Gross Anatomy of the Corpus Callosum in Alzheimer’s Disease: Regions of Degeneration and Their Neuropsychological Correlates

Abstract

Background/Aims: Differences in the gross shape of the corpus callosum (CC) and its subregional areas were investigated on brain MRI of patients with probable Alzheimer’s disease (AD) and age- and gender-matched healthy normal control subjects. The AD patients differed from the normal control subjects in terms of a more convex shape and a reduced area of the CC. Methods: As for the comparisons of the subregional areas of the CC, we adapted a splitting method which takes into account the modification of the global shape of the CC, and we implemented it by normalizing the CC, to avoid the bias introduced by the observed callosal shape variability. Results: The application of this method unveiled that the regional CC reductions were located in the anterior and posterior third of the CC, i.e. where small myelinated fibers are more frequent. None of the neuropsychological scores collected at the time of the MRI investigation of AD could predict a regional and/or overall callosal area reduction. The only measure that correlated with area of the isthmus of the CC was the MMSE that was administered to all participants. Conclusions: This latter result may be used as an in vivo indicator of the progress of neocortical disintegration in AD.

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

“…With regard to the region of interest (ROI) studies, for example, it has been shown that the earlier findings relied on manually tracing the CC and on the common callosal parcellation schemes (i.e., according to Witelson [19,44]; Weis [45][46][47]; or Hampel [11,18]) have generated a controversy regarding the assumed topography of callosal fibers [48]. In fact, in a previous study, we demonstrated that pre-defining callosal regions can give rise to misleading results [7]. This is also true for the voxelbased morphometry (VBM) technique.…”

“…Numerous ROI studies have investigated callosal changes in AD patients [7,[10][11][12][14][15][16][17][18][19]24,25,27,28,31,38,42,43]. Overall, these studies report a reduction of the total callosal area, specifically of the rostrum, genu, anterior body, isthmus, and splenium of the CC.…”

“…Many studies included AD patients with different degrees of pathology, for example, from mild to severe [7,14,15] or from mild to moderate [8,10,42] (see Tables 1, 2, 3). Thus, results may have been biased by the presence of subjects at different illness stages.…”

“…The corpus callosum (CC) has been implicated in this process [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In particular, it has been suggested that callosal atrophy in AD is the anatomical correlate of Wallerian degeneration of commissural nerve fibers.…”

“…In fact, the main result mentioned above, that is atrophy mainly in the callosal anterior and posterior subregions, comes from studies of AD groups that included patients in different illness stages, ranging from mild to severe dementia [7,8,[10][11][12][14][15][16][17][18][19][23][24][25][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] and sometimes selected using different diagnostic criteria [10,14].…”