The most notable example of thrombosis in the horse is that which is seen now and again in the iliac arteries - the vessels into which the abdominal aorta breaks up beneath the lumbar spine, and whose branches are distributed to the hind-quarters and extremities.
For the most part thrombosis of the iliac vessels is the result of sprain inflicted upon them by some violent backward stretching of the hind-limbs, such as would result when a horse falls short in jumping and slips down the bank of a drain, or when his legs fly back from under him, or " spread-eagle", while drawing a heavy load over a slippery surface, or out of deep heavy ground. The writer has also known it to be occasioned in the course of the struggles of a horse while cast in a railway box, and in another instance the disease followed upon a hunter being " hung up" across a gate. In all these positions there would be sudden and severe stretching of the vessels and injury to their coats.
The symptoms of iliac thrombosis will vary with the stage of the disease, but, when well established, they are very diagnostic. At first the patient displays slight stiffness of one or both hind-limbs, more especially on rising from the recumbent posture, or when first led out of the stable. This, however, will pass away with a little exercise, to reappear again from time to time in a more and more marked form. It may be accompanied by slight swelling of the limbs. As the arteries become more and more blocked, and the circulation obstructed, the legs are found to be cold, and the large veins are distended. This distension of the veins results from the absence of force to move on the blood within them, consequent upon the blocking up of the arteries, and is most strikingly seen during rest. When the animal is made to move, the blood disappears from the veins, and returns but slowly. The horse's movements are observed to be somewhat unsteady behind, especially during work. In the more advanced stages of the disease exertion brings on a rolling gait behind, and, if continued, results in paralysis of the posterior part of the body At this time the animal breaks out into a profuse perspiration, the breathing is hurried, the muscles quiver, and the pulse is much accelerated. In some cases the affected animal strikes the belly, looks round to the flank, and shows signs of acute pain, as if the subject of colic.
PLATE XXXII. THROMBOSIS.
Fig. i. A. Circumflex artery of ilium. B. External iliac artery, c. Internal iliac artery with Thrombus in situ.
d. Thrombus. Fig. 2. Jugular Vein. A, A. Phleboliths in situ. B, B. Phleboliths removed. C. Phlebolith in section.
After a short period of rest the symptoms subside, and the horse resumes his normal condition, and will most likely continue in apparent good health until the exertion is again repeated. Although the symptoms described are very indicative of iliac thrombosis, the diagnosis may be rendered still more complete by a careful manipulation of the affected vessels. In this connection it will be remembered that the iliac arteries are to be found striking off right and left beneath the lumbar spine, and quite within reach of the hand when pushed well forward into the rectum. In carrying out this examination the hand and arm must be well anointed with oil or vaseline, and after entering the bowel the arm is turned so that the palm is presented upward; the fingers are then directed to that part of the spine where the loin joins on to the quarters, immediately beneath which the great iliac vessels - two on either side - will be felt branching off right and left from the posterior aorta.
When healthy, they are found to pulsate forcibly with each beat of the heart, and to be distinctly compressible, though always tense. When, however, they are filled with coagulated blood and rendered solid, as in this disease, the pulsation is no longer felt, and the vessels become hard and unyielding. If they are not completely blocked a slight pulsation may be felt, as a thin stream of blood passes over the clot, but the affected vessels in any case will have lost their pliancy, and will offer very decided resistance to deep pressure.
Treatment in these cases is of no avail. The fibrinous matter plastered over the inner surface of the vessel in successive layers, or free within it and occluding the passage of the blood, cannot be removed, and the animal should therefore be destroyed.