The imaging characteristics of ischemic stroke in the super-acute phase, one article to understand

Introduction For patients suspected of ischemic stroke, CT is the first-choice auxiliary examination in clinical practice.
The application of CT perfusion, MRI and other technologies provides great help for the early diagnosis and treatment of ischemic stroke
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This article will combine the imaging data to sort out the imaging characteristics of ischemic stroke in the super-acute phase
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Typical ischemic stroke manifestations can be divided into hyperacute phase, acute phase, subacute phase and chronic phase
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Clinically, people usually classify ischemic stroke cases within 6 hours of onset as hyperacute, and some imaging literature also includes cases within 12 hours
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In the hyperacute phase, rapid identification of patients, elimination of non-ischemic stroke neurological diseases, and clarification of the infarct area will help determine the next treatment plan as soon as possible
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As a kind of emergency, CT diagnosis and treatment of ischemic stroke need to race against time
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Head CT scan is convenient and quick, and it is the first choice for patients with acute stroke.
However, in the early stage of ischemic stroke, CT has limited sensitivity
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The main goals of emergency CT are: ➤ exclude intracranial hemorrhage to determine whether the patient can be treated with thrombolysis; ➤ look for any changes in the characteristics of early cerebral infarction; ➤ exclude other intracranial lesions similar to stroke, such as tumors
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In the hyperacute phase, the brain parenchyma on CT does not show very obvious density changes, but several signs of the hyperacute phase are of great significance for early diagnosis
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Arterial compaction sign: It mostly occurs in the middle cerebral artery, internal carotid artery, and vertebral artery, which manifests as an increase in the density of a segment of the artery
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The middle cerebral artery shows more signs, which can be called "medium cerebral artery hyperdensity sign"
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CT often shows that the horizontal segment of the middle cerebral artery is located in the scoliosis, showing a strip-shaped soft tissue density shadow against the cerebrospinal fluid.
The CT value is 42 to 53 Hu, and the CT value can reach 70 to 90 Hu after infarction
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This sign is not specific and can also be seen in diabetic and hypertensive patients without cerebral infarction.
The density can also increase when the arterial wall is calcified
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Fig.
1 Local cerebral edema with high-density sign of the left middle cerebral artery: brain tissue edema caused by cerebral ischemia, CT showed the loss of regional sulci, asymmetry of basal cistern, and shift of midline structure
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When the middle cerebral artery is blocked, this sign indicates a poor prognosis
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However, studies have shown that there is a certain degree of difficulty in judging the signs.
Clinicians should carefully read the film with reference to the clinical location of the signs to look for early signs
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Cerebral parenchymal density reduction sign: It is mainly manifested as a decrease in the density of the limited brain parenchyma (gray matter and white matter), and the boundary of gray matter is not clear.
Because the vasogenic edema of hyperacute cerebral infarction is often mild, it is the same area as the healthy side Compared with the structure, the density of the lesion area usually only drops by 6-10 HU
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Figure 2 Elderly patient with sudden left side hemiplegia, instant CT scan (left image) shows the loss of the local cerebral sulci, the cerebral gyrus is slightly swollen in the blood supply area of ​​the right frontal lobe middle cerebral artery, the gray matter boundary is blurred, the density is slightly reduced, and the lateral ventricle The anterior angle was slightly compressed; 3 days later, the CT scan (right image) showed that the density of the lesion area was significantly reduced, the right lateral ventricle was significantly compressed, and the midline was shifted to the left.
CT perfusion and angiography were used when selecting patients for reperfusion therapy.
The accuracy of CT perfusion is better, especially for experts in non-imaging or neurology fields
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CT perfusion can identify the core of the infarct and the surrounding penumbra area
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CT angiography helps to identify thrombus in intracranial blood vessels, and can guide intra-arterial thrombolysis or thrombectomy treatment
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In addition, angiography can evaluate the carotid and vertebral arteries, thereby assisting clinicians to clarify the etiology of stroke, and to exclude some limiting factors of endovascular treatment, such as tortuosity and stenosis of blood vessels
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In the acute phase of cerebral infarction, the signs seen by CT angiography and CT perfusion are more obvious than CT.
When the signs on CT are ambiguous, angiography and perfusion imaging can help to further clarify the location of the patient's lesion
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Figure 3 CT angiography (left image) and CT perfusion imaging (right image) in the acute phase.
It is the same case as in Figure 2.
It can be seen that the local vascular enhancement of the right middle cerebral artery is reduced, and the blood supply area has a large area of ​​perfusion decrease.
MRIMRI ratio CT is more time-consuming and may be inconvenient to use in some cases.
However, in the first few hours after the onset, MRI is very sensitive and specific in diagnosing acute ischemic stroke
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Within a few minutes after the artery is occluded, the DWI image of the MRI can show an increase in signal and a decrease in ADC value
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At this stage, the affected brain parenchyma can show normal on other sequences, such as common sequences such as T1WI and T2WI
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T1WI will only show low-density changes 16 hours after the onset of onset, while the high signal on the T2WI sequence is usually detected 6 hours after the onset of onset.
It will be easier to see on the FLAIR image.
This change will be seen in the next It becomes more obvious within 1 to 2 days
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Figure 4 A 49-year-old woman presented to the doctor due to weakness and stiffness in her right lower extremity
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a, b: ADC image and DWI show the limited diffusion area of ​​the left motor cortex; c: FLAIR image of the corresponding area shows a slightly higher signal in the local cortex; d: T1 enhanced scan shows local arterial enhancement, but no obvious enhancement in the cerebral cortex; e: The black arrow shows the slightly high signal shadow of the left motor cortex.
In addition, other scattered non-specific subcortical high signal shadows can be seen, but they are not related to this disease; f: SWI sequence shows no hemorrhagic transformation
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However, due to changes in blood flow in blood vessels, abnormal changes can occur in MR angiography (MRA), and magnetic sensitivity weighting sequence (SWI) can also detect signs of hemorrhage embolism
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Slow or stagnant blood flow can also be manifested as the disappearance of normal vascular flow empty signal on MRI, showing high signal changes on the T2FLAIR and T1 enhancement sequences
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If the cerebral infarction is incomplete, the contrast enhancement of the cortex will be seen in 2 to 4 hours
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Summary In the diagnosis of hyperacute ischemic stroke, both CT and MRI have irreplaceable advantages
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CT imaging is rapid and widespread, and it is the first choice for stroke examination.
However, with the development of imaging technology, MRI can more sensitively reflect the pathophysiological changes of acute stroke and provide more for the diagnosis and prognosis of stroke.
Valuable information
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Combining the two methods can better make early diagnosis and evaluation
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References: [1] Radiopaedia.
org[2] Zhang Heyu, He Zhiyi.
Imaging diagnosis of ischemic stroke[J].
Chinese Journal of Brain Diseases and Rehabilitation: Electronic Edition, 2016, 6(1):1- 4.
[3] Allen LM, Hasso AN, Handwerker J, et al.
Sequence-specific MR imaging findings that are useful in dating ischemic stroke[J].
Radiographics, 2014, 32(32):1285-1297.