Study Of The Measurement Of Fetal Cerebellomedullary Cistern With Ultrasonography To Estimate The Posterior Fossa Malformations

Objective: To study the value of the measurement of fetalcerebellomedullary cistern with 2D ultrasonography to estimate the posterior fossa malformations of fetuses.Materials and methods: 156 pregnant women in 14~40 week gestationfrom Shandong provincial hospital, aged 23~34 years, were studied during December, 2003 to December, 2004. The instruments were SSD 5500 color Doppler ultrasound instrument of ALOKA company and LOGIQ 700 color Doppler ultrasound instrument of GE company. The type of probe was convex array scan and the frequency of probe was 3. 5MHz.The routine ultrasound examinations of obstetrics were given to all 158 pregnant women . The anteroposterior diameter (APD) of cerebellomedullary cistern was measured with 2D ultrasonography at cerebellar plane. The fetus whose APD of cerebellomedullary cistern was ≥ 10mm was defined positive .The advice of Magnetic Resonance (MR) imaging or re-examined ultrasonography was given to positive pregnant women . The statistical analysis was completed with software SPSS 11.0 and CS 10. 1.Results: The APD of cerebellomedullary cistern were <10mm in 101fetuses and ≥10mm in 55 fetuses of which 41 pregnant women accepted re examined ultrasonography and 13' pregnant women accepted MR imaging. Of 156 fetuses, there were 146 normal fetuses ,2 cases of exira-posterior-fossa malformations, 2 cases of Dandy-Walker malformation and 6 cases of hydrocephalus.There was no correlation between the APD of cerebellomedullary cistern and the getational age in 146 normal fetuses (P>0.05).Using APD ≥10mm to diagnose positive cerebellomedullary cistern, the sensitivity was 100%, the specificity was 67.81%, the positive predictive value was 14.55% and the negative predictive value was 100%. Using APD ≥8mm to diagnose positive cerebellomedullary cistern, the sensitivity was 100%, the specificity was 50%, the positive predictive value was 9.88% and the negative predictive value was 100%. Using APD ≥13mm to diagnose positive cerebellomedullary cistern, the sensitivity was 87. 50%, the specificity was 84.25%, the positive predictive value was 23 33% and the negative predictive value was 99. 19%.Conclusion: There is no correlation between the APD ofcerebellomedullary cistern and the getational age in normal fetuses. It is proper using the APD of cerebellomedullary cistern ≥ 13mm to diagnose positive cerebellomedullary cistern to estimate the posterior fossa malformations of fetuses. Observing the system of ventricles, the cerebellum and the change of the APD of cerebellomedullary cistern is more important to diagnosis. When the enlarged fetal cerebellomedullary cistern is found with ultrasonography, the advice of Magnetic Resonance imaging should been offered .