Neuropil vacuolation in brain: a reproducible histological processing artefact

Vacuolation, affecting principally white matter, in animal brains submitted for diagnostic histopathology was attributed to prolonged holding of fixed tissue in 70 per cent alcohol within an enclosed system automatic tissue processor. The effect was consistently reproduced in calf brains but not in pig brains, suggesting a possible species difference in tissue susceptibility. Also, the degree of vacuolation depended on undetermined processor factors additional to prolonged immersion in 70 per cent alcohol. The artefact resembles forms of intramyelinic oedema and can be avoided by holding tissue in primary fixative.