β-amyloid precursor protein immunohistochemistry in the evaluation of pediatric traumatic optic nerve injury

Objective The pathologic markers of nonaccidental injury (NAI) of the central nervous system (CNS) of infants and young children include subdural, subarachnoid, and retinal hemorrhages. Immunohistochemical staining for β-amyloid precursor protein (βAPP) has been used to investigate traumatic axonal injury of the brain, brain stem, and spinal cord injuries, and has potential as an additional indicator of traumatic head injury. A single study has reported that βAPP immunostaining of the optic nerve in CNS NAI reveals axonal damage. The purpose of our study was to explore further the utility of βAPP immunostaining of optic nerves for the detection of traumatic axonal injury. Methods We used hematoxylin-eosin and βAPP immunostaining to evaluate the eyes and optic nerves in 18 cases of CNS nonaccidental blunt force head injury, 4 cases of homicidal blunt force abdominal injury (BFAI), 1 homicidal suffocation, 1 case of sudden infant death syndrome, 1 near-drowning, 1 overlay (clinical history: "found under sleeping mother in bed"), 1 motor vehicle accident, and 6 natural deaths in children ≤5 years of age. Results Evaluation of the cases of CNS NAI revealed 17 of 18 (94%) with subdural hemorrhage; 15 of 18 (83%), subarachnoid hemorrhage; 17 of 18 (94%), retinal hemorrhage; 16 of 18 (88%), perioptic nerve hemorrhage; and 6 of 18 (33%), optic nerve βAPP immunoreactive axonal swellings. The only nontraumatic case that demonstrated βAPP immunoreactive axonal swellings was the near-drowning. No cases of BFAI, suffocation, overlay, or natural deaths revealed any retinal or perioptic nerve hemorrhage or significant optic nerve βAPP immunoreactivity. Global hypoxic-ischemic injury was present in 21 cases, of which 19 had evidence of brain swelling, and 7 demonstrated βAPP immunoreactive axonal swellings. Conclusions These findings confirm the presence of optic nerve axonal injury in some cases of fatal pediatric CNS NAI.