Imaging of Trauma Patients
Asim F. Choudhri
I. Introduction
Medical imaging provides a noninvasive assessment of bone and soft tissue injuries. The most appropriate imaging modality depends upon factors including the location and availability of equipment, stability of the patient, and local expertise and care pathways. The goal of imaging is to provide the maximum information to the trauma team as quickly as possible while minimizing risk to the patient.
Imaging modalities
Conventional radiography (“x-rays”) provides a quick method of evaluating patients; these are well suited for evaluating bony architecture and for screening in chest injuries. The immediate evaluation of the trauma patient starts with anterior–posterior (AP) chest and pelvis radiographs. These studies can be performed using the portable technique, without moving the patient from the trauma resuscitation room. Further radiography, such as of the long bones, is typically deferred until after initial resuscitation and CT scans are performed. However, x-rays can selectively be performed as a part of the primary survey as needed. Spine radiographs have a limited role for the primary detection of fractures in adults, however, remain an important part of the spine evaluation in children.
Initial chest x-ray studies are usually performed in the supine position. After the initial stabilization of the patient, an upright film may be obtained to better assess for aortic injury, pneumothorax, or pleural effusion.
Computed tomography (CT) has become the standard modality used in the early diagnosis of head, spine, thoracoabdominal, and pelvic injury, often in one combined study. CT provides a comprehensive evaluation of chest injuries and maxillofacial fractures and allows for specific diagnosis of injury to the organs of the abdomen and retroperitoneum. The increasing availability of multislice helical CT in or near the emergency department expanded the role of CT in the trauma setting.
Magnetic resonance imaging (MRI) has several advantages over CT scan, particularly in the evaluation of soft tissues. MRI offers the ability to obtain images in sagittal, coronal, and oblique planes, and can be used to define shear injuries to the brain, injuries to the spinal column and cord, or vascular abnormalities that are not apparent on other films. However, MRI is time-consuming and allows minimal access to the patient during the procedure; together, these factors limit the application in the initial evaluation of the trauma patient. Currently, MRI is used after stabilization, often to detect neurologic injuries or occult fractures.
Ultrasonography (US) is a valuable tool for the management of trauma patients. The focused abdominal sonography for trauma (FAST) has largely replaced the diagnostic peritoneal lavage (DPL) in unstable patients. A rapid diagnosis of hemoperitoneum can be made noninvasively in the trauma patient with a sensitivity of approximately 85%. US is quite accurate for the diagnosis of pericardial tamponade, allowing for decreased need for diagnostic pericardial window. US can also be used to assess for peripheral vascular injury.
Angiography. Standard two-dimensional angiography has been largely replaced by CT angiography in the diagnosis of vascular traumatic injury. If said scans are equivocal or negative in the face of a high index of suspicion, angiography is a dynamic study with a very high spatial resolution, allowing detection vascular extravasation. In addition, its therapeutic role in such injuries has expanded.
Angiography with embolization is the procedure of choice for difficult-to-access injuries (e.g., those to the vertebral artery, pelvic vessels, retroperitoneum) and selected vessels of the chest, abdomen, and large muscle masses.
II. Skull and Brain Trauma
Plain-film skull radiography is only used for penetrating injuries of the skull to determine the course, location, or number of gunshots or foreign-body fragments as well as possible depressed skull fragments.
Patients with a head injury, history of loss of consciousness (LOC), or postconcussive sequelae require evaluation by non-contrast CT scan. CT scan of the brain should be the initial screening tool for patients with symptoms indicating moderate to high risk of closed head injury. The CT scan images should be displayed with three windows: Brain (shows edema, gray–white interface, ventricles, and cisterns), bone (outlines fractures, bony fragments), and blood (mass lesions, hemorrhage). Contrast enhancement is used selectively after non-contrast if occult extra-axial fluid collections, abscess, tumor, or venous sinus obstruction is sought.
Common CT findings of brain injury
Basilar skull fractures can occur in 20% of craniofacial injuries, and CT is essential for complete evaluation. However, a negative CT scan does not exclude basilar skull fracture, especially with positive physical findings or unexplained pneumocephalus. Basilar skull fractures can be accompanied by cerebrospinal fluid (CSF) leak, damage to the internal carotid artery, and cranial nerve injury. Multislice CT with multi-planar reconstruction of thin sections greatly improves the ease and accuracy of diagnosing basilar skull fractures. CT cisternography, which is high resolution skull base imaging after the injection of intrathecal iodinated contrast, can help localize a CSF leak from an occult skull base fracture; this technique is not typically performed in the acute setting.
