Walsh & Hoyt: Size

Saccular intracranial aneurysms vary in size from less than 2 mm to more than 60 mm in diameter; the size tends to increase with the age of the patient. This finding is consistent with serial angiographic studies that show progressive enlargement of aneurysms during intervals ranging from 2 weeks to 10 years. Such growth probably reflects two mechanisms. First, there may be thinning of the wall of the aneurysm, which would allow slow expansion ofthe sac. Second, there may be recurrent, clinically silent leaks from the aneurysm. During each leak, there is a mesenchymal reaction at the site of bleeding that walls off the blood. Repeated episodes of bleeding thus result in formation of a ""pseudoaneurysm"" within the wall of the true aneurysm