Characteristic changes in T-2-value, apparent diffusion coefficient, and ultrastructure of substantia nigra evolving exofocal postischemic neuronal death in rats

To correlate the magnetic resonance (MR) imaging characteristics of exofoca l postischemic neuronal death (EPND) in the substantia nigra (SN) with asso ciated histologic changes, we occluded the left middle cerebral artery of r ats for 1, 4, 7, or 12 days. Day 1 (post-occlusion) T-2-weighted images rev ealed high signal intensity indicative of infarction in the ipsilateral cau date nucleus, putamen, and cortex but not the SN. Diffusion-weighted images (DWIs) on day 1 similarly failed to reveal any changes in the SN. However, on day 4, DWIs revealed high signal intensity in the ipsilateral SN, in wh ich the apparent diffusion coefficient (ADC) transiently decreased (P<0.05) while the T-2-value increased (P<0.05). These measures returned to and rem ained at control levels on days 7 and 12, Histologic examination on day 4 r evealed dark-staining neurons, markedly swollen perivascular astrocytic end -feet, many swollen neurons with cytoplasmic microvacuoles that mainly orig inated in the rough endoplasmic reticulum, and strongly roughed neuropils. Reactive astrocytes and dark neurons most frequently appeared on days 7 and 12. The severity of cellular swelling paralleled the change in the ADC. Th ese results demonstrate that a transient high-intensity signal on DWIs, ind icative of a decrease in the ADC, is predictive of EPND in the SN. (C) 2001 Elsevier Science B.V. All rights reserved.