In patients with ischemic stroke, there is no obvious imaging findings on CT within 24 hours , But the significance of CT is to exclude hemorrhagic diseases and other intracranial lesions, to exclude contraindications to thrombolysis, and CT imaging manifestations of cerebral infarction have different manifestations according to different situations. If the patient has a CT scan immediately after the onset of the disease, it is a normal imaging manifestation. If the patient arrives at the hospital late, it can be manifested as a low-density focus on the CT image. If the patient has a large infarct size, one side of the brain tissue will shift to the other part on the same side or the opposite side. After cerebral infarction, oozing blood and hematoma are mixed on the basis of infarction, or large mass-like high-density lesions. In the acute phase of cerebral infarction, especially in the super-acute phase, a white and brighter line-like change can be seen, suggesting severe thrombosis in the middle cerebral artery; other changes include fullness of the brain tissue on one side, lightening of the sulcus and gyri, and the color of the lesion Shallow, it can be seen that the junction of cortex and medulla becomes blurred.
According to the time of onset, cerebral infarction can be divided into 5 stages: hyperacute stage (1 month). The diagnosis or prompt diagnosis of hyperacute cerebral infarction within 6 hours of onset is particularly important. Although spiral CT perfusion imaging, MRI diffusion-weighted imaging and perfusion-weighted imaging are helpful to the diagnosis, treatment and prognosis of hyperacute and acute cerebral infarction.
Brain CT examination can not see the location and size of the thrombus, but can see the size and location of the cerebral infarction due to thrombosis. As we know, CT examination uses X-ray to do a tomographic scan, which measures the absorption coefficient of X-ray in different layers and tissues in the body, processes it through an electronic computer, and displays it in images to diagnose internal diseases of the human body. In the diagnosis of craniocerebral diseases, CT scans are non-invasive, high-resolution, accurate and rapid. Patients with cerebrovascular accidents generally require emergency CT scans to distinguish cerebral hemorrhage and cerebral infarction, and under guidance One-step treatment, so CT plain scan is still the most commonly used cranial imaging examination method.
The following are the specific manifestations of patients with cerebral thrombosis on CT at different periods:
(1) Hyperacute phase: due to cytotoxic edema of the basal ganglia, this sign indicates that the proximal middle cerebral artery occlusion has affected the blood flow of the lenticula artery The limit can be seen within 1 h of the onset of the infarction. The result of the loss of gray matter in the lateral edge of the insula. This area is supplied by the middle cerebral artery and is most sensitive to ischemia, because it is located in the most distal area and can only be seen in the front or back of the insula. The decrease in brain parenchymal density is manifested as a slight decrease in brain gray matter density. Because the vasogenic edema in the ultra-early infarct lesion area is relatively light, the degree of brain parenchymal density decrease is relatively small. Therefore, a narrower window width and appropriate The window level and bilateral comparison can only be found. When the difference in CT values of the same part on both sides is more than 1.8 HU, on the basis of excluding other diseases, the diagnosis of hyperacute cerebral infarction can be made. The important characteristic manifestations of cerebral infarction may be caused by ischemic edema of brain tissue; local brain tissue swelling: manifested as loss of brain sulci, cistern and ventricle compressed and deformed, and midline structure shifted to the opposite side, namely brain CT scan Shows a space-occupying effect, this sign can be observed 4-6 hours after the onset. Dense arterial shadow: It is an increase in the density of the main cerebral arteries, which is common in the middle cerebral artery.
Arterial occlusive cerebral infarction ultra-early <24 hours, 50-60% is normal, 40-50% can be found abnormal, manifestations:
①Dense artery sign: the middle cerebral artery, internal carotid artery, vertebral artery or other large arteries have increased density, CT Value 77～89Hu (42～53Hu), or middle cerebral artery point sign; ②Insular zone sign: the gray matter interface of the insular zone (insular cortex, outermost capsule, pleural nucleus) disappears; ③The outline or density of the lenticular nucleus is blurred Decrease; ④Swelling of the gyri, shallow sulcus, etc.
