ANEURISM OF THE ARTIERIES.
An aneurism of an artery is a dilatation of the arterial vessel, but with this difference from simple dilatation, that the enlarge ment is not general in the course of the vessel, but is at one part, and is attended with thinning, or even rupture, at the affected spot of one or more of the arterial coats, which, as we have seen, consist of an investing, an elastic, and a muscular coat, and an inner or serous lining. Aneurisms are classed under several heads. The following are the most important varieties of an eurism.
(a) Fusiform aneurism. In which the dilated part is like a spindle, large in the middle and reduced at both ends.
(b) Vascular aneurism. In which the dilatation is round like a hollow ball or sac.
(c) Diffused arterial aneurism. In which the sac or surround ing wall is not made by the dilated artery itself, but by the surrounding tissues, which have become united or adhe rent with the broken arterial coats.
(d) Dissecting arterial aneurism. In which there is partial tear or rupture of the internal tissues of the artery, and effusion of blood between the coats of the vessel, extending for some distance, and dissecting its way between the coats.
(e) Traumatic arterial aneurism. Aneurism in which the dila tation has been caused by a wound inflicted on the artery.
(f) Aneurism by anastomosis. Aneurism by arterial vessels which are carrying on a new circulation owing to obstruction in the main arterial current through which the blood originally passed.
There are some other varieties of aneurismal disease which are of rarer occurrence, such as arterio-venous aneurism, aneu rismal varix, varicose aneurism, and arterial varix; but those classified above concern us most as being the more decisive and frequent. Aneurism of the large vessels, as of the great aorta at its commencement or arch, and of the vessels springing from the arch, are the more serious and common aneurisms; but aneurism of the popliteal artery, the artery running through the hollow space at the back of the lower limb between the thigh and the leg, behind the knee joint, is also common. Aneurism is in duced by acts which cause great strain on the arterial system, and especially when such acts subject the body to rapid jerks and shocks. In the old posting days aneurisms of the aorta were so frequent, that the term " post-boy's disease" was applied to them.
Aneurisms are specially liable to occur in persons who are disposed to degenerative disease of the arterial coats, and it has recently been observed that persons who are born suffering from syphilitic taint, or who have themselves contracted that specific disease, are more liable to aneurism than other persons who are free of such constitutional affection. The question whether an eurism is hereditary in character has not been satisfactorily set tled. It affects those who have approached the middle term of life more frequently than it does the young, but I have neverthe less seen it affecting the young, under fifteen years of age. An aneurism is occasionally healed, spontaneously, by deposits on its inner surface of fibrine from the blood and by gradual oblitera tion of its sac or pouch by that gradual process of deposition.
Rupture of an Artery.
Rupture of an artery means a breakage through the arterial coats, without preceding dilatation or aneurismal enlargement. Rupture occurs from two causes : (a) From disease in the artery itself by which the coats are weakened and destroyed.
(b) From disease of the structures outside the artery and ex tension of the disease into the vessel, as when an artery is in volved in an abscess or in an ulceration.