Diagnosis Of Fetal CNS Using Combination Of Ultrasonography And Magnetic Resonance Imaging

Backround and objectiveAbout one million infants with congenital malformation were born every year in our country, which accounts for 4% to 6% of newborns. To diagnose those the fetal CNS abnormalities accurately is critical for both clinical management and the aristogenesis.Ultrasonography (US) is the front line modality for the evaluation of the fetus. It is safe for both fetus and mother. It is less expensive, real-time, readily available and is readily available and is easy to use. US may be performed during the whole pregnancy. The brain structure may be observed transvaginally during the first trimester. The fetus brain and brain anomalies can be demonstrated clearly at some cross sections during the second or the third trimester. However, US has some limations to show certain kind of anomalies such as oligohydramnios and large maternal body habitus.Large gestational weeks can also degrade image quality.Magnetic resonance imaging (MRI) with high spatial and tissue resolution has been being used routine clinically. The advent of faster sequences has revolutionized the ability of MR imaging to assess the fetus abnormities, particllay for the fetal CNS abnormity. The fetal MR imaging allows better visualization of both normal in brain development as well as abnormatlities in it. MRI can be performed on large maternal body habitus and larger gestational weeks, although clausphobia and fetus with overfrequency of movement preclude pregnant women from being examined.The purpose of our research is to study the application of both US and MR in diagnosis of the fetus CNS abnormities. Materials and methods1. study population(1) From January 2005 to January 2008 ninety-three singleton pregnancy women whose fetus with CNS abnormities were investigated in this study. The age ranged from 23 to 38 years old. The gestational weeks ranged from 26 to 40 weeks.(2) From January 2005 to December both US and MRI were performed on 48 singleton pregnancy women. The age ranged from 23 to 39 years old. The gestational weeks ranged from 27 to 40 weeks Both of them are healthy and their periods is regular.(3) From January 2005 to October 2007,three hundred and thirty seven women with singleton pregnancy were referred for routine sonographic examination between 22 and 38 weeks gestation The pregnant women age ranged from 23 to 36 years old.Gestational age was determined on the basis of the last menstrual period and was confirmed by at least one previous sonographic examination performed during the first trimester. Normal cranial and fetal growth was obtained by measuring the biparietal diameter, head circumference, transverse cerebellar diameter, abdominal circumference and femur length.2. methods(1) Fetus US was performed. The lateral cerebral ventricle plane, the thalamus plane and the cerebellum plane scanning were studied.(2) MRI was performed.The sequences included a multiplanar single-shot fast spin-echo(SSFSE). and gradient-echo sequence (GE). The total examination time was approximately 30 minutes.3. observe index(1)The results of the ninety-three fetus with CNS abnormalities or suspected of CNS abnormities by using US were campared with MRI.(2)The transverse diameter of the cerebellum was measured on both US and MR imaging in forty-eight fetus due to prenatal diagnosis. The height of the vermis ,the anteroposterior diameter and the area of the vermis were also measured on the MR imaging.(3)The anteroposterior diameter of the cisterna magna was measured between the cerebellum and the internal surface of the occipital bone on the transcerebellar plane. The anteroposterior diameter of the cisterna magna was measured on US in three three hundred and thirty seven fetus. In addition, fetal MRI was performed on those fetuses with mega cisterna magna by US.4. statistics analysisStatistical analysis was performed using the SPSS 12.0 package for Windows. The results of the are presented as mean±standard deviation. The 2-tailed Student's t-test was used to assess the mean interclass. Fisher's exact probabilistic method and the Pearson chi-square (x~2) test were used to the percentual comparison. The dependability and regression analysis were performed and the regression equation was established. The variance analysis and t test were used to analyze the significance and the fitting degree of the equation. p<0.05 was considered statistically significant.Results1. Ninety-three singleton pregnancy women whose fetus were confimed or suspected of CNS abnormities by prenatal US accepted MR imaging. Ninety cases got satisfactory images. MR imaging was precluded because of claustrophobia (2 cases) and overfrequency of fetal movement (one case).2. In 30 (33.33%,30/90) of 90 cases with confirmed or suspected of CNS abnormities by US, the diagnoses established by US and MR imaging were correct when compared with postnatal diagnosis ; MR imaging provided more information than did US in 53 (58.89%,53/90) cases, particularly in the fetus with ventriculomegaly and the mega cisterna magna (20.75%,11/53; 62.26%,33/53); MR corrected the US diagnosis in 6cases (6.67%,6/90), particularly in the fetus with mega cisterna magna (83.33%,5/6). One case provided more abnormal information on US and MR could not show.3.The transverse diameter of the cerebellum ,the height of the vermis ,the anteroposterior diameter of the vermis ,and the area of the vermis showed close positive correlation (r=0.939 P<0.001; r=0.820P<0.001; r=0.834 P<0.001; r=0.762 P<0.001) with the gestation weeks.The linear regression equation of them by regression analysis show P<0.001, coefficient of regression and t text P <0.001.4. The transverse diameter of the cerebellum on MR imaging and the measure value on US showed close positive correlation(r=0.995 P<0.001) . The regreesion equation show the result as follows: y=0.988x+0.927 (y: the transverse diameter of the cerebellum -MRI, x: the transverse diameter of the cerebellum -US), F=4370.56 P<0.001 coefficient of regression t test showed the result as follows t=66.110 P<0.001 R~2=0.990.5. The normal range of anteroposterior diameter of the cistema magna was 5mm-14 mm. The mean value of anteroposterior diameter of the cistema magna f was 8.01mm±1 .79. In all 179 male fetuses the mean anteroposterior diameter of the cistema magna was 8.63mm±2.16. In the 158 female fetuses the mean anteroposterior diameter of the cistema magna was 7.87mm±1.74. The size difference was statistically significant (p<0.001). Pearson's correlation coefficient between the anteroposterior diameter of the cistema magna and gestational weeks is 0.125 and the p- value is 0.058.6.More male fetuses with mega cisterna magna were observed than female fetuses with mega cistema magna. The ratio of the fetuses with mega cistema magna in the male group was significantly higher than the fetuses in female group. (p<0.05)Conclusions1. US was very useful for demonstrating the fetuses' CNS abnormities.It could be used both for diagnosis and screeing.2. MRI had advantage over US for detecting fetuses CNS abnormalities.3.Combining US with MRI, the fetuses abnormalities could be diagnosed more definitively.4. The transverse diameter of the cerebellum, the height of the vermis, the anteroposterior diameter of the vermis, and the area of the vermis which were measured on MR imaging showed close positive correlation with the gestation weeks. The two measurement methods including US and MR have close correlation. The fetus biometry measurement may be well performed on MR imaging as well as US in order to evaluate the development of the fetus.5. Male fetuses had larger sonographic measurement on anteroposterior diameter of the cisterna magna than female fetuses.The proportion of the fetuses with maga cisterna magna in the male group was significantly higher than the fetuses in the female group. Isolated mega cisterna magna is prone to be considered the normal variation.