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Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023
| Contributor Information
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Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
The above image shows complete occlusion of the middle cerebral artery (MCA) (arrow) on an angiogram following injection of the left internal carotid artery (ICA).
Ischemic stroke (also known as cerebrovascular accident [CVA]) is a clinical term for acute interruption of blood flow to a portion of the brain, resulting in cell death and loss of associated neurologic function in the affected areas. Stroke is a common cause of patient morbidity and mortality, being the fifth leading cause of death in the United States and responsible for 1 in 6 deaths from cardiovascular disease (CVD).[1,2] The annual costs of stroke in the United States is $56.5 billion.[2] Prompt recognition and treatment of stroke are necessary to return blood flow to deprived areas and restore neurologic function. Do you know how best to diagnose patients presenting with symptoms of stroke?
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Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
A 52-year-old man presents with a history of worsening right-side weakness and aphasia. What does his noncontrast head computed tomography (CT) scan (shown) demonstrate?
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Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
Answer: The CT scan demonstrates extensive hypodensity and sulcal effacement involving the left anterior cerebral artery (ACA) and MCA territories, consistent with large acute infarction. Scattered curvilinear areas of hyperdensity are apparent (arrow), suggestive of developing petechial hemorrhage in this sizeable area of infarction.
Image courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
These CT scans of the brain reveal a right MCA ischemic stroke on day 1 (left), day 2 (middle), and day 6 (right), showing hemorrhagic transformation and progressive mass effect with midline shift.
Strokes may be divided into two types, ischemic and hemorrhagic.[1] More than 795,000 people suffer strokes each year in the United States; about 87% of these strokes are ischemic.[2] Ischemic strokes occur as a consequence of thromboembolic occlusion of cerebral arteries. Occlusion of blood flow begins an ischemic cascade that, if unchecked, will result in irreversible infarction; hypoxia-induced cell death causes inflammatory swelling, which may alter the brain architecture, producing a midline shift (shown).
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Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
This CT scan reveals signs of an early ischemic left MCA stroke, with loss of the normal gray-white differentiation in the left insular cortex and temporal operculum (arrow).
Noncontrast CT of the head is the first-line imaging modality in the assessment of a suspected stroke. It is employed primarily to exclude intracranial hemorrhage (ICH) or a stroke mimic, which would preclude the administration of thrombolytic therapy.[3,4]
CT is insensitive for ischemic stroke within the first 6-12 hours because edema and infarction have not yet developed enough to be identified; therefore, a normal CT scan does not rule out the possibility of an ischemic stroke.[5] However, CT is highly sensitive for detecting ICH, which appears as a readily identifiable hyperdense area within the brain. Guidelines have emphasized that noncontrast CT by itself, without supplementary magnetic resonance imaging (MRI), is sufficient to justify thrombolytic treatment with tissue plasminogen activator (tPA).[6]
Image courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
This noncontrast head CT scan reveals acute hemorrhage in the left gangliocapsular region (red arrow) with surrounding white matter hypodensity consistent with vasogenic edema (yellow arrow).
ICH is responsible for about 13% of all strokes,[2,7] with a majority originating in the brain parenchyma (10%) and a smaller number presenting with subarachnoid blood (3%).[7] Patients with hemorrhagic strokes present similarly to those with ischemic strokes, except that they tend to appear more ill, with signs of increased intracranial pressure (ICP).
Ischemic and hemorrhagic strokes cannot be reliably differentiated on the basis of clinical examination findings alone. Further evaluation, especially with brain imaging tests, is necessary.[8]
Image courtesy of Lars Grimm, MD.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
In the first 12-24 hours after ischemic stroke onset, as cell death progresses, signs of stroke become progressively more visible on CT of the head. The edema from cell death results in parenchymal hypodensities and mass effect.[5]
The head CT scan shown is from 1 day after a patient sustained an acute stroke. There is evidence of bilateral MCA ischemia (yellow circles), as well as subsequent regional mass effect on the left lateral ventricle (red arrow).
