Part 52

Causes of Embolism. As already stated embolism results from a detached portion of a thrombus passing to a smaller vessel and obstructing it. Such detachment is favored by molecular softening, liquefaction or suppuration in the clot or beneath it, by the destructive action of microbes, or by friction or manipulation of the obstructed vessel. Excess of white globules (leukæmia) favors the formation of minute coagula and embolism. Bubbles of air, globules of fat, or cholesterine crystals block the fine pulmonary capillaries, and the debris from atheromatous patches, ulcers, and tumors opening on the inner wall of the artery form emboli in various parts. Finally parasites, especially the larval strongyli in solipedes and filaria and spiroptera in dogs, themselves obstruct the vessels and determine coagulation.

Pathogenesis. In the larger arteries (aorta, radical stump of the mesenteric artery) clots (as from strangles) rarely produce dangerous obstruction. In the smaller vessels stenosis is complete and anæmia and gangrene are liable to occur unless the blood supply is partially maintained by anastomotic vessels. When the embolism affects a number of smaller arteries or capillaries in a vascular organ like the lungs, the blood filters in from the adjacent capillaries, in which circulation is still carried on, and this passes through the softened and ruptured capillary walls so that the tissue is charged with globules and constitutes a black infarction. In the lung this usually affects one or several lobulettes, forming a pear shaped mass corresponding to the distribution of the obstructed vessel. The cut surface is black, compact and granular. The lymph thrown out around it forms an organized fibrous sac, and the unclosed sequestrum undergoes a slow necrobiosis, blanching and liquefaction into a pus-like fluid which is removed by absorption. Such results are met with in the parenchymatous organs (lungs, liver, spleen, kidneys, etc.) and less frequently in the limbs. The symptoms will correspond to the particular organ invaded.

In the fore or hind limbs the result is usually less radical. The vessels below the obstructed trunk are connected more or less freely by anastomosing branches, so that the circulation in the tissues below, though somewhat restricted, remains active enough to sustain a fair measure of nutrition. Apart from the suffering, attendant on the preliminary inflammation, the morbid phenomena are largely confined to the absence of pulsation in the lower part of the limb and the inability of the muscles to sustain active contraction.

=Chronic Embolism of the External Iliac or Femoral Artery.= In this condition the pulsations in the digital arteries are imperceptible, if it has been of long standing there may be obvious atrophy of the muscles of the thigh, but when standing quietly or walking there is usually no lameness. In continuous rapid walking and above all in the trot, however, he soon begins to halt on the affected limb, and this rapidly increases, the joints bending under his weight, the toe dragging and the animal threatening to drop altogether. If stopped and allowed to rest for ten or fifteen minutes he gradually recovers and may be led quietly back to his stable without a sign of lameness. But if again trotted fifty or one hundred paces the lameness develops anew and disappears in the same way when left at rest. The circulation in the muscles is enough for a moderate nutrition but altogether inadequate to sustain active work.

=Chronic Embolism of the Internal Iliac Artery.= In this case the control of the muscles of the limb may be perfect but there is some indication of paresis of tail, bladder, rectum and anus. Impaction of the rectum is liable to occur. By examination through the rectum the pulsations are felt to be strong in the aorta and external iliac, but imperceptible in the internal iliac blocked by the embolus.

=Chronic Embolism of the Axillary Artery.= Here there are the same general symptoms, the absence of the radial and digital pulsations, the wasting of the muscles of the forearm, and the intermittent lameness, developed rapidly by exercise and recovering promptly under rest.

=Acute Embolism of the Mesenteric Arteries.= This will be fully treated under the title of verminous colic in solipedes. The blocking of the branches, usually of the anterior mesenteric artery, leads to derangement of the innervation, congestions, spasms, involutions and other disorders. The presence of the strongyli in the fæces, the general symptoms of intestinal worms, and the recurrence of the indigestions and spasms would serve to indicate the nature of the complaint.

Treatment of Chronic Embolism. As affecting the arteries of the limbs the repair must be largely left to nature, and we must place the patient in condition, favorable to such repair. Except in the early stages absolute rest is not necessary. Gentle exercise stimulating to a freer circulation solicits a slow enlargement of the anastomosing vessels (arterial or capillary), and when this has reached a given stage, weak pulsations may again be felt in the vessels beyond and the muscles will once more stand moderate work without lameness. Alkalies and iodide of potassium may be given to solicit solution of the clot, but this can rarely be counted on to the extent of rendering the vessel once more pervious. A small paddock in which the patient can move around quietly is desirable, and in a few months a tolerable recovery may have taken place.

Embolism in other organs must be treated on the same general expectant method, and a considerable time is usually necessary to secure a fair recovery.

ANEURISM.

Definition. Divisions, true, false, dissecting, arterio-venous, mixed, traumatic, spontaneous. Causes, violence, rupture, debilitated vascular walls, strains, stretching, force of blood current, overloaded intestine, strongyli, contiguous inflammation, embolism, microbian invasion of the walls, arteritis, concussion. Symptoms, soft tumor pulsating with the heart, a double rushing sound, diagnosis from abscess, nervous disorders through pressure, cramps, palpitations. Treatment, when desirable, rest, moderate, laxative diet, iodides, bromides, icebags, compression, ligature, galvano-puncture, wire coils, injections.

Definition. A pulsating swelling on an artery, consisting of a sac filled with arterial blood.

Divisions. =A true aneurism= (=aneurism by dilatation=, =arteriectasis=) is a simple dilatation of the artery, the tumor being surrounded on all sides by the distended arterial walls. It is usually fusiform or cylindroid, but may have the form of a more or less rounded sac.

