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Purpose: To describe the correlation between fetal imaging (in vivo and ex vivo) and neuropathology in two fetuses at early gestational age (GA) with isolated thick corpus callosum (CC), a rare finding whose pathological significance and neuropathology data are scarce., Methods: Two fetuses at 21-week GA underwent fetal MRI (fMRI) for suspected callosal anomalies at ultrasound (US). After fMRI results, termination of pregnancy (TOP) was carried out and post-mortem MRI (pmMRI) was performed. Neuropathology correlation consisted in macro and microscopic evaluation with sections prepared for hematoxylin-eosin and immunohistochemistry staining., Results: Fetal imaging confirmed in both cases the presence of a shorter and thicker CC with respect to the reference standard at the same GA, without a clear distinction between its different parts. Moreover, on pmMRI, an abnormal slightly T2-weighted hyperintense layer along the superior and inferior surface of CC was noted in both cases. At histopathology, these findings corresponded to an increased amount of white matter tracts but also to an abnormal representation of embryological structures that contribute to CC development, naming induseum griseum (IG) and the glioepithelial layer (GL) of the "callosal sling." After reviewing the literature data, we confirmed the recent embryological theory regarding the CC development and provide new insights into the pathophysiology of the abnormal cases., Conclusions: An abnormally thick CC at the early fetal period could be associated to an abnormal representation of the midline glia structures, so to result in potential disturbance of the axon guidance mechanism of callosal formation and eventually in CC dysgenesis., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Introduction: The main purpose was to investigate any early diffusion tensor imaging (DTI) changes in corpus callosum (CC) associated with acute cerebral hemisphere lesions in term newborns., Methods: We retrospectively analysed 19 cases of term newborns acutely affected by focal or multi-focal lesions: hypoxic-ischemic encephalopathy, hypoglycaemic encephalopathy, focal ischemic stroke and deep medullary vein associated lesions. DTI was acquired at 1.5 Tesla with dedicated neonatal coil. DTI metrics (apparent diffusion coefficient (ADC), fractional anisotropy (FA), axial λ(∐) and radial λ(⟂) diffusivity) were measured in the hemisphere lesions and in the CC. The control group included seven normal newborns., Results: The following significant differences were found between patients and normal controls in the CC: mean ADC was lower in patients (0.88 SD 0.23 versus 1.18 SD 0.07 μm(2)/s) and so was mean FA (0.50 SD 0.1 versus 0.67 SD 0.05) and mean λ(∐) value (1.61 SD 0.52 versus 2.36 SD 0.14 μm(2)/s). In CC the percentage of ADC always diminished independently of lesion age (with one exception), whereas in hemisphere lesions, it was negative in earlier lesions, but exceeded normal values in the older lesions., Conclusion: CC may undergo early DTI changes in newborns with acute focal or multi-focal hemisphere lesions of different aetiology. Although a direct insult to CC cannot be totally ruled out, DTI changes in CC (in particular λ(∐)) may also be compatible with very early Wallerian degeneration or pre-Wallerian degeneration.