Ventral and dorsal visual streams in posterior cortical atrophy: A DT MRI study

Abstract

Using diffusion tensor magnetic resonance imaging tractography, ventral (inferior longitudinal fasciculus) and fronto-occipital (inferior fronto-occipital fasciculus) and dorsal (fronto-parietal superior longitudinal fasciculus) visual pathways were assessed in 7 patients with posterior cortical atrophy (PCA), showing either predominantly ventral or additional dorsal cognitive deficits. Corpus callosum and corticospinal tracts were also studied. Gray and white matter atrophy was assessed using voxel-based morphometry. In all PCA patients, abnormal diffusivity indexes were found in bilateral inferior longitudinal fasciculus and inferior fronto-occipital fasciculus, with a left-side predominance. Patients also had mild microstructural damage to the corpus callosum. The 2 patients with more dorsal symptoms also showed right fronto-parietal superior longitudinal fasciculus abnormalities. Corticospinal tracts were normal, bilaterally. When studied separately, patients with ventral clinical impairment showed a pattern of atrophy mainly located in the ventral occipitotemporal regions, bilaterally; patients with both ventral and dorsal clinical deficits showed additional atrophy of the bilateral inferior parietal lobe. Magnetic resonance imaging patterns of abnormalities mirror closely the clinical phenotypes and could provide reliable ante mortem markers of tissue damage in PCA.

White Matter Degeneration in Atypical Alzheimer Disease

“…The most important finding of the present study is that WM damage was more severe and more widely distributed than expected on the basis of cortical atrophy and the cognitive profiles, particularly in the atypical AD forms in which cortical atrophy remains localized and the clinical symptoms relatively focal. Together with the few previous studies in which WM damage was assessed in separate series of EOAD (4,18), PCA (22)(23)(24), and lvPPA (19)(20)(21), our findings indicate that DT MR imaging may be able to demonstrate subtle abnormalities along WM pathways that link atrophic regions with still unaffected gray matter regions. More importantly, we found that DT MR imaging has the potential to allow assessment of the extensive disorganization of brain networks in focal AD, even before overt cognitive deficits become apparent.…”

“…Despite the growing number of studies that show that severe microstructural abnormalities occur NEURORADIOLOGY: White Matter Degeneration in Atypical Alzheimer Disease Caso et al along WM tracts in late-onset AD besides the known loss of neurons in the gray matter, to date, a few DT MR imaging studies have demonstrated the WM network involvement in EOAD (4,18), lvPPA (19)(20)(21), and PCA (22)(23)(24). To our knowledge, no study has been conducted to compare the patterns of WM damage in EOAD, lvPPA, and PCA.…”

Visuospatial deficits in posterior cortical atrophy: structural and functional correlates

“…In the present study, we focused on line bisection because in our experience other tests, such as target cancellation, are more likely to be contaminated by simultagnosia or object recognition deficits 17. As a consequence, line bisection was sometimes more likely to demonstrate signs of spatial bias in PCA than cancellation tests 18 19.…”

Insights into White Matter Damage in Alzheimer's Disease: From Postmortem to in vivo Diffusion Tensor MRI Studies

“…In early-onset AD, WM damage was found to be widespread and severer in the posterior fibers of the cingulum and CC compared to late-onset AD [16], while in PCA [65] and lvPPA patients [66,67] a prominent WM damage along visuospatial and language pathways, respectively, was found (fig. 2).…”