What Is a Diffuse Axonal Injury?

Diffuse axonal injury (DAI): refers to a type of primary brain parenchymal injury that occurs after the head is traumatized and is mainly diffusely distributed in the white matter of the brain. Axonal injury is the main change. It is characterized by extensive white matter degeneration, small focal hemorrhage, axonal retraction globules, microglia clusters appear, often combined with other craniocerebral injuries, and high mortality.

Diffuse axonal injury (DAI): refers to a type of primary brain parenchymal injury that occurs after the head is traumatized and is mainly diffusely distributed in the white matter of the brain. Axonal injury is the main change. It is characterized by extensive white matter degeneration, small focal hemorrhage, axonal retraction globules, microglia clusters appear, often combined with other craniocerebral injuries, and high mortality.

Basic overview of diffuse axonal injury

Since Strich described the pathological changes of DAI through autopsy in 1956 and was officially named by Adams et al. [1] in 1982, DAI has been accepted by the neurosurgery community as an independent type of disease. For the classification of DAI, the standards proposed by Adams and others are mostly used. With the improvement of pathological diagnosis technology, the establishment of multiple animal models and the improvement of high-resolution and high-resolution imaging technology have provided powerful help for the diagnosis and treatment of the disease. However, the research on the disease is preliminary so far, there is no unified diagnostic standard, and the relationship with other types of brain injury is not clear, which hinders the understanding of the nature of the disease and makes it difficult to achieve breakthroughs in treatment measures.

DAI Study on DAI injury mechanism of diffuse axonal injury

At present, the understanding of the pathogenesis of DAI is basically the same, that is, due to trauma, the craniocerebral generates rotational acceleration and / or angular acceleration, which makes the brain tissue susceptible to shear forces, resulting in axonal and small blood vessel damage. Animal models made according to this principle have also successfully simulated DAI seen in the clinic. At the junction of white matter and gray matter, the corpus callosum between the two hemispheres of the brain, the head of the brainstem, the cerebellum, the inner capsule and the basal ganglia are vulnerable areas under shear stress. It is found that traffic accidents are still the main cause of injuries. Because in traffic injuries, brain tissue is more susceptible to shear stress and can cause multiple injuries. Therefore, patients with head injuries in traffic accidents should be alert to the presence of DAI. Direct violence acts on one side of the top, pillow, forehead, indirect violence acts on the maxillofacial region, and the head whip-like movement caused by indirect violence can produce multi-directional head rotation, causing DAI.

Diagnosis of diffuse axonal injury

At present, the diagnosis of brain injury mostly relies on imaging techniques such as CT and MRI. DAI, especially non-hemorrhagic lesions and needle-point bleeding points, is difficult to identify on CT. Although MRI has higher resolution and sensitivity than CT, For small lesions and light DAI, false negatives are still not uncommon. Therefore, the missed diagnosis rate of DAI is quite high. Gentleman et al. Used a highly sensitive -amyl precursor protein (-APP) immunohistochemical method to study a group of brain slices of fatal closed head injury, and found that almost all DAI was present. This reflects the severity of DAI and the breadth of its existence. Graham et al. Found that clinically significant injuries, such as skull fractures, brain contusions, and large intracranial hematomas, are not likely to be the most important related injury factors between clinical manifestations, pathology, and prognosis through pathological and clinical studies. The important related factors, DAI, are often difficult to identify, and high-resolution CT, MRI, and / or microscopy are needed. Therefore, clinical judgment and imaging should be emphasized at the same time in clinical work. When the two do not match, especially when the clinical injury is severe, and CT and MRI show non-functional brain contusions or no obvious abnormal changes, Coexisting DAI should be highly suspected. When performing internal decompression surgery for patients with brain injury, silver staining and -precursor protein detection should be taken as far as possible. Electron microscopy can also be performed if possible to improve the detection rate and diagnostic accuracy of DAI.

Identification of diffuse axonal injury

Cerebral contusion and DAI are more strictly defined. However, the two can be caused by the same type of injury mechanism's angular acceleration. The magnitude of the angular acceleration determines the difference between the above two types of brain injury. However, the chance of coexistence of the two greatly exceeds the traditional concept and has important clinical significance.

Concussion is a mild diffuse brain injury. At present, the mechanism of injury is non-hemorrhagic damage to deep brain structures caused by rotational acceleration or angular acceleration. Axon swelling is the main cause, which temporarily interrupts the connection between the cortex and subcortical structures. The degree of damage is light and reversible. This could explain the shorter duration of the patient's disturbance of consciousness and the common concussion sequelae or post-head injury syndrome.

In short, DAI is a common diffuse brain injury, which can be divided into three types: light, medium and severe. Concussion and primary brainstem injury are included, and it is often accompanied by cerebral cortical contusion. Understanding of the pathogenesis of DAI, It provides a basis for the diagnosis and treatment of brain injury, and is expected to change the existing classification methods of primary brain injury.