Evaluation Of Fetal Cortical Development Using Prenatal Ultrasound By Trans-cerebellar Section

In the process of fetal brain development,due to the unbalanced growth rate of brain parenchyma and skull,the increase of the whole surface area in the process of cerebral parenchyma development is faster than that of skull,and the development rate of the whole intracranial parenchyma is also unbalanced,so the cerebral cortex invaginates and folds to form brain sulci.The expansion and folding of the cerebral cortex is a key factor affecting cognitive ability and sensorimotor skills.The destruction of the growth and folding of the cerebral cortex will lead to the deformity of the cerebral cortex development,which will lead to serious intellectual retardation and intractable epilepsy in human.Therefore,it is particularly important to diagnose the diseases related to the deformity of the cerebral cortex in the prenatal period.The development of cerebral cortex is mainly divided into three processes: the proliferation and differentiation of neurons and glial cells,the migration of neurons and the formation of cortical structures.The developmental abnormalities of different processes will lead to different types of cerebral cortical developmental deformities.Abnormal proliferation and differentiation of neurons and glial cells can lead to microcephaly and hemimegalencephaly.Neuronal migration disorder can lead to lissencephalic and heterotopic gray matter.Abnormal formation of cortical structures can lead to polymicrogyri and,schizencephaly.It is easier to diagnose diseases such as hemimegalencephaly,lissencephalic,polymicrogyri and schizencephaly than microcephaly which the false positive rate of prenatal diagnosis is up to 43%.At present,there is no gold standard for prenatal diagnosis of fetal microcephaly.Fetal head circumference is less than 3 standard deviations of the mean value of normal fetuses in the same gestational week,which is the clue for prenatal diagnosis of fetal microcephaly.Microcephaly can also be shown on imaging as sulcus retardation,which means that sulcus development is more than 3 weeks later than that of normal fetuses at the same age.As one of the main cerebral sulcus,the development of the Sylvian fissure is representative,so the study of the development of the Sylvian fissure can further indicate the development of the cerebral cortex.There are some studies at home and abroad to evaluate the development of fetal Sylvian fissure,which is mainly evaluated by thalamic section.This study found that the Sylvian fissure shows clearer on the trans-cerebellar section than on the trans-thalamic section,but there is no related evidence to prove this suggestion.Therefore,it is expected to obtain relatively reliable and objective data of fetal cerebral cortical development and provide valuable information for further evaluation of fetal cerebral cortical development through the development of unified standard research sections for large sample imaging studies.In addition,microcephaly is the result of brain dysplasia,especially frontal lobe dysplasia.Therefore,it is expected to improve the prenatal diagnosis coincidence rate of fetal microcephaly with combining with the development of frontal lobe and sulcus.This study is mainly divided into four parts:(1)A study of the clearness rate of fetal Sylvian fissure shown on different sections by prenatal ultrasound;(2)Evaluation of the development of Sylvian fissure in mid-late pregnancy by transverse cerebellar section;(3)Evaluation of the development of frontal lobe in mid-late pregnancy by transverse cerebellar section;(4)Evaluation of the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe by trans-cerebellar section.Part 1 A study of the clearness rate of fetal Sylvian fissure shown on different sections by prenatal ultrasoundObjective To compare the clearness rate of fetal Sylvian fissure revealed by prenatal ultrasonography on trans-cerebellar section and trans-thalamic section,and to provide scientific basis for selecting the best section of prenatal ultrasound to evaluate the developmental parameters related to fetal Sylvian fissure.Methods This was a retrospective study.We analyzed all the fetal images on trans-cerebellar section and trans-thalamic section stored in the imaging system who were undergoing grade III prenatal ultrasound examination in our hospital from January 2017 to December 2018.The gestational age was divided into three groups which were 21 to 24 weeks,25 to 28 weeks and 29 to 32 weeks respectively.The evaluation criteria for the clear appearance of the Sylvian fissure were complete morphology of the Sylvian fissure and clear apical and anteriorly edges of the Sylvian fissure.The results of showing Sylvian fissure clearly were divided into four groups: only on trans-cerebellar section shown clear,only on trans-thalamic section shown clear,both on trans-cerebellar section and trans-thalamic section shown clear,and both on trans-cerebellar section and trans-thalamic section not shown clear.The clearness rate of each group and the total clearness rate of each section were analyzed statistically.Results The clearness rates of showing Sylvian fissure only on trans-cerebellar section were 62.3% at 21 to 24 weeks,70.1% at 25 to 28 weeks and 63.6% at 29 to 32 weeks.The clearness rates of showing Sylvian fissure only on trans-thalamic section were 11.1% at 21 ~ 24 weeks,10.5% at 25 ~ 28 weeks and 9.1% at 29 ~ 32 weeks.The clearness rates of showing Sylvian fissure both on trans-cerebellar and trans-thalamic sections were 22.1% at 21 to 24 weeks,15.0% at 25 to 28 weeks and 13.0% at 29 to 32 weeks.The unclearness rates of showing Sylvian fissure both on trans-cerebellar and trans-thalamic sections were 4.5%at 21 ~ 24 weeks,4.4% at 25 ~ 28 weeks and 14.3% at 29 ~ 32 weeks.The clearness rate of showing Sylvian fissure on trans-cerebellar section was significantly higher than on trans-thalamic section(P < 0.05).The total clearness rate of showing Sylvian fissure on trans-cerebellar section and trans-thalamic section were 83.1% and 28.3% respectively.Conclusion In this study,it was suggested that prenatal ultrasound selection of trans-cerebellar section is better than trans-thalamic section in evaluating the developmental parameters related to the Sylvian fissure.Part 2 Evaluation