In Vivo Structural Neuroanatomy of Corpus Callosum in Alzheimer's Disease and Mild Cognitive Impairment Using Different MRI Techniques: A Review

Abstract

Abstract. The corpus callosum (CC), which connects the two cerebral hemispheres, is the largest white matter fiber bundle in the human brain. This structure presents a peculiar myelination pattern: it has small diameter fibers, located in the genu, which myelinate much later in normal development, and large diameter fibers of the splenium, which myelinate early in development. Although the pathology of AD mainly involves the cerebral gray matter structure, there is evidence that white matter may also be involved. To illustrate callosal white matter changes in AD pathology, in this review we summarize in vivo imaging studies in humans, focusing on region of interest, voxel-based morphometry, diffusion-weighted imaging, and diffusion tensor imaging techniques. Our aims were to identify where in the CC, when in the different stages of AD, and how callosal changes can be detected with different MRI techniques. Results showed that changes in the anterior (genu and anterior body) as well as in the posterior (isthmus and splenum) portions of the CC might already be present in the early stages of AD. These findings support the hypothesis that two mechanisms, Wallerian degeneration and myelin breakdown, might be responsible for the region-specific changes detected in AD patients. Wallerian degeneration affects the posterior CC subregion, which receives axons directly from those brain areas (temporo-parietal lobe regions) primarily affected by the AD pathology. Instead, the myelin breakdown process affects the later-myelinating CC subregion and explains the earlier involvement of the genu in CC atrophy.

Human neural stem cell transplantation into the corpus callosum of Alzheimer's mice

“…The CC is a prime target, given that it is the largest white matter tract affected early in AD 11. Moreover, it connects numerous areas of the brain, including the nucleus basalis of Meynert, a cholinergic structure affected in AD 9.…”

“…One of the proposed targets is the corpus callosum (CC), a large white matter tract that includes the neural pathway starting at the nucleus basalis of Meynert, and connects the majority of frontal, parietal, and occipital cortical areas to corresponding regions in the contralateral hemisphere. CC size changes and atrophy occur in AD patients and correlate with progression of dementia severity 9, 10, 11. This, coupled with the fact that stem cells migrate through large white matter tracts,12, 13, 14 makes the CC a potentially effective target.…”

White Matter Integrity Disruptions Associated With Cognitive Impairments in Type 2 Diabetic Patients

“…The CC plays an important role in interhemispheric functional integration. In AD (31,32) and MCI (32,33), the loss of WM connectivity and regionally specific atrophy of the CC are observed. It follows that CC abnormalities may be related to cognitive deficits.…”

Structural Neural Phenotype of Autism: Preliminary Evidence from a Diffusion Tensor Imaging Study Using Tract-Based Spatial Statistics

“…This was followed by the right and left inferior fronto-occipital fasciculi, respectively. Abnormalities in the corpus callosum may be a nonspecific manifestation of generalized deficits in long-range connectivity because abnormalities also have been reported in other neuropsychiatric disorders such as schizophrenia, 35 Alzheimer disease, 36 and bipolar disorder. 37 However, significant findings in the inferior fronto-occipital fasciculus may reflect ASD-specific atypicalities given its connections to all major cerebral lobes, thus potentially connecting all major modules in the social brain network (Fig 1).…”