| Print Date: | May 26, 2013, 1:25 am |
| Title | 1. Diffuse axonal injury (DAI) of the frontal/parietal lobes, corpus callosum, and cerebellum. 2. Intraventricular hemorrhage |
| Text | Diffuse axonal injury is one of the two most common types of traumatic parenchymal lesions encountered in patients with severe head injury. DAI lesions constituted 48% of all primary intra-axial lesions in one prospective MR study of patients with moderately severe head injuries. Pathologically, DAI is characterized by multiple, small, focal traumatic lesions scattered throughout the white matter. Most lesions spare the overlying cortex, frequently being located at the gray-white matter interface. Occasionally, the cortex may be secondarily involved by larger lesions. Initially, DAI lesions are usually (80%) nonhemorrhagic, although over time small petechial hemorrhages may occur within some of the lesions. DAI lesions of lobar white matter usually range in size from 5-15 mm while those of larger white matter tracts, such as the corpus callosum, tend to be much larger. DAI lesions are usually ovoid to elliptical in shape with the long axis parallel to the orientation of the axonal tracts that are involved. When present, DAI lesions are usually multiple with as many as 15-20 lesions found in some severely injured patients.
DAI tends to occur in three fundamental anatomical areas: 1. cerebral lobar white matter, 2. corpus callosum, and 3. dorsolateral aspect of the upper brain stem. Adams has emphasized that DAI is inclined to occur in these three areas in successive stages, with the involvement becoming sequentially deeper with increasing severity of trauma. In patients with mild head trauma, DAI lesions may be confined to the white matter of the frontal and temporal lobes (Grade 1). Patients with more severe rotational acceleration may develop lesions in the lobar white matter as well as the posterior half of the corpus callosum (Grade 2). If the trauma is of even greater severity, DAI lesions will additionally be found in the dorsolateral aspect of the midbrain and upper pons (Grade 3). Lobar DAI characteristically involves the parasagittal aspects of the frontal lobes and the periventricular regions of the temporal lobes. The parietal lobe, occipital lobe, internal capsule, and cerebellum are also occasionally involved in decreasing order of frequency. Corpus callosum DAI invariably occurs in conjunction with lobar white matter DAI (Grade 2 DAI). The vast majority of callosal lesions occur in the splenium and posterior body of the corpus callosum. Callosal DAI lesions may be quite large and may occasionally involve the entire corpus callosum. Laceration by the free edge of the falx was initially thought to be the mechanism that was responsible for corpus callosum injury. It is now generally accepted, however, that injury is mediated through rotationally induced "shear strain" forces. Even though callosal DAI lesions tend to be much larger than lobar DAI, they can also be difficult to detect on initial CT scans. A helpful clue to the presence of callosal DAI, as evidenced in this case, is the presence of associated IVH. In one series of trauma patients, 80% of those with corpus callosum DAI had associated IVH, as compared to only 20% of those without such injury. The same shearing forces that are responsible for callosal injury easily tear the subependymal plexus of veins that normally lie along the undersurface of the corpus callosum. |
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| Contributor | Neuroradiology Learning File - © ACR (ACR Learning File®) |
| Author | Lindell R. Gentry, MD |
| Peer Reviewer | James G. Smirniotopoulos, M.D. (Uniformed Services University) |
| Record Number | : 1547 |
| Created | 2001-03-27 13:33:25-05 |
| Modified | 2005-05-19 15:22:00-04 |
| Category: | Trauma |
| Location: | Brain and Neuro |
| Sublocation: | Corpus Callosum |
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