(2) Acute phase: Generally, the first 5 days after the onset is regarded as the acute phase. Ischemic cerebral infarction: Within 24 hours of onset, CT scans of most cases show no abnormal changes, and a few can see slightly low-density areas with unclear borders. Obvious low-density areas can be seen in 24 hours, which are characterized by the range of low-density areas that are consistent with the blood supply area of the occluded blood vessel. Gray matter and white matter are involved at the same time. They are mostly triangular, wedge-shaped or fan-shaped with the base facing the convex surface of the brain, with unclear boundaries and density. Uneven, accompanied by peripheral cerebral edema and space-occupying effect. Within 24 hours of the onset of acute cerebral infarction, imaging changes are often not shown. If the patient has persistent signs of neurological impairment, such as consciousness disorder, language disorder, facial paralysis, limb paralysis, etc., it is also diagnosed as acute cerebral infarction . Do a head CT scan 24 hours later, you will find that the patient's head CT has a dot and sheet-like low-density shadow, which is the imaging change of cerebral infarction. The increase of moisture in the lesion area causes two effects on the CT image. One is that the density of the lesion area decreases, and the cortex and medulla lack the density difference. In the early stage, this density decrease is generally insignificant, mostly in a wedge shape, consistent with the blood supply range of the involved artery. The boundary is blurred; the other is the space-occupying effect or mass effect caused by the increase in the volume of the lesion area due to the increase of water. The mild manifestation is the swelling of the brain tissue in the lesion area, the sulcus and brain oil disappeared, and the severe manifestation is the midline structure. Contralateral displacement, the so-called intracerebral herniation, the degree of space-occupying effect is related to the area of cerebral infarction, the larger the area, the more significant the space-occupying effect. The above two effects generally reach their extremes in the 3rd to 5th days after the onset. It should be pointed out that it takes 3 to 6 hours at the earliest for early cerebral infarction to show changes on CT, and later, it takes 24 hours or more before the typical manifestations appear. If there are typical clinical symptoms of cerebral infarction and the CT findings are negative, CT should be reviewed in a short time to avoid missed diagnosis.
(3) Subacute phase: refers to the 6-21 days after the onset of the disease, the edema is obviously absorbed, and the space-occupying effect is weakened or disappeared. In most cases, it is also low-density, and the boundary is clearer than in the acute phase; but a small number of patients show isodensity lesions, which are not easy to find, the so-called "fog" effect, which is caused by the average effect of mixing components with different density in the lesion area. (Low-density substances such as water and lipids are mixed with high-density components such as blood, calcification, and iron). An enhanced scan at this time is very helpful for diagnosis. After the injection of the contrast agent, the typical cerebral infarction is manifested as gyrus-like enhancement, and the gyrus of the cerebral cortex and the nuclei of the basal ganglia in the infarcted area are enhanced. The local brain tissue is swollen, manifested by the shallowness and disappearance of the sulci of the local brain tissue, the surface of the brain tissue is smooth, and the lesion is fan-shaped or patchy. The pathological basis is the space-occupying effect of brain tissue edema. Depending on the location and size of the lesion, the following signs can appear separately or at the same time: ①Asymmetric on both sides of the basal cistern; ②Disappearance of local sulci; ③Ventricle compression and deformation, when When the lesion is close to the ventricle, the adjacent ventricle is compressed and narrowed.
(4) Chronic phase: After 21 days, the brain tissue of avascular necrosis is cleared by phagocytes, leaving a cavity containing cerebrospinal fluid, combined with glial hyperplasia, and the lesion area is still low-density, similar to cerebrospinal fluid, with clear boundaries but reduced volume , Manifested as the affected side of the ventricle enlarged, the subarachnoid space including the split brain, sulcus, deepening and widening of the cistern, cortical atrophy.
(5) Lacunar infarction: most of them are located in the deep white matter of the basal ganglia or cerebral hemispheres, and the size of the lesion is less than 1.5cm. Generally, there is no space-occupying effect such as displacement of the ventricular system.
(6) Hemorrhagic infarction: CT findings are characterized by scattered and uneven high-density bleeding areas on the background of low-density infarction. Unlike hematoma, its density is not as high as hematoma, and it is not as uniform as hematoma. CT brain examination should show low density shadows.
