ANEURISM (Gk. ancurysma, a dilatation. from api, ana, up + eurys, wide). A pulsating tumor, consisting of a sac or pouch into which blood flows through an open ing in an artery. The sac of an arterial an eurism may be formed in the first instance by one or more of the tunics of the vessel, generally the outer one, the two inner having given way. This is called a true aneurism, m contradistinc tion to the false. The pathological condition underlying most aneurisms is a weakening of the arterial walls from disease. Thus, in the early stages of the disease of the arteries known as arteriosclerosis, the walls of the vessels are weak ened, and so less resistant. The changes in the vessel walls being uniform, the resulting an eurism is apt to consist of an even dilatation of the entire vessel, making what is called a fusiform aneurism. If, however, there is one particularly weak point in the coats of the ar tery, the distention is greatest at that point and an aneurismal sac is formed. Such an aneurism is described as a saccular aneurism. An aneurism may occur at a point where an artery branches, and be irregular in shape from involvement of both main trunk and one or more of the branches, eirsoid aneurism. Owing to injury to the inter nal coat of an artery, the blood may get in be tween the layers of the vessel walls and work its way up or down between them. This form of
aneurism is called a disseettng aneurism. Some times a direct communication is found between an artery and a vein, in which case the latter, being exposed to unusual- pressure, is apt to be come distended and tortuous. Such a condition is called uneurismal rarix. A false aneurism. is one in which there is rupture of the entire wall of an artery and the blood comes in direct con tact with the surrounding tissues. This is some times called a diffuse aneurism. Aneurisms prove fatal by their pressure on some important part, or by bursting and allowing a sudden es cape of blood. They are cured by the deposit, within the sac, of fibrin from the blood, a result the surgeon can promote by obstructing the artery above the aneurism by compression or by ligature, applying the latter close to the sac if time aneurism is of the "false" variety, but at a distance if it is the result of disease; by inserting needles into the tumor; or by inserting and coil ing silver wire within the sac and passing an electric current through it. Internal aneurisms are treated by those remedies which moderate the heart's action, as digitalis, rest, etc.