When a weak area of an artery supplying the brain with blood expands or bulges, it is called an intracranial aneurysm (also known as a brain aneurysm).
The feared complication of an intracranial aneurysm is rupture of the weakened vessel wall, causing bleeding in the area between the brain and the surrounding arachnoid membrane (called a subarachnoid hemorrhage ). This is a medical emergency that may result in brain damage or death. Prior to rupture, most intracranial aneurysms are without symptoms, but may in some cases cause symptoms such as severe headaches, double vision, seizures, or vomiting.
It is estimated that intracranial aneurysms can be found in 2-3% of the adult population. Most of these never rupture, are without symptoms, and are never diagnosed. The estimated incidence of ruptured intracranial aneurysms ranges from 2 to 22 cases per 100,000 individuals per year. Up to half of those who experience a rupture of intracranial aneurysms and the consequential subarachnoid hemorrhage die and a third of survivors suffer moderate to severe disability.
Genetic factors play a recognized, albeit not yet fully known role, in the development of intracranial aneurysms. About one in every 10 patients with a subarachnoid hemorrhage has a family history of intracranial aneurysms and those who have a family history are usually younger at the time of diagnosis and more commonly have multiple and large aneurysms. Recently, our scientists at deCODE genetics identified a common genetic variant on chromosome 9 that is associated with increased risk of intracranial aneurysms.
The deCODEme Genetic Scan identifies a variant on chromosome 9 that correlates strongly (r²= 0.9) with the variant associated with increased risk of intracranial aneurysms and provides an interpretation of the risk of developing this type of aneurysm for individuals of European ancestry.
The same variant also increases the risk of heart attack in individuals of both European and Asian ancestry and increases the risk of abdominal aortic aneurysms in individuals of European descent.
At the present time, information about the risk of intracranial aneurysms conferred by this genetic variant on individuals of ethnicities other than European is not available.
risk factors
- Age and gender: Intracranial aneurysms can occur in all age groups but are most commonly detected in individuals between the ages of 40 and 60. The average age of a ruptured or bleeding intracranial aneurysm is 50 years of age.
- Hypertension: High blood pressure increases the risk of development of intracranial aneurysms and their bleeding.
- Other: Smoking, alcohol abuse, and cocaine use have been associated with intracranial aneurysms. Rare causes include infections, connective tissue disorders and trauma.
- Ethnicity: Studies have indicated that subarachnoid hemorrhage is less common in individuals of European descent than in African-Americans, Asians and Hispanics.
- Genetics: Autosomal dominant polycystic kidney disease and various other rare hereditary conditions are associated with intracranial aneurysms. Additionally, about 10% of patients diagnosed with an intracranial aneurysm have a first-degree family member also with the condition. A family history of intracranial aneurysms has been found to be equally common among individuals of European descent, African-Americans and Hispanics.
prevention and treatment
Intracranial aneurysms can be treated with either open surgery or minimally invasive endovascular methods (the aneurysm is treated through thin plastic tubes or catheters inserted in a groin artery). Ruptured aneurysms are generally treated immediately to prevent further tears and bleeding. Whether treatment is recommended for asymptomatic and incidentally diagnosed aneurysms depends on the size and location of the lesion.
Screening has been recommended for patients with autosomal dominant polycystic kidney disease and for individuals who have two immediate relatives with intracranial aneurysms (although the latter indication remains controversial).
scientific references
- Helgadottir A, Thorleifsson G, Magnusson KP, et al. The same sequence variant on 9p21 associates with myocardial infarction, abdominal aortic aneurysm and intracranial aneurysm. Nature Genetics. 2008 Feb;40(2):217-24.
- Ingall T, Asplund K, Mähänen M, Bonita R. A multinational comparison of subarachnoid hemorrhage epidemiology in the WHO MONICA stroke study. Stroke. 2000 May;31(5):1054-61.
- Rosen D, Novakovic R, Goldenberg FD, Huo D, Baldwin ME, Frank JI, Rosengart AJ, Macdonald RL. Racial differences in demographics, acute complications, and outcomes in patients with subarachnoid hemorrhage: a large patient series. J Neurosurg. 2005 Jul;103(1):18-24.
- Vega C, Kwoon JV, Lavine SD. Intracranial aneurysms: current evidence and clinical practice. Am Fam Physician. 2002 Aug 15;66(4):601-8.