P4‐108: Ventral and dorsal visual streams in posterior cortical atrophy

Posterior cortical atrophy (PCA) is characterized by a progressive cognitive impairment involving visual and visuo-motor functions. Recently, a classification of PCA into dorsal and ventral subtypes has been suggested. The ventral subtype is mostly characterized by visual agnosia, prosopagnosia, achromatopsia, and alexia, while the dorsal subtype is associated with optic ataxia and apraxia, neglect, and agraphia. Our aim was to explore the brain pathways underlying cognitive deficits in PCA, using diffusion tensor (DT) MRI tractography. Seven PCA patients and 13 age- and sex-matched healthy controls were studied. Bilateral inferior longitudinal (ILF), inferior fronto-occipital (IFOF), arcuate, and fronto-parietal superior longitudinal (SLF) fasciculi were tracked. The corpus callosum (CC) and cortico-spinal tracts (CST) were also studied. From each tract, mean diffusivity (MD), fractional anisotropy (FA), as well as parallel (ParD) and transverse (TraD) diffusivities were obtained. Grey (GM) and white (WM) matter atrophy patterns were assessed using voxel-based morphometry. PCA patients showed a clinical syndrome primarily characterized by visual object agnosia and prosopagnosia. Compared with controls, they had significantly higher MD, ParD and TraD and lower FA in the left ILF and IFOF. In addition, the right ILF had significantly higher MD and TraD and lower FA, the right IFOF had higher MD and TraD, and the CC higher MD. The fronto-parietal SLF, arcuate fasciculus, and CST were spared bilaterally. PCA patients also had GM atrophy in posterior temporal, inferior parietal and occipital regions bilaterally, and WM atrophy in the ventral occipito-temporal region, bilaterally.