Trauma Overview
Main Text
Preamble
Trauma is one of the most frequent indications for emergent neuroimaging. Because imaging plays such a key role in patient triage and management, we begin this book by discussing skull and brain trauma.
We start with a brief consideration of epidemiology. Traumatic brain injury (TBI) is a critical public health and socioeconomic problem throughout the world. The direct medical costs of caring for acutely traumatized patients are huge. The indirect costs of lost productivity and long-term care for TBI survivors are even larger than the short-term direct costs.
We then briefly discuss the etiology and mechanisms of head trauma. Understanding the different ways in which the skull and brain can be injured provides the context for understanding the spectrum of findings that can be identified on imaging studies.
Introduction
Epidemiology of Head Trauma
Trauma—sometimes called the silent epidemic—is the most common worldwide cause of death in children and young adults. Neurotrauma is responsible for the vast majority of these cases.
At least 10 million people worldwide sustain TBI each year. Approximately 10% sustain fatal brain injury. Lifelong disability is common in those who survive. Between 5-10% of TBI survivors have serious permanent neurologic deficits, and an additional 20-40% have moderate disability. Even more have subtle deficits (“minimal brain trauma”).
Etiology and Mechanisms of Injury
Trauma can be caused by missile or nonmissile injury. Missile injury results from penetration of the skull, meninges, &/or brain by an external object, such as a bullet. Gunshot wounds are most common in adolescent and young adult males but are relatively rare in other groups.
Nonmissile closed head injury (CHI) is a much more common cause of neurotrauma than missile injury. Falls have now surpassed road traffic incidents as the leading cause of TBI.
So-called ground-level falls (GLFs) are a common indication for neuroimaging in young children and older adults. In such cases, brain injury can be significant. With a GLF, a six-foot-tall adult’s head impacts the ground at 20 MPH. Anticoagulated older adults are especially at risk for intracranial hemorrhages, even with minor head trauma.
Motor vehicle collisions occurring at high speed exert significant acceleration/deceleration forces, causing the brain to move suddenly within the skull. Forcible impaction of the brain against the unyielding calvarium and hard, knife-like dura results in gyral contusion. Rotation and sudden changes in angular momentum may deform, stretch, and damage long vulnerable axons, resulting in axonal injury.
Classification of Head Trauma
The most widely used clinical classification of brain trauma, the Glasgow Coma Scale (GCS), depends on the assessment of three features: Best eye, verbal, and motor responses. With the use of the GCS, TBI can be designated as a mild, moderate, or severe injury.
TBI can also be divided chronologically and pathoetiologically into primary and secondary injury, the system used in this text. Primary injuries occur at the time of initial trauma. Skull fractures, epi- and subdural (SDH) hematomas, contusions, axonal injury, and brain lacerations are examples of primary injuries.
Secondary injuries occur later and include cerebral edema, perfusion alterations, brain herniations, and CSF leaks. Although vascular injury can be immediate (blunt impact) or secondary (vessel laceration from fractures, occlusion secondary to brain herniation), for purposes of discussion, it is included in the chapter on secondary injuries.
CLASSIFICATION OF HEAD TRAUMA
Primary Effects
• Scalp and skull injuries
• Extraaxial hemorrhage/hematomas
• Parenchymal injuries
• Miscellaneous injuries
Secondary Effects
• Herniation syndromes
• Cerebral edema
• Cerebral ischemia
• Vascular injury (can be primary or secondary)
Imaging Acute Head Trauma
Preamble
Imaging is absolutely critical to the diagnosis and management of the patient with acute TBI. The goal of emergent neuroimaging is twofold: (1) Identify treatable injuries, especially emergent ones, and (2) detect and delineate the presence of secondary injuries, such as herniation syndromes and vascular injury.
How to Image
Injuries to the head and brain are often separated into acute (0-7 days), subacute (< 3 months), and chronic (> 3 months) phases. NECT is typically the first-line imaging modality for suspected acute head injury. CTA is helpful in cases with suspected injury to the cervical or intracranial vasculature. MR is rarely used in the acute trauma setting but can be useful for evaluating persistent subacute or chronic neurologic deficits.