=A false aneurism= is where the wall of the artery has been lacerated and the blood is enclosed in an adjacent sac of condensed connective tissue and communicates with the interior of the vessel. The same name has been given to cases in which the inner coat only has given way, and the middle and outer coats constitute the walls of the sac. From its liability to extend and separate the tissues this is further known as a =dissecting aneurism=. =Arterio-venous aneurism= in which an intervening sac communicates with both artery and vein, has been found in the human subject.

=Mixed aneurisms= are those in which a dilatation of the artery is complicated by the presence of an outside pouch.

A distinction has also been made according to origin into traumatic and spontaneous. The former is of necessity false, whereas the latter may be false or true.

Causes. Apart from rupture of the arterial coat by direct violence, the common cause is a debility and loss of resistance in the walls. In horses a far larger proportion of aneurisms are deep-seated than in man, in whom forced muscular effort is less common. Yet even in horses the most common seat—the posterior aorta—is liable to overstretching and to inflammation and softening by reason of contiguity to dorsal sprains. The posterior aorta too, from its size and direction on leaving the heart, is in the direct line of the strongest blood current, and under long continued, forced and violent efforts (as in racing, hunting, and heavy uphill draughts), has to sustain an extraordinary blood pressure. Bouley claims as an additional cause the pressure of a loaded colon. This is also the point of all others where the vessels suffer from the presence of the larval strongyli. From whatever cause originating, congestion of the arterial coats leads to more or less attenuation, softening or lack of cohesion, and they tend to yield under the blood pressure. Similar conditions operate on the smaller vessels in different parts of the body, and thus overstretching, contiguous inflammation, and excessive blood pressure cause such lesions in the chest, trunk and limbs.

Another cause is embolism which by blocking an artery at once increases the tension in the vessel on the cardiac side of the obstruction, and develops inflammation in the arterial coats, robbing them of their cohesion and resisting power.

Eppinger has shown the importance of infectious microbes in weakening the arterial walls and predisposing to aneurism.

The larval strongylus armatus already referred to is the most potent factor in solipedes. They accumulate in the anterior mesenteric artery, leading to clotting of the blood, inflammation of the serous coat, and dilatation, so that in some verminous localities nearly every old horse shows a lesion of this vessel.

All forms of arteritis, and disease of the vascular walls which entail attenuation or weakening, predispose to aneurism.

Of direct traumatism may be mentioned an aneurism of the arch of the aorta in a horse struck by a wagon pole, during a sharp descent (Jacob), and two with aortic aneurism after violent blows on the back with shafts of wagons.

Symptoms. An aneurism within reach of the hand is to be recognized primarily by the pulsation of the swelling synchronously with the beats of the heart, and by a double rushing sound with each beat of the heart, observed on auscultation. An abscess over a large artery lying on a bone may pulsate but it is to be distinguished by the presence of a single in place of a double rushing sound on auscultation, by the possibility of causing more or less complete collapse under pressure, and by the history of an active phlegmonous inflammation followed by softening which steadily extends from the centre of the previously dense mass. In a case of aneurism of the gluteal artery of the horse reported by King and in one observed by the author the symptoms were unmistakable. Other similar examples on the popliteal artery and other failed to be recognized during life though attended by lameness.

In internal aneurism the symptoms are mostly indefinite. Ollivier found tympany and vomiting in a goat which at the necropsy showed an aneurism of the anterior aorta as large as the closed fist and enclosing a sewing needle. A more careful diagnosis should have detected a retarding of the maxillary pulse and a double rush over the carotid with each beat of the heart. Pressure on the vagus doubtless led to the symptoms noticed. In aneurism of the posterior aorta there have been noticed a loss of life and energy, dulness, lack of appetite and stiffness of the loins. Torpor of the bowels, expulsion of fæces with effort and groaning, intermittent colics, lameness in one or both hind limbs, and finally cramps in the hind limbs, and palpitations. In one case Maillet was able to reach the aneurismal tumor through the rectum.

Treatment. The treatment of internal aneurism will be seldom called for in the lower animals, as the disease is seldom diagnosed, is beyond reach of mechanical applications, and survival without certain power of endurance would seldom be desirable. In some valuable breeding animals it might be worth while to seek prolongation of life. The most promising measures are absolute rest, and low, non-stimulating diet of a laxative nature and in small bulk. Iodide of potassium is often useful in man, and although in the lower animals there is not the excuse of specific disease, yet the rest to the circulation and reduction of blood tension are not to be undervalued. Bromides may be given with the same object.

Other measures applicable only to aneurisms, within reach and essentially of a surgical nature include: Ice bags and compression. The compression should as a rule begin at the distal end of the limb and be concentrated by suitably shaped pads on the swellings. Ligature of the diseased artery above or below or both above and below the tumor. Galvano-puncture of the aneurism with the object of inducing coagulation. The introduction of coils of fine wire through a hypodermic needle with the same object in view. In both horse and dog the persistent compression with the finger seconded as it is by the plasticity of the blood has succeeded in checking the flow from large arterial orifices, and offers great encouragement in the application of this measure to aneurisms. The injection into the sac of tincture of chloride of iron with firm compression to prevent motion of the blood is another available resort.

ARTERIO-SCLEROSIS.

Fibrous thickening of the arterial coats and calcification are well known lesions in the posterior aorta particularly of the horse. Commencing in congestion or degeneration which lessens the resistance of the vascular walls, the condition tends to dilatation, and if this is checked by compensatory thickening, the condition of sclerosis is induced. The combination of a slight fusiform dilatation and fibrous or calcareous sclerosis is well known in the posterior aorta of the horse. Unless it advances to marked aneurismal dilatation the condition is not often recognized. If diagnosed, rest and quieting of the circulation are especially indicated. Should it occur in other parts of the body the symptoms would correspond to the organ invaded.