Thick and Short Fetal Corpus Callosum on Ultrasound: Added Value of Fetal Magnetic Resonance Diffusion Tensor Imaging With Tractography.

Background: Thick fetal corpus callosum (CC) is a rare finding and its significance in isolation is not clear. In this retrospective study, we aim to gain insight into the microarchitecture of CC in a cohort of fetuses with thick and short CC (isolated or associated with mild extra-/intracranial abnormalities) as seen on ultrasound (US), by using prenatal magnetic resonance (MR) diffusion tensor imaging (DTI) with fiber tractography, thereby allowing better characterization for postnatal prognosis.

Methods: Twelve fetuses met the inclusion criteria on US. The fetuses were further divided into group 1 (eight of twelve) with mild intra-/extracranial abnormalities or apparently isolated and group 2 (four of 12) with callosal lipoma (CL) on US. In all fetuses, both conventional MR imaging and DTI with tractography were done on 3T MRI.

Results: DTI fiber tractography showed an aberrant midline longitudinal supracallosal bundle (ASB) in all eight fetuses in group 1. Three of four fetuses in group 2 showed normal callosal architecture, and one showed an abnormal sigmoid bundle suggestive of partial agenesis of CC.

Conclusions: We have for the first time demonstrated an ASB on MR DTI with tractography in eight of 12 fetuses with thick and short CC (isolated or mild associated intra-/extracranial abnormalities). Postnatally, ASB is reported to be associated with abnormal neurodevelopmental outcomes even in isolation and hence is important in counseling and prognosis. In fetuses with CLs, DTI would demonstrate normal or abnormal callosal architecture which is obscured by echogenicity and help in counseling.