EXCITING CAUSES.—Weakness and thinness of the internal and medial coats of the arteries predispose to aneurisms, especially in localities like the popliteal space, subject to frequent movements. Small, incomplete tears occur in the wall of the vessel, and these gradually increase, Violence may then produce a rupture of one or two of the coats of an artery and act as an exciting cause.
An artery may be torn or unduly stretched by a fracture or dislocation, or by attempts made to reduce the latter.
Case of traumatic aneurism of the axil lary artery due to attempts at reduction of a dislocation of the shoulder. Death soon after the operation. A small open ing found in the axillary artery only large enough to admit the end of a probe; the sae was enormous and dur ing life had not pulsated. The veins, which had been also injured, opened into the aneurism.
Case of traumatic aneurism due to at tempted freeing of the shoulder-joint, in a case of ankylosis following gonorrlimal arthritis. Sonnenburg (Berliner klin. Woch., p. 681, July 27, '96).
Any violent or sudden exertion may also act as an exciting cause either by unduly stretching the artery, by forcing blood under a high pressure through it, or by causing the heart to act irregularly and forcibly.
Case of child which, when first seen, when nine days old, had in the left axilla a tumor, soft and compressible, dilating synchronously with the heart, and over which a bruit could be heard, but there was no aneurismal thrill apparent. This tumor had not been noticed at birth by the midwife, but some days later a small, soft swelling was observed which gradu ally filled the entire axilla. The tumor w as flattened and soft, covering the an terior aspect of the shoulder and a small part of the upper arm; beneath, it ex tended beyond the posterior border of the axillary space. The child had been roughly handled a day or two after birth, during the performance of some occult ceremonial rites, part of which rites con sisted in handling the child dangling by one arm from one person to another over the banisters. When shown, child was
in excellent health, after having passed, however, through a period of some months' suffering. W. C. Mardorf (Med. Bev., May 14, '98).
Riders are frequently the subjects of popliteal aneurisms. This is due to ob struction of the arteries caused by the bending of the legs and the contraction of the leg-muscles, to which may be added the jars which are constantly given to the column of blood thus formed.
Pathology. — The structure of a sac ciliated aneurism, from without inward, is as follows:— 1. An adventitious sac formed of con densed areolar tissue.
2. The real sac, which may consist of the thickened external coat and, per haps, a portion of the middle coat (false aneurism) or of all the coats (true aneu rism). The atheromatous and calcareous patches may serve to distinguish the in ner and middle coats.
3. Concentric decolorized fibrinous lay ers, harder and drier toward the exterior and toward the interior softer and redder.
4. A soft, currant-jelly coagulum, which may, however, be formed previ ous to or after death.
The fibrinous deposit on the wall of the sac acts favorably by diminishing the dilating force of the circulation in the sac and by strengthening the wall. The mouth of the sac is round or oval, and measures much less than a section of the sac.
If the contents of the sac be exam ined they will be seen to vary according to the stage of the disease. The wall of the sac is very thin in the first stage, and contains fluid blood only; in the second stage the centre only of the sac will contain fluid blood, around which are placed laminar and fibrin; at the periphery a much thicker wall of fibrin is present. The lamin? of fibrin next to the wall are dry, friable, and opaque, while, as the centre of the aneurism is approached, they are soft and red.
Fibrin is rapidly deposited in sac culated aneurism, being more rapidly formed where the obstruction to the free passage of the blood into and out of the sac is greater.