Tissue tears in the white matter after lateral fluid percussion brain injury in the rat: relevance to human brain injury.

A characteristic feature of severe diffuse axonal injury in man is radiological evidence of the "shearing injury triad" represented by lesions, sometimes haemorrhagic, in the corpus callosum, deep white matter and the rostral brain stem. With the exception of studies carried out on the non-human primate, such lesions have not been replicated to date in the multiple and diverse rodent laboratory models of traumatic brain injury. The present report describes tissue tears in the white matter, particularly in the fimbria of Sprague-Dawley rats killed 12, 24, and 48 h and 7 days after lateral fluid percussion brain injury of moderate severity (2.1-2.4 atm). The lesions were most easily seen at 24 h when they appeared as foci of tissue rarefaction in which there were a few polymorphonuclear leucocytes. At the margins of these lesions, large amounts of accumulated amyloid precursor protein (APP) were found in axonal swellings and bulbs. By 1 week post-injury, there was macrophage infiltration with marked astrocytosis and early scar formation. This lesion is considered to be due to severe deformation of white matter and this is the first time that it has been identified reproducibly in a rodent model of head injury under controlled conditions.