnatal MRI and/or sonography in five. During a mean follow-up of 4.5 (range, 1-7.5) years, all children developed normally, with no neurological complications.

CONCLUSION

The finding of an enlarged cisterna magna on standard- (axial-)plane ultrasound should be evaluated further in the sagittal plane to determine whether the cause is rotation of a normal vermis. This may spare patients unnecessary tests, anxiety and, in some cases, pregnancy termination.

Molar tooth sign in fetal brain magnetic resonance imaging leading to the prenatal diagnosis of Joubert syndrome and related disorders

Joubert syndrome is a rare autosomal recessive disorder characterized by ataxia, developmental delay, and oculomotor and respiratory abnormalities in relation to cerebellar vermian and midbrain dysgenesis. The midbrain dysgenesis is responsible for the molar tooth sign on axial magnetic resonance imaging (MRI). This classic hallmark of Joubert syndrome has been identified in other disorders sharing overlapping clinical and radiologic features with Joubert syndrome. Recent identification of two different genes points to genetic heterogeneity in this group of disorders, now entitled Joubert syndrome and related disorders, making a genetic prenatal diagnosis not readily available. In addition, fetal ultrasonography lacks sensitivity in regard to posterior fossa malformation. Fetal MRI is now acknowledged as the method of choice to delineate posterior fossa malformation in a fetus. The identification of a molar tooth sign has, however, rarely been documented by a fetal brain MRI. We report a case of Joubert syndrome diagnosed prenatally using fetal MRI. We also discuss the etiology of Joubert syndrome in view of the recent genetic advances and murine models of cerebellar dysgenesis.

Fetal MRI of a Severe Dandy-Walker Malformation with an Enlarged Posterior Fossa Cyst Causing Severe Hydrocephalus

We present a case of severe Dandy-Walker malformation with enlarged posterior fossa cyst extruding through the incisura of the tentorium and causing severe hydrocephalus. A posterior fossa malformation was suspected by ultrasonography and was further evaluated by fetal magnetic resonance imaging (MRI). Fetal MRI demonstrated that there were no associated anomalies and the decision was made to continue with labor instead of terminating the pregnancy. The precise diagnosis and absence of associated anomalies revealed by MRI aided in parent counseling and obstetrical management.

Ultrasonographic nomograms of the fetal fourth ventricle: additional tool for detecting abnormalities of the posterior fossa

OBJECTIVE

To characterize normal growth of the fetal fourth ventricle on ultrasonography throughout pregnancy.

METHODS

Consecutive biometric measurements and fetal organ scans were obtained from 299 patients undergoing fetal anatomic surveys between 13 and 40 weeks' gestation. Using 7- and 3.5-MHz transducers for early (13- to 17-week) and late (>17-week) examinations, respectively, we scanned the fetal head in the axial plane with special focus on the posterior fossa of the brain. The fourth ventricle was identified, and its anteroposterior diameter and width were measured. A "triangle" formula was used for calculating its circumference and area.

RESULTS

The fourth ventricle was shown as a hypoechoic triangle below the level of the cerebellum. A linear regression line of the fourth ventricle was observed across gestational age, and a first-degree correlation was found between gestational age and anteroposterior diameter of the fourth ventricle (r = 0.894; P < .0001; y = -0.84 + 0.23 x gestational age), its width (r = 0.657; P < .0001; y = 3.82 + 0.14 x gestational age), its circumference (r = 0.843; P < .0001; y = 5.11 + 0.58 x gestational age), and its area (r = 0.844; P < .0001; y = -10.11 + 1.17 x gestational age). Twelve enlarged fourth ventricles were found between 14 and 16 weeks, but results of follow-up scans at 20 weeks were normal.

CONCLUSIONS

An isolated enlarged fourth ventricle in the early second trimester might represent a normal variant; it should be followed, but decisions about the fate of the pregnancy should not be based solely on this finding.

The fetal cerebellar vermis: normal development as shown by transvaginal ultrasound

OBJECTIVE

To determine the normal appearance and development of the fetal cerebellar vermis using mid-sagittal planes obtained by transvaginal sonography.

SUBJECTS AND METHODS

A total of 101 fetuses were evaluated by transvaginal sonography between 21 and 39 weeks of gestation. The mid-sagittal antero-posterior and cranio-caudal vermian diameters, circumference and surface area were measured and calculated. Nomograms were produced.

RESULTS

The vermis was observed in 96% of the cases and all the measurements were performed in 92%. The vermis grows in a linear fashion throughout pregnancy. The growth pattern correlates well with gestational age, biparietal diameter, head circumference and transverse cerebellar diameter.

CONCLUSION

Transvaginal sonography is a valuable tool in the study of the fetal vermis during the second half of pregnancy. Knowledge of its normal appearance may help identify developmental anomalies and enable accurate prenatal counseling.