Mechtler Neuroimaging, An Issue of Neurologic Clinics,

1. Auflage 2014
ISBN: 978-0-323-26671-0
Verlag: Elsevier Health Care - Major Reference Works
Format: PDF
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band Volume 32-1, 100 Seiten

Reihe: The Clinics: Radiology

With each passing year neuroimaging becomes more and more central in the diagnosis of neurologic disease, as its capacity to detect subtle changes in nervous system tissue increases. This issue of Neurologic Clinics features twelve articles that address the key clinical applications of the several radiologic modalities. Topics include: Neuro-Imaging of Infectious Disease; Neuro-Imaging of Dementia; Imaging of Traumatic Brain Injury; 3. MR Guided Focused Ultrasound: A New Technology for Clinical Neurosciences; Novel Multi- Modality Imaging Techniques for the Diagnosis and Evaluation of Arteriovenous Malformations; Neuroimaging in the Critical Care Environment; Imaging of Cerebral Ischemia: From Acute Stroke to Chronic Disorders; Imaging of Cancer-Related Neurotoxicity; Neurocutaneous Syndromes; Imaging of Chiari Malformation and Hydrocephalus; and others.

Autoren/Hrsg.

Mechtler, Laszlo

Leseproben

Advanced Neuroimaging of Mild Traumatic Brain Injury
Laszlo L. Mechtler, MDab*[e-mail], Kalyan K. Shastri, MD, MSb and Kevin E. Crutchfield, MDc,     aDepartment of Neurology and Neuro-Oncology, State University of New York at Buffalo, 3435 Main Street, Buffalo, NY 14223, USA; bDent Neurologic Institute, 3980A Sheridan Drive, Suite 101, Amherst, NY 14226, USA; cComprehensive Sports Concussion Program, The Sandra and Malcolm Berman Brain & Spine Institute, 5051 Greenspring Avenue, Baltimore, MD 21209, USA *Corresponding author. Dent Neurologic Institute, 3980A Sheridan Drive, Suite 101, Amherst, NY 14226. This article focuses on advancements in neuroimaging techniques, compares the advantages of each of the modalities in the evaluation of mild traumatic brain injury, and discusses their contribution to our understanding of the pathophysiology as it relates to prognosis. Advanced neuroimaging techniques discussed include anatomic/structural imaging techniques, such as diffusion tensor imaging and susceptibility-weighted imaging, and functional imaging techniques, such as functional magnetic resonance imaging, perfusion-weighted imaging, magnetic resonance spectroscopy, and positron emission tomography. Keywords Mild traumatic brain injury Concussion Diffuse axonal injury Diffusion tensor imaging Susceptibility-weighted imaging Magnetic resonance spectroscopy Key points
• Traumatic brain injury (TBI) is an important cause of death and disability in the United States, with annual incidence of approximately 1.7 million and overall annual costs estimated to be $76.5 billion. • 75% of all TBIs can be classified as mild TBI (mTBI), defined as Glasgow Coma Scale score of 13 or more. Concussion, a term commonly used in sports-related injuries, is a form of mTBI. • The goals of neuroimaging in TBI are to identify treatable injuries, assist in the prevention of secondary damage, and provide useful prognostic information on a patient's long-term clinical condition. • Advanced neuroimaging of mTBI includes anatomic/structural imaging techniques, such as diffusion tensor imaging and susceptibility-weighted imaging, and functional imaging techniques such as functional MRI, perfusion-weighted imaging, MR spectroscopy, and positron emission tomography. Introduction
Traumatic brain injury (TBI), a major public health concern at the beginning of the 21st century, has been called a “silent epidemic”1 because it is underreported, often remains undiagnosed, and its long-term consequences are generally underrecognized. However, owing to growing experience with combat-related TBI among military personnel, media focus on TBI-related long-term disability in professional athletes, educational initiatives, such as the “Heads Up” program of the Centers for Disease Control and Prevention,2 and the voices of patients and affected families, the silence is beginning to be broken. Approximately 75% of all reported TBIs can be classified as mild TBI (mTBI).3 Although most patients with mTBI become asymptomatic within days to weeks, some develop persistent troubling symptoms that have been referred to as “persistent postconcussive syndrome.”4,5 One of the inherent challenges in applying neuroimaging to predict clinical outcome in mTBI is that patients who develop persistent symptoms typically have no detectable abnormalities on conventional neuroimaging, such as computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. Novel structural and functional neuroimaging techniques have emerged that have the sensitivity to identify hitherto undetected brain abnormalities in mTBI. This article focuses on advancements in neuroimaging techniques, compares the advantages of each of the modalities in the evaluation of mTBI, and discusses their contribution to our understanding of the pathophysiology as it relates to prognosis. mTBI: brief overview
