 Welcome back to intracranial bleed. In this section, we will discuss the investigations. The investigations of intracranial bleed starts with a non-contrast CT scan of the head. On a non-contrast CT head, acute bleeding will be white. Let's see what the different bleeds will look like on CT heads. First, epidural hematoma. An epidural hematoma, as you might remember, is on top of the dura. Since the dura is deeply attached to the inner table of the skull, the blood will look lentiform. On a CT head, it will look like this. The white is the epidural hematoma. You may also notice that the contour of the skull is uneven here, suggesting a skull fracture. Notice also how the ventricle on this side is completely obliterated. That is due to the mass effect of the epidural hematoma. Next, subdural hematoma. Since the blood is now underneath the dura, it has more of a crescent shape. On a non-contrast CT head, it will look like this. Which side is the subdural on? This is the subdural hematoma. When you look at the lateral ventricles, you would also notice that there is mass effect from this hematoma, causing a shift in the midline. Traumatic subarachnoid hemorrhage will be seen in the subarachnoid space. On a CT head, it will look like this. Can you spot the traumatic subarachnoid hemorrhage? What about a subarachnoid hemorrhage that comes from an aneurysm? Since most aneurysms arise from the circle of Willis, when there is an aneurysmal rupture, the blood will be around a circle of Willis on the CT scan. Like this. You can see the blood outlining the circle of Willis and the CSF space around it very well. Let's move on to parenchymohematoma. For trauma, the parenchymohematoma will occur where the trauma is. On a CT scan, it will look like this. That is the parenchymohemorrhage. Do you see another type of bleed in here as well? What about this bright white line? It's bright, so it's likely to be fresh blood. It lines the inner table of the skull, forming a crescent shape. This is a small, subdural hematoma. For non-traumatic parenchymohematoma, it is usually caused by hypertension. The bleeding tends to concentrate on a few areas. The thalamus, basal ganglia, the pons, and the cerebellum. Those tend to be the area where the non-traumatic parenchymohematoma occurs. On the CT head, it will look like this. As you can see, this parenchymoblead is in the basal ganglia. Even though CT is the first investigations in patients with potential intracranial bleed, it has its limitations. It is related to the age of bleeding and the amount of bleeding. As you have seen before, fresh blood is bright white on CT scan. However, as it ages, the fresh blood will become less and less white and eventually become isodense as CSF at around two weeks time. That makes the diagnosis more difficult, as it is harder to appreciate the bleeding on the CT scan. That phenomenon is often seen in patients with subacute subdural hematoma. Remember for subdural hematoma, since the bleeding is venous, it tend to be slow. With the gradual accumulation of blood, the patient may not be investigated until much later after the initial bleeding has occurred. Therefore, if you were to investigate a patient who have had a two-week-old subdural hematoma, the CT scan might look like this. You can appreciate that we do not see any bright white. However, on the left side, there is a much larger CSF space. This is the subacute subdural hematoma that is likely at least two weeks old. If you look in the right frontal area, there is also likely a subacute subdural hematoma as well. You can see how them can be tricky to diagnose. The second limitation has to do with the amount of blood. When the amount of blood is quite small, it is simply very difficult to see on CT. This is especially relevant in patients with subarachnoid bleeding from aneurysms. Remember that in some patients with aneurysmal subarachnoid bleeding, before the aneurysm rupture, they can have a warning event, a leak of the aneurysm, also known as a sentinoblide. That sentinoblide tend to be in very small amount. Therefore, if you see a patient and you're really worried about a sentinoblide from the history, you would first order a CT scan. If the CT scan is negative, often we will do a lumbar puncture. That gives us samples of their CSF. In the CSF, we will look for red blood cells and xanthochromia, helping us to diagnose whether there is any blood in the CSF. In a patient that we're working up for a sentinoblide, if the CT scan is negative, when should we do the LP? There are different studies in literature that will shape our management. It has to do with the onset of the symptoms, how good the CT scanner is, and who's interpreting the images. In the patients that has extremely high risk for a subarachnoid bleed, a lumbar puncture remains the gold standard. It is best to discuss each case with your attending physician to decide on management. To diagnose a non-traumatic subarachemorrhage, either the patient would have a positive CT scan, or if the initial CT scan is negative, a positive LP. In summary, we discussed the CT findings of patients with intracranial bleed. Based on the kind of bleed, the location and the shape will be different. We also talked about the limitations of CT scan based on the age of the bleeding and the amount of bleeding. We also discussed how we might want to do a lumbar puncture in a patient with subarachnoid bleed when the CT scan is negative. We hope you find this useful. Thank you for watching.