Axonal Injury in Falls

Abstract

Amyloid precursor protein (APP) immunocytochemistry was used as a marker for axonal injury (AI) in a series of 16 cases of head trauma associated with fatal falls. Nine cases were falls from not more than the person's own height (falls from ≤ own height) and seven cases were falls from a distance greater than the person's own height (falls from > own height). AI was recorded on a series of line diagrams of standard brain sections divided into 116 sectors. AI around focal lesions (infarcts, hemorrhages, contusions) was distinguished from nonfocal axonal injury that was distant from any focal area of damage. The percentage of sectors showing focal AI provided the Focal Axonal Injury Score (FAIS) and the percentage showing nonfocal AI the Non-Focal Axonal Injury Score (NFAIS). The FAIS is a measure of secondary AI and the NFAIS of diffuse axonal injury (DAI). The percentage of sectors involved with AI (focal and nonfocal) provided the cumulative Axonal Injury Score (AIS). A semiquantitative grading system was also used to assess the severity of axonal injury in each sector and the sum of the grades from all sectors was expressed as a percentage to provide the Axonal Injury Severity Score (AISS). Widespread AI was present in all cases irrespective of the height of the fall. AI was present in the midbrain (94%), pons (94%), corpus callosum (100%), central grey matter (100%), and cerebral hemispheric white matter (94%). AIS ranged from 10 to 94 in falls from ≤ own height (mean 73) and from 38 to 92 in falls from > own height (mean 82). AISS ranged from 6 to 95 in falls from ≤ own height (mean 65) and 28 to 95 in falls from > own height (mean 72). There was no statistically significant difference in AIS or AISS between the two groups. The extent and severity of AI cannot be predicted from biomechanical data, such as the height of the fall, as the total AI in a given case is a variable mixture of Nonfocal AI (DAI) and Focal AI arising by secondary mechanisms, and APP immunostaining is unable to distinguish primary from secondary AI. However, the combination of the Hypoxic-Ischemic Score (HIS) defined as the percentage of sectors showing any hypoxic-ischemic damage ranging from neuronal "red cell change" to infarction in conjunction with the FAIS and NFAIS provided a measure of the relative contribution of primary and secondary AI in a given brain.