3. Dissecting Aneurysms.
—The dissecting aneurysms are nearly always expressions of previous atheromatous changes, by which blood is forced between the arterial coats, separating them and causing them to bulge at one or more points into sacculations or distortions. In a false aneurysm there is no true arterial coat; the sac is made up of surrounding tissue.
Fig. 150
Traumatic aneurysm of axillary artery. (Park.)
4. Traumatic Aneurysms.
—Traumatic aneurysms are generally sacculated by the time they come under the surgeon’s observation. They are circumscribed and diffuse. According to their age and other circumstances they may contain old and dense laminated clots as well as those which are fresh and stratified. Much will depend upon whether the artery has been extensively injured or only slightly punctured, and also upon the location and distensibility of the surrounding tissue. Such a case seen in a fresh state will show infiltration of blood and ecchymosis ([Fig. 150]). Arteriovenous aneurysms are now seldom seen. When venesection was more frequently performed the artery and one of the veins at the bend of the elbow were often thrown into communication, as the result of the indifferent performance of this operation and the use of the old-fashioned lancet. When the communication is direct such a condition is known as an aneurysmal varix; when indirect and through the sac it is called a varicose aneurysm ([Figs. 151], [152] and [153].)
Fig. 151
Aneurysmal varix. (Bryant.)