You are in: eMedicine Specialties > Emergency Medicine > NEUROLOGY Emergency NeuroradiologyArticle Last Updated: Jun 12, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Alice Kwan, MD, Staff Physician, Department of Emergency Medicine, New York University Medical Center Coauthor(s): Nancy S Kwon, MD, MPA, Assistant Professor of Clinical Surgery, Consulting Staff, Department of Emergency Medicine, New York University School of Medicine and Bellevue Hospital Center; Michael Rothman, MD, Section Chief, Department of Radiology, Division of Magnetic Resonance Imaging, Saint Luke's Hospital Editors: Dana A Stearns, MD, Assistant Director of Undergraduate Education, Department of Emergency Medicine, Massachusetts General Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gino A Farina, MD, Program Director, Associate Professor of Clinical Emergency Medicine, Department of Emergency Medicine, Long Island Jewish Medical Center, Albert Einstein College of Medicine; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; Jonathan Adler, MD, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital; Division of Emergency Medicine, Harvard Medical School Author and Editor Disclosure Synonyms and related keywords: neuroimaging, head trauma, cranial trauma, head injury, cranial injury, cranial imaging, computed tomography, head CT, magnetic resonance imaging, head MRI, angiography INTRODUCTIONSection 2 of 9
  Trauma is the leading cause of death in patients younger than 45 years. Cranial trauma accounts for a substantial proportion of morbidity and mortality in all age groups and is the leading cause of death in patients younger than 30 years. Accurate, rapid, noninvasive assessment of people with cranial trauma is required for appropriate triage and management. Computed tomography (CT) is the diagnostic procedure of choice for acute injury, while magnetic resonance imaging (MRI) has great value for evaluation in the subacute and long-term. Approximately 1.4 million people sustain traumatic brain injury (TBI) annually in the United States resulting in more than 50,000 deaths. TBI is twice as likely in men than in women. Children (<14 y) and elderly persons (>60 y) are at the highest risk for TBI and TBI-related hospitalizations and death, respectively. Child abuse accounts for more than 1 million cases of TBI each year. The overall direct and indirect medical costs including lost productivity and permanent disability from TBI totaled an estimated $60 billion in the United States in 2000. Although TBI from closed head and penetrating trauma account for the majority of cerebral injuries, other processes such as acute cerebral infarction (stroke) or subarachnoid hemorrhage (SAH) due to rupture of intracranial aneurysms, may mimic a traumatic injury on presentation and radiologic evaluation. Stroke is the third leading cause of death in the United States, behind heart disease and cancer and is the leading cause of long-term disability. CLINICALSection 3 of 9
History
Physical
DIFFERENTIAL DIAGNOSESSection 4 of 9
Acute stroke (embolic/hemorrhagic) Cardiac syncope Hypertensive crisis/hemorrhage Intracranial hemorrhage Rupture of arteriovenous malformation/aneurysms Intracranial mass Seizure; postictal state Meningitis/encephalitis/systemic infection Toxic/metabolic disorders DIAGNOSTIC WORKUPSection 5 of 9
Computed tomography scanning CT is the imaging procedure of choice in evaluation of acutely injured patients or patients with acute neurologic deficit. Quick, easy, reliable, and routinely available, CT is valuable in making a firm diagnosis, as well as in excluding alternative diagnoses or the sequelae of other pathology, even in uncooperative patients. Patient monitoring is simple and safe, and CT is compatible with patient stabilization devices. Identification and localization of calvarial fractures and bony/metallic fragments are easily achieved. Assessment for acute hemorrhage and mass effect is optimal. Primary indications for CT include acute head trauma, suspected acute intracranial hemorrhage, mental status changes, headache, acute neurologic deficits, suspected intracranial infection, suspected hydrocephalus, brain herniation, and suspected mass tumor. Where MRI is primarily indicated but unavailable, contraindicated, or delayed, CT may also be used. In cases of trauma, CT is recommended in all patients with severe TBI (GCS <8) and moderate TBI (GCS 9-12). In mild TBI (GCS >13), CT is more controversial. Recent studies suggest that the presence of (1) headache, (2) vomiting, (3) age older than 60 years, (4) drug/alcohol intoxication, (5) deficits in short-term memory, (5) physical evidence of trauma above the clavicles, or (6) seizure are highly sensitive (up to 100%) with a negative predictive value up to 100% in the detection of all intracranial injuries in patients that present with a GCS 15. However, many providers still recommend that patients who have history of neurosurgery, coagulopathy, and loss of consciousness should also be scanned. The routine cranial CT protocol should include contiguous sections, 5-10 mm thick, from the skull base through the vertex (thinner at base, thicker at vertex) without contrast, reviewed at the following windows widths/levels (in Hounsfield units):
