What are aneurysms?

What are aneurysms?
5 Min Read

Aneurysms are weakened, thinned areas in a blood vessel wall that may bulge and expand to form a bubble. When an aneurysm bursts open (ruptures), a catastrophic


Aneurysms are weakened, thinned areas in a blood vessel wall that may bulge and expand to form a bubble. When an aneurysm bursts open (ruptures), a catastrophic hemorrhage occurs. Aneurysms occur most often in the arteries at the base of the brain or within the circle of Willis). They can also develop in other parts of the body such as the aorta (the major artery supplying blood from the heart) and occasionally veins.

The majority (~85%) of all intracranial aneurysms arise from branches off of either the Circle of Willis or its parent artery, which is usually one of four paired vessels: ipsilateral internal carotid artery (a branch of the Circle of Willis) contralateral internal carotid artery (also a branch in the Circle of Willis) ipsilateral posterior cerebral artery (a branch off the Circle of Willis in front of the brainstem in its upper division, or posteriorly)

contralateral vertebral artery (the only unpaired vessel providing blood to parts of the brain stem).

The remaining aneurysms (~15%) arise from smaller arteries that are not normally considered part of the Circle of Willis, such as branches off the anterior cerebral artery. These aneurysms account for ~14% of all intracranial aneurysms.

Risk factors

The risk factors for developing an aneurysm include smoking, high cholesterol, hypertension and atherosclerosis. The most common risk factor is smoking.

Aneurysms Causes

Aneurysms occur when the walls of a blood vessel become weak and balloon out, forming a bulge. This may be due to an inherited weakness in the wall of the blood vessel or deposits within the wall that make it more likely to weaken and break open (rupture). Any site in the body can be affected by aneurysms. The most common type is a cerebral aneurysm which is located near where arteries branch off from major vessels supplying blood to the brain.


The following are the most common symptoms of aneurysms. However, each individual may experience symptoms differently. Symptoms may include:

Headache - Usually a sudden, severe headache unlike any previous headaches experienced.

Nausea and Vomiting - Extreme nausea and vomiting may occur when there is pressure from the blood accumulating in the brain or if an aneurysm has burst open (ruptured).


Vision Abnormalities - Loss of vision may occur if an aneurysm bursts open (rupture) causing bleeding within the brain.

Weakness - The individual may experience general weakness on one side of the body or drooping of the eyelid on one side due to increased pressure on that side of the brain. Aneurysms are often discovered incidentally during imaging for another medical condition not directly related to aneurysms.


Ansus cannot be diagnosed definitively without a test such as a CT scan or MRI. However, doctors can usually diagnose an aneurysm by testing for increased blood pressure and pulse rates in the brain or decreased level of consciousness. The doctor may also order a venous angiogram which is a special type of x-ray that uses dye injected into veins to outline the arteries supplying blood to the brain. Once hemorrhage from rupture has been ruled out, other tests such as MRA, CTA scans or conventional cerebral CAT scans are performed if necessary to further define the diagnosis. In cases where there is no history of trauma and near normal findings on physical examination, normal catheter arteriogram often suffices.