Epidural hematomas result from the rupture of arteries and large venous sinuses resulting in an accumulation of blood that strips the dura off the inner table of the skull. The temporal region of the skull is most commonly injured, resulting in a tear of the middle meningeal artery. The characteristic appearance of an epidural hematoma is a biconvex (lentiform) fluid collection that does not cross intact skull suture lines but can cross the midline if venous sinuses are ruptured.
Subdural hematomas result from the dissection of blood from ruptured veins that bridge through the subdural space. These hematomas are generally located between the dura and the arachnoid membrane. The typical subdural hematoma is a crescent-shaped fluid collection that conforms to the calvarium and underlying cerebral cortex. Recognition of atypical subdural hematomas is sometimes aided by coronal CT scan or repeat CT scan with enhancement. Subdural hematomas often are accompanied by nearby parenchymal contusion.
Subarachnoid hemorrhage is seen commonly in the basilar cisterns of patients following head trauma. Non–contrast-enhanced CT detects about 90% of subarachnoid bleeding within the first 24 hours, regardless of cause, as the higher density of blood replaces the water density of CSF in the cistern and sulci. Like non-traumatic subarachnoid hemorrhage, vascular evaluation with angiography is important if the degree of hemorrhage is out of proportion to the mechanism of trauma.
Shear injury or diffuse axonal injury (DAI). Most brain parenchymal injuries are caused by shear-strain lesions; multiple and bilateral injuries are common. Linear and rotational acceleration–deceleration mechanisms cause shearing along interfaces of tissue of different densities, such as CSF and brain as well as gray–white junctions with the brain and meninges. Unenhanced CT scan may show multiple small focal hemorrhagic lesions with minimal mass effect, but it is an insensitive test. In a patient who is severely depressed
neurologically with a relatively normal CT study, the possibility of diffuse brain injury (or cerebrovascular injury) should be considered. MRI is more accurate in diagnosing diffuse axonal brain injury, in particular susceptibility weighted imaging (SWI). If SWI is not available, a hemosiderin sensitive gradient imaging (GRE) should be performed in all trauma patients. Areas of hemorrhage will appear as focal dark spots. Multiple petechial hemorrhages, predominantly at the gray–white interface and within the corpus callosum, is characteristic of DAI.
Cerebral contusions and parenchymal hematomas are relatively common findings seen on brain CT after injury. Such injuries can coalesce or enlarge. Routine follow-up CT is recommended in these patients within 24 to 48 hours, or sooner if there are changes in the neurologic examination. MR of the brain with SWI/GRE can be helpful evaluating the extent of injury which may be underestimated by CT.
III. Facial Trauma
Facial injuries are seldom directly life threatening, but often are associated with airway obstruction, head or cervical spine injury, or globe injury. Occasionally, hemorrhage into the nose, nasopharynx, or mouth requires immediate attention.
CT is preferred to evaluate facial fractures; plain films often miss injuries and are challenging to interpret due to bony overlap.
CT scans of the face can be obtained at the time of head CT scan if patient condition permits. Helically acquired CT imaging can be reformatted into thin section axial and coronal bone algorithm datasets. Three-dimensional (3D) reconstructions from the volumetric dataset provide optimal delineation of midfacial fractures and the spatial relationship of the fragments.
IV. Spine Injuries
Every patient with an appropriate mechanism of injury (MOI) must be considered to have a spine injury until ruled out with imaging or by clinical features.
Cervical spine. An alert, communicative adult trauma victim without distracting injury who denies symptoms, such as neck pain, without drugs or alcohol on board, and has no signs, such as neck tenderness, may be “cleared” on the basis of clinical examination. Patients with head injury often have accompanying cervical spine (C-spine) injuries, and radiographic evaluation of the C-spine is essential. The unconscious, intoxicated, noncommunicative, or multi-injured patient needs radiographic clearance. The cervical collar must not be removed until the C-spine has been evaluated and cleared.
Techniques for obtaining adequate plain-film radiographs for C-spine clearance
The plain-film lateral view of the C-spine is not adequate unless C1 through the top of T1 are visualized. If the shoulders obscure the lower cervical and upper thoracic spine, caudal traction of the arms must be applied during filming, unless contraindicated on clinical grounds. Useful techniques to further define the C-spine include the “swimmer’s view” or left and right oblique views. Failure to adequately visualize the cervicothoracic junction or the craniocervical junction will necessitate CT scan.
