HEMODIALYSIS INCREASES APPARENT DIFFUSION-COEFFICIENT OF BRAIN WATER IN NEPHRECTOMIZED RATS MEASURED BY ISOTROPIC DIFFUSION-WEIGHTED MAGNETIC-RESONANCE-IMAGING

The nature of brain edema in dialysis disequilibrium syndrome (DDS) wa s investigated by diffusion-weighted magnetic resonance imaging (DWI). DWI was performed on normal or bilaterally nephrectomized rats before , and immediately after, hemodialysis. Hemodialysis was performed with a custom-made dialyzer (surface area 150 cm(2)) against a bicarbonate -buffered bath for 90 min with or without 70 mM urea. Hemodialysis wit h non-urea bath decreased plasma urea by 21 mM, and plasma osmolality by 22 mos-mol/kg H2O, and increased brain water content by 8.0% (all P <0.05), while hemodialysis with urea bath did not affect plasma urea, osmolality, or brain water content, Three sets of axial DWI images of the brain were obtained at different gradient weighing factors with a n in-plane resolution of 0.39 mm(2). The apparent diffusion coefficien t (D-app) of the brain water was not affected by bilateral nephrectomy , or by hemodialysis in normal rats, In nephrectomized rats, brain D-a pp was significantly increased after dialysis with non-urea bath (1.15 +/-0.08 vs 0.89+/-0.07 x 10(-9) m(2)/sec, P <0.01). No significant cha nges of brain water D-app could be observed after dialysis with urea b ath. The increased D-app associated with DDS indicates that brain extr acellular water increases and/or intracellular water decreases after h emodialysis, Our results strongly suggest that the brain edema induced by hemodialysis in uremic rats is due to interstitial edema rather th an cytotoxic edema, Furthermore, our results support a primary role fo r the ''reverse urea effect'' in the pathogenesis of brain edema in DD S, DWI may be a useful diagnostic tool for DDS in patients with end-st age renal disease.