Definition
Brain aneurysm is a localized bulge in the wall of an artery, normally filled with blood. It could have different shapes.
Epidemiology
The radiological and autoptic prevalence of aneurysms is 3,2% (in people without comorbidity) with a mean age of 50y and 1:1 ratio between male and female.
Note than in population older than 50y, gender ratio is 2:1 for women because of estrogenic deficiency.
Aneurysmal subarachnoid hemorrhage (SAH) occurs in 6-16 cases/100.000 people.
85% of the aneurysm are located in the anterior circulation, on the circle of Willis.
Risk Factors
Genetic Factors
Some studies revealed the importance of this type of factors on the development of the aneurysms.
- Hereditary Syndromes has to be suspected if more than one family member develops intracranial aneurysms;
- Familial aneurysm even in absence of hereditary syndrome.
Morphology
There are three type of intracranial aneurysm:
- Saccular aneurysm - Thin-walled protrusion of the artery with absence or reduction of both the tunica media and the internal elastic lamina;
- Fusiform aneurysm - Dilatation of the entire wall of the artery usually due to atherosclerosis;
- Mycotic aneurysm - Caused by mycotic emboli (for example in the setting of an infective endocarditis).
Note that saccular aneurysms are responsible of most cases of SAH (subarachnoid hemorrhage).
Pathogenesis
The pathogenesis is thought to be multifactorial.
Some risk factors and hemodynamic patterns contribute to the development of the aneurysm.
- Hemodynamic stress (due to hypertension, cigarette smoke, etc.) causes a damage of the internal elastic lamina with a probably breakdown of it;
- Turbulent blood flow associated with high-flow states can cause a stress-response that damage the wall of the artery.
The pathogenesis reflects the histology of the arterial wall of the aneurysm: this is a characteristic that is important to evaluate the risk of rupture.
Clinical Presentation
Most of the aneurysms are asymptomatic and so they can be found:
- Incidentally
- In the setting of aneurysmal SAH
If aneurysms are symptomatic, the fundamental symptoms and signs are (depending on the site):
- Headache (comparable to SAH’s headaches)
- Facial pain
- Pyramidal dysfunction
- Cranial nerves neuropathies (for example III nerve palsy)
- Visual acuity loss
- Cerebral ischemia due to formation of emboli in aneurysms
Complications
The major complication is the rupture of the aneurysm.
The risk factors for the rupture of aneurysms are:
Size
- The cut-off value in aneurysm diameter to define a lower risk of rupture is 7mm. With higher diameter, the risk of rupture increase progressively. Note that biggest aneurysm grows faster, too.
Site
- Cavernous carotid artery aneurysms - Lower risk of rupture;
- Anterior circulation aneurysms (including ICA’s aneurysm) - Intermediate risk of rupture;
- Posterior circulation aneurysms - Highest rates of rupture.
Racial differences
In Japan there is a higher risk of rupture than in Europe and North America.
Precipitating event
Acute physical exercises and emotional stress can increase the risk of aneurysm rupture.
Prior hemorrhage and family history
Diagnosis
If there is a suspect of aneurysm because of the presence of both the risk factors and the symptoms, there are two different strumental tests:
- Magnetic resonance angiography (MRA)
- CT angiography (CTA)
- Cerebral Angiography
Authors
|
Federico Nicolosi, MDNeurosurgeon |
Giorgio Saraceno, MSMedical Student |
