Continuing Education Activity
Diffuse axonal injury (DAI) is a type of traumatic brain injury (TBI) that results from a blunt injury to the brain. In the United States, traumatic brain injury is a leading cause of death and disability among children and young adults. The Center for Disease Control and Prevention (CDC) estimates that there are over 1.5 million reported cases of traumatic brain injury every year in the United States. Traumatic brain injury is classified as mild, moderate, and severe based on the Glasgow coma scale (GCS). Traumatic brain injury patients with GCS of 13 to 15 are classified to be mild, which includes the majority of traumatic brain injury patients. Patients with a GCS of nine to 12 are considered to have a moderate traumatic brain injury, while patients with a GCS below eight are classified as having a severe traumatic brain injury. This activity reviews the workup of diffuse axonal injury and the role of health professionals working together to managing this condition.
Objectives:
Outline the Adams classification for axonal injury.
Review the management of axonal injuries.
Describe the presentation of axonal injury.
Outline the workup of diffuse axonal injury and the role of health professionals working together to manage this condition.
Introduction
Diffuse axonal injury (DAI) is a type oftraumatic brain injury (TBI) that results from a blunt injury to the brain.[1]In the United States, traumatic brain injuryis a leading cause of death and disability among children and young adults. The Center for Disease Control and Prevention (CDC) estimates thatthere are over 1.5 million reported cases of traumatic brain injuryevery year in the United States. Traumatic brain injuryis classified as mild, moderate, and severe based on the Glasgow coma scale (GCS). Traumatic brain injurypatients with GCS of 13 to 15 are classified to be mild, which includes the majority of traumatic brain injurypatients. Patients with a GCS of nine to 12 are considered tohave a moderate traumatic brain injury, while patients with a GCS below eight are classified as having a severe traumatic brain injury.
The GCS measures the following three functions:
Eye Opening (E): 4-spontaneous, 3-to voice, 2-to pain, 1-none
Verbal Response (V):5-normal conversation, 4-oriented conversation, 3-words, but not coherent, 2-no words, only sounds, 1-none
Motor Response (M):6-normal, 5-localized to pain,4-withdraws to pain,3-decorticate posture,2-decerebrate
Diffuse axonal injury (DAI)primarily affects the white matter tracts in the brain. Clinically, patients with DAI can present in aspectrum of neurological dysfunction. This can range from clinically insignificant to acomatose state. However, most patients with DAIare identified to be severeand commonly have a GCS of less than 8. A diffuse axonal injuryis a clinical diagnosis.
Etiology
The most common etiology of diffuse axonal injuryinvolves high-speed motor vehicle accidents.[2]The most common mechanism involves an accelerating and decelerating motion that leads to shearing forces to the white matter tracts of the brain. This leads to microscopic and gross damage to the axons in the brain at the junction of the gray and white matter. Diffuse axonal injurycommonly affects white matter tracts involved in the corpus callosum and brainstem. Interestingly, there is no association between diffuse axonal injuryand underlying skull fractures.
Epidemiology
The true incidence of DAI is unknown. However, it is estimated that roughly 10% of all patients with TBI admitted to the hospital will have somedegree of DAI.[3]Of the patientswith DIA, it is estimated that roughly 25% will result in death. This statistic maybe underestimated as patients with subdural hematomas, epidural hematomas, and other forms of TBI will not carry a true diagnosis of DAI. Postmortemstudies have shown that patients with severe TBI have a significantincidence ofdiffuse axonal injury.
Pathophysiology
The primary insults of diffuse axonal injurylead to disconnection or malfunction of neuron's interconnection.[4]This affects numerous functional areas of the brain. Usually, patients with diffuse axonal injurypresent with bilateral neurological examination deficits frequently affecting the frontal and temporal white matter, corpus callosum, and brainstem. The Adams classification of diffuse axonal injuryutilizes pathophysiological lesions in the white matter tracts and clinical presentation.
The Adams Diffuse AxonalInjury Classification
Grade 1: A mild diffuse axonal injurywith microscopic white matter changes in the cerebral cortex, corpus callosum, and brainstem
Grade 2: A moderate diffuse axonal injurywith gross focal lesions in the corpus callosum
Grade 3: A severe diffuse axonal injurywith finding as Grade 2 and additional focal lesions in the brainstem
Histopathology
Axonal portions of neurons have a mechanical disruption of cytoskeletons resulting in proteolysis, swelling, and other microscopic and molecular changes to the neuronal structure.
History and Physical
DAI is a clinical diagnosis.Typically, DAI is consideredin patients with a GCS of less than 8 for over six hours. The clinical presentation of patients with diffuse axonal injury relates to the severity of a diffuse axonal injury. For example, patients with mild diffuse axonal injury present with signs and symptoms that reflecta concussive disorder. These symptoms most commonly include a headache. The other post-concussive symptoms can include dizziness, nausea, vomiting, and fatigue. However, patients with a severe diffuse axonal injurymay also present with a loss of consciousness and remain in a persistent vegetative state. A very small number of those patients with severe diffuse axonal injurywill regain consciousness in the first year after the injury.
Other common neurological manifestations include dysautonomia. Dysautonomic symptomscommonly include tachycardia, tachypnea, diaphoresis, vasoplegia, hyperthermia, abnormal muscle tone, and posturing.
Evaluation
In general,diffuse axonal injuryis a severe form of traumatic brain injury.[5]Therefore, the implementation of an advanced trauma life support protocol is a standard of care for all head-injured patients.
A definitive diagnosis of diffuse axonal injurycan be made in the postmortem pathologic examination of brain tissue. However, in clinical practice, a diagnosis of diffuse axonal injuryis made by implementing clinical information and radiographic findings. Understanding the mechanism of head injury facilitates a differential diagnosis of DAI. Patients who experience rotational or acceleration-deceleration closed head injury should be suspected to have DAI. Generally, DAIis diagnosed after a traumatic brain injurywith GCS less than 8 for more than six consecutive hours.
