Organising white matter in a brain without corpus callosum fibres

Abstract

Isolated corpus callosum dysgenesis (CCD) is a congenital malformation which occurs during early development of the brain. In this study, we aimed to identify and describe its consequences beyond the lack of callosal fibres, on the morphology, microstructure and asymmetries of the main white matter bundles with diffusion imaging and fibre tractography. Seven children aged between 9 and 13 years old and seven age- and gender-matched control children were studied. First, we focused on bundles within the mesial region of the cerebral hemispheres: the corpus callosum, Probst bundles and cingulum which were selected using a conventional region-based approach. We demonstrated that the Probst bundles have a wider connectivity than the previously described rostrocaudal direction, and a microstructure rather distinct from the cingulum but relatively close to callosal remnant fibres. A sigmoid bundle was found in two partial ageneses. Second, the corticospinal tract, thalamic radiations and association bundles were extracted automatically via an atlas of adult white matter bundles to overcome bias resulting from a priori knowledge of the bundles' anatomical morphology and trajectory. Despite the lack of callosal fibres and the colpocephaly observed in CCD, all major white matter bundles were identified with a relatively normal morphology, and preserved microstructure (i.e. fractional anisotropy, mean diffusivity) and asymmetries. Consequently the bundles' organisation seems well conserved in brains with CCD. These results await further investigations with functional imaging before apprehending the cognition variability in children with isolated dysgenesis.

Isolated agenesis of the corpus callosum and normal general intelligence development during postnatal life: a case report and review of the literature

“…In fact, the spectrum of clinical features of this defect is heterogeneous and depends on several factors, such as the extension of the CC damage (complete or partial), the presence and severity of associated defects, clinical comorbidities, as well as on the magnitude of residual interhemispheric transfer through other commissures (anterior, posterior, and hippocampal) [5]. Probst and heterotopic bundles also develop in patients with AgCC and may provide a certain degree of compensatory connectivity [25,26].…”

“…These patients often present neuropsychological defects at the end of childhood and beginning of adolescence, when myelination and development of the CC is completed and the reliance on this structure becomes maximum [18,29]. Before such a moment, the presence of other cerebral commissures provides a certain degree of compensatory connectivity [25,26]. However, individuals with AgCC and apparent normal intelligence become more susceptible to increases in cognitive demand over time.…”

The use of diffusion tractography to characterize a corpus callosum malformation in a dog

“…Being able to identify the exact white matter malformation present and whether LCFs are formed therefore is important for understanding which pathophysiological pathway is the cause for the malformation in an individual case. In vivo diagnosis is limited with standard structural MRI because of its inherent inability to resolve specific white matter tracts, but more recently the advanced technique of fiber tractography has been applied to the evaluation of white matter in humans with CCM . This technique uses diffusion tensor imaging to virtually reconstruct and delineate white matter fiber tracts in 3‐dimensional (3D) space .…”

Contralateral targeting of the corpus callosum

“…However, using diffusion magnetic resonance imaging (dMRI) and tractography, it has been demonstrated that contralateral callosal targeting can be highly variable and misregulated in humans with gross structural malformations of the corpus callosum at the midline (Tovar-Moll et al, 2007;Wahl et al, 2009;Bénézit et al, 2015). These defects in contralateral targeting appear to be highly variable across individuals with similar callosal remnants at the sagittal midline ( Figure 1.1 and continues to elaborate both anteriorly and posteriorly at the midline until at least 20 gestational weeks (Rakic and Yakovlev, 1968;Huang et al, 2006).…”

“…For instance, failure of midline crossing often results in callosal agenesis, which is a congenital brain malformation occurring in 1 in 4000 human live births, which includes complete or partial absence of the corpus callosum as well as callosal hypoplasia (Hetts et al, 2006;Paul et al, 2007;Edwards et al, 2014). The primary aetiology of callosal agenesis is a failure of the midline substrate to fuse (Gobius et al, 2016), which causes callosal axons to stall in the ipsilateral hemisphere, commonly forming Probst bundles (Probst, 1901;Tovar-Moll et al, 2007;Bénézit et al, 2015).…”