Emerg Radiol DOI 10.1007/s10140-014-1226-0
REVIEW ARTICLE
Magnetic resonance imaging of traumatic brain injury: a pictorial review Christopher Aquino & Sean Woolen & Scott D. Steenburg
Received: 10 February 2014 / Accepted: 10 April 2014 # Am Soc Emergency Radiol 2014
Abstract Traumatic brain injury (TBI) is a significant source of major morbidity and mortality in blunt trauma patients. Computed tomography (CT) is the primary imaging modality of choice for patients with potential brain injury in the acute setting, with magnetic resonance imaging (MRI) playing a role in evaluating equivocal CT findings and may help with determining long-term prognosis and recovery. MRI is being utilized more commonly in the acute and subacute setting of TBI; therefore, radiologists should be familiar with the MRI appearance of the various manifestations of TBI. Here, we review the imaging of common intracranial injuries with illustrative cases comparing CT and MRI. Keywords Traumatic brain injury . Magnetic resonance imaging . Intracranial hemorrhage
magnetic resonance imaging (MRI) plays a role in evaluating both equivocal CT findings due to its high sensitivity for the detection of intracranial hemorrhage and other disease entities that may not be detected on admission head CT. The imaging features of TBI on CT are well known; however, brain MRI is being employed earlier in the work up of patients with TBI, and therefore radiologists who evaluate these patients should be familiar with the MRI appearance of primary and secondary brain injuries. In this review article, we will discuss the epidemiology of TBI. Imaging techniques with particular attention to MRI will be presented. This article will compare and contrast the imaging appearances of blunt TBI as seen on CT and MRI, focusing on primary extra-axial, primary intra-axial, and secondary traumatic brain injuries. Finally, disease entities that may escape detection on CT, such as axonal shear and fat embolism, will be discussed with several examples.
Introduction Traumatic brain injury (TBI) is a significant source of major morbidity and mortality in blunt trauma patients. Computed tomography (CT) is the primary imaging modality of choice for patients with potential brain injury in the acute setting, and C. Aquino Department of Diagnostic Imaging, Kaiser Permanente San Diego Medical Center, San Diego, CA, USA S. Woolen : S. D. Steenburg Division of Emergency Radiology, Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA S. D. Steenburg (*) Department of Radiology and Imaging Sciences, Indiana University Health Methodist Hospital, 1701 N. Senate Blvd, Room AG-176, Indianapolis, IN 46202, USA e-mail: [email protected]
Epidemiology In the USA, at least 2 % of the population per year is affected by TBI with an estimated societal cost of $60 billion annually [1]. The young-adult population is particularly inflicted with TBI as it is a major cause of disability and death [2–4]. Approximately 235,000 hospitalizations for nonfatal TBIs occur each year, and of the 1.1 million Americans who are treated and released from emergency departments annually, approximately 50,000 die each year as a result of their injuries [5].The major risk factors for TBI are age, male gender, and low socioeconomic status. People at the extremes of age, younger than 10 and older than 74 years old, have the highest incidence rates [5]. Overall, for all hospital discharges, with ED visits and deaths combined, falls are the leading cause of TBI (35.2 %), followed by motor vehicle collisions (MVC; 20 %), blunt trauma (not otherwise specified, 19 %), and assaults (11 %) [5].
Emerg Radiol
Imaging of traumatic brain injury A TBI refers to the damage sustained by the intracranial structures following trauma to the head. Although many classification schemes exist, the severity of TBI is usually based on the Glasgow Coma Scale (Mild, 13–15; moderate, 9–12; severe, 8 or less) [6]. CT continues to be the imaging modality of choice for the initial assessment of patients who have suffered acute head injury. It provides fast and accurate assessment of primary and secondary brain injury and skull fractures and is compatible with most life-support devices [7]. Although CT remains the mainstay for imaging in the acute setting due to its speed, cost-effectiveness, and ability to demonstrate surgically treatable injuries, MRI is the most sensitive modality in depicting craniocerebral injuries and may play a role in the prognosis of TBI patients [8]. MRI is typically recommended for stable patients with acute TBI when clinical symptoms cannot be fully understood by findings on CT alone, with the role of MRI shifting to evaluate patients in the acute and subacute phase of injury. More advanced magnetic resonance techniques continue to be developed and utilized in the assessment of victims of TBI.