of the development of Sylvian fissure in mid-late pregnancy by trans-cerebellar sectionObjective On the basis of retrospectively analysis the trans-cerebellar section showing the Sylvian fissure of normal fetus is better than trans-thalamic section in middle and late trimester,we prospectively established the normal reference range of developmental parameters and studied the morphological changes related to the Sylvian fissure of normal fetus in the trans-cerebellar section in order to provide valuable information for the diagnosis of fetal cerebral cortical dysplasia.Methods A prospective cross-sectional study was conducted on 845 normal fetuses at 21 to 32 weeks of gestation from January 2019 to June 2020.The depth,width and the angle of the posterosuperior horn of Sylvian fissure were measured respectively,and regression analysis was performed according to different gestational age groups.Based on the angle,the morphology of the Sylvian fissure was divided into four shapes included ︹ shape(Angle >90°),П shape(Angle ≈90°),π shape(Angle <90°)and 工 shape(Angle ≈0°).Results The depth of Sylvian fissure was positively correlated with gestational weeks,the width and the angle of the posterosuperior horn of Sylvian fissure was negatively correlated with gestational weeks,with correlation coefficients 0.751,0.825 and 0.966 respectively(all P < 0.001).Taking gestational weeks as the independent variable,the depth,width and angle of the posterosuperior horn of Sylvian fissure of fetus as the dependent variables,linear regression analysis showed that there was a linear relationship between the independent variables and the dependent variables.The obtained equation was simplified to a formula: Fetal Sylvian fissure depth(mm)=7+0.6×(gestational weeks-21),Sylvian fissure width(mm)=8-0.6×(gestational weeks-21),the angle of posterosuperior horn of Sylvian fissure(°)=140-13×(gestational weeks-21).It was found that the morphological changes of the Sylvian fissure were related to the gestational age.The morphology of the Sylvian fissure was ︹-shaped at 21 to 24 weeks of gestation,П-shaped at 25 to 26 weeks of gestation,π-shaped at 26 to 30 weeks of gestation,and the Sylvian fissure was almost closed and appeared after 工 shape 31 to 32 weeks of gestation.Conclusion The reference range of the depth,width and the angle of posterosuperior horn of Sylvian fissure of normal fetus at 21 to 32 weeks of pregnancy by the trans-cerebellar section were established.Besides,this study preliminarily elucidates that the morphological changes of the posterosuperior horn of the Sylvian fissure of normal fetuses at 21 to 32 weeks of gestation,which could provide valuable information for the evaluation of the normal development of the lateral fissure of fetus and the prenatal diagnosis of fetal cortical hypoplasia.Part 3 Evaluation of the development of frontal lobe in mid-late pregnancy by trans-cerebellar sectionObjective To establish a reference range of developmental parameters related to the frontal lobe of normal fetuses in different gestational weeks,which can provide a basis for the evaluation of normal development of the frontal lobe and the diagnosis of suspected fetal microcephaly.Methods A prospective cross-sectional study was performed on 870 normal fetuses between 21 and 36 weeks from January 2019 to June 2020,and the anterior-posterior diameter and transverse diameter of the frontal lobe were measured in trans-cerebellar plane.Linear regression analysis was performed by grouping different gestational weeks.Results Fetal anterior-posterior diameter and transverse diameter of the frontal lobe were positively correlated with gestational week with correlation coefficients 0.871 and 0.971 respectively(P < 0.001).There was a linear relationship between gestational weeks and frontal lobe parameters,and the equations were simplified to obtain the simple correlation formula: fetal frontal lobe anterior-posterior diameter(mm)=14.5+0.7×(gestational week-21),frontal lobe transverse diameter(mm)=41+2.5×(gestational week-21).Conclusion The reference ranges of the frontal lobe anterior-posterior diameter and the frontal lobe transverse diameter of normal fetuses between 21 to 36 weeks in trans-cerebellar plane were established,which can provide valuable information for the evaluation of normal development of the frontal lobe and the diagnosis of suspicious fetal microcephaly.Part 4 Evaluation of the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe by trans-cerebellar sectionObjective On the basis of a prospective study of evaluating the development of frontal lobe in mid-to-late trimester by trans-cerebellar section,it had been found that the transverse frontal diameter had a higher correlation with gestational age than the anteroposterior frontal diameter.In order to provide more valuable information for the prenatal diagnosis of suspected fetal microcephaly,the reference value range of the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe by trans-cerebellar section was further prospectively established.Methods A prospective cross-sectional study was conducted on 870 normal fetuses at 21 to 36 weeks of gestation from January 2019 to June 2020.The transverse diameter of cerebellum and the transverse diameter of frontal lobe were measured by trans-cerebellar section,and the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe was calculated,and the correlation was analyzed statistically.Results The ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe increased positively with gestational age which correlation coefficient was 0.413(P < 0.001).Taking gestational age as the independent variable and the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe as the dependent variable,it showed that there was a linear relationship between the gestational age and the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe.We got a correlation formula that the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe =0.004×(gestational age-21)+0.530.Conclusion This study has preliminarily established the normal reference range of the ratio of the transverse diameter of cerebellum to the transverse diameter of frontal lobe by trans-cerebellar section in normal mid-to-late pregnancy fetuses,which can provide valuable information for the prenatal diagnosis of suspected fetal microcephaly.