Pathology
Lecture 6 Thrombosis, Embolism, and Infarction
1) To understand the principle of thrombus formation and differences between
thrombus and post-mortem clot. A thrombus is the formation of a solid mass
(tissue-like consistency) of blood within living blood vessels or heart in a noninterrupted cardiovascular system. This involves blood vessel walls, formed elements
of blood, and coagulation system. Lines of Zahn, alternating layers of platelet-fibrin
columns and red blood cell columns, may also be present. A post-mortem clot
involves only the coagulation system, is gelatinous, and made of a plasma mass.
2) To know predisposing factors for thrombosis. 1) Endothelial injury (e.g.
atherosclerosis), 2) Altered blood flow (e.g. turbulence, stasis), and 3) Increased
coagulability of blood (e.g. trauma, burns, post-partum).
3) To know the outcomes of thrombosis and adverse effects associated with it.
Outcomes include: 1) Resolution/dissolution, 2) Embolization, 3) Propagation
(enlargement), 4) Organization (with attachment to vessel wall and/or recanalization).
Adverse Effects include: 1) decreased vascular flow (partial or total), with ischemia or
infarction (ischemic necrosis) of tissue supplied by thrombosed vessel and 2)
Embolization to another site.
4) To be familiar with clinical risk factors for thrombosis. 1) Advanced age, 2) Bed
rest or other immobilization, 3) Decompensated heart disease, 4) Extensive tissue
damage, 5) Malignancy, usually advanced – Migratory thrombophlebitis (Trousseau’s
sign), 6) Late pregnancy, post-partum status, and 7) Oral contraceptives.
5) To know the clinical features and possible outcome of venous thrombosis.
Venous thrombosis occurs mainly in the large veins of the lower extremities and
pelvis. Patients may present with swelling and pain. They may embolize to another
area, mainly the lungs.
6) To understand the general and specific mechanisms of embolism. Embolism is the
passage and eventual trapping within the vasculature of any of a wide variety of mass
objects, the most common of which are fragments of thrombi.
7) To know the settings for, and the potential outcomes of, pulmonary embolism.
Pulmonary embolism usually occurs in immobilized postoperative patients and in
those with CHF. A venous thrombosis forms in the lower extremities and a fragment
breaks away traveling through the heart to the pulmonary arteries. Possible outcomes
include: 1) clinically silent (60-80%) – resolution common, 2) sudden death (5%) –
“saddle embolism,” 3) Pulmonary infarction (10-15%) or hemorrhage (10-15%) –
usually in patients with compromised cardiovascular function, and 4) pulmonary
hypertension (2-3%) – usually multiple episodes of small thromboemboli.
8) To be aware of the origin and outcome of arterial emboli. Arterial emboli usually
arise from thrombi in the heart (80-85%) or from thrombi overlying atherosclerotic
arterial lesions. These usually cause infarction of tissue distal to the site of lodgment
(lower extremities, kidney, spleen, etc.).
9) To be familiar with forms of embolism other than thromboembolism. Other types
of emboli include: Amniotic fluid embolism (at time of delivery), air (or gas)
embolism (decompression sickness), and fat embolism (trauma). Miscellaneous
sources of emboli include fragments of atherosclerotic plaques, clumps of inflamed
infected tissue and tumor fragments.
10) To know the nature of infarction. Infarction is a localized area of ischemic necrosis
secondary to arterial (more commonly) or venous occlusion.
11) To understand the differences between anemic and hemorrhagic infarction,
mechanisms of formation of each and examples of sites of each. Anemic infarcts,
or white infarcts, involve arterial occlusion in solid tissues forming pale areas of
coagulation necrosis (ex. heart, kidneys). Hemorrhagic infarcts, or red infarcts,
involve venous occlusion in tissues with dual or overlapping blood supplies and
tissues previously congested, or when blood flow returns to an area already necrotic
due to arterial occlusion. They usually appear hemorrhagic or purple grossly.
Microscopically, they show coagulation necrosis with accompanying hemorrhage (ex.
lung, ovary, testis, small bowel.
12) To know the pathologic features (gross and microscopic) of infarction. Grossly,
infarcts are usually wedge-shaped (apex towards site of vascular occlusion) and may
initially have a darker color than usual but later have a pale (white infarcts) or red to
purple (red infarcts) color. Tissue is often more firm than normal. Microscopically,
coagulation necrosis is apparent with or without hemorrhage.
13) To be familiar with all information provided in handout on Thrombosis,
Embolism, and Infarction. Review handout.