Abstract:
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Purpose: To define easily identifiable measurements and markers of normal anatomic development of the fetal cerebellar vermis in vivo. Previous studies of the cerebellum have been performed in vitro, only between 6 and 25 weeks gestational age, with few in vivo studies, and minimal attention to the vermis per se.
Methods and Materials: Retrospective analysis of the midline sagittal view of the cerebellar vermis was performed in over 50 consecutive fetal MRI examinations performed for CNS and non-CNS indications. Analysis included identification of the fastigial point and vermian fissures, the degree of coverage of the 4th ventricle, and the measurement and ratio of cerebellar tissue above and below a line drawn through the fastigial point perpendicular to the dorsal surface of the brainstem. Fetuses imaged for the specific assessment of inferior vermian hypoplasia, cerebellar anomalies and neural tube defects were evaluated separately.
Results: Preliminary data: Post-conceptual age ranged from 19 to 37 weeks with a mean of 25 weeks. Useful imaging was obtained in over 40 studies for a total of over 130 measurements. Average craniocaudal diameter of the cerebellar vermis follows growth approximately predicted by the linear equation: diameter(mm)=0.75 x gestational age(weeks)-6, with an R2 value of 0.9. Average height above and below the fastigial point also followed a linear progression, with average percentages above and below of 47% and 53% respectively, and no significant change of this ratio with gestational age. Appearance of the cerebellar vermian fissures was seen at approximately the following gestational ages: primary and secondary at 20-21 weeks, prepyramidal and preculmenate at 23-24 weeks. Coverage of the 4th ventricle occured by approximately 23-24 weeks. Exceptions were noted among those fetuses being investigated for posterior fossa abnormalities. Correlation with in vitro studies shows a delay of approximately 4-5 weeks in the gestational age at which these features are seen.
Conclusion: Useful anatomic landmarks included identification of the fastigial point, presence of the fissures, the degree of coverage of the 4th ventricle and the measurements and ratio of cerebellar tissue above and below a line drawn through the fastigial point perpendicular to the dorsal surface of the brainstem. Fetuses not meeting these criteria are also described with clinical, pathologic and genetic diagnoses where available, although difficulties in the final clinical diagnosis remain.
Questions about this event email: ashley.robinson@utoronto.ca
Robinson MD, A,
MR Imaging of the Fetal Cerebellar Vermis in Utero: Description of Some Useful Anatomical Criteria for Normal and Abnormal Development. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3103637.html