Technically adequate lateral, AP, and open-mouth odontoid C-spine films are the minimal views necessary to evaluate the C-spine radiographically. A very small percentage of patients with C-spine injury have isolated ligamentous injury and grossly normal static plain radiographs. Other studies, such as flexion–extension views, left and right oblique views, CT scan, or MRI, may delineate these injuries or investigate areas that are not well visualized on plain films.
Active flexion–extension views are done voluntarily by the alert and cooperative patient only to the limit of pain tolerance. Recent practice tends to use flexion–extension views less often and rely on CT with reformatting and MRI when needed.
The purpose of the radiographic evaluation is to identify potential C-spine bony injury that has not caused a neurologic deficit. In the hemodynamically unstable patient, protect and immobilize the spine, treat the condition causing instability, and clear the spine when the patient’s condition permits. Do not spend time attempting to clear the C-spine in a hemodynamically unstable patient.
The availability of a CT scan within or near the emergency department facilitates emergent evaluation of C-spine trauma. In particular, MDCT offers the opportunity to obtain definitive and easily interpretable imaging of the C-spine quickly. These scanners also offer greater flexibility in 3D image reconstructing. Reliable coronal and sagittal reformations are easily obtained from the initial scan without the need for reimaging. CT scan is the imaging modality of choice for suspected fractures and fracture–dislocations of the spine in which plain films are not diagnostic. These scans are usually performed on an axial plane with thin (1 mm) cuts.
MRI is the imaging procedure of choice for evaluation of injuries to the spinal cord, ligaments, and discs. While MRI is very sensitive to detect marrow edema from fractures or bone contusions; it is best used as a complementary technique to CT and does not replace it. In patients with myelopathy, MRI can establish the location, extent, and nature of the cord injury, as well as demonstrate the location and nature of nerve root injury in patients with radiculopathy. Blood products within a cord contusion (hematomyelia) predict subsequent functional deficits. An MRI should be obtained to evaluate the spinal cord or suspected ligamentous injury, such as disruption of the posterior ligament complex due to anterior subluxation (whiplash).
Thoracic and lumbar spine. Plain films of the thoracic and lumbar spine are an initial screening option signs; symptoms of MOI suggest a spine injury. If head and thoraco-abdominal CT is planned, spine reformats are easily obtained and offer better detail, obviate the need for plain films, and result in no additional radiation exposure. In the patient with distracting injuries (e.g., chest or pelvic fractures) or a concomitant C-spine injury, a complete thoracic and lumbar (T&L) spine series is necessary. Certain mechanisms of injury warrant radiographic evaluation of the T&L spine: Automobile–pedestrian collisions, rollovers, ejections from a vehicle, collisions involving unrestrained automobile passengers, motorcycle crashes, or falls from a height.
Plain radiographs must include two views of the area of concern: Usually AP and lateral. Oblique views can be helpful, but CT scan directed to the suspected area of injury is preferred. Portable studies are often impractical because of patient size, and the osseous detail required to exclude a fracture. In this circumstance, the patient should have done these films in the radiology department, with proper monitoring and trauma team presence. MDCT also offers the ability to reliably review areas of concern by reformatting images obtained from scans of the chest, abdomen, and pelvis. Some institutions routinely generate 3D reconstruction of the CT thoracolumbar spine images as part of the chest/abdomen/pelvis CT.
V. Chest Trauma
The chest x-ray is the fundamental and primary examination in chest trauma. A frontal AP chest radiograph should be obtained in all major trauma cases. Ideally, an erect chest film is obtained because the anatomic alterations caused by the supine position can simulate disease (e.g., a widened mediastinum or interstitial lung disease) and mask pleural effusions or pneumothorax. However, the upright position is usually not possible. To decrease magnification artifacts, the distance from the x-ray tube (camera) to the film should be maximized to approximately 60 to 72 in. (5 to 6 ft) in either the supine or reverse Trendelenberg position.
Acute aortic injury should be suspected in any patient who suffers a significant deceleration injury. The most common type and site of aortic injury is an incomplete tear through the intima and media of the descending thoracic aorta, just distal to the left subclavian artery. Mediastinal hemorrhage is present in most patients with aortic injury. However, 7% to 10% of patients with thoracic
aortic injury have a normal admission chest x-ray study. In addition, only 10% to 20% of patients with plain chest film findings of mediastinal widening prove to have an aortic laceration.Related posts:
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