Contrast infusion is rarely indicated in the search for mass lesions or vascular pathology, except in patients with a history of human immunodeficiency virus infection and neurological examination abnormalities. If CT findings are normal, stable patients who suffer from mild TBI can be discharged safely after a period of clinical observation. In those who suffer from moderate or severe TBI, a negative CT does not rule out the delayed development of hemorrhage. These patients and patients with a positive CT should undergo a follow-up scan within 24 hours or earlier if symptoms change and/or deteriorate. Magnetic resource imaging MRI is valuable in identifying subtle abnormalities on initial and subacute evaluation and in dating injury. MRI is generally better than conventional CT at detecting abnormalities in and progression of posterior fossa and brain stem injuries, child abuse, cortical contusions, and shearing injuries. However, MRI is not as readily available as CT. Appropriate patient monitoring is difficult and unreliable due to strong magnetic fields, time-varying magnetic gradients, and restricted access to the patient. Many newer generation MRI machines have improved these conditions. Primary indications for MRI include evaluation of seizures, cranial nerve dysfunction, diplopia, ataxia, acute and chronic neurologic deficits, suspicion of neurodegenerative disease, primary and secondary neoplasm, aneurysm, vasculitis, encephalitis, headache, mental status change, hydrocephalus, ischemic disease and infarction, suspected pituitary dysfunction, inflammation or infection of the brain or meninges or their complications, demyelination and dysmyelination disorders, vascular malformations, and arterial or venous/dural sinus abnormalities. Patients who have cardiac pacemakers, ferromagnetic intracranial aneurysm clips, and certain ferromagnetic foreign bodies or electronic devices or implants should not undergo MRI. The routine MRI protocol varies considerably based on strength of the unit's field, machine capabilities, and suspected diagnosis. Most centers perform sagittal T1-weighted and axial T1- and T2-weighted sequences of the brain routinely, with the addition of specific additional sequences depending on the clinical indications. T2-weighted gradient echo sequences are more sensitive for subacute/chronic parenchymal hemorrhage/shearing injuries, while fluid-attenuated inversion recovery (FLAIR) sequences have been shown to be more sensitive for subtle subarachnoid blood. Magnetic resonance angiography and venography, diffusion and perfusion imaging, and spectroscopy may all be valuable in selected circumstances. MRI with diffusion-weighted imaging (DWI) has become more routinely used in the detection of acute stroke because of its improved sensitivity, negative predictive value, and accuracy compared with CT and conventional MRI. MRI with DWI has also been helpful in the detection of the early stages of brain infection such as meningitis, toxoplasmosis, herpes simplex, and West Nile virus. Conventional catheter angiography Conventional catheter angiography is useful in defining pathologic vascular neuroanatomy and can also serve as a treatment modality. Depending on practice patterns at individual centers, angiography is indicated in patients with penetrating trauma for examining possible vessel injury, subarachnoid hemorrhage, parenchymal hemorrhage, aneurysm, vascular malformation, thromboembolic/hemorrhagic stroke, veno-occlusive disease, and vasospasm. Relative contraindications include hypotension, severe hypertension, coagulopathy, renal insufficiency, congestive heart failure, and sensitivity to iodinated contrast material. Patients should be stabilized and tenuous conditions should be corrected prior to study. Conventional radiography Due to the advancements and accessibility of imaging technology, conventional radiography generally does not serve a role in the evaluation of the patient with acute head injury unless CT and MRI are unavailable. Where skull radiographs may be requested in the past, CT is significantly more sensitive for soft tissue injury and is superior for spatial localization and assessment of bony alterations. Radiography is not a useful screening tool and negative findings on skull films do not exclude intracranial injury. TYPES OF INJURYSection 6 of 9
