Variants in the circle of Willis and white matter disease in Ecuadorian Mestizos.

BACKGROUND AND PURPOSE: Studies on Whites and Asians have shown contradictory results on the association between an incomplete circle of Willis (CoW) and white matter disease (WMD). We evaluated such relationship in Ecuadorian Mestizos. METHODS: Ecuadorian Mestizos aged ≥40 years were evaluated with MRI and MRA. WMD was graded according to the modified Fazekas' scale, and the CoW was classified as complete or incomplete according to the presence or absence of one A1 segment of the anterior cerebral artery or one or both P1 segments of posterior cerebral arteries. RESULTS: A total of 315 persons (mean age 64.7 ± 13.4 years, 56.5% women) were prospectively enrolled over 6 months. MRAs revealed a complete CoW in 65.1%, and MRIs showed WMD in 62.5% of cases. Irrespective of age and sex, incompleteness of the CoW was not associated with a higher prevalence or severity of WMD. In contrast, age was an independent risk factor for the occurrence of WMD. CONCLUSIONS: In the Ecuadorian Mestizo population, WMD occurrence and severity do not seem to be related to incompleteness of the CoW.

Structural connectivity of the default mode network and cognition in Alzheimer׳s disease.

Disconnectivity between the Default Mode Network (DMN) nodes can cause clinical symptoms and cognitive deficits in Alzheimer׳s disease (AD). We aimed to examine the structural connectivity between DMN nodes, to verify the extent in which white matter disconnection affects cognitive performance. MRI data of 76 subjects (25 mild AD, 21 amnestic Mild Cognitive Impairment subjects and 30 controls) were acquired on a 3.0T scanner. ExploreDTI software (fractional Anisotropy threshold=0.25 and the angular threshold=60°) calculated axial, radial, and mean diffusivities, fractional anisotropy and streamline count. AD patients showed lower fractional anisotropy (P=0.01) and streamline count (P=0.029), and higher radial diffusivity (P=0.014) than controls in the cingulum. After correction for white matter atrophy, only fractional anisotropy and radial diffusivity remained significantly lower in AD compared to controls (P=0.003 and P=0.05). In the parahippocampal bundle, AD patients had lower mean and radial diffusivities (P=0.048 and P=0.013) compared to controls, from which only radial diffusivity survived for white matter adjustment (P=0.05). Regression models revealed that cognitive performance is also accounted for by white matter microstructural values. Structural connectivity within the DMN is important to the execution of high-complexity tasks, probably due to its relevant role in the integration of the network.