Blast-induced Mild Traumatic Brain Injury
Section snippets
Mechanisms of blast-related injury
A variety of explosives including mortar shells, rocket propelled grenades, and IEDs cause blast injuries. In Iraq and Afghanistan, IEDs have been the most common cause of blast injuries and are estimated to be responsible for about 40% of coalition deaths in Iraq, and a roughly similar percentage of TBIs.11 Although diverse in design, IEDs typically consist of an explosive charge coupled to a detonator.12 The explosive charge may be a conventional artillery shell or be made from commercially
The primary blast wave and the brain
How the primary blast wave affects the brain is at present incompletely understood. Computer simulations23, 24, 25, 26, 27, 28, 29 predict various potential mechanisms of injury, including induction of high strain effects in traditional coup and contrecoup regions29 and high shear stresses in white matter regions that could be associated with diffuse axonal injury (DAI).23 Some models also predict preferential damage to the brainstem.29 Others suggest that, as the blast wave passes through the
Experimental studies in animals
Animals have been exposed to various forms of blast ranging from direct exposure to live explosives to controlled blast waves produced by compressed-air generators. In most studies, to concentrate the blast wave, anesthetized animals have been placed in special holders designed to limit body movement. The animals are secured in the end of a metal tube termed a shock tube if live explosives are used or a blast tube if compressed air is used. Effects of body alignment can be determined by
Blast-related TBI in humans
Blast injury is infrequent in civilian life. A survey of 57,392 trauma cases seen in a large urban trauma center found only 89 cases of blast injury (0.2%),50 with private dwelling explosions and industrial accidents being the most common causes. The best understood pathophysiological mechanisms associated with the type of blunt impact TBI seen most commonly in civilian settings are bleeding, direct tissue damage, and DAI.51 DAI results when angular forces cause shearing or stretching of axons
Neuroimaging in mild TBI
Use of in vivo measures to understand the mechanisms of brain damage, particularly mild TBI, as a result of acute and repeated exposure to blast is in its infancy. Conventional structural imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) have been used historically in both civilian and military patients with TBI, and are capable of rapid identification of contusions or hemorrhages in the dural and parenchymal spaces as well as cerebral edema. However,
Distinguishing blast-related mild TBI from PTSD
One of the striking features of the mild TBI cases being seen in the current OIF/OEF veterans is the high prevalence of PTSD. PTSD or depression is present in more than one-third of OIF/OEF veterans with suspected postconcussion syndromes secondary to mild TBI.2 This coincidence could reflect dual exposure to blast as well as stressors that can independently cause PTSD. However, the clinical distinction between a postconcussion syndrome and PTSD is often difficult, with the 2 disorders having
Diagnosis and screening for blast-related TBI
The diagnosis of moderate to severe TBI is straightforward even in theater because the traumatic incident is generally apparent along with prolonged alterations of consciousness; other clinical signs and symptoms, and often neuroimaging abnormalities, are discovered later. By contrast, accurate identification of mild TBI can be challenging because of the more subtle signs of injury, the paucity of objective physical findings, and the overlap of postconcussion symptoms with those of other
Treatment principles for the veteran with a blast-related mild TBI
The cornerstones in the treatment of veterans with mild TBI are education, symptom management, and care coordination. Veterans and their families are educated on the causes, symptoms, treatments, and prognosis of mild TBI. The educational interventions take into account the veteran’s cognitive and emotional impairments as well as their cultural and religious beliefs and preferred method of learning. Educational materials must be written at an appropriate reading level and in a language that the
Concluding remarks
TBI has been a major cause of mortality and morbidity in the wars in Iraq and Afghanistan. In both theaters of operation, blast exposure has been the most common cause of TBI. Blast injuries occur through multiple mechanisms that likely activate many of the same pathophysiological cascades seen in closed impact injuries in civilian life. What is less clear is whether the primary blast wave causes brain damage through mechanisms that are pathophysiologically distinct from those common in
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Work in the author’s labs is supported by grants from the Department of Veterans Affairs (1I01RX000179-01 and I01CX000190-01). The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government.