Epidural hematoma The dura mater is composed of 2 layers closely invested with each other: the visceral or meningeal layer, which lines the intracranial space, and the parietal layer, which functions as the periosteum of the calvarium. The dura, therefore, adheres tightly to the cranial sutures. A skull fracture that crosses an arterial branch may bleed into the closed space between the calvarium and the periosteal layer, forming a homogeneously high-density lens-shaped or biconvex collection, termed epidural hematoma (EDH) (see Media files 1-2). Because of the transmitted arterial pressure, EDH tends to continue to enlarge, with resultant increasing mass effect. This explains the classic presentation associated with EDH of an initial loss of consciousness followed by a "lucid interval" with subsequent neurologic deterioration. However, a lucid interval is present in only 40% of cases and is not pathognomonic for EDH. Prognosis is generally good for acute hematomas in conscious patients who undergo immediate surgical correction. Mortality is approximately 5%. Subdural hematoma The subdural space is bound externally by the meningeal layer of the dura and internally by the arachnoid mater. Hematomas are confined by the reflected dura of the tentorium and falx but easily spread into the intervening potential space to form crescentic or convex-out/concave-in collections called subdural hematomas (SDH) (see Media file 5). Abrupt acceleration/deceleration injury tearing bridging cortical veins that traverse this space accounts for most SDH. This is more likely to occur in elderly patients and other patients with atrophy, where the subdural space is enlarged. Acute hemorrhage is dense on the brain windows, assuming normal hematocrit. As blood ages, it becomes less dense, so that by about 7-10 days, it approximates the same density as adjacent brain tissue. At this stage, the isodense SDH (see Media file 6) is described. Careful inspection of the subdural or intermediate windows usually shows inward displacement of the cortical gray/white matter junction and mass effect, otherwise unexplained by the imaging findings. Contrast enhancement of the bridging veins may define the collection (see Media file 7). Homogeneous density within a subdural collection generally represents interval hemorrhage into a preexisting chronic SDH. The mortality rate for acute SDH is 37-57%. Most patients with decreased sensorium have poor outcomes, likely secondary to associated diffuse cerebral brain swelling. In these cases, immediate surgical evacuation does not always improve outcome. Subarachnoid hemorrhage The subarachnoid space extends between the subdural space and the cortical/pia mater surface of the brain. Hemorrhage into this space interdigitates with the sulci and gyri of the brain as seen in traumatic subarachnoid hemorrhage (SAH) (see Media file 8). Focal dense clot often signifies the location of hemorrhage, particularly in patients with aneurysm rupture. More subtle or diffuse bleeding is often due to cortical contusion, dilution from a focal collection, or intraventricular hemorrhage due to delayed presentation. Catheter angiography is usually indicated on an emergency basis to identify cerebral aneurysms and to define their anatomy prior to surgical intervention (see Media file 9). The prognosis for patients with SAH is variable depending on the extent of injury. Traumatic SAH is common and often associated with other injuries affecting outcome. Parenchymal lesions Focal cortical hemorrhage is common as a sequela of head trauma and may be multifocal, as in coup (direct) and contrecoup (indirect) injuries, or diffuse. Focally dense gyri with subjacent edema, particularly those adjacent to the inner calvarial structures (ie, orbit roof-frontal pole, petrous ridge, sphenoid wing-temporal pole) represent contusions (see Media files 10-11). Diffuse axonal injury (DAI), caused by shearing of the white matter, is due to the differing density or fixation between two structures and the differing response to rotation, acceleration, and deceleration. The lobar white matter, brainstem, and corpus callosum are most often affected, with focal ovoid or elongated regions of decreased density. Patients usually present with severe impairment of consciousness from the moment of impact. MRI (FLAIR or T2 weighted) is most useful in defining the extent of axonal shearing and nonhemorrhagic injury. CT results are often negative, but acute areas of