Terminology
“Traumatic brain injury” refers to an alteration in brain function or other evidence of brain pathology caused by external force6 and traditionally is classified as mild, moderate, and severe based on the Glasgow Coma Scale (GCS).7 TBI with GCS score of 13 or more is classified as mild, 9 to 12 as moderate, and 8 and lower as severe.8 mTBI is defined as a traumatically induced physiologic disruption of brain function as manifested by at least 1 of the following: (1) any period of loss of consciousness up to 30 minutes, (2) any loss of memory for events before or after the accident not exceeding 24 hours, (3) any alteration in mental state at the time of the accident, and (4) focal neurologic deficits that may or may not be transient.9,10 Concussion is a form of mTBI, and “concussion” is a term commonly used in sports, whereas “mTBI” is used more often in the medical context.11 Pathophysiology
Pathophysiologically, TBI involves 2 phases of tissue injury: primary and secondary. Whereas primary injuries are almost immediate and generally irreversible, secondary injuries are delayed and can continue for an extended period of time and thereby provide an opportunity for therapy.12 The primary injury phase involves direct and indirect mechanical damage from impact and acceleration/deceleration that could result in cortical contusions, subdural or epidural hematomas, axonal shearing, and microvascular injury. Secondary injury is the nonmechanical damage that results from a complex metabolic cascade set off by neuronal cell membrane disruption and axonal stretch.13 Neuronal membrane deformity leads to ionic flux and release of excitatory neurotransmitters. Attempts to restore homeostasis lead to a cellular energy crisis. Depletion of cellular energy stores leads to initiation of apoptosis and neuronal death. Impaired cerebrovascular autoregulation that leads to decreased cerebral blood flow (CBF), inflammatory response with activation of microglia,14 and release of free radicals are additional mechanisms of tissue damage during the secondary injury phase of TBI. Diffuse axonal injury (DAI) is best described after severe TBI and is characterized by axonal stretching leading to axolemmal disruption, ionic flux, neurofilament compaction, and microtubule disassembly. The effect of these pathophysiologic processes is axonal swelling and eventual disconnection.15,16 Although best described in severe TBI, DAI occurs in mTBI as well and is recognized as an important determinant of long-term cognitive and neuropsychiatric outcome in mTBI.17,18 As discussed in subsequent sections, key advances in neuroimaging of mTBI involve newer techniques that can detect disruption of axonal integrity. Symptomatology
mTBI can lead to a wide range of symptoms, including loss of consciousness, if any, at the time of injury and memory loss, if any, for events before and after the injury. Postconcussion syndrome refers to symptoms from multiple “symptom categories” that develop within a maximum of 4 weeks following head trauma.19 Broad symptom categories include somatic, cognitive, affective, and sleep-related. Typical symptoms include headache, dizziness, memory impairment, difficulty concentrating, insomnia, mood alteration, and anxiety. Most people with mTBI recover within a few days to weeks with rest and minimal symptomatic treatment. Approximately 15% of patients with mTBI suffer from long-term complications.4,5 Chronic traumatic encephalopathy (CTE) is a rare progressive degenerative condition that is thought to be a consequence of repetitive TBI. First described as dementia pugilistica in boxers,20 CTE is equally concerning for other professional athletes who are at risk for repeated concussions. For instance, retired professional football players with history of 3 or more concussions are 5 times more likely to develop mild cognitive impairment.21 From the autopsy studies of 3 professional athletes with CTE, we know that it is related to deposition of tau protein in neurons and resultant progressive degeneration of the central nervous system.22 Conventional neuroimaging of traumatic brain injury
General Considerations
The goals of neuroimaging of TBI are to identify treatable injuries, assist in prevention of secondary damage, and provide prognostic information about long-term clinical outcome. Conventional neuroimaging continues to play a crucial role in the initial management of TBI. CT is generally the imaging modality of choice for initial screening to exclude serious intracranial injury in patients who present with head injury. MRI, particularly at 3 T strength, improves structural sensitivity and is indicated in acute TBI when neurologic findings cannot be explained by CT. MRI...