RESUMEN
Objective To explore the value of the cavum vergae vanishing sign for prenatal ultrasound diagnosis of fetal agenesis of the corpus callosum ( ACC ) . Methods Fifty-one cases of ACC of 20 - 32 gestational weeks were confirmed by MRI or induced fetal autopsy . A random selection of 80 normal fetuses of 20 - 32 gestational weeks were chosed as control group . The displays of the cavum septum pellucidum ( CSP) and the cavum vergae( CV ) in the two groups were observed . Results There were 36 cases of complete agenesis of the corpus callosum ( CACC) and 15 cases of partial agenesis of the corpus callusom ( PACC) in ACC group . In 51 ACC cases ,43 cases were confirmed by prenatal MRI ,while 8 cases were confirmed by postnatal MRI . The comparison of display of CSP and CV between the ACC group and the health group was as follows : ① CSP vanishing rate in ACC group was 70 .6％ ( 36/51 ) ,meanwhile the disappearance rate of CSP in the health group was 0 ( 0/80 ) ,the difference between the two groups was statistically significant( χ2 = 77 .870 , P = 0 .000) . ② CV vanishing rate in ACC group was 96 .1％ (49/51) , meanwhile the disappearance rate of CV in the health group was 1 .2％ ( 1/80) ,the difference between the two groups was statistically significant ( χ2 = 118 .673 , P = 0 .000) . The correlation coefficient between the CV vanishing sign and the occurrence of ACC was 0 .952 ( P = 0 .000) ,while the correlation coefficient between the CSP vanishing sign and the occurrence of ACC was 0 .771 ( P = 0 .000) . There were significant differences in CSP disappearance rate and CV disappearance rate between ACC group and control group at different gestational weeks ( 20 - 24 weeks ,25 - 28 weeks and 29 - 32 weeks) ( all P < 0 .001) . Conclusions The cavum vergae vanishing sign ,as an important indirect sign of fetal agenesis of the corpus callosum ,can be obtained quickly from horizontal transverse section of the cavum septum pellucidum . During the middle pregnancy ,it could be an important prenatal ultrasound screening clue for fetal agenesis of the corpus callosum .