Structure, Integrity, and Function of the Hypoplastic Corpus Callosum in Spina Bifida Myelomeningocele

Abstract

Although there are many studies of people with complete or partial hypogenesis of the corpus callosum (CC), little is understood about the hypoplastic CC in which all structures are present but thinned. Spina bifida myelomeningocele (SBM) is a model organism for such studies because many have either a hypogenetic or hypoplastic CC. We used diffusion tensor tractography (DTT) to evaluate the hypoplastic CC in SBM and its relation to interhemispheric functions and intelligence quotient (IQ). Participants were individuals with SBM and an intact or hypoplastic CC (n = 28), who were compared to a typically developing comparison group (n = 32). Total and regional DTT volume and integrity measures (fractional anisotropy, axial diffusivity, and radial diffusivity) of the CC were related to measures of intelligence (IQ), bimanual motor functioning, and dichotic auditory performance. As predicted, DTT showed variations in volume and integrity that were maximized in the entire CC and the posterior CC. IQ correlated with entire CC volume, anterior and posterior regional CC volumes, and also with measures of integrity. Bimanual motor functioning correlated with the anterior and posterior volumes of the CC but not with any integrity measures. Axial diffusivity in the posterior CC was negatively correlated with right ear dichotic listening performance. The hypoplastic CC is not macrostructurally or microstructurally intact in SBM, even when it appears radiologically intact. Both volume and integrity of the posterior regions were related to reductions in IQ and to interhemispheric processing. These findings may transfer to other disorders characterized by a hypoplastic CC.

Plasticity of Interhemispheric Temporal Lobe White Matter Pathways Due to Early Disruption of Corpus Callosum Development in Spina Bifida

“…In support of this hypothesis, we found that people with SBM and both CC hypoplasia and hypogenesis showed decreased FA and AD, and increased RD compared to the TD group. These results are supported by a previous investigation of CC microstructure that was restricted to CC hypoplasia in SBM, which showed reduced FA and increased RD in the entire CC, with posterior subregions showing the greatest reductions in integrity (Crawley et al, 2014).…”

“…Diffusion tensor imaging (DTI) and tractography methods have made it possible to examine the structure of the CC and identify various atypical white matter connections. Crawley et al (2014) used DTI and deterministic tractography to segment the CC in individuals with thinning of the CC due to hydrocephalus in spina bifida and found that posterior sections had the greatest reductions in volume and microstructural integrity. In addition, Probst bundles, which are anomalous, anterior-posterior coursing connections, as well as interhemispheric sigmoid-shaped bundles connecting heterotopic cortical regions, have been identified in individuals with congenital disorders affecting CC development (Barkovich and Raybaud, 2012;Lee et al, 2004;Owen et al, 2013;Tovar-Moll et al, 2007Wahl et al, 2009).…”

Spina bifida

“…Quantitative studies of the corpus callosum show marked volume and integrity differences, especially posteriorly in cases with hypogenesis or severe hypoplasia 49. Reduced integrity has also been shown in the genu, but not in the anterior commissure 50. There is recent evidence that corpus callosal defects can also be associated with closed spinal dysraphism 51.…”

The clinical features of paediatric neural tube defects changed in a tertiary care centre between 1997 and 2015

“…The patients were diagnosed late and often as a consequence of urologic symptoms or skin pits. Other studies have reported that hydrocephalus and Chiari II malformation are present in the majority of children with open NTDs , with the occurrence of severe brainstem dysfunction and subsequent need for surgical decompression in 4–8.8% . Cognitive difficulties have been described in children with open NTDs both in regard to low IQ and the need for assistance with schoolwork .…”

“…Previous research has pointed to the associated presence of hydrocephalus as an explanation , which is in agreement with our data. There may be an association between reduced cognition and hydrocephalus as a result of anomalies in cortical thickness and gyrification or corpus callosum hypoplasia .…”