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.