page_title: Diffuse axonal injury
section_title: Cytoskeleton disruption
hierarchical_section_title: Diffuse axonal injury / Characteristics / Cytoskeleton disruption
caption_attribution_description: English: Photomicrographs of coronal sections of a mouse brain stained with APP at 24h post brain injury (A,B). The box indicates the region of interest, which is shown at a higher magnification. Sagittal section of a mouse brain (C-H). Immunoreactive axonal profiles were observed as either granular (bulb) (B,G,H) or more elongated, fusiform (F) swellings at 24h post traumatic brain injury. Example of APP immunoreactive neurons (arrow heads) observed in the cortex underneath the impact site (E,G). No APP staining was observed in healthy control animals (D). Tissue sections were counterstained with hematoxylin.
context_page_description: Diffuse axonal injury is a brain injury in which scattered lesions occur over a widespread area in white matter tracts as well as grey matter. DAI is one of the most common and devastating types of traumatic brain injury and is a major cause of unconsciousness and persistent vegetative state after severe head trauma. It occurs in about half of all cases of severe head trauma and may be the primary damage that occurs in concussion. The outcome is frequently coma, with over 90% of patients with severe DAI never regaining consciousness. Those who do wake up often remain significantly impaired.
  DAI can occur across the spectrum of traumatic brain injury severity, wherein the burden of injury increases from mild to severe. Concussion may be a milder type of diffuse axonal injury.
context_section_description: Axons are normally elastic, but when rapidly stretched they become brittle, and the axonal cytoskeleton can be broken. Misalignment of cytoskeletal elements after stretch injury can lead to tearing of the axon and death of the neuron. Axonal transport continues up to the point of the break in the cytoskeleton, but no further, leading to a buildup of transport products and local swelling at that point. When it becomes large enough, swelling can tear the axon at the site of the break in the cytoskeleton, causing it to draw back toward the cell body and form a bulb. This bulb is called a retraction ball, the hallmark of diffuse axonal injury.
  When the axon is transected, Wallerian degeneration, in which the part of the axon distal to the break degrades, takes place within one to two days after injury. The axolemma disintegrates, myelin breaks down and begins to detach from cells in an anterograde direction (from the body of the cell toward the end of the axon), and nearby cells begin phagocytic activity, engulfing debris.
caption: Immunoreactive axonal profiles are observed as either granular (B, G, H) or more elongated, fusiform (F) swellings in the corpus callosum and the brain stem (H) at 24h post traumatic brain injury. Example of APP immunoreactive neurons (arrow heads) observed in the cortex underneath the impact site (E, G). No APP staining was observed in healthy control animals (D).[23]
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