Radiographically, computed tomography (CT) head findings of small punctate hemorrhages to white matter tracts can indicate diffuse axonal injury in the setting of an appropriate clinical presentation. Overall, CT head has a low yield in detecting diffuse axonal injury-related injuries. Currently, magnetic resonance imaging (MRI), specifically diffuse tensor imaging (DTI), is the imaging modality of choice for the diagnosis of diffuse axonal injury. A recent report suggests that acute gradient-recalled echo (GRD) MRI willenhance the detection of axonal injury in grade 3 diffuse axonal injurypatients, suggesting that it is most likely a better diagnostic tool.
It should be of note that DAI should be strongly considered in patientsthat fail to improve after receiving surgical evacuation of subdural or epidural hematomas. Conversely, if patients drastically improve after surgical evacuation of a subdural or epidural hematoma, DAI may not be present.
Currently, there are no laboratory tests for the diagnosis of DAI.[6]However, thereiscurrent research on identifying molecular markers inthe serum of traumatic brain injurypatients to help aidthe diagnosis of DAI.
Treatment / Management
Treatment of patients with diffuse axonal injuryis geared toward the prevention of secondary injuries and facilitating rehabilitation. It appears to be the secondary injuries that lead to increased mortality. These can include hypoxia with coexistenthypotension, edema, and intracranial hypertension. Therefore, prompt care to avoid hypotension, hypoxia, cerebral edema, and elevated intracranial pressure (ICP) is advised.
Initialtreatment priority in traumatic brain injuryis focused on resuscitation. In a non-neuro trauma center, trauma surgeons and emergency physicians may perform the initial resuscitation and neurologic treatment to stabilize and transport the patient to a designated neurotrauma center expeditiously. ICP monitoring is indicated in patients with a GCS of less than 8 after consultation with neurosurgery. Otherconsiderations for ICP monitoring include patients that cannot have continual neurologic evaluations.These are typically in patientsreceiving general anesthesia, opioid analgesia, sedation, and prolonged paralysis for other injuries.Cerebral oxygen saturation monitoring can be used with ICP monitoring toassessthe degree ofoxygenation. Short-term, usually seven days, anticonvulsant treatment can be used to prevent early post-traumatic seizures. There is no evidence that this will prevent long-term post-traumatic seizures, however. There is emerging evidence that progesterone treatment in acute traumatic brain injurymay reduce morbidity and mortality. This cannot be routinely recommendedat this time.
Overall, the goal of the treatment of patients with diffuse axonal injury is supportive care and prevention of secondary injuries.
Differential Diagnosis
Subdural hematoma
Epidural hematoma
Subarachnoid hemorrhage
Various Intracerebral hemorrhage types
Ischemic and hemorrhagiccerebrovascular accident
Concussion/post-concussive syndrome
Hypoglycemia
Prognosis
Prognosis is considered to be poor in patients with severe DAI.
Complications
Dysautonomia is frequently encountered. Unfortunately, no definitive treatment exists, and supportive care is advised.[7][8][9]
Postoperative and Rehabilitation Care
Postoperative care, if operative intervention is pursued, typically is aimed at reducing ICP and improving cerebral blood flow.
Patients and families should expect prolonged rehabilitative therapies after severe DAI. This can include physical, occupational, speech, and other psychosocial therapies.
Consultations
Typically neurosurgery, neurology, trauma surgery, and intensive care can help guide therapies.
Pearls and Other Issues
A diffuse axonal injury is a type ofsevere traumatic brain injurythat affects patients and their families. Patients with diffuse axonal injuryhave a range of multiple neurological deficits that affect the physical and mental status of the patient. These changes usually compromise social reintegration, return to productivity, and quality of life of patients and their families. For most patients and families, the clinical status of patients with diffuse axonal injury will continue to persist for a minimum of two years. Then, most patients and families will achieve and accept a new baseline. Recent epidemiological studies indicate that the outcomes of patients with diffuse axonal injury are associated with the number of lesions identified through imaging. There are emerging studies suggesting that during the acute phase of diffuse axonal injury, hypoxia, and hypotension are associated with increased mortality. Therefore, it is important to continue investigating the clinical, pathophysiological, and radiographic studies to advance the management of patients with diffuse axonal injury.
Enhancing Healthcare Team Outcomes
Patients with DAI often have a severe brain injury and are best managed by an interprofessional team that includes a neurologist, neurosurgeon, physical and occupational therapist, speech therapist, intensivist, internist, ICU nurses, neuroscience nurses, and rehabilitation nurses.[10]Pharmacists review prescribed medications, including anticonvulsants, and check for drug-drug interactions. Nurses monitor patients and inform the team about changes in status. Patients with diffuse axonal injury have arange ofmultiple neurological deficits that affect the physical and mental status of the patient. These changes usually compromise social reintegration, return to productivity, and quality of life of patients and their families. For most patients and families, the clinical status of patients with diffuse axonal injury will continue to persist for a minimum of two years.[11]
The outcome for patients with DAI is generally poor. The recovery is long, and complete recovery is usually not possible in cases of severe injury. For many, there is life long disability with a poor quality of life.[12][13][14][Level 5]
References
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Disclosure: Fassil Mesfin declares no relevant financial relationships with ineligible companies.
Disclosure: Nishant Gupta declares no relevant financial relationships with ineligible companies.
Disclosure: Angela Hays Shapshak declares no relevant financial relationships with ineligible companies.
Disclosure: Roger Taylor declares no relevant financial relationships with ineligible companies.
