an abnormal balloon-like swelling in the wall of an artery. This may be due to degenerative disease or infection, which damages the muscular coats of the vessel, or it may be the result of congenital deficiency in the muscular wall. An aortic aneurysm most frequently occurs in the abdominal aorta, below the level of the renal arteries. Beyond a certain size it is prone to rupture, presenting as an acute surgical emergency with abdominal and back pain and haemorrhagic shock. A dissecting aneurysm usually affects the first part of the aorta and results from a degenerative condition of its muscular coat. This weakness predisposes to a tear in the lining of the aorta, which allows blood to enter the wall and track along (dissect) the muscular coat. A dissecting aneurysm may rupture or it may compress the blood vessels arising from the aorta and produce infarction (localized necrosis) in the organs they supply. The patient complains of severe chest pain that has a tearing quality and often spreads to the back or abdomen. Surgical repair may help in some cases. A ventricular aneurysm may develop in the wall of the left ventricle after myocardial infarction. A segment of myocardium becomes replaced by scar tissue, which expands to form an aneurysmal sac. Heart failure may result or thrombosis within the aneurysm may act as a source of embolism. See also arteriovenous aneurysm.
Most aneurysms within the brain are congenital: there is a risk that they may burst, causing a subarachnoid haemorrhage. Berry aneurysms are small saccular aneurysms most commonly occurring in the branches of the circle of Willis. Usually associated with congenital weakness of the vessels, these aneurysms are a cause of fatal intracranial haemorrhage in young adults. Charcot-Bouchard aneurysms are small aneurysms found on tiny arteries within the brain of elderly and hypertensive subjects. These aneurysms may rupture, causing cerebral haemorrhage. Options for treatment of cerebral aneurysms include surgical clipping of the aneurysm and placing metallic coils within the aneurysm to establish a clot within it (endovascular coiling).
In a pseudoaneurysm (or false aneurysm) the swelling of the artery is contained by clotted blood rather than the wall of the artery.
aneurysmal adj.

The new mediacal dictionary. 2014.