Radiography
Findings
Skull radiographs are notoriously unhelpful in predicting underlying brain injury. However, scalp hematomas or skull fractures are usually good indicators of a significant direct force to a focal region. As such, the radiographic findings are usually associated with underlying brain contusions, although significant brain injury may occur without these findings.
Degree of Confidence
Skull radiographs are unreliable.
False Positives/Negatives
The rate of false-negative findings is high, but few false-positive findings occur.
Computed Tomography
Findings
Contusions may progress with time. Imaging findings in brain contusions tend to vary because of the stages of evolution common to these lesions.
Acute CT initially demonstrates isoattenuating contusions that become more evident on follow-up CT (see Image 4). CT scans often demonstrate progression over time in the size and number of contusions and the amount of hemorrhage in the contusions (see Images 4-6). Initially, CT findings can be normal or minimally abnormal because the partial volumes between the dense microhemorrhages and the hypodense edema can render contusions isoattenuating relative to the surrounding brain tissue (see Images 2-4).
Gliding contusions are due to sagittal angular acceleration with stretching and tearing of the parasagittal veins (see Image 6). Gliding contusions are often hemorrhagic, not only from the differential motion of subcortical structures (commonly referred to as shear injury), but also from tearing of parasagittal veins. When the brain abruptly shifts at the time of impact, the subcortical tissues glide more than the cortex. The convexities of each hemisphere are anchored to the dura by arachnoid granulations. Gliding contusions also tend to be bilateral.
Image 7 shows a CT scan compared with a xenon blood-flow image. On CT scan, the contusions are seen in the bifrontal regions as hyperintense areas. The corresponding xenon blood-flow image shows dark regions that indicate decreased perfusion in the contused areas of the brain.
Image 8 shows CT and MRI of acute contusions.
Degree of Confidence
CT is an excellent modality for defining contusions. Contusions often are not appreciated on the first CT scan obtained immediately after trauma, but they become obvious on follow-up scans.
False Positives/Negatives
Initially, the false-negative rate is high, but false-positive findings are negligible.
Contusions often are not appreciated on the first CT scan obtained immediately after trauma, but they become obvious on follow-up scans.
Magnetic Resonance Imaging
Findings
MRIs typically demonstrate brain contusions from the onset of injury. MRI is sensitive to hyperacute hemorrhagic contusions ( <12 h).
On MRI, contusions are isointense to hyperintense on T1-weighted (see Images 8-11) and hyperintense on T2-weighted images (see Images 9-11). Gradient-echo MRIs (see Image 11) may reveal hypointensity, which is critical to the detection and delineation of contusions. Image 12 shows a T2-weighted MRI on which the subdural hematoma is inconspicuous. Image 12 also demonstrates how the gradient-echo MRI reveals the hypointensity of the subdural hematoma.
Use of fast fluid-attenuated inversion recovery (FLAIR) sequences has made detection of accompanying subarachnoid hemorrhage possible, with a sensitivity that is equal to or greater than that of CT. The use of FLAIR in identifying brain contusions is shown in Images 8-10). Using FLAIR sequences, subarachnoid hemorrhage produces dramatic hyperintensity in the normally hypointense cerebrospinal fluid. Additionally, companion FLAIR images show the extent of contusions better than most traditional MRIs.
Image 8 shows the ability of traditional MRIs to depict the site of the cortical contusion. The companion FLAIR image shows the full extent of the hyperintense cortical contusion more clearly. This advantage is also demonstrated in Image 9, which shows traditional MRIs and a comparison FLAIR image that shows the subdural hemorrhage and its' extension into the brain more clearly.
Use of diffusion-weighted imaging (DWI) in acute brain trauma has not been described in depth in the literature. DWI allows the rapid detection of an ischemic region after the onset of brain injury. The signal intensity is increased in the affected region on DWIs. The use of DWI to identify cerebral contusions is demonstrated in Images 9-11). DWIs show areas of restricted diffusion in areas associated with cerebral contusions.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble
movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Degree of Confidence
The degree of confidence is excellent with FLAIR imaging.
False Positives/Negatives
MRI is sensitive but nonspecific for brain injuries. MRI is the criterion standard for defining contusions. Ischemic lesions often depicted in the normal aging brain may be difficult to distinguish from traumatic injuries in the acute phase.
