OC18.09: From fetal neurosonography to autopsy: comparative analysis of fetal corpus callosum malformations

To evaluate the accuracy of neurosonographic findings in fetuses diagnosed with corpus callosum (CC) abnormalities, when compared to brain autopsy findings. A retrospective analysis of 39 fetuses prenatally diagnosed with corpus callosum anomalies, and underwent TOP and autopsy. The cohort included three groups: complete agenesis of the CC (cACC), partial agenesis of the CC (pACC) or dysgenesis of the CC (dCC), either as isolated or non-isolated findings. Brain US findings were correlated to the macro and microscopic autopsy findings. Of the 39 prenatally diagnosed fetuses; cACC was diagnosed in 15/39 (38.5%), of which 9/15 (60%) were non-isolated (mainly sulcation abnormalities and ventriculomegaly), dCC was diagnosed in 18/39 fetuses (46%), of which 9/18 (50%) were non-isolated (mainly cavum septum pellucidum and sulcation abnormalities), and pACC was diagnosed in 6/39 fetuses (15.5%), of which 3/6 (50%) were non-isolated (sulcation, cerebellar and parenchymal findings). According to the macroscopic findings, the sensitivity, specificity, PPV and NPV of the US exam for the presence of cACC, dCC and pACC were 92 %, 86%, 92%, 86.7% / 72.4%, 71%, 84%, 55% / 94%,100%,100% and 66%, respectively. Microscopically, in 5/15 (30%) fetuses with cACC, rudimentary callosal fibers were found crossing the midline over the septum pellucidum or alternatively a significant thinning of all CC segments was found. Overall, in 30/39 (76.9%) of the autopsies, microscopic findings (mostly involving the cortex parenchymal lesions) were found. Neurosonography shows high accuracy in diagnosing CC abnormalities according to postmortem macroscopic exam. When cACC is diagnosed on US, rudimentary callosal fibers are present in 30% of cases. This may suggest that “typical” cACC represent, at least in some cases, an early arrest/limited fiber crossing, When callosal abnormalities are diagnosed prenatally on US, additional microscopic changes are commmon.