an'eurism

A tumor formed by localized dilatation of an artery through which blood circulates. Such tumors are distinguished by their expansive pulsation with each systole of the heart, by a thrill to be felt in them on palpation, and by a bruit heard on auscultation. As they increase in size they produce absorption of adjacent structures and give rise to distre ing symptoms by their pre ure on nerves. Their final tendency is to burst and, if a large artery is the seat of the tumor, to cause death. They are cla ed as: (1.) true arterial a. and (2.) arteriovenous a. A pulsating arterial hematoma, even though its walls are not formed by the wall of an artery must be cla ified with aneurisms. a. by anastomosis. 1. J. Bell's term for a vascular tumor made up of enlarged and proliferated capillaries. 2. See arteriovenous a. 1. true arterial a. If only a portion of the wall of an artery is affected, a saccular a. is formed: if the entire wall is involved, a cylindrical or cirsoid a. develops. Other varieties of arterial a. are: a. by erosion, congenital a. di ecting a. embolic a. false traumatic a. spontaneous a. True arterial a. is about twice as frequent in the male as the female and develops most often between the thirtieth and fiftieth year, involving the following arteries in the order of frequency given: thoracic aorta, popliteal, femoral, abdominal aorta, subclavian, innominate, axillary, iliac, visceral, central, and pulmonary. arteriovenous a. Those having sac, connecting with a vein on one side and an artery on the other, called aneurismal varix; those having a false sac without direct communication with vein or artery called varicose a; and the rare form occurring when a true arterial a. erodes the wall of a vein and ruptures into it, called arteriovenous a. with arterial sac. Arteriovenous a. is usually due to punctured wounds and the ve els usually involved are the following in the order of frequency given: brachial, femoral, popliteal, carotid, arteries of the head, especially the temporal and the subclavian and axillary arteries, varicose a. An a., either traumatic or spontaneous, consisting in the communication of an artery with a vein through the medium of a distinct sac formed between the two. [Gr., aneurysm a, a dilatation, from aneurynein, to dilate.]