OC14.03: Added value of fetal MR tractography in evaluation of the short corpus callosum: preliminary results

Improved prenatal imaging lead to a significant increase in diagnosis of a short corpus callosum (SCC). However, the differentiation between dysgenesis or transient developmental variations of the corpus callosum is crucial. In dysgenesis of the corpus callosum, postnatal studies demonstrated failure of fibres to cross the midline, resulting in an aberrant longitudinal tract named a “Probst bundle” (PB). Recently fibre tractography have become feasible in fetal MRI, enabling virtual delineation of fibre trajectories. To assess the feasibility and potential benefit of fetal MR tractography in distinguishing different patterns of SCC, beyond conventional imaging. Prospective study of cases referred for MRI evaluation because of a SCC < - 2 Z-score between November 2015 and January 2019. Fibre tractography were performed in all cases. One operator (AEM) evaluated the quality of the tractography based on a score ranging from 0 (poor quality) to 2 (good quality). Only cases with scores ≥1 were considered. The morphology of the frontal horns, colpocephaly and the presence of PB on the tractography were evaluated. 30 fetal MRI with tractography were performed. Four MRIs were excluded (complete agenesis of the CC). The 26 remaining fetuses were diagnosed with a SCC at a median GA of 31 weeks [28–34.5] with an average CC length of -3.8 SD. Quality scores were 0, 1 and 2 in 3 (12%), 5 (19%) and 18 (69%) cases, respectively. PB were identified in 11/23 cases (48%) with morphological abnormalities in 91 % of those cases (10/11) compared to the 12 cases with no Probst bundles identified (52%) with no morphological abnormalities (p < 0.005). Fetal tractography appears to be feasible and differentiate 2 patterns of fibers in SCC. Our preliminary results suggest that the ventricular dysmorphology may be associated to the presence of PB. Clinical and genetic correlations are now required in order to better understand the significance and prognostic value of these findings.