petechial hemorrhage have been seen in early stages. DAI is one of the most common injuries resulting in long-term severe disability and vegetative state. Cerebral edema may result from loss of normal autoregulation and hyperemia or diffuse edema from other causes. Diffuse loss of normal sulci and cisterns with small ventricles is noted (see Media files 12-13). Mass effect, increased intracranial pressure, ischemia, and herniation contribute to poor outcomes. MRI is more sensitive than CT for subtle injuries of these types, especially in the subacute or chronic phases. Children are most commonly affected; they have a 50% mortality rate, 3 times that of adults. Herniation syndromes Herniation syndrome can develop as a major consequence of any of the aforementioned primary brain injuries. The cranial vault is divided into multiple compartments by bone and dura. When a primary injury develops and expands, pressure is applied to contiguous structures adjacent to the displacing injury. Elevation in cranial pressure adds to the demise of the patient. Medical and surgical control of increasing intracranial pressure is of ultimate priority. (See eMedicine article, Brain, Herniation.) Parenchymal hemorrhage Focal parenchymal hematomas occurring in regions of end-arteries, such as the basal ganglia, thalamus, brainstem, and cerebellar hemispheres, occur most frequently in patients with chronic hypertension or hypertensive crisis, probably due to spontaneous rupture of these tiny vessels. Less than 1% of such patients have a radiographically definable lesion; thus, angiography is rarely indicated (see Media file 14). Focal lobar parenchymal hematomas, by contrast, are far more likely to be secondary to a structural lesion, often an arteriovenous malformation (AVM), vasculitis, or mass lesion (see Media file 15). If an appropriate clinical history has been obtained, angiography (AVM) or contrast-enhanced MRI is the diagnostic procedure of choice prior to surgical intervention, unless secondary mass effect is life threatening and patient management decisions dictate otherwise (see Media file 16). Stroke Patients with stroke in the emergency setting may present a different course for decision-making. Acute (12-48 h) occlusion of one or more large vessels results in focal, wedge-shaped peripheral areas of loss of grey/white matter differentiation involving the cortex and contiguous white matter, or simply as a focal mass effect (see Media file 17). Anoxia or hypotension results in diffuse loss of gyral/cortical markings and diffuse mass effect (see Media file 18). Such changes are exceedingly difficult to appreciate on CT studies obtained hyperacutely (<6-12 h from ictus). One exception is the dense middle cerebral artery (MCA) sign, which represents acute clot within the horizontal portion of the middle cerebral artery (see Media file 19). Patients with resolved neurologic deficits (ie, transient ischemic attacks) rarely demonstrate acute pathology on CT examinations without having sustained acute trauma. MRI with DWI techniques allows earlier identification and diagnosis in less than 30 minutes from initial insult with changes up to 2 weeks. Brain injury protocols have shown excellent results in treating such patients with intravenous (<3 h) or intra-arterial (<6 h) thrombolytic agents. Child abuse Child abuse merits specific mention because of the severe morbidity and mortality of cranial injuries inflicted in abusive settings and because of the possibility of intervention to spare other household members further trauma. The key to diagnosis of child abuse is repeated injury, which is present in the majority of victims. Presence of hemorrhages of various ages and locations is pathognomonic (see Media files 20-22). Retinal hemorrhages, rib and long bone fractures, burns, and other skin lesions are common. MRI is ideal for the evaluation of such patients because of its superior sensitivity and ability to date the injuries with accuracy. It further offers the benefit of not using ionizing radiation. Penetrating trauma CT is the diagnostic procedure of choice for patients with gunshot wounds and other penetrating trauma. The course of the projectile may be identified, and the location of foreign bodies can be noted. Hematomas and mass effect are easily assessed (see Media files 23-27). Angiography may also aid in the diagnosis and treatment of vascular disruptions from penetrating trauma. TABLE 1Section 7 of 9
Glasgow Coma Scale: GCS is a common tool used to access the grade and the progression of head injury over time and multiple observers.
MULTIMEDIASection 8 of 9
REFERENCESSection 9 of 9
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