ERIO-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