Aneurysms are blister-like dilatations which may develop on any blood vessel in the body. When they occur on the arteries supplying blood to the brain they are termed cerebral aneurysms or berry aneurysms, a reference to an early description of them resembling berries on a stalk. Studies suggest that unruptured aneurysms are present in about 3.2% of the population. Some aneurysms bleed causing a disease called Aneurysmal Subarachnoid Haemorrhage (aSAH). Not every aneurysm will bleed however and aSAH affects about 9 in every 100,000 people each year. This therefore accounts for about 5% of stroke in the United Kingdom annually but with a particular preponderance in younger people.
The rates of aSAH in Finland and Japan are higher although the numbers of unruptured aneurysms in the population is about the same suggesting there are other factors in those populations which put them at particular risk. While we know that smoking, cocaine use and uncontrolled high blood pressure seem to increase the risk that any given aneurysm will bleed work continues to understand other factors that may promote rupture. Enviromental factors (for example cigarette smoke) may have a particularly profound effect on genetically susceptible individuals. To learn more about unruptured aneurysms click here or VIA the link in the menu bar at the right of this section.
Infections of the heart valves (Endocarditis) can cause small pockets of infection to spread through the blood stream and into the walls of the arteries in the brain. These pockets can weaken the wall of the artery causing aneurysms to form. Traumatic injuries to the blood vessels e.g. stab wounds to the head or injuries to vessels during surgery on the brain or sinuses are very rare causes of certain types of aneurysms.
Aneurysms are sometimes classified according to their shape. The commonest type found in the brain is a berry like out-pouching from the blood vessel called a saccular aneurysm. These usually develop at the branch-points of blood vessels. Aneurysms developing on the side-wall of vessels may also be saccular or when very thin-walled as blood-blister like aneurysms. Axial dilations of the the vessel are termed fusiform while those resulting from infection are called bacterial (or less correctly mycotic).
Alternatively they may classified according to size, the most important distinction being for aneurysms with diameters greater than 25mm. These giant aneurysms pose particular challenges for treatment and have an unfavorable natural history.
To learn more about subarachnoid haemorrhage and how aneurysms are treated please explore the menu on the right of this page. If you have further questions you are welcome to get in touch.