Ultrasonography
Findings
Ultrasound has no role in acute brain injury.
Nuclear Imaging
Findings
Umile et al note that single-photon emission computed tomography (SPECT) blood-flow imaging with technetium-99m hexamethylpropyleneamine oxime (HMPAO) uptake is sensitive enough to detect diffuse changes in patients with decreased blood flow due to depression. Many studies of mild, moderate, and severe TBI in the acute, subacute, and chronic stages have shown that SPECT is more sensitive than CT and MRI, and scans can depict changes even when findings are normal.10 SPECT findings are particularly sensitive in patients with mild postconcussive symptoms. SPECT scans can depict focal changes in 53% of patients with mild head injury who showed few abnormal findings on MRI and CT scans.11
SPECT results are correlated with the severity of injury. A negative finding on SPECT in the first 4 weeks is predictive of a good outcome. SPECT findings also can help in predicting a poor outcome, posttraumatic headaches, and clinical deterioration in patients with intracerebral hematomas. Studies correlating SPECT with neuropsychologic testing have been inconsistent. One study reported that SPECT can reveal significant increases in blood flow following cognitive rehabilitation therapy 2 years after TBI; these findings were correlated with improvements on neuropsychological tests.12
Xenon is an inert noble gas that is diffusible across the blood brain barrier. The inhalation of nonradioactive xenon can be used to calculate physiologic aspects of brain function, including regional cerebral blood flow, by using CT. Xenon imaging has been used for the documentation of brain death. Brain trauma is a potential application for xenon CT scanning.
At the current time, xenon blood-flow imaging has not achieved widespread use because of a number of factors. Xenon gas is expensive; without a rebreathing apparatus, approximately 10 L of xenon is required for each study, adding additional costs to each examination. Also, anesthetic equipment must be used, and special software must be purchased for the CT scanner. The anesthetic effects of xenon are somewhat worrisome as well. Multiple, rapid-sequence images must be obtained at the same level, limiting the total number of section levels that can be obtained. This factor may limit the scan to a few regions, when a given patient may have multiple pathologic areas.
Degree of Confidence
SPECT blood flow imaging has excellent sensitivity.
False Positives/Negatives
Caution must be taken not to mistakenly attribute the diffuse changes seen in psychiatric disorders with focal TBI changes.
Angiography
Findings
Focal vascular spasm may be seen in the acute/subacute injury phase.
Traumatic aneurysms are rare, but may occur as a result of either blunt or penetrating brain trauma. Intracranial aneurysms may result from fracture, with laceration of the adjacent artery by bone spicules, or by shearing forces secondary to rapid deceleration injury. Penetrating wounds, usually from bullets or shrapnel, are another etiology. Most traumatic aneurysms are pseudoaneurysms, meaning that they are hematoma cavities contained by the soft tissues adjacent to an arterial laceration. As the hematoma organizes and resolves, it becomes surrounded by a fibrous pseudocapsule, which is highly prone to rupture.
Cerebral aneurysms are potentially catastrophic lesions and many persons who do survive aneurysms rupture are permanently disabled. Treatment of unruptured aneurysms has low morbidity and mortality, which makes accurate and timely diagnosis important.
Conventional angiography remains the definitive procedure for the preoperative evaluation of aneurysms. However, the cross-sectional imaging modalities, including computed tomographic angiography (CTA) and magnetic resonance angiography (MRA), add indispensable information concerning the size of the lesion, location, presence of thrombus, associated hemorrhage, and the condition of surrounding brain tissue.
Degree of Confidence
Spasm is a good indicator of subarachnoid hemorrhage and underlying brain injury.
False Positives/Negatives
Few false-positive findings occur, but angiography may not reveal the true extent of injury.
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Further Reading
Keywords
brain injury, acute traumatic CNS damage, central nervous system injury, head trauma, head injury, skull injury, skull fracture, facial injury, facial soft tissue injury, cranial soft tissue injury, cranial fracture, concussion, brain hemorrhage, cranial contusion, laceration of the brain, punctate parenchymal hemorrhage, microhemorrhage, traumatic brain injury, TBI, coup contusion, contrecoup contusion, brain contusion, scalp hematoma
