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Occasionally a small thrombus situated behind a valve in a varicose vein or in the terminal end of a dilated vein for example in a pile undergoes calcification, and is then spoken of as a phlebolith; it gives a shadow with the X-rays.
When infected with pyogenic bacteria, the thrombus becomes converted into pus and a localised abscess forms; or portions of the thrombus may be carried as emboli in the circulation to distant parts, where they give rise to secondary foci of suppuration pyæmic abscesses.
Bryce records a case of anuria of seventeen days' standing. Butler speaks of an individual with a single kidney who suffered suppression of urine for thirteen days, caused by occlusion of the ureter by an inspissated thrombus. Dubuc observed a case of anuria which continued for seventeen days before the fatal issue. Fontaine reports a case of suppression of urine for twenty-five days.
The bruising of the vessel wall, especially if it is diseased, may result in the formation of a thrombus which occludes the lumen temporarily or even permanently, and in rare cases may lead to gangrene of the limb beyond. #Subcutaneous Rupture.# An artery may be ruptured subcutaneously by a blow or crush, or by a displaced fragment of bone.
Under these various conditions the formation of a thrombus is not necessarily associated with the action of bacteria, although in any of them this additional factor may be present. The most common cause of venous thrombosis, however, is inflammation of the wall of the vein phlebitis.
Occlusion of the inferior vena cava as a result of infective thrombosis is a well-known condition, the thrombosis extending into the main trunk from some of its tributaries, either from the femoral or iliac veins below or from the hepatic veins above. Portions of the softened thrombus are liable to become detached and to enter the circulating blood, in which they are carried as emboli.
Alterations in the blood itself, such as occur, for example, in certain toxæmias, also favour coagulation. When the thrombus is formed slowly, it consists of white blood cells with a small proportion of fibrin, and, being deposited in successive layers, has a distinctly laminated appearance on section.
Phlebitis and thrombosis are common sequelæ of varix, and may prove dangerous, either by spreading into the large venous trunks or by giving rise to emboli. The larger the varix the greater is the tendency for a thrombus to spread upwards and to involve the deep veins.
#Phlebitis.# Various forms of phlebitis are met with, but for practical purposes they may be divided into two groups one in which there is a tendency to the formation of a thrombus; the other in which the infective element predominates.
The infective form usually begins as a peri-phlebitis arising in connection with some focus of infection in the adjacent tissues. The elements of the vessel wall are destroyed by suppuration, and the thrombus in its lumen becomes infected with pyogenic bacteria and undergoes softening.
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