Manual of Surgery Volume First: General Surgery. Sixth Edition.

by Alexis Thomson; Alexander Miles

Arterio-Venous Aneurysm

An abnormal communication between an artery and a vein constitutes an arterio-venous aneurysm. Two varieties are recognised—one in which the communication is direct—aneurysmal varix; the other in which the vein communicates with the artery through the medium of a sac—varicose aneurysm.

Either variety may result from pathological causes, but in the majority of cases they are traumatic in origin, being due to such injuries as stabs, punctured wounds, and gun-shot injuries which involve both artery and vein. In former times the most common situation was at the bend of the elbow, the brachial artery being accidentally punctured in blood-letting from the median basilic vein. Arterio-venous aneurysm is a frequent result of injuries by modern high-velocity bullets—for example, in the neck or groin.

In aneurysmal varix the higher blood pressure in the artery forces arterial blood into the vein, which near the point of communication with the artery tends to become dilated, and to form a thick-walled sac, beyond which the vessel and its tributaries are distended and tortuous. The clinical features resemble those associated with varicose veins, but the entrance of arterial blood into the dilated veins causes them to pulsate, and produces in them a vibratory thrill and a loud murmur. In those at the groin, the distension of the veins may be so great that they look like sinuses running through the muscles, a feature that must be taken into account in any operation.

As the condition tends to remain stationary, the support of an elastic bandage is all that is required; but when the condition progresses and causes serious inconvenience, it may be necessary to cut down and expose the communication between the artery and vein, and, after separating the vessels, to close the opening in each by suture; this may be difficult or impossible if the parts are matted from former suppuration. If it is impossible thus to obliterate the communication, the artery should be ligated above and below the point of communication; although the risk of gangrene is considerable unless means are taken to develop the collateral circulation beforehand (Makins).

Varicose aneurysm usually develops in relation to a traumatic aneurysm, the sac becoming adherent to an adjacent vein, and ultimately opening into it. In this way a communication between the artery and the vein is established, and the clinical features are those of a combination of aneurysm and aneurysmal varix.

As there is little tendency to spontaneous cure, and as the aneurysm is liable to increase in size and finally to rupture, operative treatment is usually called for. This is carried out on the same lines as for aneurysmal varix, and at the same time incising the sac, turning out the clots, and ligating any branches which open into the sac. If it can be avoided, the vein should not be ligated.

ANEURYSMS OF INDIVIDUAL ARTERIES

Thoracic Aneurysm.—All varieties of aneurysm occur in the aorta, the fusiform being the most common, although a sacculated aneurysm frequently springs from a fusiform dilatation.

The clinical features depend chiefly on the direction in which the aneurysm enlarges, and are not always well marked even when the sac is of considerable size. They consist in a pulsatile swelling—sometimes in the supra-sternal notch, but usually towards the right side of the sternum—with an increased area of dulness on percussion. With the X-rays a dark shadow is seen corresponding to the sac. Pain is usually a prominent symptom, and is largely referable to the pressure of the aneurysm on the vertebræ or the sternum, causing erosion of these bones. Pressure on the thoracic veins and on the air-passage causes cyanosis and dyspnœa. When the œsophagus is pressed upon, the patient may have difficulty in swallowing. The left recurrent nerve may be stretched or pressed upon as it hooks round the arch of the aorta, and hoarseness of the voice and a characteristic “brassy” cough may result from paralysis of the muscles of the larynx which it supplies. The vagus, the phrenic, and the spinal nerves may also be pressed upon. When the aneurysm is on the transverse part of the arch, the trachea is pulled down with each beat of the heart—a clinical phenomena known as the “tracheal tug.” Aneurysm of the descending aorta may, after eroding the bodies of the vertebræ ([Fig. 71]) and posterior portions of the ribs, form a swelling in the back to the left of the spine.