Diffuse axonal injury in infants with nonaccidental craniocerebral trauma: enhanced detection by beta-amyloid precursor protein immunohistochemical staining.

OBJECTIVE: Accurate identification of diffuse axonal injury is important in the forensic investigation of infants who have died from traumatic brain injury. beta-Amyloid precursor protein (beta-APP) immunohistochemical staining is highly sensitive in identifying diffuse axonal injury. However, the effectiveness of this method in brain-injured infants has not been well established. The present study was undertaken to assess the utility of beta-APP immunohistochemistry in detecting diffuse axonal injury in infants with either shaken baby syndrome or blunt head trauma.

MATERIALS AND METHODS: Archival formalin-fixed, paraffin-embedded blocks from infants (<1 year old) with shaken baby syndrome (7 cases) and blunt head trauma (3) and blocks from 7 control cases that included nontraumatic cerebral edema (1), acute hypoxic-ischemic encephalopathy (1), and normal brain (5) were immunostained for beta-APP. A semiquantitative assessment of the severity of axonal staining was made. Corresponding hematoxylin-eosin-stained sections were examined for the presence of axonal swellings.

RESULTS: Immunostaining for beta-APP identified diffuse axonal injury in 5 of 7 infants with shaken baby syndrome and 2 of 3 infants with blunt head trauma. Immunoreactive axons were easily identified and were present in the majority of the sections examined. By contrast, hematoxylineosin staining revealed axonal swellings in only 3 of 7 infants with shaken baby syndrome and 1 of 3 infants with blunt head trauma. Most of these sections had few if any visible axonal swellings, which were often overlooked on initial review of the slides. No beta-APP immunoreactivity was observed in any of the 7 control cases.

CONCLUSIONS: Immunostaining for beta-APP can easily and reliably identify diffuse axonal injury in infants younger than 1 year and is considerably more sensitive than routine hematoxylin-eosin staining. We recommend its use in the forensic evaluation of infants with fatal craniocerebral trauma.