Alexander Peter Lin, Presenter: Nothing to Disclose

Kevin Berry, Abstract Co-Author: Nothing to Disclose

Willis Wong BS, Abstract Co-Author: Nothing to Disclose

Brian D. Ross MD, Abstract Co-Author: Nothing to Disclose

Hydrocephalus results in dramatic but reversible compression of the white matter of the brain. To elucidate the underlying physiological mechanisms we applied quantitative MRS and DTI.

Proton MRS and DTI were acquired in 10 patients at various stages of ventricular dilation, 10 patients with confirmed hydrocephalus, and 10 normal, non-hydrocephalic age-matched controls. Proton MRS was acquired using single voxel short-echo MRS in volumes of interest located in the grey and white matter. DTI was acquired using mutli-slice spin-echo echo planar imaging using pulsed-gradient/Stejskal-Tanner diffusion weighting and spectral-spatial RF excitation. Tensorcalc (Moseley et al, Stanford University) was used to generate ADC and FA maps of the raw data. DTIstudio (Mori et al, Johns Hopkins University) was used to generate fiber tracts based on the FACT algorithm. FA and ADC measurements were made at the centrum semuiovale, corpus callosum, and grey and white matter regions.

MRS results demonstrated normal metabolite concentrations in hydrocephalus patients. This would appear to indicate that cerebral metabolite and osmolyte concentrations remain constant thus explaining how some patients can retain normal intellectual function despite the decrease in brain volume. Fractional anisotropy demonstrates significant increases to the lateral edges of the ventricles and decreases in the corpus callosum. Furthermore, fiber tracking results demonstrate a bowing effect of the fibers tracts at the lateral ventricles. These fibers are involved in the corticospinal tract that supply motor function to the legs, possibly explaining the gait disturbances in some of the patients. The sacral fibers of the same tract are involved in urinary function which also appear to be affected based on the virtual dissection results.

No change in the principle brain metabolite concentrations was observed, however, DTI showed increase FA in the periventricular white matter and decreased FA in the lateral fibers due to “bowing” of the fiber tracts that may explain the gait disturbance exhibited in patients with normal pressure hydrocephalus.

Lin, A, Berry, K, Wong, W, Ross, B, Virtual Dissections: Noninvasive Characterization of Fiber Tracts in Normal Pressure Hydrocephalus with Diffusion Tensor Imaging and MR Spectroscopy.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4412373.html