Diagnostic Imaging of Brain Contusion
RADIOGRAPH
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.
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CT SCAN
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).
Image 4 (type CT):
Evolution of an acute brain contusion. (A) Axial CT scan obtained immediately following severe blunt trauma to the head shows a small, left frontal epidural hematoma (arrow). Extensive subgaleal bicranial hematomas are seen. (B) Companion CT scan obtained 6 days after trauma shows the small, left frontal epidural hematoma (long arrow) and smaller areas of subgaleal bicranial hematomas. Note that the previously isoattenuating contusion in the right posterior temporal area is now evident (short arrows in B).
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).
Image 6 (type CT):
Acute gliding brain contusions. Axial CT scan obtained immediately after blunt trauma to the left convexity of the skull resulted in severe swelling of the entire left cerebral hemisphere with loss of the gyral pattern secondary to edema. A small collection of subarachnoid blood is present (up arrow). The right hemisphere shows contrecoup gliding contusions (down arrows).
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).
Image 2 (type CT):
Acute brain contusion. Axial CT scan obtained in a patient immediately after a high-speed motor vehicle accident demonstrates a large, right frontal contusion with hemorrhage and surrounding edema. A smaller, subtle, right temporal cortical contusion (short arrow) is noted, as well as a small, left frontal subdural hematoma (long arrow).
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.
Image 7 (type CT):
Comparison of a CT scan with a xenon blood-flow radionuclide scan. (A) CT scan shows bifrontal contusions following severe head trauma (arrows). (B) Companion CT scan showing xenon uptake demonstrates dark regions (arrows), indicating decreased perfusion in the contused brain.
Image 8 (type CT):
Comparison of a CT scan and MRIs showing acute contusions. (A) Contrast-enhanced axial CT scan obtained immediately after head trauma shows a foreign body in the scalp (arrow) that marks the site of direct impact. Blood is noted in the right lateral ventricle. Chronic white-matter changes are present. (B) Axial T1-weighted MRI obtained on the same day shows the scalp changes at the site of the trauma (arrow). There is minimal underlying superficial cortical hyperdensity consistent with cortical contusion. (C) Comparison gadolinium-enhanced T1-weighted MRI shows minimal enhancement of the left posterior temporal-occipital cortex below the site of the scalp trauma (arrow). (D) Companion fluid-attenuated inversion recovery (FLAIR) MRI shows the extent of the left cortical contusion (arrow). Note the hyperintense signal from blood in cerebrospinal fluid and the displaced right lateral ventricle with surrounding signal intensity changes in the adjacent optic radiations (arrow).
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.
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MRI
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)
image 8:
See CT
Image 11 (type MRI):
Comparison of a CT scan and MRIs obtained 4 hours after acute trauma. (A) CT scan shows focal contusion in the left superior temporal gyrus (arrow) and a posterior falx subdural hematoma (arrows). Incidental white matter changes are present in both hemispheres. Incidental left parietal bone postsurgical changes are present. (B) T1-weighted MRI shows slight hypointensity in the contusion (arrows) and isointense signal in the subdural (arrows). Incidentally noted in the anterior corpus callosum is a small, hypointense scar from a prior intraventricular shunt (white arrow). Postsurgical changes in the left parietal bone are depicted. (C) Spin-density MRI shows a large area of hyperintense signal at the contusion site (arrows) and hyperintensity in the subdural blood (arrows).(D) T2-weighted MRI shows hyperintense edema surrounding the hemorrhagic area, which has a hypointense ring (arrow) and an isointense center. The subdural blood is inconspicuous on this image. Chronic white-matter signal abnormalities match those seen on the CT scan (A). (E) Gradient-echo MRI shows marked hypointense signal in the falcine subdural hematoma (arrows), contusion (arrow), and right frontal region, representing magnetic susceptibility products due to subacute hemorrhage. (F) Diffusion-weighted MRI shows restricted diffusion in a zone surrounding the contusion (arrows). Artifacts are depicted in the cortex of both hemispheres (red and yellow arrows).
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.
Image 9 (type MRI):
MRI in a 2-day-old brain contusion. (A) T1-weighted image shows obliteration of the left temporal horn due to subdural hemorrhage (arrows). (B) T2-weighted and (C) fluid-attenuated inversion recovery (FLAIR) images show hyperintense signal surrounding isointense blood in the left temporal lobe. The FLAIR image shows the left anterior temporal subdural hemorrhage and a posterior extension more clearly (arrow). (D) Diffusion-weighted MRI shows areas of restricted diffusion in the left temporal lobes and 2, small, abnormal areas in the right midbrain (arrows). The bilateral anterior frontal and temporal hyperintense areas represent artifacts (arrows).
Image 11:
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.
Image 10 (type MRI)
Comparison of a CT scan and MRIs obtained 1 day after acute trauma. (A) Acute CT scan shows a large, temporal-lobe contusion lateral to the displaced left temporal horn (arrows). (B) T1-weighted MRI shows hypointense signal in the left temporal lobe, with mass effect causing a clear loss of sulcal pattern (arrows). (C) Spin-density MRI shows mixed signals within the contusion with predominant isointensity. Note partial volume artifacts surrounding the brainstem.(D) Spin-echo T2-weighted MRI shows mixed intensity throughout the large left temporal contusion. (E) Fluid-attenuated inversion recovery (FLAIR) MRI demonstrates petechial hemorrhages that are isointense to the brain. Note the accompanying abnormally bright signal in the left optic radiations (arrows); one of many small shearing injuries is seen at the right occipital cortex/gray matter junction (arrow). (F) Diffusion-weighted MRI shows mixed signals with restricted diffusion in the most posterior aspect of the large left temporal contusion. An artifact appears in the right temporal lobe.
image 8:
See CT
image 9:
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.
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.
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ULTRASOUND
Findings
Ultrasound has no role in acute brain injury.
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NUCLEAR MEDICINE
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.
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.
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.
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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.
Reference
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