DIFFUSION ABNORMALITY OF CORPUS CALLOSUM IN ALZHEIMER’S DISEASE Ayşe Serap Fındıkoğlu, M.D. ¹ Karabekir Ercan, M.D. 2 H.Pinar Gunbey, , M.D. ¹Taksim Education and Research Hospital, Istanbul, Turkey 2Ataturk Education and Research Hospital, Ankara,

Background Alzheimer disease (AD), a progressive neurodegenerative disorder associated with disruption of neuronal function and gradual deterioration in cognition, function, and behaviour , is the most common cause of dementia in the elderly. Although AD is generally considered to affect grey matter, histological studies show pathological changes, such as a loss of axons and oligodendrocytes together with a reactive astrocytosis in the white matter (WM).

Wallerian degeneration, axonal damage , gliosis, and myelin breakdown have been suggested as possible pathologic mechanisms of WM lesions in AD.

The corpus callosum (CC) is the major white-matter tract that crosses the interhemispheric fissure in the human brain. It connects homologous regions of the cerebral cortex. The corpus callosum plays an integral role in relaying sensory, motor and cognitive information between homologous regions in the two cerebral hemispheres .

DTI (diffusion tensor imaging )is based on the nonbrownian movement of water molecules and a non-invasive technique with increased sensitivity that can identify white matter tracts. The anisotropic movement of water dominates in regions with high concentrations of axons. Therefore, quantitaive measurement of diffusion anisotropy can be an indicator of the integrity of cerebral WM .

Purpose Evaluate FA (fractional anisotropy ) and ADC (apparent diffusion coefficiency ) values of the sub-regions of the corpus callosum in patients with AD and the healty group This would lead to an understanding of the pathophsiology of the cognitive decline and would provide a proper background for interpreting the observed changes in AD

Materials and Methods Ethical committee approval 21 patients (16 F,5 M) with clinical AD based on the Diagnosis and Statistical Manual of Mental Disorders-IV criteria and examinations (Mini-Mental State Examination (MMSE) ) of cognitive status. Mean age 70.5 years (55-81) 20 healthy volunteers (10F, 10M) Mean age 69 years (55-75)

The mean MMSE score was 20. 5± 5 The mean MMSE score was 20.5± 5.9 (range 8-28) for patients with AD and, 29.4 ± 0,50 (range 29-30) for normal controls. 1.5T

Diffusion Tensor Imaging Single-shot spin-echo echo-planar sequence Diffusion sensitizing gradients were applied simultaneously along 6 non-collinear directions (b= 1000 s/mm²) FA and ADC values were obtained from the average of these slices 160 contiguous slices were acquired with 1 mm slice thickness and no gap The total acquisition time; 6 minutes and 30 s

The regions of interest (ROIs) were placed the following areas: the rostrum, the body and the splenium of the corpus callosum. They were sampled on the three consecutive slices on which they were fully volumed. Differences between these regions for the two subject groups were analysed by analysis of variance (ANOVA).

Results The FA values in the genu, body and in the splenium of the corpus callosum of patients with AD were lower and the ADC values were higher than controls. In patients with AD, the lowest values were found in the rostrum of the corpus callosum and also corpus callosum body’s FA values were lower than the splenium . But the difference did not reach statistical significance.

Conclusion Developments begins anteriorly at the genu and proceeds posteriorly to the splenium,except for the rostrum, which is the last area showing crossed fibers. As in all other parts of the brain, myelination of the corpus callosum proceeds in a posterior to anterior direction.

Age is a strong risk factor in AD. At older ages, loss of myelinated fibers and decreased axonal density would lead to lower FA values . The lowest FA values of rostrum result from two processes:development and degradation.