D. Inflammatory and degenerative processes occurring in and about the vessel walls tend always to produce coagulation. This is well seen in the influence exerted by the so-called atheromatous ulcers—i. e., the degeneration of certain areas in the walls of large vessels.
E. Microörganisms and their products are perhaps the most frequently effective of all the accessory causes of thrombosis. In other words, in all the surgical infectious diseases we may expect to find more or less, sometimes extensive, thrombosis in the vessels of the affected part. This may so far shut off circulation as to produce temporary or permanent edema, or it may lead to gangrene, which may be local or may terminate the life of the patient.
Thrombi are classified as:
- 1. Primary; and
- 2. Propagated.
The primary thrombus is one which has originated at the spot where it has been first produced, and is usually co-extensive with its cause. The propagated thrombus may be one which has been carried to a considerable distance, and is met with at a point widely different from that where it originated, or one which has extended along the vascular channel in which it was first formed, but far beyond the limits of its prime cause. When a thrombus attaches itself to a part of the vessel wall it is called parietal or valvular, because it does not completely occlude the vessel; when it involves the entire circumference of the vessel, but does not completely occlude it, it is spoken of as annular. The obstructive thrombus is that which completely fills a given vessel and shuts off all circulation through it.
The propagated thrombus extends usually in both directions, and always much farther in veins than in arteries. Thus, thrombi may be met with extending from the ankles even into the inferior vena cava. The venous valves may on one hand excite coagulation, or on the other tend to fix the coagula more firmly in their place. In arteries thrombi usually extend only to the first collateral channel on the cardiac side, but occasionally they spread farther. The cause of a primary thrombus is to be sought at the site of its lodgement; the cause of propagated thrombi is often observed at a wide distance from the effect.
Thrombosis is, again, to be spoken of as—
- a. Marasmic;
- b. Mechanical or traumatic;
- c. Infective.
a. The marasmic forms are due to essential alterations in the constituents of the blood, which are due mainly to starvation or wasting disease. Marasmic thrombi seldom give rise to serious disturbance during life until the condition is so complex and grave that the patient is at death’s door. Postmortem evidences of marasmic thrombi, however, are often found, and yet have but little surgical significance. They are seen perhaps as often in the cranial sinuses as anywhere.
b. Thrombi of mechanical or traumatic origin are those, for instance, which are due to the presence of foreign bodies, to stagnation of blood as the result of ischemia or local anemia, to compression by tumors, etc.