Skull Radiography
Skull radiography (whether “plain film” or “digital radiography”) is no longer indicated in the initial evaluation of head injury. While it detects calvarial fractures reasonably well, skull radiography does not depict the far more important presence of extraaxial hemorrhages and parenchymal injuries and therefore has no appropriate role in the current management of the head-injured patient. Keep in mind: Between 1/4 to 1/3 of autopsied patients with fatal brain injuries have no identifiable skull fracture!
NECT
CT is now accepted as the “workhorse” screening tool for imaging acute head trauma. The reasons are simple: CT depicts both bone and soft tissue injuries. It is also widely accessible, fast, effective, and comparatively inexpensive.
Nonenhanced CT (NECT) scans (4 or 5 mm thick) from just below the foramen magnum through the vertex should be performed. Two sets of images should be obtained: One using brain and one with bone reconstruction algorithms. In addition, viewing the brain images with a wider window width (150-200 HU, the so-called subdural window) should be performed on PACS. The scout view should always be displayed and examined as part of the study (1-1).
Multidetector row CT (MDCT) is now routine in trauma triage. Coronal and sagittal reformatted images using the axial source data improve the detection rate of acute traumatic SDHs.
Three-dimensional shaded surface displays (3D SSDs) are helpful in depicting skull and facial fractures. If facial bone CT is also requested, a single MDCT acquisition can be obtained without overlapping radiation exposure to the eye and lower 1/2 of the brain.
Head trauma patients with acute intracranial lesions on CT have a higher risk for cervical spine fractures compared with patients with a CT-negative head injury. Because up to 1/3 of patients with moderate to severe head injury, as determined by the GCS, have concomitant spine injury, MDCT of the cervical spine is often obtained together with brain imaging. Soft tissue and bone algorithm reconstructions with multiplanar reformatted images of the cervical spine should be obtained.
CTA
While there is no relevant literature to support the use of CT angiography (CTA) in the initial imaging evaluation of acute head trauma without suspected vascular injury, it is often obtained as part of a whole-body trauma CT protocol. Craniocervical CTA should also be specifically considered (1) in the setting of penetrating neck injury, (2) if a fractured foramen transversarium or facet subluxation is identified on cervical spine CT, or (3) if a skull base fracture traverses the carotid canal or a dural venous sinus. Arterial laceration or dissection, traumatic pseudoaneurysm, carotid-cavernous fistula, or dural venous sinus injury are nicely depicted on high-resolution CTA.
MR
Although MR can detect traumatic complications without radiation and is more sensitive for abnormalities, such as contusions and axonal injuries, there is general agreement that NECT is the procedure of choice in the initial evaluation of brain trauma. Limitations of MR include acquisition time, access, patient monitoring and instability, motion degradation of images, and cost.
With one important exception—suspected child abuse—using MR as a routine screening procedure in the setting of acute brain trauma is not appropriate. Standard MR together with susceptibility-weighted imaging and diffusion tensor imaging (DTI) is most useful in the subacute and chronic stages of TBI. Other modalities, such as fMRI, are playing an increasingly important role in detecting subtle abnormalities, especially in patients with mild cognitive deficits following minor TBI but are not utilized in the acute setting.
Who and When to Image
Who to image and when to do it are paradoxically both well established and controversial. Patients with a GCS score indicating moderate (GCS = 9-12) or severe (GCS ≤ 8) neurologic impairment are invariably imaged. The real debate is about how best to manage patients with GCS scores of 13-15. Keep in mind that there is a big difference between a GCS of 15 (normal) and one of 13 or 14, as confusion, motor response localizing to pain, and eyes open only to verbal command do indicate some degree of neurologic impairment. Some investigators also distinguish between mild and minimal head trauma (i.e., GCS of 15 without loss of consciousness or posttraumatic amnesia).
GLASGOW COMA SCALE
Best Eye Response (Maximum = 4)
• 1 = no eye opening
• 2 = eyes opening to pain
• 3 = eyes open to verbal command
• 4 = eyes open spontaneously
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