Image courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
The fluid-attenuated inversion recovery (FLAIR) image (left) demonstrates high signal in the centrum semiovale with corresponding restricted diffusion (right) on diffusion-weighted imaging (DWI), indicating infarction due to left ICA occlusion.
MRI is more sensitive than CT for the detection of early brain injury, though CT remains the test of choice in most acute stroke patients within the window for treatment, by virtue of its comparative speed, availability, and lack of contraindications.[9] DWI, a form of MRI, detects the free motion of water particles, which becomes restricted in the presence of cell death and cytotoxic edema. DWI can detect injury within 15-30 minutes of symptom onset.
Image courtesy of Lars Grimm, MD.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
Both CT and MRI are sensitive for intracerebral blood products. MRI has the added benefit of being useful for estimating the age of the hemorrhage if this cannot be determined clinically. Hyperacute blood appears isointense to the brain on T1- and T2-weighted imaging, whereas acute blood (1-2 days) appears dark on T2-weighted imaging and isointense on T1-weighted imaging. The above MRIs show low signal on T2-weighted imaging and intermediate signal on T1-weighted imaging (yellow arrows), findings consistent with an acute bleed.
As blood continues to age, the signal characteristics change. Early subacute blood (2-7 days) appears bright on T1-weighted imaging and dark on T2-weighted imaging; late subacute blood (7-28 days) appears bright on T1- and T2-weighted imaging; and chronic hemosiderin appears dark on T1- and T2-weighted imaging.
Image courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
Perfusion weighted images (PWIs) of a patient who suffered a left ICA occlusion are shown above. The mean transit time image on the left shows diffuse ischemia in the left hemisphere. The cerebral blood volume image on the right reveals a smaller central area of infarction (arrows).
PWI is another form of MRI; it enables detection of at-risk brain tissue by directly measuring tissue perfusion. Differences between the perfusion abnormality and the diffusion abnormality show the ischemic penumbra around a core of infarcted tissue.
Perfusion imaging in acute stroke is not currently widespread and should not delay treatment decisions.[10]
Image courtesy of Lars Grimm, MD. ACA = anterior cerebral artery; MCA = middle cerebral artery.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
In the above CT angiogram (CTA), the brain and soft tissues have been subtracted, leaving only the bone and blood vessels; an occluded right MCA is visible (arrow).
Evaluation of the cerebral vasculature can be performed by means of CTA, MR angiography (MRA), or conventional angiography. Conventional angiography offers the highest spatial resolution, but it carries a fixed (albeit low) risk of stroke.
Both CTA and MRA perform well at identifying large-vessel occlusions, and CTA has the added benefits of speed and good spatial resolution. Imaging of the extracranial vessels and carotids is also of benefit if patients are eligible for thrombectomy.
Image courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
The angiogram above demonstrates near-complete occlusion of the left ICA, with a "string sign" demonstrating minimal filling of the lumen (arrow).
Conventional angiography is typically performed if an endovascular intervention is to be carried out. Such intervention would include endovascular therapy for treatment of acute ischemic stroke or evaluation and treatment of an aneurysm identified on CTA or MRA. Of all the imaging modalities employed in this setting, conventional angiography offers the best spatial resolution; it also allows therapeutic intervention. Unfortunately, there is a small risk of stroke secondary to the intervention.
Table courtesy of Medscape.
Acute Stroke: Critical Diagnostic Findings
Lars Grimm, MD, MHS | August 1, 2023 | Contributor Information
The National Institutes of Health (NIH) developed a 15-item, 42-point stroke scale that allows quantification of neurologic impairment. This scale provides insight into the location of vascular lesions, is correlated with outcomes for ischemic strokes, and identifies patients who are candidates for thrombolytic therapy. Points are assigned on the basis of performance in six major areas: level of consciousness, visual function, motor function, sensation, cerebellar function, and language. The scale is used at the initial presentation and can be repeatedly employed over the hospital course to assess the evolution of the patient's neurologic status.[11] Patients with minor strokes usually have a score of less than 5.
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Contributor Information
Author
Lars Grimm, MD, MHS Associate Professor
Department of Diagnostic Radiology
Duke University Medical Center
Durham, NC
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
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