Transcription
Hello everyone. This is Dr. Sam, and in this video, we will compare the normal brain appearances with ischemic stroke on a CT scan. We will only look at non-contrast CT scans of the brain.
On the left side is a normal brain in axial view. The outer layer of the cerebral cortex consists of gray matter, and it is slightly hyperdense—slightly brighter than the deeper structures. This deeper layer of cerebral cortex consists of white matter, and it appears slightly hypodense, or slightly darker than the outer layer. This area is the Sylvian fissure. This is the third ventricle, and over here is the quadrigeminal cistern.
This is a case of ischemic stroke in the immediate setting. The earliest signs of ischemic stroke on a CT scan is the hyperdense middle cerebral artery sign, or hyperdense MCA sign. We will see a bright, or hyperdense MCA in a non-contrast CT scan. These are images of the brain at the level of the cerebellum. This is the cerebellum. This is the fourth ventricle. These two lobes are the temporal lobes. The location of the middle cerebral artery is at this point. In this image of ischemic stroke, we can see a hyperdense MCA; both the middle cerebral arteries are hyperdense—both these arteries are bright.
Here is another case of immediate ischemic stroke. We can see a hyperdense MCA. The middle cerebral artery is the most common artery involved in stroke. These are sagittal views of the brain. Here we can see a hyperdense MCA in immediate stroke; it is at the location of the Sylvian fissure. These are coronal views showing the brain. The corpus callosum is present between the cerebral hemispheres. These are the lateral ventricles. The thalamus is present at this location, and just below the lateral ventricles is the third ventricle. This is the third ventricle, and in this image, we have ischemic stroke with hyperdense MCA. We can clearly see a bright MCA over here; it is the earliest sign of an ischemic stroke. A bright dot, or a hyperdense dot, may appear in some cases of ischemic stroke. So, instead of seeing a hyperdense MCA, we may see a hyperdense dot within the MCA.
Here is another image showing a hyperdense MCA dot sign within the Sylvian fissure. In a hyperacute ischemic stroke, the time from onset can be between 6 to 24 hours. Its features include loss of gray-white matter differentiation. Normally, you will see a slightly hyperdense outer layer of the brain—that is the gray matter—and hypodense central area, which is the white matter. Normally, we are able to see both these gray matter and white matter separately, but in cases of hyperacute ischemic stroke, we may find it harder to differentiate between the gray matter and white matter in the affected area. At this location, you can see a hypodense area, which is not seen at the opposite side of the brain, and it is also not seen in the normal brain image. The cortex is hypodense at this location; it is harder to differentiate between gray matter and white matter over here. Here we can see hypodense cortex, which leads to loss of gray-white matter differentiation. These features are usually seen in hyperacute ischemic stroke. The infarction is much larger in this case; there is a hypodense cortex. We are unable to differentiate between the gray matter and the white matter at this location. The gyrus, or gyri, of the brain are these folds of the cerebral cortex, and these grooves between the gyri are the sulci; its singular is sulcus. So these dark lines, or hypodense lines, are the sulci. In a hyperacute ischemic stroke, the gyri may become flattened. This is known as gyral effacement. We can see these folds are straight. Also, we will notice disappearance of sulci; we do not see these grooves between the gyri. This is due to increasing swelling of the brain tissue at the affected site. We will also find hypodense cortex at the site of infarction.
In acute ischemic stroke, the time from onset is 24 hours to one week, and its features include a hypodense cortex. Here is another case of acute ischemic stroke. We can clearly see hypodense areas within the brain. As time passes, more features are seen along with hypodense areas. We will find cytotoxic cerebral edema—that is swelling—which will cause mass effect and may cause a midline shift. Here, the swollen brain tissue has compressed the lateral ventricle. So this type of compression is known as mass effect. Due to this swelling, the structures in the midline of the brain may move to the opposite side; this is known as midline shift. In acute stroke, the swelling is significant and usually causes mass effect. So-called disappearance is also seen. We can see the sulci at the opposite side of the brain, but at the site of the stroke, they are missing. This happens due to swollen brain tissue.
In a subacute ischemic stroke, the time from onset is between one to three weeks. Stroke is difficult to diagnose during this period because appearance on a CT scan may appear normal. The swelling subsides; we will not see any swelling during this period, and the hypodense areas start to become isodense, which leads to a normal appearance. In simple words, the density of the tissue at the affected side increases because of the repairing mechanism of the brain tissue, which works on reducing the swelling and attempts to repair the brain tissue. In some cases of subacute ischemic stroke, petechial hemorrhages may be seen. These rounded, hyperdense, small hemorrhages may be seen at the site of infarction.
A chronic ischemic stroke is considered when the time from onset is more than three weeks. It includes many features. In gliosis, there is an increase in glial cells or astrocytes of the brain. This is also a repairing mechanism; it is seen as a hypodense area. In encephalomalacia, the infected brain tissue is replaced by cerebrospinal fluid. There will be degeneration of brain tissue, and it will be replaced by fluid. These are the areas of encephalomalacia. The density of these areas will be similar to the density of cerebrospinal fluid that is seen within the lateral ventricles. Another feature is the ex vacuo dilatation of the lateral ventricle adjacent to the chronic infarct. We can see the lateral ventricle is dilated as compared to the lateral ventricle on the other side. This is a compensatory mechanism done to preserve brain function and is often seen in cases of chronic ischemic stroke.
Here is another case of chronic ischemic stroke. We can see a dilated lateral ventricle due to ex vacuo dilatation of the lateral ventricle right next to the chronic infarct. There won’t be any swelling at this stage. There are areas of encephalomalacia and gliosis. Usually, the area of encephalomalacia is much darker than the area of gliosis. This is another case of chronic ischemic stroke. No swelling, mass effect, or midline shift is seen. There is ex vacuo dilatation of the lateral ventricle right next to the chronic infarct, and also we are seeing encephalomalacia and gliosis.
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