Diagnostic Imaging Chest 2nd Edition [PDF] Rosado De Christenson
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Part I – Trauma
Section 1 – Central Nervous System Introduction to CNS Imaging, Trauma
> Table of Contents > Part I – Trauma > Section 1 – Central Nervous System > Introduction to CNS Imaging, Trauma
Anne G. Osborn, MD, FACR
Diagnostic Imaging: Emergency
Approach to Head Trauma
Epidemiology. Trauma is the most common worldwide cause of death and disability in children and young adults. In these patients, neurotrauma is responsible for the vast majority of cases. In the USA and Canada, emergency departments (ED) treat more than 8 million patients with head injuries annually, representing 6-7% of all ED visits. The vast majority of patients with head trauma are classified as having minimal or minor injury. Minim al head injury is defined as no neurologic alteration or loss of consciousness (LOC). Minor head injury or concussion is epitomized by a walking, talking patient with a Glasgow Coma Score (GCS) of 13-15 who has experienced LOC, amnesia, or disorientation. Of all head-injured patients, approximately 10% sustain fatal brain injury whereas another 5 -10% of neurotrauma survivors have permanent serious neurologic deficits. A number have more subtle deficits (“minimal brain trauma”) whereas 20-40% of patients have moderate disability.
Etiology and Mechanisms of Injury
The etiology of traumatic brain injury (TBI) varies according to patient age. Falls are the leading cause of TBI in children younger than 4 years and in elderly patients older than 75 years. Gunshot wounds are most common in adolescent and young adult males but relatively rare in other groups. Motor vehicle and auto-pedestrian collisions occur at all ages without gender predilection.
TBI can be a missile or non-missile injury. Missile injury results from penetration of the skull, meninges, &/or brain by an external object (such as a bullet).
Non-missile closed head injury (CHI) can be caused by direct blows or penetrating injuries. However, non-missile CHI is a more common cause of neurotrauma. High-speed accidents exert significant acceleration/deceleration forces, causing the brain to move suddenly within the skull. Forcible impaction of the brain against the unyielding calvaria and hard, knife -like dura results in gyral contusion. Rotation and abrupt changes in angular momentum may deform, stretch, and damage long vulnerable axons, resulting in axonal injury.
Classification of Head TraumaThe most widely used clinical classification of brain trauma, the GCS, depends on the assessment of three features: Best eye, verbal, and motor responses. Using the GCS, TBI can be designated as mild (13-15), moderate (9-12), or severe (≤ 8).TBI can also be divided pathoetiologically into primary and secondary injuries. Primary injuries occur at the time of initial trauma. Skull fractures, epi- and subdural hematomas, contusion, and axonal injuries are examples of primary traumatic injuries.
Secondary injuries occur later and include cerebral edema, perfusions, and brain herniations. Large arteries, such as the internal carotid, vertebral, and middle meningeal arteries, can be injured either directly at the time of initial trauma or indirectly as a complication of brain herniations.
How to Image Acute Head Trauma Imaging is absolutely critical to the diagnosis and management of the patient with acute TBI. The goal of emergent imaging is twofold: (1) Identify treatable injuries, and (2) detect and delineate the presence of secondary injuries such as
herniation syndromes. CT. CT has gradually but completely replaced skull radiographs as the “workhorse” of brain trauma imaging. Nonenhanced
CT scans (4-5 mm thick) from the foramen magnum to the vertex with both soft tissue and bone algorithm should be performed. “Subdural” windowing (e.g., window width of 150-200 HU) of the soft tissue images on PACS (or film, if PACS is not available) is highly recommended. The scout view should always be displayed and evaluated as part of the study. MDCT and CTA. Because almost one-third of patients with moderate to severe head trauma also have cervical spine injuries, multidetector row CT (MDCT) with both brain and cervical imaging is often performed. Soft tissue and bone algorithm reconstructions with multiplanar reformatted images of the cervical spine should be obtained. CT angiography (CTA) is an appropriate modality in the setting of penetrating neck injury, cervical fracture/subluxation, skull base fractures that traverse the carotid canal or a dural venous sinus, and suspected vascular dissections. MR. MR is generally a secondary modality, most often used in the late acute or subacute stages of brain injury. It is helpful in detecting focal/regional/global perfusion alterations, assessing the extent of hemorrhagic and nonhemorrhagic injuries, and assisting in long-term prognosis. MR should also be considered if nonaccidental trauma is suspected either clinically or
on the basis of initial CT scan findings.
Who and When to Image?
Many clinical studies have attempted to determine whom to image and when. Three major and widely used appropriateness criteria for imaging acute head trauma have been published: The American College of Radiology (ACR) Appropriateness Criteria, the New Orleans Criteria (NOC), and the Canadian Head CT Rule (CHCR).
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