Characteristic histopathological and molecular changes are found in the central nervous system. The most important diagnostic lesion is the presence of bilaterally symmetrical neuronal vacuolation, in processes and in some. Neurons with somal vacuolation frequently have an otherwise normal appearance. However, scattered necrotic some are seen and, as with natural scrapie, neuronal loss is an occasional but rarely conspicuous feature. Hypertrophy of astrocytes often accompanies vacuolation.
Cerebral amyloidosis is an inconstant histological feature of the scrapie family of diseases.
It is present in BSE but mostly as sparse, focal deposits in a small proportion of cases. Congophilic plaques showing characteristic dichroism in polarized light were found in the thalamus of one out of 20 cases examined systematically for amyloid. In contrast, the vacuolar change was often minimal in the cerebellum, hippocampus, cerebral cortex and basal nuclei. The vacuolar patterns in the brain were remarkably uniform in contrast to the variability described in sheep scrapie. These included numerous membrane-bound intracellular vacuoles, predominantly in dendrites.