Why brain aneurysms rupture? Rupture risk of small and thin-walled intracranial aneurysm. 2
How to find brain aneurysms that are at increased risk of rupture? How cerebrovascular aneurysm’s rupture risk relates to location of brain aneurysm? Brain aneurysms. The risk of rupture of brain aneurysms is 1% per aneurysm per year on average. Dr. Anton Titov, MD. However, some patients have much higher risks of rupture for brain aneurysms. You have done research on risks of formation of brain aneurysms. You also studied various factors that affect the risks of rupture of brain aneurysm. Dr. Anton Titov, MD. How do you assess risk of rupture of brain aneurysm? Dr. Mika Niemela, MD. It depends on the location and size of the aneurysm. The bigger the brain aneurysm, the bigger the risk of rupture. There are posterior circulation and vertebrobasilar area aneurysms. These brain aneurysms are known to rupture more easily. Sometimes the aneurysms have secondary pouches or irregular shape. That may predispose cerebral aneurysms to rupture a little bit easier. There are external risk factors that are related to the patient. It is smoking, hypertension. Smoking especially is a very big risk factor for formation and rupture of brain aneurysms. Dr. Anton Titov, MD. Family history may mean something for risk of brain aneurysm rupture. But it’s not as clear as we used to think. Because family history of brain aneurysms may be related to smoking and hypertension. It might not be related to the actual genetic defect. This has not been found to be related to brain aneurysm rupture. Dr. Mika Niemela, MD. We participated in an international study trying to find the so-called “aneurysm gene”. But we couldn’t find anything. Brain aneurysm rupture is more related to genes that are related to hypertension and general cardiovascular diseases. It is not a single gene defect in aneurysm formation. Some of the research that you have done relates to the inflammation in the wall of the brain aneurysm. It is a risk factor for aneurysm rupture. What did your research show? Presence of inflammation increases risk of rupture of brain aneurysm. Brain aneurysm with thinner walls have a higher inflammation. Dr. Mika Niemela, MD. We should be able to image brain aneurysms before they rupture. This is how we can prevent the rupture of brain aneurysm. Dr. Anton Titov, MD. But there is no means to image brain aneurysm wall so far. We are just planning for that. We also try to understand why the inflammation happens inside a brain aneurysm. It has to do with smoking. It has to do with maybe food intake. Higher cholesterol levels may predispose to inflammation more than we previously thought. High cholesterol is a risk factor for aortic aneurysms. Hypercholesterolemia is also a risk for brain aneurysms. Dr. Mika Niemela, MD. Hypertension may cause hemodynamic changes in the aneurysm wall. Inflammation and high cholesterol (hypercholesterolemia) together may predispose a brain aneurysm for rupture. Some risk factors for brain aneurysm rupture also relate to the particular location of aneurysm. Brain aneurysms in the middle cerebral artery aneurysms or aneurysms in the anterior circulation or posterior brain circulation may have a higher risk of rupture. Dr. Anton Titov, MD. How does the location correlate with the risk of brain aneurysm rupture? Dr. Mika Niemela, MD. Posterior circulation aneurysms, vertebrobasilar aneurysms, PICA aneurysms have more risk of rupture than anterior circulation aneurysms. In Finland, MCA [Middle Cerebral Artery] is the most common location for a ruptured aneurysm. It is also more common for brain aneurysms in general. But MCA [Middle Cerebral Artery] branches are more susceptible to aneurysm formation. It is because of the blood flow to the brain. MCA bifurcation has a higher risk for brain aneurysm formation. So the blood flow has a lot to do with aneurysm formation. It is also smoking and potential other risk factors. Brain aneurism risk of rupture also depends on the anatomy. Some brain aneurysms tend to rupture at a smaller size. Dr. Anton Titov, MD. Certain brain aneurysms also have a higher risk of rupture have a higher risk of rupture. Dr. Mika Niemela, MD. Yes, it is true. Brain aneurysms in posterior circulation, basilar tip aneurysms, even small ones, can rupture. There may be so-called blister aneurysms in carotid or basilar arteries. Blister aneurysms are very thin-walled brain aneurysms. Blister aneurysms can rupture. So it is not necessarily a safe situation with a very small brain aneurysm. A very thin-walled brain aneurysm can have a high risk of rupture. Are there imaging methods that can assess the wall motion of the brain aneurysm? Dr. Anton Titov, MD. How thick is the wall of brain aneurysm? There are no specific imaging methods to see a wall of brain aneurysm. But we can take a look at the size of brain aneurysm. We can also see the brain aneurysm shape. Dr. Mika Niemela, MD. We can recognize whether brain aneurysm looks like a blister. Blister aneurysm is a very thin-walled aneurysm. But in general the aneurysm wall cannot be imaged so far very reliably. Dr. Anton Titov, MD. Is there anything in the research on brain aneurysm wall imaging? Dr. Mika Niemela, MD. The idea is that we could show the inflammation in aneurysm. So there may be means to do that with some contrast media. We could see the inflammation in the aneurysm wall. But this technology is experimental. So far there is nothing in clinical use to see a thickness of brain aneurysm’s wall specifically.
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