MRI sequences Typical MRI protocols for TBI include axial and sagittal T1, axial T2, axial fluid attenuation inversion recovery (FLAIR), diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), gradient-recalled echo (GRE), and susceptibilityweighted imaging (SWI) sequences. These sequences are well known to radiologists and allows for direct comparison between CT and MRI imaging modalities for TBI. Contrast-enhanced imaging is not routinely performed unless there is concern for intracranial infection, usually in the setting of prior cranial surgery or open-skull fracture. There are a few sequences that are particularly useful in the routine evaluation of the trauma patient [9]. Fluid attenuation inversion recovery (FLAIR) is a T2-weighted sequence that increases visibility of signal abnormality by suppressing the high signal intensity of CSF seen on routine T2-weighted images. This allows for better detection of focal parenchymal injuries and increased sensitivity for subarachnoid hemorrhage (SAH) and axonal shear injuries [10–12]. FLAIR images, in concert with iron-sensitive sequences, are especially helpful in detecting diffuse axonal injury (DAI) involving areas that may be difficult to evaluate on routine axial T2-weighted imaging, such as the corpus callosum and the fornix [7]. Gradient-recalled echo (GRE) T2* imaging allows detection of ferritin and hemosiderin; the breakdown products of blood. GRE is very sensitive to the local magnetic field inhomogeneities caused by ferromagnetic blood products
[13, 14] resulting in areas of signal loss on GRE images. GRE is useful for detection of remote TBI as hemosiderin particles may persist indefinitely in areas of injured cortex. However, GRE provides limited evaluation at the skull base because of artifact caused by the bones, paranasal sinuses, and mastoid air cells [15, 16]. SWI is a high-resolution imaging sequence that is exquisitely sensitive to magnetic susceptibility caused by hemorrhage and has increased spatial resolution compared with conventional GRE [17, 18]. It is extremely sensitive to blood products in hemorrhage and deoxyhemoglobin in venous blood [19]. SWI has been shown to detect microhemorrhages at locations that conventional CT and MRI studies do not, such as the boundary of gray–white matter and at the junction of branching vessels, especially the veins [20]. However, SWI has the disadvantage of an increased acquisition time (2– 4 min) compared with conventional GRE (
REVIEW ARTICLE
Magnetic resonance imaging of traumatic brain injury: a pictorial review Christopher Aquino & Sean Woolen & Scott D. Steenburg
Received: 10 February 2014 / Accepted: 10 April 2014 # Am Soc Emergency Radiol 2014
Abstract Traumatic brain injury (TBI) is a significant source of major morbidity and mortality in blunt trauma patients. Computed tomography (CT) is the primary imaging modality of choice for patients with potential brain injury in the acute setting, with magnetic resonance imaging (MRI) playing a role in evaluating equivocal CT findings and may help with determining long-term prognosis and recovery. MRI is being utilized more commonly in the acute and subacute setting of TBI; therefore, radiologists should be familiar with the MRI appearance of the various manifestations of TBI. Here, we review the imaging of common intracranial injuries with illustrative cases comparing CT and MRI. Keywords Traumatic brain injury . Magnetic resonance imaging . Intracranial hemorrhage
magnetic resonance imaging (MRI) plays a role in evaluating both equivocal CT findings due to its high sensitivity for the detection of intracranial hemorrhage and other disease entities that may not be detected on admission head CT. The imaging features of TBI on CT are well known; however, brain MRI is being employed earlier in the work up of patients with TBI, and therefore radiologists who evaluate these patients should be familiar with the MRI appearance of primary and secondary brain injuries. In this review article, we will discuss the epidemiology of TBI. Imaging techniques with particular attention to MRI will be presented. This article will compare and contrast the imaging appearances of blunt TBI as seen on CT and MRI, focusing on primary extra-axial, primary intra-axial, and secondary traumatic brain injuries. Finally, disease entities that may escape detection on CT, such as axonal shear and fat embolism, will be discussed with several examples.
