OC152: Comparison between ultrasound and fetal MRI in normal and abnormal brains for cerebellar pathology

Abstract

Ultrasound (US) examination of the posterior fossa includes measurement of the transcerebellar diameter (TCD) and subjective evaluation of the vermis and fourth ventricle. It is limited in its ability to detect subtle anomalies. Fetal MRI allows better definition of posterior fossa structures and potentially more precise measurement of neuro-anatomical structures. This study demonstrates comparison between the two modalities and their value in quantifying cerebellar structures. 54 fetuses had ultrafast MRI of the brain, 34 fetuses with normal and 20 with abnormal posterior fossa findings on US. 20 fetuses from each group underwent MRI and US examination within a median interval of 3.5 days. We compared the TCD of 40 fetuses measured by US and MRI. In addition, MRI measurements of the cerebellar vermis and 4th ventricle in both groups were obtained. MRI revealed more detailed images of the posterior fossa compared with US especially of the cerebellar vermis. MRI confirmed vermial pathology in 13/20 (65%) fetuses with ultrasonographically suspected anomalies of the vermis. There was no significant difference in TCD measurements using either modality between the normal controls and those with cerebellar pathology. MRI measurements of the height of the vermis and 4th ventricle increased with GA in normal fetuses. In normal fetuses, the median vermial height was 14.2 mm (6.4–24.1) and in the abnormal group 14.2 mm (10–18). The height of the 4th ventricle in normal fetuses was 5.4 mm (2.1–7.9) and in the abnormal group 7.3 mm (2.4–10.1). This difference did not reach significance for both parameters. MRI allowed more precise diagnosis of anomalies of the cerebellar vermis. MRI also allowed accurate cerebellar and ventricular measurements although differences in the normal and abnormal groups were not significant. Larger numbers of patients would be required to demonstrate a significant difference.