ANEURYSM or ANEURISM, a cavity or sac which com municates with the interior of an artery and contains blood. The walls of the cavity are formed partly by the dilated artery and partly by the tissues around that vessel. The dilatation of the artery is due to local degeneration or injury of the inner coats of the vessel. In a rare variety (dissecting aneurysm) the blood is contained at first in the region of the middle coat of the artery which may be opened up from arch of the aorta to the iliac vessels. Aneurysms may be spontaneous or traumatic. The man who has chronic inflammation of a large artery, the result, for instance, of syphilis, gout, arduous straining work, or kidney-disease, and whose artery yields under cardiac pressure, has a spontaneous aneurysm ; the barman or window-cleaner, who has cut his radial artery, the soldier whose brachial or femoral artery has been bruised by a rifle bullet or grazed by a bayonet, and the boy whose naked foot is pierced by a sharp nail, are apt to be the subjects of traumatic aneurysm. In saccular aneurysms bulging on one side of an artery the blood may be induced to coagulate, or may of itself deposit layer upon layer of pale clot, until the sac is oblit erated, and the aneurysm is cured. But in those aneurysms which are f usi f orm dilatations of the vessel there is but slight chance of such cure, for the blood sweeps evenly through it without staying to deposit clot or laminated fibrine.
In the treatment of aneurysm the aim is generally to lower the blood pressure by absolute rest and moderated diet, but a cure is rarely effected except by operation. Speaking generally, if an aneurysm can be dealt with surgically the, sooner that the artery is tied the better. Other measures are too apt to prove painful, dangerous, ineffectual and disappointing. For aneurysm of the great arteries in the chest or abdomen (which cannot be dealt with by operation) treatment is unsatisfactory and consists, mainly, in measures designed to avoid strain. Usually such an aneurysm ends life by rupture.