Introduction Traumatic brain injury (TBI) is a significant source of major morbidity and mortality in blunt trauma patients. Computed tomography (CT) is the primary imaging modality of choice for patients with potential brain injury in the acute setting, and C. Aquino Department of Diagnostic Imaging, Kaiser Permanente San Diego Medical Center, San Diego, CA, USA S. Woolen : S. D. Steenburg Division of Emergency Radiology, Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA S. D. Steenburg (*) Department of Radiology and Imaging Sciences, Indiana University Health Methodist Hospital, 1701 N. Senate Blvd, Room AG-176, Indianapolis, IN 46202, USA e-mail: [email protected]
Epidemiology In the USA, at least 2 % of the population per year is affected by TBI with an estimated societal cost of $60 billion annually [1]. The young-adult population is particularly inflicted with TBI as it is a major cause of disability and death [2–4]. Approximately 235,000 hospitalizations for nonfatal TBIs occur each year, and of the 1.1 million Americans who are treated and released from emergency departments annually, approximately 50,000 die each year as a result of their injuries [5].The major risk factors for TBI are age, male gender, and low socioeconomic status. People at the extremes of age, younger than 10 and older than 74 years old, have the highest incidence rates [5]. Overall, for all hospital discharges, with ED visits and deaths combined, falls are the leading cause of TBI (35.2 %), followed by motor vehicle collisions (MVC; 20 %), blunt trauma (not otherwise specified, 19 %), and assaults (11 %) [5].
Emerg Radiol
Imaging of traumatic brain injury A TBI refers to the damage sustained by the intracranial structures following trauma to the head. Although many classification schemes exist, the severity of TBI is usually based on the Glasgow Coma Scale (Mild, 13–15; moderate, 9–12; severe, 8 or less) [6]. CT continues to be the imaging modality of choice for the initial assessment of patients who have suffered acute head injury. It provides fast and accurate assessment of primary and secondary brain injury and skull fractures and is compatible with most life-support devices [7]. Although CT remains the mainstay for imaging in the acute setting due to its speed, cost-effectiveness, and ability to demonstrate surgically treatable injuries, MRI is the most sensitive modality in depicting craniocerebral injuries and may play a role in the prognosis of TBI patients [8]. MRI is typically recommended for stable patients with acute TBI when clinical symptoms cannot be fully understood by findings on CT alone, with the role of MRI shifting to evaluate patients in the acute and subacute phase of injury. More advanced magnetic resonance techniques continue to be developed and utilized in the assessment of victims of TBI.
MRI sequences Typical MRI protocols for TBI include axial and sagittal T1, axial T2, axial fluid attenuation inversion recovery (FLAIR), diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), gradient-recalled echo (GRE), and susceptibilityweighted imaging (SWI) sequences. These sequences are well known to radiologists and allows for direct comparison between CT and MRI imaging modalities for TBI. Contrast-enhanced imaging is not routinely performed unless there is concern for intracranial infection, usually in the setting of prior cranial surgery or open-skull fracture. There are a few sequences that are particularly useful in the routine evaluation of the trauma patient [9]. Fluid attenuation inversion recovery (FLAIR) is a T2-weighted sequence that increases visibility of signal abnormality by suppressing the high signal intensity of CSF seen on routine T2-weighted images. This allows for better detection of focal parenchymal injuries and increased sensitivity for subarachnoid hemorrhage (SAH) and axonal shear injuries [10–12]. FLAIR images, in concert with iron-sensitive sequences, are especially helpful in detecting diffuse axonal injury (DAI) involving areas that may be difficult to evaluate on routine axial T2-weighted imaging, such as the corpus callosum and the fornix [7]. Gradient-recalled echo (GRE) T2* imaging allows detection of ferritin and hemosiderin; the breakdown products of blood. GRE is very sensitive to the local magnetic field inhomogeneities caused by ferromagnetic blood products
[13, 14] resulting in areas of signal loss on GRE images. GRE is useful for detection of remote TBI as hemosiderin particles may persist indefinitely in areas of injured cortex. However, GRE provides limited evaluation at the skull base because of artifact caused by the bones, paranasal sinuses, and mastoid air cells [15, 16]. SWI is a high-resolution imaging sequence that is exquisitely sensitive to magnetic susceptibility caused by hemorrhage and has increased spatial resolution compared with conventional GRE [17, 18]. It is extremely sensitive to blood products in hemorrhage and deoxyhemoglobin in venous blood [19]. SWI has been shown to detect microhemorrhages at locations that conventional CT and MRI studies do not, such as the boundary of gray–white matter and at the junction of branching vessels, especially the veins [20]. However, SWI has the disadvantage of an increased acquisition time (2– 4 min) compared with conventional GRE (
