Blast injury

Blast injuries are injuries sustained due to the energy released during a rapid chemical or nuclear reaction or the escape of gas under high pressure. They can affect numerous organ systems.

Epidemiology

Blast injuries may occur in any number of situations including in combat, in industrial accidents and in terrorist attacks.

Clinical presentation

The injuries sustained during an explosion depends on the type and size of the blast and distance of the patient from the blast. The surrounding environment (e.g. the presence of buildings or cars) and whether the patient was wearing any protective equipment are also factors .

Commonly patients may present with hearing loss, bleeding, lacerations, orthopedic injuries such as fractures, and respiratory distress. Musculoskeletal injuries are however the most common .

Pathology

The pathology of blast injuries can be categorized into three mechanisms of injury :

• primary blast injuries: usually suffered by those in close proximity to the blast (~ tens of meters). Injuries are caused by barotrauma from the increased air pressure and rarefaction of the atmosphere following the explosion. Common injuries include:
  • ruptured tympanic membrane
  • ossicular fracture and dislocation
  • pulmonary injury ("lung blast syndrome") with alveolar rupture and hemorrhage, alveolovenous fistula formation, subpleural cyst formation, pneumothorax and pulmonary laceration being possible
  • bowel injury (more common in underwater explosions) with contusion, perforation, shearing of the mesenteric vessels and resulting ischemia
  • facial bone fractures
  • central nervous system injury is also possible with the foramina of the skull allowing the transmission of pressure waves directly into the brain parenchyma
• secondary blast injuries: due to the effect of high-velocity shrapnel, these can suffered hundreds or thousands of meters away and may result from either environmental material (e.g. glass) or material from the explosive device (e.g. ball bearings) being propelled through the air.
  • can cause penetrating gunshot type injuries to any region of the body
  • amputation injuries are possible
• tertiary blast injuries: due to effect of the patient being thrown against objects (e.g. walls, cars).
  • various blunt (e.g. aortic) or penetrating injuries are possible depending on the area of the body injured and the encountered object
• combination injuries: these are due to a combination of any of the above mechanisms

Radiographic features

The choice of imaging modality depends principally on whether the patient is medically stable and any concerns about any specific underlying injury.

Plain radiograph

A chest and abdominal radiograph is useful in the acute setting to show any evidence of foreign bodies or chest trauma such as hemorrhage, pneumothorax or rib fractures and abdominal trauma such as perforation . Extremity radiographs are also helpful in defining foreign bodies and fractures .

Ultrasonography

The FAST scan is useful in the medically unstable patient to define any injuries which may require prompt intervention (e.g. tension pneumothorax or cardiac tamponade) .

CT

CT is the main imaging modality used in blast injuries. Imaging may reveal any of the injuries listed above. It is also useful to define the presence and location of any foreign bodies within the patient as a result of secondary blast injuries . CT angiography is useful to define the presence of any vascular injury in the affected region .

MRI

In the acute setting MRI may be contraindicated until the presence of metallic foreign bodies have been excluded due to the risk of movement and heating of the objects in the strong magnetic field .