A 49 year old neighbor of some friends recently recovered from a brain aneurysm and while discussing her remarkable recovery I was asked if it was true that brain aneurysms were caused only by genetic factors.

Certainly genetic factors play a role: one study showed a 9% increase in risk among first-degree relatives. Having said that, there are a number of other factors that put people at risk for intracranial aneurysms. These can be categorized in three ways:

1. Genetic factors
2. Morphological factors
3. Other factors

1. Genetic factors are divided into 2 parts: familial and hereditary. The difference between them is that although there may be a clustering of specific diseases in a family it may be coincidental, or due to environmental issues. No major genetic defects were identified. When diseases are hereditary, then generally there is a specific gene associated with the disease.

2. Morphological factors refer to the structure of the tissue in this case, the blood vessels that go on to become weakened and likely to rupture. This has to do with the forces exerted on the vessel walls that can cause structural defects to occur.

3. Other risk factors

• Cigarette smoking – there is a 15 fold increase in risk of a subarachnoid hemorrhage. Scientists believe that smoking effects the stretchability of blood vessels.
• Hypertension – high blood pressure >160/95 was present in 62% of patients with aneurysms in one study published in the Journal of Neurology in 1985.
• Estrogen deficiency causes collagen wasting which may contribute to aneurysm development. Studies have shown that estrogen replacement reduced to risk of subarachnoid hemorrhage in  post-menopausal women.

Given that only 1/3 of people have a good outcome as a result of a brain aneurysm, my friend’s neighbor is indeed fortunate to be up and about again. My we all be so fortunate.

The National Institutes of Health has some good information about brain aneurysm for those interested in learning more.

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