Contributor: Gordon K. Klintworth
An aneurysm is a localized sac formed by the dilatation of the wall of a vascular structure. It can form in an artery , arteriole, vein, venule, capillary or in the heart. Specific terms have been applied to specific aneuryms. These terms include berry aneurysm , arteriovenous aneurysm, dissecting aneurysm, microaneurysm, macroaneurysm, fusiform aneurysm, saccular aneurysm and Charcot-Bouchard aneurysm.
Aneurysms form in the elastic arteries when there is a breakdown in the tunica media and especially of its elastic layers. They form with aging in association with severe atherosclerosis in the abdominal aorta and major cerebral vessels especially when hypertension is present. A dissecting aneurysm most often affects the aorta and its major branches and most often occurs in persons with hypertension. Some aneuysms are a complication of infections, such as syphilis, tuberculosis or a bacterial abscess. An aneursym in the left ventricle of the heart often complicates a healed transmural myocardial infarct and mural thrombi that form within the aneursym are a source of emboli [embolism] to various distant sites including the eye. An aneurysm of the coronary artery may form in Kawasaki disease. Arterioles may become aneurysmally dilated in the thrombotic microangiopathies [microangiopathy - thrombotic]. Aneurysmal dilatations of the retinal veins have been noted in Rothmund-Thomson syndrome.
Mural thrombi form in the lumen of aneursyms and can be the source of emboli to structures supplied by blood vessels that are located distal to the aneurysm. A berry aneurysm or macroaneurysm in the cerebral blood vessels can rupture and lead to death. The blood vessels in the conjunctiva and retina are often tortuous with saccular aneurysms in persons with sialidosis type I.